10 th Frontiers in Low Temperature Plasma Diagnostics

April 28 th – May 2nd 2013 Rolduc, Kerkrade, The Netherlands

Book of Abstracts

We wish to express a warm welcome to all attendees to the 10 th Workshop on Frontiers in Low Temperature Plasma Diagnostics (FLTPD) in the historic Conference Centre Rolduc, Kerkrade, the Netherlands from 28 th of April to 2 nd of May. The Workshop is the continuation of a very successful biennial series that began in 1995 at Les Houches (France). It is co- organized by the Eindhoven University of Technology (TU/e) and the Dutch Institute for Fundamental Energy Research (DIFFER), two institutions which are strongly involved in the plasma physics and technology research in the Netherlands. The workshop offers the opportunity to present recent results on plasma diagnostics. The aim of the workshop is to bring together experts in the field of low temperature plasma diagnostics. It is an important and fruitful opportunity for the new generation of plasma scientists to share and discuss the knowledge of these diagnostics with the leading scientists of the field. To facilitate interaction among participants free time is scheduled on Monday and Tuesday afternoon. In line with the nine previous meetings, the program consists of expert presentations from 10 invited speakers, 16 topical speakers and 57 posters. Several companies will exhibit their products. The excursion on Wednesday is to the historical city of Aix-la-Chapelle / Aachen where a guided tour of the cathedral or the city is arranged. The conference dinner is on Wednesday evening. During the conference dinner, two prizes will be awarded for the best poster and the best oral presentation for which only students are eligible. The number of participants for the 10 th FLTPD is 87 and participants are coming from 18 different countries. Special thanks are for the members of the International Scientific Committee of the 10 th FLTPD for the selection of invited speakers, the review of submitted papers and the organization of the scientific program. The invaluable financial supports from the Royal Dutch Academy of Sciences and the sponsors is greatly appreciated and allowed us to reduce the conference fees, particularly in a significant amount for the students. Our gratitude goes to the Local Organizing Committee members for all their efforts in preparing and organizing the meeting. On behalf of the LOC and ISC, we wish the participants an interesting scientific meeting, fruitful discussions, new exciting scientific ideas and a wonderful stay in Kerkrade. We would like to express our gratitude for all your contributions and participation in this event as it is the corner stone of a successful scientific meeting.

Nader Sadeghi and Peter Bruggeman

Chairs International Scientific Committee and Local Organizing Committee

We would like to thank the sponsors for their generous support

The 10 th Frontiers in Low Temperature Plasma Diagnostics is organized by

* Eindhoven University of Technology (TU/e)

* Dutch Institute for Fundamental Energy Research (DIFFER)

International Scientific Committee

Nader Sadeghi, Grenoble (F) - chair Georgio Dilecce, Bari (I) Uwe Czarnetzki, Bochum (D) Richard Engeln, Eindhoven (NL) Nick Braithwaite, Milton Keynes (UK) František Kr čma, Brno (CZ)

Local Organizing Committee

Peter Bruggeman, TU/e-EPG – chair Richard Engeln, TU/e-PMP – co-chair Gerard van Rooij, DIFFER – co-chair Ana Sobota, TU/e-EPG Ecole Polytechnique, LPP Jose Maria Palomares Linares, TU/e-PMP Hennie van der Meiden, DIFFER The venue

Rolduc – the abbey

This Augustinian abbey originally called Kloosterrade was founded in 1104 by a priest called Ailbertus of Antoing. His motivation for building a new religious community was the dissatisfaction with the lack of discipline in the collegiate church at Tournai (in present-day Belgium). Adelbert, Count of Saffenberg from Mayschoß an der Ahr (in the German Eifel), the owner of the castle in Herzogenrath, gave him permission to settle on a tract of his land and to build a small chapel. Ailbertus got support from Embrico von Mayschoß and his family; they donated all their possessions to the young community. In 1106, they started to build a stone crypt and laid the foundations to the future monastic church.

The first abbot of the monastic community was Abbot Richer who came from Rottenburch in Bavaria. The community was made up of canons regular (Augustinians) who initially lived according to extremely strict principles. Community life, prayers, lack of possessions, fasting and manual work were all part and parcel of the daily cycle.

In 1136 the land of Rode, including the abbey, fell into the hands of the Duchy of Limburg. During the 12th and 13th century Kloosterra flourished. In 1250 the abbey owned more than 3,000 hectares of land and the number of regulars grew steadily. The library developed into one of the most important of its age and the abbey provided pastoral and spiritual care to many parishes throughout the Netherlands. Other communities were founded by Kloosterrade: Marienthal in the Ahr valley of the Eifel, Sinnich near Aubel (B) and Hooidonk near Eindhoven. Five communities in Friesland were placed under the authority of the Abbot of Kloosterrade, the most important of these being the Abbey of Ludingakerke. During the 14th, 15th and 16th centuries times were harder for the abbey in both spiritual and material terms. The buildings were heavily damaged during the Eighty Years War. Prosperity began again in the late 17th century when revenue was generated from the exploitation of coal mines. In around 1775, the abbey employed 350 mineworkers.

The abbey was dissolved by the French in 1796 and the canons regular were forced to leave the community. It is around this time that a new name for the abbey wad adopted, the French name for Herzogenrath (Rode- le-Duc = Rolduc).

The buildings stood empty for 35 years. In 1815, when the Kingdom of the Netherlands was formed (see Vienna Congress), the border was drawn through the ancient land of Rode, separating the abbey from the castle. The eastern part (including the castle) became Prussian Herzogenrath and the western part (including the abbey) became part of the Dutch municipality of Kerkrade.

In the 19th century Rolduc became a famous boarding school run by Jesuits, and a seminary of the Diocese of Roermond. Many influential Dutch Roman were educated at Rolduc. The former abbey is now a secondary school (Charlemagne College, formerly College Rolduc), a Roman Catholic seminary, and the Rolduc Congress Center.

This 12th century abbey church is an example of Mosan art. The crypt, the choir and chancel above have a cloverleaf pattern. The interior of both the church and the crypt contains richly carved capitals. Remarkable is the fact that the columns in the crypt all have a different design. In 1853, the young architect Pierre Cuypers was commissioned to restore the crypt and to reinstate as much as possible the original Romanesque fabric. The cloisters are largely 18th century. The abbey has a richly decorated Rococo library with an important collection of books. During the Middle Ages, the Rolduc library was one of the most famous libraries in the Meuse region. The history of the abbey was recorded in the so-called Annales Rodenses, a chronicle about the years between 1104-1157. The interior painting above the altar is by the Nazarene movement painter Matthias Goebbels. Kerkrade – the city and the surroundings

The history of Kerkrade is closely linked with that of the adjacent town of Herzogenrath, just across the German border. Herzogenrath began as a settlement, called Rode, near the river Worm (or Wurm in German) in the 11th century. In 1104 Augustinian monks founded an abbey, called Kloosterrade, to the west of this settlement.

One part of the border between the Netherlands and Germany runs along the middle of the street Nieuwstraat/Neustraße. Because of relatively unrestricted cross-border travel within the European Union, this border was for many years marked only with a low wall, about 30 cm high, running along the length of the street. There was a separate 2-way road on each side, and cars had to pass through the official crossing points, but pedestrians could readily step over the wall (although there were signs informing of the border). In 1995, it was decided to remove the wall completely. Nieuwstraat/Neustraße is now a single two-way road, with the extra space now occupied with trees and bicycle lanes. The border is unmarked, and is crossed even when going round a roundabout or overtaking a vehicle.

The appearance of the present-day Kerkrade is closely connected to its coal mining history. Kerkrade was the oldest mining town in the Netherlands. Coal was being mined here as far back as the Middle Ages. The mining history in the twentieth century would ultimately define the image of the whole region. Since the closing of the mines in 1965, the former mining sites were restructured in the “black to green” operation. On the Market Place is the miner’s statue ‘d’r Joep’, The Nulland Shaft has been rebuilt into an atelier and the sites where the slag was once dumped have been transformed into green walking areas.

Places of interest in Kerkrade are the city park, the botanical garden, GaiaZOO (a modern zoo where animals live in roomy, natural enclosures), Discovery Center Continium (not a museum with showcases, but a journey through time, science, industry and society) and the Rolduc Abbey. A steam train of the South Limburg Steam Train Society runs to and from Kerkrade via the ‘Miljoenenlijntje’. Finally Kasteel Erenstein is another lovely place worth visiting. This 18th century castle is situated at the edge of the Anstel Valley. In and around Kerkrade there are many green areas.

The Kerkrade tourist center offers a choice of walking routes. These are:

Anstelvallei route – a walk in the Anstel Valley (8 km), marked with red route markers, starting at the parking of the Ehrenstein castle (Kasteel Ehrenstein)

Ehrenstein route – a walk along Ehrenstein estates, the castle and a view of the Anstel Valley (6 km), marked with blue route markers and starting at the parking of the Ehrenstein castle (Kasteel Ehrenstein)

Hamdal – Wormdal route – a walk that takes you along the Anstelerbeek, the Crombacherbeek and the border of the river Worm. You will also see several monuments: shaft Nulland (a tangible reminder of the mining history of Kerkrade), remnants of the Siegfried Line (German defenses) and the Abbey Rolduc. (9 km).

Carboonroute – a walk that starts at the historic Abbey Rolduc (Sundays by appointment). You will walk through the Wormdal, where you can still find coal on the ground surface. You will also pass the medieval Burg Red on German territory and remnants of the Siegfried Line, the German defenses (12 km).

Eygelshovener route – a walk that will take you through the green Eygelshoven and Rimburger forest. There is beautiful scenery to enjoy along the way. You will see the eleventh century church hall of Eygelshoven, Castle Rimburg, the Rimburgermolen to the fast flowing river boundary Worm and protected townscape Rimburg (12 km). Steenbergroute – this walk starts at the Botanical Garden and runs through Park Gravenrode where Strijthagerbeek and Anstelerbeek in the course of thousands of years have carved deep valleys. There is a great variety of natural landscapes, streams, ponds, hillside forests, castles, farms, lake Crane Weyer. You will pass the international gardens of Mondo Verde, the indoor ski resort Snow World, recreation Carisborg with its nature trail, Castle Erenstein and GaiaZOO (14 km).

Ommetje Hambos – this trail starts at the rail crossing near the Continium and is marked with poles (yellow route marking with letter O). The Ommetje Hambos is an initiative of the Platform Residents Kerkrade East, that won a prize in 2011 in the framework of the Ommetje Contest Conservation Foundation small landscape elements in Limburg. The route goes along the Anstelerbeek, fishponds and Elisabeth Stift, the first hospital of Kerkrade. There are beautiful carvings of chainsaw artist Roel van Wijlick to see on the way (5 km).

Weiße Weg – the “White Way” is a walking and cycling route through the Pferdelandpark, a landscape between Aachen, Herzogenrath and Kerkrade. There are ten artfully landscaped areas, called 'Stations', and several beautiful viewpoints. In total, the route is thirty kilometers long. Using a map, you can take a 5 km walk from the Continium (Museumplein 2). This map is available on the website of the Pferdelandpark.

Abdijroute – the abbey route is a walking route from the Orange Square in Kerkrade centre to Rolduc Abbey. Along the path there are nine tableaux describing the history of Rolduc (1 km). There is a leaflet available in Rolduc Abbey.

Botanical garden – the garden was created in 1939. It was designed as an English garden, but specialized in the flora of Limburg. The subtropical greenhouse houses succulents from Madagascar. The garden belongs to the European Garden Heritage Network, a network of special historical gardens in Europe.

In addition, South Limburg (Zuid Limburg) has a 600 km long network of cycling routes. Maps are available at the tourist office.

Source: www.rolduc.com www.kerkrade.nl The program

Presentations

The time slots for the invited lectures are 50 minutes long, 45 minutes for the talk and 5 for questions. Topical lectures should be planned with 20 minutes for the talk and 5 minutes for questions. Please allow time for discussion.

Poster sessions

The poster sessions are planned after the dinner on Monday and Tuesday. Please make sure that your poster is put on the board well before the beginning of the poster session. We have assigned a number to each poster. Please use the board with the corresponding number to hang your poster.

During the poster sessions drinks will be served.

Industrial exhibition

The following exhibitors will be present:

* Laser2000 www.laser2000.com

* Bronkhorst www.bronkhorst.com

* Avantes www.avantes.com

* Impedans www.impedans.com

Lunch breaks and the discussion time on Monday and Tuesday are ideal moments to visit the exhibition booths.

The excursion to Aachen

The excursion is planned for Wednesday May 1 st right after lunch. We will take a bus ride to Aachen, where we have planned a choice of two guided tours, one of the Aachen cathedral, the other one of the old city.

Tour of the old town – The historic old town of Aachen invites to go for a stroll. Let yourself be guided through narrow alleys and across historic squares through the 2000 year-old history of Aachen. Experience all facets of Aachen, a modern city with beautiful historic town houses, many old and new fountains and innumerable stories all about the Cathedral and the town hall (1.5 hours).

Guided tour of the Cathedral – The Aachen Cathedral is a special kind of World Heritage Site. The core of this building is more than 1200 years old. The former Palace Chapel of Charlemagne has developed into one of the most interesting cathedrals of Western Europe. Coronation church of German kings, burial site of Charlemagne and major pilgrimage church - the Aachen Cathedral is a "must" for anyone who loves historic buildings and churches (45 min).

Conference dinner

The conference dinner will be held on Wednesday after the excursion in the conference center. Two students’ awards will be given: a best poster prize and a best presentation prize will be awarded during the conference dinner. Sunday 28 th April Monday 29 th April Tuesday 30 th April Wednesday 1st May Thursday 2nd May 8:15 – 8:30 Opening 8:15 – 8:30 8:30-9:20 L Overzet K Sasaki M Šimek G Kroesen 8:30-9:20 9:20-10:10 C Laux M Gigosos T Trottenberg S J You 9:20-10:10 10:10-10:50 Coffee break Coffee break Coffee break Coffee break 10:10-10:50 10:50-11:15 A van Gessel M Obradović R Brandenburg O Guaitella 10:50-11:15

11:15-11:40 S Tsikata D Schram P Kochkin T Tsankov 11:15-11:40 11:40-12:05 E Carbone St Meier G van Rooij N Sadeghi 11:40-12:05 Closure 12:15-13:15 Lunch Lunch Lunch Lunch 12:15-13:15 Informal Informal 13:15-16:15 13:15-16:15 discussions discussions 16:15-16:45 Coffee break Coffee break 16:15-16:45 16:45-17:35 E Stamate J P Booth 16:45-17:35 Registration excursion 17:35-18:00 K Achkasov T Verreycken 17:35-18:00

18:00-18:25 M Tichý C Douat 18:00-18:25 18:45-19:00 18:45-19:00 Dinner Dinner 19:00-20:00 Welcome party 19:00-20:00 Conference dinner 20:00-22:00 Poster session Poster session 20:00-22:00

Invited Topical Posters Social

Invited talks

1 Overzet, L Radio frequency diagnostics of microplasmas

2 Laux, C O Repetitively pulsed discharges in air and water vapor

3 Stamate, E Electrical diagnostics for electronegative plasmas

Saturation spectroscopy and related phenomena in Balmer-α line of atomic 4 Sasaki, K hydrogen

5 Gigosos, M A Stark broadening calculations for plasma diagnostics

Dynamics of Cl inductively-coupled plasmas: 6 Booth, J P 2 Role of electronic and vibrational excitation Time-resolved ICCD microscopy and spectrometry of single streamer micro- 7 Šimek, M discharges in atmospheric gases

8 Trottenberg, T Diagnostics for particle fluxes and sputter effects

Probing dusty plasmas with photo-detachment, microwave interferometry and 9 Kroesen, G M W particles

10 You, S J Recent progress of the cutoff probe research in KRISS

Radio Frequency Diagnostics of Microplasmas.

L. Overzet1,2,3*, M. Goeckner1, R. Dussart2, P. Lefaucheux2, V, Felix2, M. Kulsreshath2, J. Golda3 and V. Schulz-von der Gathen3.

1The University of Texas at Dallas, TX USA 2GREMI – CNRS, University d’Orléans, Orléans FRANCE 3Le Studium – CNRS, Orléans FRANCE 4Ruhr-Universität, Bochum, GERMANY *Contact e-mail: [email protected]

1. Abstract: the microplasma in the hole depends more on the The use of Radio Frequency (RF) current/voltage DC current flowing through it than on the pressure. and phase measurements to study microplasma These RF impedances can be used to estimate the sources will be reviewed in detail in this average plasma conductivity using the dimensions of presentation. Using RF diagnostics provides several the hole as well as the electron density using an significant advantages as well as some electrical model for the plasma. disadvantages compared to other diagnostic The RF diagnostic technique will be explained techniques. Particularly attractive advantages and both RF and optical data from Ar and He include the speed at which the measurements can be plasmas containing N2 will be presented. made (they can be used to diagnose plasmas in real time), the repeatability of the measurements and the relatively small expense of setting up the measurement. In addition, the technique can be used with reasonable time resolution (~1 to 2 RF cycles[1]). In principle, it can be used to diagnose microplasmas formed using either AC or DC power. Disadvantages include the fact that the plasma Fig. 1: Schematic of a DC microplasma source. The parameters are not measured directly but must be dashed lines indicate the approximate equipotential lines for the RF impedance measurement. inferred from an electrical model of the plasma and the fact that the measurements are spatially averaged. In order to demonstrate the technique, we will use data from DC microplasmas made in approximately 200 μm diameter holes through 500 μm thick alumina and having ~5-10 μm thick nickel electrodes. The plasmas were made in either Ar or He with small admixtures of N2. A schematic of the device is shown in Fig. 1. The plasma is shaded blue and represented as if the cathode electrode were at the top and the anode at the bottom. We have used the same electrodes for the RF diagnostic. The placement of the RF on these electrodes allows us to Fig. 2: An example of RF impedance measurements for Ar define the through-hole to be the measurement microplasmas (with 0.075 Torr N2 added.) volume. This is shown in Fig. 1 by indicating the approximate shape of equipotential lines for the RF. References The magnitudes of the measured RF impedances [1] L.J. Overzet, F.Y. Leong-Rousey: Plasma (Zin) as a function of the DC current flowing through Sources Sci. Technol. 4, pp. 432-43 (1995). the microplasma are shown in Fig. 2 at four Ar pressures. Zin decreases monotonically with LJO is supported in part by the European increasing DC current and has only a small Community 7th Research Program FP7/2007-2013 dependence upon the ambient pressure. This is very under grant agreement no 298741. much like the DC I-V curves, which are essentially RD, PL, VF and MK are supported in part by the flat (characteristic of the normal glow regime) and ‘Agence Nationale de la Recherche’ contract no have only a small dependence upon the ambient ANR-09-JCJC-0007-01 “SIMPAS project”. pressure as well. It indicates that the conductance of JG and V. SvdG are supported in part by PROCOPE grant 54366312 of the DAAD.

I-1 Repetitively pulsed discharges in air and water vapor

C.O. Laux 1*, D.L. Rusterholtz 1, F.P. Sainct 1, D.A. Xu 1, D. Lacoste 1, G.D. Stancu 1

1Laboratoire EM2C, CNRS UPR288, Ecole Centrale Paris, France *Contact e-mail : [email protected]

1. Introduction formation of shock waves that were evidenced by Nanosecond repetitively pulsed (NRP) high speed Schlieren imaging [5]. This mechanism discharges represent one of the most energy efficient is supported by recent numerical simulations [6]. techniques to produce radicals, internally excited molecules, and charged species in atmospheric 3. NRP discharges in atmospheric pressure water pressure gases. In this contribution, we will describe vapor the effects of these discharges in air and water NRP discharges have been also applied to water vapor. These NRP discharges are produced by vapor at atmospheric pressure. The species and applying short (~10 ns), high-voltage (~10 kV) temperature produced by the discharges have been pulses at frequencies of 10-100 kHz between pin measured by OES and Laser-Induced Fluorescence electrodes with gap distances of a few millimeters. of OH [7]. The results show that a high level of The time interval between pulses is chosen short excitation is obtained after each pulse, with up to relative to the recombination time of the active 10 16 electrons/cm 3 determined from the Stark- species produced in order to ensure synergetic broadened Balmer beta hydrogen line, as well as effects. In both air and water vapor, three regimes long-lived OH species. We also observe a can be observed in order of increasing applied surprising result, namely the presence of an voltage: a corona regime, with light emission just anomalously broad Balmer H beta line with around the anode, a glow regime corresponding to a Lorentzian FWHM of several nm, persisting several diffuse nonequilibrium plasma, and an spark regime, microseconds after the pulse. characterized by higher temperatures and higher active species densities. 4. Conclusions NRP discharges in air and water vapor effectively 2. NRP discharges in atmospheric pressure air produce large amounts of reactive species at The glow regime in air was first obtained in air atmospheric pressure. Because air and water vapor preheated at 2000 K [1]. Then, Pai et al. [2] and two of the most important carrier gases, these extended the existence of the glow regime down to discharges open a wide range of new applications 700 K, and proposed a model defining the ranging from plasma-assisted combustion to conditions required to obtain the glow at lower gas chemical, biological or medical treatment. temperatures. Based on these results, Rusterholtz [3] succeeded in obtaining a stable glow in ambient References air at 300 K by using a judicious combination of [1] C.H. Kruger, C.O. Laux, L. Yu, D.M. Packan, electrode geometry (radius of curvature and gap L. Pierrot, Pure Appl. Chem. 74 , pp. 337 (2002). distance), pulse duration, PRF, and applied voltage. [2] D.Z. Pai, D.A. Lacoste, C.O. Laux, J. Appl. We will present these results and describe the Phys. 107 , 093303 (2010). characteristics of the discharge obtained in room air.

[3] D.L. Rusterholtz, Ph.D. Thesis, Ecole Centrale The spark regime was also studied. Through a Paris (2012). combination of Two-photon Absorption Laser [4] G.D. Stancu, F. Kaddouri, D.A. Lacoste, C.O. Induced Fluorescence (TALIF), Cavity Ring-Down Laux, J. Phys. D: Appl. Phys. 43 124002 (2010). Spectroscopy (CRDS) and quantitative Optical [5] D.A. Xu, D.A. Lacoste, D.L. Rusterholtz, P.Q. Emission Spectroscopy (OES), it was shown that Elias, G.D. Stancu, C.O. Laux, App. Phys. Lett. NRP discharges induce an ultrafast mechanism of 99 , 121502 (2011). gas heating (about 1000 K in 20 ns) and large [6] N. Popov, 19th Int. Conf. Gas Discharges and oxygen dissociation (up to 50% dissociation of O 2) Applications, China (2012). [3,4]. This phenomenon was found to be explained [7] F.P. Sainct, D.A. Lacoste, C.O. Laux, M. by a two-step process involving the excitation of Kirkpatrick, E. Odic, 51 st AIAA Aerospace molecular nitrogen followed by exothermic Sciences Meeting (Jan. 2013). dissociative quenching of molecular oxygen. The ultrafast heating process is accompanied by the

I-2 Electrical diagnostics for electronegative plasmas

E. Stamate1*,

1Technical University of Denmark, Department of Energy Conversion and Storage, Roskilde 4000, Denmark *Contact e-mail: [email protected]

1. Introduction ions is also associated with a lower heat flux to the Plasmas produced in electronegative gases, such probe for potentials higher that plasma potential, a as CF4, Cl2, SF6 and O2, and not only, are widely fact that led to the development of a thermal probe used in micro and nano-electronic industry for that allows one to record at the same time not only etching, ashing, oxidation and other surface the current bias, I(V), but also a temperature bias functionalization processes. H2 plasmas are also characteristic, T(V), so increasing the available used to produce negative ions for fusion and information to extract the plasma parameters [4]. extensive research is devoted recently to create The recent discovery of the discrete and modal negative ion sources for neutral beam processing focusing effects, associated with three-dimensional and space propulsion. In a broader perspective most plasma-sheath-lenses created the possibility to detect of the reactive gases are also electronegative so that, even low densities of negative ions using the sheath- the role of negative ions in plasma processing cannot lens probe [5]. Alternative electric diagnostics be neglected. The continuous decrease of the techniques for negative ions can be based on the features size in nano-electronic industry (now below very sharp transition from a positive sheath to the 40 nm) requires a more precise control of plasma anodic glow [6]. parameters including not only pressure, gas flow and temperature profile but also the density of reactive 3. Properties of electronegative discharges. species including the negative ions. Despite of a The positive ion extraction from electropositive good progress in plasma diagnostics, yet more is to plasmas is rather easy as one can control the plasma be done for developing inexpensive but reliable potential with the bias of a large electrode. However, techniques compatible with the strict requirements this is not the case of electronegative discharges. for device-making setups. Moreover the properties The influence of biased electrodes, of small or large and possibilities to control the electronegative dimensions on plasma parameters in electronegative discharges are not completely understood. discharges can give more information about the The aim of this work is to review the main possibility to control and used these plasmas for electrical diagnostics techniques available to processing. Development of negative ion sources for investigate electronegative discharges and also to both applications and basic science is rather present some of the most recent results on properties challenging and some of these efforts will be of electronegative discharges and plasma sources for presented in direct correlation with diagnostic negative ion production. approaches [6-8].

2. Electrical probes References Electrostatic probes have been used to detect [1] H. Amemiya, J. Phys. D 23 999 (1990). negative ions since 70’s. While the use of this [2] E. Stamate and K. Ohe, Appl. Phys. Lett. 78 153 technique can give good results for density ratios of (2001). negative ion to electron higher than 10 its [3] E. Stamate, G. Popa and K. Ohe, Rev. Sci. applicability for lower density ratios is questionable Instrum. 70 58 (1999). [1]. In this context is was demonstrated that double [4] E. Stamate H. Sugai and K. Ohe, Appl. Phys. hump structures observed in the electron energy Lett. 80 3066 (2002). probability function close to plasma potential cannot [5] E. Stamate, H. Sugai, O. Takai and K. Ohe, J. be associated with negative ion parameters because Appl. Phys. 95 830 (2004). those structures are produced by a particular change [6] M. Draghici and E. Stamate, J. Appl. Phys. 107 in the work function over the probe surface as a 123304 (2010). result of discrete ion focusing [2]. Another way to [7] M. Draghici and E. Stamate, J. Phys. D 43 detect the plasma parameters in the presence of 155205 (2010). negative ions is to use the sensibility of the test [8] E. Stamate and M. Draghici, J. Appl. Phys. 111 function in the mid and high energy tail of the 083303 (2012). distribution function [3]. The presence of negative

I-3 Saturation spectroscopy and related phenomena in Balmer-ααα line of atomic hydrogen

K. Sasaki 1, S. Nishiyama 1, and M. Goto 2

1Division of Quantum Science and Engineering, Hokkaido University, Japan 2National Institute for Fusion Science, Japan *Contact e-mail: [email protected]

1. Introduction coefficient without the pump beam and the Since the resolution of saturation spectroscopy is difference in the absorption coefficients with and finer than the Doppler broadening (Doppler-free without the pump beam, respectively. The magnetic spectroscopy), it is used for the precise field strength in this experiment was 60 G, where the determination of the wavelengths of transitions in magnitude of the Zeeman splitting is narrower than the field of fundamental spectroscopy. However, the widths of the peaks. As shown in the figure, we there are a small number of works which apply observed many Doppler-free peaks. Most of the saturation spectroscopy to plasma diagnostics. major peaks were assigned to the fine-structure The final goal of this work is to measure a components of the Balmer-α line as indicated in the Zeeman-split spectrum of the Balmer-α line of figure. A major peak and half of minor peaks were atomic hydrogen in the Large Helical Device (LHD) assigned to the cross-over signals, which appeared at at the National Institute for Fusion Science. We can the center between two transition lines with common know the location of excitation/ionization in LHD lower levels. Similar but more complicated Doppler- from the Zeeman-split spectrum, and this free spectra with Zeeman splitting were observed at information is useful for investigating the particle higher magnetic field strengths. balance in the fusion experimental plasma. However, The saturation spectrum shown in Fig. 1 has the Zeeman-split spectrum is masked by the Doppler several anomalies which are not explained by the broadening and is not measured by usual usual theory of saturation spectroscopy. The first spectroscopic methods. In this work, we examined anomaly is the broadband bias components at the the fundamental characteristics of saturation bottom of the spectrum. The bias components have spectroscopy at the Balmer-α line of atomic broader tails in the high-frequency side. The second hydrogen using a linear magnetized plasma source. anomaly is the peaks indicated by big arrows in the figure. These peaks are observed at the center 2. Experiment between two transition lines, but they do not have The system of saturation spectroscopy employed common lower levels. If the peaks indicated by big an oscillator-amplifier system of diode lasers, which arrows are anomalous cross-over signals, they yielded tunable, single-mode, cw radiation with a suggest the frequent interchanging and/or the mixing power of 200 mW. A part of the laser beam obtained among 2S 1/2 , 2P 1/2 , and 2P 3/2 levels of atomic from the master oscillator was picked up using a hydrogen. The anomalies of the saturation spectrum beam splitter and was used as the probe beam. The will be discussed in detail at the conference. other part of the master oscillator beam was injected 50mTorr 0.5 100mTorr RF 750W into the amplifier to obtain the intense pump beam. MAG 60G 200mTorr 5/2

The probe and pump beams were launched into a -3D 3/2 0 0.4 300mTorr 3/2 hydrogen plasma produced in a linear magnetized 400mTorr -3D 3/2 2P 1/2 ∆α/α 1/2 -3P 1/2

plasma source from the counter axial directions. The -3S 0.3 2P 1/2 1/2 -3P 3/2

probe and pump beams were overlapped carefully. 2S 2P 1/2 -3D

0.2 2S 3/2 1/2 3. Results and discussion 2P When the pump beam was switched off, we 0.1 -3S 3/2 Saturation spectrum observed well-known Doppler-broadened absorption 2P spectrum of the Balmer-α line, which was composed 0 of two broadened peaks. When the pump beam was -8 -6 -4 -2 0 2 4 6 8 10 switched off, many dip components appeared in the Relative Frequency (GHz) absorption spectrum of the probe beam. Figure 1 shows an example of the dip spectrum, Fig. 1 Saturation spectrum observed at where the scale of the vertical axis is ∆α(ν) /α0(ν) various gas pressures. The magnetic field strength was 60 G. with α0(ν) and ∆α(ν) being the absorption

I-4 Stark broadening calculations for plasma diagnostics

M.A. Gigosos and D. González-Herrero

Departamento de Óptica, Facultad de Ciencias. Universidad de Valaldolid. 47071 Valladolid (Spain)

The emitting ions and atoms in a plasma are un- and computer simulations [4, 5, 6]. der strong local electric fields created by the other The computer simulations are based on a very particles in the plasma and thus the emission process simple idea: through the numerical calculation a cer- is altered, giving rise to the widely known Stark ef- tain plasma region is reproduced. In this area the par- fect. Due to the fact that this phenomenon depends ticles —ions, electrons and neutral atoms— move un- strongly on the density of charged particles in the der some conditions which represent a certain config- plasma and on the temperature, the study of broad- uration of density and temperature. Then the local ening and shift spectra is a very efficient technique. electric field on emitting atoms or ions is calculated This sort of diagnostic is an indirect technique, and the quantum evolution equations for the emitters so it is necessary to have an accurate model of the are solved. Thus the detail of the emission process in plasma and the emission process in order to interpret each case of configuration can be determined. properly this information. The first theoretical treat- This process is repeated a huge number of times ments about Stark broadening process are from the (about tens of thousands) with several different physi- fifth decade of the last century. Those theories [1] cal conditions chosen randomly in a sample with well split the study of the Stark broadening into two sorts controlled statistics. The statistical mean of these of phenomena: those which are produced by elec- emission process allows us to evaluate how the spec- trons —whose mobility is very high— and the phe- tral line will be under the physical conditions of the nomena due to ions, which are much slower because plasma reproduced in the simulation. of their large mass. The models developed in the Several spectral lines and several plasma config- sixties and seventies follow this scheme: The elec- urations have been obtained. All this information trons cause impact broadening and the calculation is together with software packages which fit the spec- based on a collisions statistic. The ions cause a qua- tra from the laboratory to the models developed is sistatic electric field broadening and its treatment is an essential tool for plasma diagnosics through spec- based on a statistic of local microfield. Of course, the troscopy methods. models mix these two phenomena, however it does so considering each one as independent from the other. The first mechanism —electronic impact— originates References lines whose width is proportional to the charged par- [1] H.R. Griem, Spectral Line Broadening by Plas- ticle density. The second mechanism is more com- mas, Academic Press, New York, (1974). plicated since the Stark shift can depend linearly on the field —Hydrogen and Hydrogen-like lines— or [2] J. Seidel, Z. Naturforsch. 32a, 1195–1206 quadratically, and therefore more weakly. (1977). These two broadening mechanisms are present in the majority of spectral lines, so it is necessary [3] A. Calisti, F. Khelfaoui, R. Stamm, B. Talin and to include both in all cases. Furthermore the real- R.W. Lee, Phys. Rev. A 42, 5433–5440 (1990). ity is quite more complicated and neither of the two approximations adopted —extremely fast fields for [4] M.A. Gigosos and V. Cardeñoso, J. Phys. B: At. electrons and completely static for ions— are suitable Mol. Opt. Phys. 29, 4795–4838 (1996). under usual plasma laboratory conditions. This fact [5] M.A. Gigosos, M.A. González and V. led the researchers to develop other methods more re- Cardeñoso, Spectrochimica Acta Part B liable to calculate spectral line shapes. In the sev- (Electronica) 58, 1489–1505 (2003). enties and eighties plenty of works in this field were published. Particularily, we should mention the so- [6] N. Lara, M.A. González and M.A. Gigosos, called “Model Microfield Method” —MMM[2]—, Astronomy and Astrophysics 542, A75 1–7 the “Frequency Fluctuation Method” —FFM [3]— (2012).

I-5 Dynamics of Cl2 inductively-coupled plasmas: Role of electronic and vibrational excitation

J.P.Booth*1, N.Sirse1, P.Chabert1 P. Indelicato2, A. Surzhykov3, and M.J Kushner4 1Laboratoire de Physique des Plasmas, CNRS/Ecole Polytechnique, 91128Palaiseau France 2Laboratoire Kastler-Brossel, ENS, Paris, France, 3Physics Institute, University of Heidelberg, 69120, Germany 4University of Michigan, Ann Arbor, Michigan, USA *Contact e-mail: [email protected]

Chlorine-based inductively-coupled plasmas are lower temperatures, albeit still high (1200K under widely used for etching of CMOS gates for the same conditions). This discrepancy could be integrated circuit manufacture. A key parameter explained by significant vibrational excitation of the characterising such a discharge is the density of Cl2 molecules, which would lower the Cl2 chlorine atoms. Relative densities of Cl atoms in the absorption at 355nm, leading to underestimation of 5 2 ground (3p ) P3/2 state can be determined by Two- the Cl2 density and overestimation of the gas Photon Absorption Laser-Induced Fluorescence temperature. Indeed, vibrational excitation of Cl2 by (TALIF) with laser excitation at 233.277 nm [1], and electron-impact is expected to be fast[4]. If recently a new calibration technique[2] was accompanied by efficient vibration-translation demonstrated to put these densities on an absolute energy transfer to Cl atoms this mechanism could be scale using 355 nm photolysis of Cl2. Cl atoms have the source of the large gas heating observed. a low-lying (0.109 eV) spin-orbit excited state Inclusion of these mechanisms into HPEM gave gas 5 2 ((3p ) P1/2) which has not previously been studied in temperatures that were in good agreement with the plasmas. We detected Cl atoms in this state by IRLAS measurements. Furthermore, the model TALIF, with two photon excitation at 235.603 nm to agreement with other measured parameters such as 2 the same fluorescing level as for P3/2 detection. electron density was greatly improved. Work partly Reactor details are described in ref [2]. Calculations financed by ANR project INCLINE (ANR-09 of the relative two-photon excitation cross-sections BLAN 0019) and by Applied Materials University performed at LKB allow the population ratio of the Research Partnership Program and US Dept. of two states to be determined, as shown in Fig 1. The Energy Office of Fusion Energy Science. 5 2 (3p ) P1/2 state density approaches 25% of that of the 0.25 ground state at the 500W RF power and at 20 mTorr pressure, conditions where the electron density is 0.20 maximal. We also performed kinetic measurements 3/2 RF power:

/ P / 500W in the afterglow of pulsed plasmas. At low pressure 1/2 0.15 2 the P1/2 atoms are lost by diffusion to the reactor 200W walls where they are quenched with a probability 0.10 close to unity, whereas at higher pressure collisional 100W quenching by Cl2 plays an important role. Using

Density ratio P ratio Density 0.05 electron-impact excitation/de-excitation cross- sections between the two states of Cl calculated at [3] 5 2 0.00 Drake University we included the (3p ) P1/2 state 0 20 40 60 80 100 in the Hybrid Plasma Equipment Model (HPEM), Cl pressure (mTorr) 2 2 yielding results in good agreement with our Fig. 1. Density of Cl atoms in the P1/2 state relative to the experimental observations. ground state as a function of gas pressure and RF power

If 355nm laser photolysis is performed during in a pure Cl2 inductively coupled discharge. plasma operation, the Cl ground state TALIF signal is increased by an amount that should be References proportional to the local Cl2 molecule density. [1] Ono K, Oomori T, Tuda M and Namba K, J Vac Knowing the Cl2 and Cl absolute densities and the Sci Technol A, 1992, 10, 1071-1079 total gas pressure allows the local gas temperature to [2] Booth J P, Azamoum Y, Sirse N and Chabert P, be estimated. This calculation indicated very high J. Phys. D: Appl. Phys., 2012, 45, 195201 gas temperatures, reaching 1800K at 50mTorr [3] Wang Y, Zatsarinny O, Bartschat K and Booth J- 500W. However, measurements of the gas P, Phys Rev A, 2013, 87, 022703 temperature by IRLAS of Ar metastables [4]Gregorio J and Pitchford L C, Plasma Sources (introduced in small quantity) indicated significantly Sci T, 2012, 21, 032002

I-6 Time-resolved ICCD microscopy and spectrometry of single streamer micro-discharges in atmospheric gases

M. Šimek1

1Institute of Plasma Physics v.v.i., Czech Academy of Sciences, Prague, Czech Republic *Contact e-mail: [email protected]

1. General and rate constants of the electron-impact excitation, Various filamentary streamer-based micro- dissociation and ionization processes exponentially discharges in atmospheric gases have currently depend on the electric field. Radial non-uniformity become hot-topics in connection with environmental of the densities of various species have to be issues (e.g., air pollution control or ozone synthesis), therefore seriously considered when using optical- material treatment technologies (e.g., surface based diagnostics with limited spatial, temporal or modification and hardening), plasma assisted spectral resolutions or when comparing results of combustion (e.g. automotive engines and gas numerical simulations with experimental results turbines), aerodynamic applications (flow control) based on streamer-induced emission spectra. and biomedical applications (e.g., sterilization or Experimental radial distributions of emitting treatment of living tissues). species might be obtained through high-quality The most important issue for all such images of propagating streamers captured applications is a requirement to optimize the simultaneously with sufficiently high spatial, efficiency and to scale-up laboratory devices so as to temporal and spectral resolutions. Such already achieve maximum performance at minimal cost. In images revealed the presence of pre-breakdown addition to that, development of many emerging (Townsend) phase several tens of ns before the onset applications in plasma medicine critically depends of a fully developed streamer occurs [1,2]. on local parameters of individual micro-discharges In this talk, an overview of diagnostic studies that are often supposed to interact with living performed recently on streamers triggered in pure organisms without causing any (severe) damage. argon, nitrogen and synthetic air at atmospheric and A filamentary streamer is a rather frequent form sub-atmospheric pressures will be given. In order to of high-pressure transient discharge which develops study the evolution of an individually developing from an electron avalanche in an overvolted gap. streamer we have used a system based on positive Streamers are usually produced in the gas phase high-voltage pulses of ~150 ns duration and of ~3 between metallic electrodes in high-voltage systems. kV amplitude superimposed with amplitude- Nevertheless, they may also occur between modulated AC high voltage waveforms which electrodes fully or partially covered with a dielectric allows to trigger streamers with sub-nanosecond barrier, on the interface between gaseous and liquid precision. Emission or LIF spectra produced by such phases, and they may even be produced in liquids. triggered streamers may be recorded and analysed The most important streamer characteristics are with nanosecond time-resolution. very high propagation velocity, a small streamer Basic differences between UV-vis-NIR spectra channel radius, and high density and mean energy of produced during pre-breakdown and subsequent free electrons occurring in the streamer head. streamer channel evolution phases will be presented Because of such specific characteristics, filamentary and possible diagnostic approaches based on 1-D or streamers produced in volume (by e.g. pulsed corona 2-D projections of cylindrically symmetric streamers discharges) and especially those produced on the to determine radial distributions of excited species surface (by e.g. surface DBD discharges) are within the streamer channel will be discussed. extremely difficult for experimental observations with sufficient spatial and temporal resolutions. Optical emission produced by filamentary Acknowledgements streamer discharges is determined by the spatial This work was supported by the Czech Science distribution of various species within the streamer Foundation (GAČR contract no. P205/12/1709). channel that were excited to radiative states by streamer-head electrons. Radial distributions of References excited species and radicals produced by streamer- [1] M.Šimek, P.F.Ambrico and V.Prukner: Plasma head electrons are strongly non-uniform because the Sources Sci. Technol. 19, 025010 (2011) maximum electric field in the head of a propagating [2] M.Šimek, P.F.Ambrico: Plasma Sources Sci. streamer occurs on the axis of the streamer filament Technol. 21, 055014 (2012)

I-7 Diagnostics for particle fluxes and sputter effects

T. Trottenberg∗ , A. Spethmann , J. Rutscher, H. Kersten

Institute of Experimental and Applied Physics, University of Kiel, Kiel, Germany ∗Contact e-mail: [email protected]

Plasma–wall interactions as well as the action of tive only to the latter one. This particularity is due to particle beams, e.g. from broad beam ion sources, on its construction and orientation: The rotor spins hor- targets depend on the fluxes of charged and neutral izontally in the vertical beam (see Fig. 1). From a species in front of the wall. Often, only the electri- measurement of the angular acceleration of the rotor, cal currents are experimentally accessed, which rep- the force acting on the targets in horizontal direction resent the first moments of the velocity distributions can be derived. Since the momentum of the incident of electrons and ions. Much more information about beam particles is parallel to the rotor axis, only the re- the processes in front of and on a limiting wall could pulsion due to the released particles in the sputtering be obtained by measurements of the second and third process drives the instrument. moments, i.e. momentum and energy fluxes, and in- cluding the neutral plasma species. This presentation reports on non-electrostatic, rather non-conventional, diagnostics for plasmas and ion beams, which are able to measure momentum and energy fluxes. A force probe is presented, which measures the pressure on a small test surface [1]. The target is a thin metal disk which is mounted at the end of a thin lever arm which pivots around the axis of a galvanometer. A current through the galvanometer coil produces additional opposed torque and keeps the lever arm in its home position. The required cur- rent serves as a measure for the exerted force. The re- sults are compared with an experiment, where falling microparticles have been used as microscopic force Fig. 1: Sputter-propelled instrument. Four thin targets are probes [2, 3]. mounted like the blades of a cross-shaped windmill rotor. Known for a long time are calorimetric tech- niques [4, 5, 6]. Calorimetric probes consist basically of a thermally insulated thin metal plate as target and References a thermocouple for continuous reading of its temper- [1] T. Trottenberg et al., Contrib. Plasma Phys. 52, ature. 584 (2012). Both in case of the force probes and the calori- [2] V. Schneider et al., Rev. Sci. Instrum. 81, metric probe, sputtering might have a significant in- 013503 (2010). fluence on the resulting forces and heat fluxes, when the energies of the impinging ions or neutrals are [3] T. Trottenberg et al., Phys. Plasmas 17, 103702 above the sputter threshold. The repulsion from sput- (2010). tered target atoms and backscattered beam particles transfers additional momentum to the target. Simi- [4] C. van de Runstraat et al., J. Phys. E: Sci. In- larly, sputtered target atoms and backscattered beam strum. 3, 575 (1970). particles remove energy from the target in form of ki- netic energy and binding energy. Such effects can be [5] J. A. Thornton, Thin Solid Films 54, 23 (1978). investigated by comparison measurements with elec- [6] M. Stahl et al., Rev. Sci. Instrum. 81, 023504 trostatic, force and calorimetric techniques. (2010). A recently presented novel method for the mea- surement of the sputtering related momentum trans- [7] T. Trottenberg et al., Plasma Phys. Control. Fu- fer to a target is realized in the “sputter-propelled in- sion 54, 124005 (2012). strument” (SPIN) [7, 8]. While the above mentioned force probe measures the sum of momenta from in- [8] J. Rutscher et al., Nucl. Instrum. Methods B, cident and released particles, this instrument is sensi- submitted (2013).

I-8 Probing dusty plasmas with photo-detachment, microwave interferometry and particles

G.M.W. Kroesen, J. Beckers, F.M.J.H. van de Wetering, D.J.M. Trienekens

Technische Universiteit Eindhoven, The Netherlands *Contact e-mail: [email protected]

1. Introduction sheath and Poisson’s equation, a system of three We used microparticles under hypergravity and coupled differential equations is obtained. The microgravity conditions, induced by either a equations are evaluated for values of the centrifuge or parabolic flights, in order to measure gravitational constant between 0 and 10 g. The nonintrusively and spatially resolved the electric results clearly show the transition from sheath (g field strength as well as the particle charge in the values from 1 to 10) to pre-sheath (g-values from 0 collisional RF plasma sheath. These experiments are to 1). As a teaser, figure 2 shows the values of the completed by tilting a complete RF reactor, in this ion density and the electron density in the sheath and way using the horizontal repelling force between the pre-sheath. particles. When all data are put together and analyzed, we obtain not only the field strength, ion density and particle charge, but we also find out more details about the electrical screening of particles suspended in the RF sheath. A second line of research involves photo- detachment. The plasma is integrated in a microwave cavity. When a laser is fired through the cavity, the electrons sitting on the negative ions in the plasma are being released, and temporarily increase the electron density. This density is measured by determining the microwave resonance frequency.

2. Method In figure 1, the vertical force equilibrium of a single Fig. 2: Density of ions and electrons in the sheath and dust particle suspended in the plasma sheath is pre-sheath. represented. This force equilibrium is the central In the photo-detachment experiments, the electron feature in the data analysis. The force equilibrium density is temporarily increased if a laser is fired leads to the equation of motion of the dust particle. through the dusty plasma. Figure 3 illustrates this. Together with the conservation of ion flux in the In the presentation, lots of results will be shown.

Fig. 3: Temporary increase of the electron density (represented by the microwave resonance frequency) Fig. 1: Force equilibrium of a single dust particle upon firing a laser in the dusty plasma. suspended in the sheath o an RF plasma.

I-9 Recent Progress of the Cutoff Probe Research in KRISS

ShinJae You*1, J. H. Kim 1, D. W. Kim 1, B. K. Na 2, K. H. You 2, H. Y. Chang 2

1Vacuum Center, Korea Research Institute of Standards and Science, Republic of Korea

1Dept. Physics, Korea Advanced Institute of Science and Tech., Republic of Korea *Contact e-mail: [email protected]

1. General (Times 11, bold) In this paper, we present the recent progress of the cutoff probe research which has been performed for last decade. This paper shows the whole progress for the cutoff probe including how to start to develop the cutoff probe in the initial period, what idea has been included during the development, how to evolve the probe during ten years.

The cutoff probe was made by simple intuition for the cutoff phenomenon of the plasma wave. Fig. 1: Transmission spectrum of the original cutoff However, the unexpected complicated S21 probe (blue line), Oscillation probe spectrum (red line), spectrum gave big confusion for the cutoff Absorption spectrum (green line) frequency. At that time, just compared the cutoff probe result with the other probe result such as Langmuir probe and oscillation probe, the cutoff frequency could be determined. Later, EM waver simulation supported the validation for the cutoff frequency determination. Recently, by supposing the circuit modeling, the physics behind for the cut off probe spectrum (S21) was revealed and the accuracy and the application window of the probe were established. In addition to them, By cooperating with the accuracy measurement of the cutoff probe reactance, the e-n collision frequency as well as the electron density were calculated with good precision. The fast measurement cutoff probe Fig. 2: Reactance spectrum of the cutoff probe at various “named fourier cutoff probe ” which can applied to gas pressures, which is obtained by APE (Auto Port the rapid change environment of plasma has been Extention) also developed.

Based on recent developments we also introduce a References [1] J.-H. Kim, et al. Metrologia 48, pp. 306, 2011. novel methodology to interpret the probe spectrum [2] D. W. Kim, et al. Appl. Phys. Lett. 99, pp. that eliminates the sheath and collisional effects 131502, 2011. and enables the use of this precise diagnostic [3] J. H. Kwon et al. J. Appl. Phys. 110, p. 023304, technique in a broad range of practical processing 2011. conditions. [4] J. H. Kwon et al. Appl. Phys. Lett. 96, p. 081502, 2010.

I-10

Topical lectures

The chemistry of a microwave plasma jet at atmospheric pressure investigated van Gessel, A F H 1 using various laser diagnostics

2 Tsikata, S The coherent Thomson scattering application to Hall plasma thruster research

Determination of electron-impact transfer rate coefficients between argon 3p 54s Carbone, E A D 3 states by laser pump-probe technique

4 Achkasov, K Diagnostics for negative ion surface production in hydrogen plasmas

Systematic measurements by ball-pen probe in magnetized low-temperature Tichý, M 5 plasma Spectroscopic measurement of electric field in atmospheric pressure helium Obradovi ć, B M 6 discharges

7 Schram, D C Analysis of plasmas by absolute emission spectroscopy and line analysis

8 Meier, St M Plasma density measurements by THz time domain spectroscopy

Comparison of independent methods for the absolute calibration of the OH 9 Verreycken, T density in a plasma filament in atmospheric pressure He-H2O Spatio-temporal resolved density measurements of He metastable atoms by Douat, C 10 absorption spectroscopy in an atmospheric micro-plasma jet propagating in air Spatio-temporal development of dielectric barrier micro-discharges: Brandenburg, R 11 New insights by means of fast optical and spectroscopic methods

12 Kochkin, P On the origin of hard X-rays in the growth of meter long sparks

Spectroscopic characterization of the 400.9 nm tungsten inverse photon efficiency van Rooij, G J 13 near the ionization threshold

Vibrational relaxation of N 2 on catalytic surfaces studied by infrared titration with Guaitella, O 14 time resolved Quantum Cascade Laser diagnostics Experimental investigations on ion energies and the Bohm criterion in multi-ion Tsankov, Ts V 15 species plasma

16 Sadeghi, N Species density oscillations launched in the reactor by pulsing the plasmas

The chemistry of a microwave plasma jet at atmospheric pressure investigated using various laser diagnostics

A.F.H. van Gessel *, S.C. van Grootel and P.J. Bruggeman

1Eindhoven University of Technology, The Netherlands *Contact e-mail: [email protected]

1. Introduction ing measurements. O is found to recombine mainly In this contributions the air chemistry is investigated into species other than O 2 in the afterglow, which is in a microwave plasma jet at atmospheric pressure, suggested to consist of O 3 and oxidized components operated with a flow of He with a few percent of air, of NO. Electron densities of 7 · 10 18 m-3 are found in ending in ambient air (figure 1). This type of micro- the plasma core. wave jets is investigated in the context of applica- The measured concentrations and plasma proper- tions for surface treatment, and biomedical applica- ties as function of the plasma power and the ad- tions, for which plasma produced species like O and mixed air concentration are used to explain the basic NO are believed to play a key role in the plasma in- plasma induced air chemistry. duced effects on living tissues and cells.

Fig. 1: Atmospheric pressure microwave plasma jet oper- ated with a flow of helium in open air.

2. Diagnostics Fig. 2: Spatially resolved NO density in a jet with 3.2% To investigate the air chemistry in the plasma jet, added air and 30 W microwave power. densities of plasma produced species NO, O and electrons are measured spatially resolved, using var- ious laser diagnostics. These diagnostics are adapted to the needs of an atmospheric pressure plasma in an open air environment. The absolute electron density is measured using Thomson scattering, with absolute calibration by Raman scattering, which is also used to measure the N 2 and O 2 densities. The NO density is measured using laser induced fluorescence (LIF), calibrated using a known mixture of NO [1]. The O density is measured using two-photon absorption laser induced fluorescence (TALIF), calibrated with a mixture containing Xe [2]. Also gas temperatures are determined by measur- Fig. 3: Spatially resolved O density in a jet with 3.2% ing and comparing rotational temperatures of NO X, added air and 30 W microwave power. NO A and N 2 C using LIF and optical emission spec- troscopy. References [1] A.F.H. van Gessel, B. Hrycak, M. Jasinski, J. 3. Results Mizeraczyk, J.J.A.M. van der Mullen and P.J. O densities are found which indicate that O 2 is Bruggeman, 2013 J. Phys. D: Appl. Phys. 46 , close to fully dissociated in the core of the plasma 095201 (figure 3). The NO density is maximal on the edge [2] A.F.H. van Gessel, S.C. van Grootel and P.J. of the plasma jet (figure 2). The high dissociation Bruggeman, 2013 (submitted) degrees for O 2 are confirmed by the Raman scatter-

T-1 The coherent Thomson scattering application to Hall plasma thruster research

S. Tsikata1∗ , C. Honore´2 , D. Gresillon´ 2, J. Cavalier3, N. Lemoine3

1ICARE, Centre National de la Recherche Scientifique, Orleans,´ France 2LPP, Ecole Polytechnique, Palaiseau, France 3IJL, Universite´ de Nancy, Nancy, France ∗Contact e-mail: [email protected]

1. Introduction late thruster performance with the presence of this The Hall thruster is used today on geosyn- instability. Regimes of thruster operation which chronous telecommunications satellites for station- show high-amplitude discharge current oscillations keeping and positioning. Its use for primary propul- are found to correspond to regimes in which the fluc- sion was demonstrated in 2003 during its deployment tuation amplitude of the instability is high. Such dis- on ESA’s Earth-Moon SMART-1 mission, and as with charge current oscillations tend to result in damaged other electric propulsion technologies, it is particu- power supplies and a smaller operating envelope for larly well-suited to long-duration and long-distance the thruster; controlling the amplitude of the insta- space flight, unlike chemical propulsion. In the fu- bility in such regimes may lead to improved perfor- ture, missions requiring high-thrust engines are en- mance. Certain regimes in which the thrust efficiency visaged, including cargo transport, deorbit and inter- is highest are also seen to be those with the weakest planetary flights. However, the complexity of Hall mode amplitude. Discussions of certain new insights thruster physics has meant that the development of into the links between the thruster operation and the such next generation thrusters has been hindered. instability will be presented. Phenomena such as anomalous erosion, anomalous transport and plasma-wall interaction must first be better understood. Anomalous electron transport, which manifests as an unusually high electron current in the device, is a long-standing enigma which has implications for thruster performance and lifetime. 2. Coherent Thomson scattering investigations In 2008, the first experiments were performed us- ing coherent Thomson scattering on the Hall thruster plasma. These experiments demonstrated the pres- ence of an azimuthal instability predicted to play a role in anomalous transport. The instability, driven by the fast azimuthal electron drift at the thruster exit, was previously studied using linear ki- Fig. 1: PRAXIS setup at the thruster facility netic theory analysis and 2D PIC simulations [1]. Experiments were done using a specially-designed, References highly-sensitive coherent scattering optical bench [1] J-C. Adam, A. Heron´ and G. Laval. Study of sta- (PRAXIS), in order to detect weak electron density tionary plasma thrusters using two-dimensional fluctuations associated with the instability. The ex- fully kinetic simulations. Phys. Plasmas 11, No. periments since performed have allowed the detec- 1, pp. 295-305 (2004) tion of the predicted instability [2], and provided de- tailed and unprecedented characterizations of its am- [2] S. Tsikata, N. Lemoine, V. Pisarev, and D. M. plitude, directivity and spatial extent [3]. This infor- Gresillon.´ Dispersion relations of electron den- mation has aided the refinement of theoretical mod- sity fluctuations in a Hall thruster plasma, ob- els for the instability and enabled some progress to served by collective light scattering, Phys. Plas- be made in understanding how such instabilities con- mas 16, 033506 (2009) tribute to transport. This is key because in the plume region where this instability arises, electron transport [3] S. Tsikata, C. Honore´ , N. Lemoine and D. M. exceeds that predicted by neoclassical models by 2-3 Gresillon.´ Three-dimensional structure of elec- orders of magnitude. tron density fluctuations in the Hall thruster This work reports on the latest experiments per- plasma: ExB mode. Phys. Plasmas 17, 112110 formed using this diagnostic which seek to corre- (2010)

T-2 Determination of electron-impact transfer rate coefficients between argon 3p54s states by laser pump-probe technique

E.A.D. Carbone1∗, N. Sadeghi2, S. Hubner¨ 1, J.J.A.M. van der Mullen1, G.M.W. Kroesen1

1 Department of Applied Physics, Technische Universiteit Eindhoven, The Netherlands 2 LIPhy, Universite´ Joseph Fourier-Grenoble & CNRS (UMR 5588), BP87, 38402 St Martin d’Heres,` France ∗Contact e-mail: [email protected]

Metastable atoms play an important role in low tuned up to 5 kHz, with a maximum energy per pulse temperature plasma kinetics. Having a long lifetime, of 4 mJ. With a pyridine-1 dye dissolved in ethanol, they can store significant amounts of energy. Al- the 1s5 metastable state could be depopulated by tun- though being the first stage in the stepwise ioniza- ing the laser on the 696.54 and 706.72 nm lines cor- tion of ground state argon atoms, these metastable responding to the 2p2 and 2p3 states, respectively. An atoms cannot be monitored by optical emission spec- external cavity diode laser was used to record the ab- troscopy. It makes their experimental investigation sorption profiles of the 772.42 and 772.38 nm lines, more challenging. In a high electron density plasma, absorbed by atoms in the 1s3 and 1s5 state, respec- the strong collisional coupling of the 1s5 and 1s3 (we tively. A second diode laser, working in the 810 nm use Paschen notations) metastable states with the res- region, probed 1s4 and 1s5 states when tuned to the onant 1s4 and 1s2 states will greatly reduced the ef- 810.37 and 811.53 nm argon lines, respectively. The fective lifetime of the metastables due to the radiative latter line was used in the high pressure regime when losses via the resonant levels. However, due to the the 1s5 density was too low to be detected by absorp- radiation trapping, the effective radiative lifetime of tion on the 772.38 nm line. Due to the < 10 MHz these resonance states is a few µs . A large number of spectral width of the lasers, the absorption line pro- models have been developed to determine the steady files, with bandwidth of about 1 GHz, can directly state densities of these metastable atoms. But there be recorded. In this contribution, we will report pre- have been almost no experimental studies for the de- liminary results for the direct electron impact trans- termination of electron-impact transfer rate coeffi- fer rate coefficients between different 1s states. As cients between the four 1s metastable and resonance an example, we have measured a rate coefficient of states of argon, which control the kinetics of these about 9.0 · 10−13 m3s−1 for the transfer coefficient states. In this work, the population transfer between from the metastable state 1s3 to the resonance state 1s states of argon is studied by time resolved pump- 1s2. This value is much larger than the theoretical probe technique: a nanosecond laser pulse tuned to value found in the literature for this transfer [2] or a 1s-2p transition depopulates one of the 1s states the 2.0 · 10−13 m3s−1 commonly accepted for the and hence the time variation of the densities in that 1s5 → 1s4 transfer [3]. state and the other 1s states are monitored by laser ab- sorption measurements with continuous diode lasers. References The gas temperature was deduced from the absorp- [1] E A D Carbone et al. Experimental investi- tion line profiles and the electron density and tem- gation of the electron energy distribution func- perature were measured by Thomson scattering. The tion (EEDF) by Thomson scattering and optical plasma used in this study to generate atoms in the 1s emission spectroscopy. Journal of Physics D: states is a surfatron plasma of the category of surface Applied Physics, 45(47):475202, (2012). wave discharges. At low pressure, this plasma has the properties of an almost constant electron temperature [2] K. Bartschat and V. Zeman. Electron-impact ex- along the column while the electron density decreases citation from the (3p)54s metastable states of (quasi) linearly from the launcher till the end of the argon. Phys. Rev. A, 59:R2552-R2554, (1999). plasma column [1]. One of the 1s states was selec- tively depopulated by optical pumping to one of the [3] Sumio Ashida, C. Lee, and M. A. Lieberman. 2p states by using a pulsed dye laser pumped by a fre- Spatially averaged (global) model of time mod- quency doubled Nd:YAG laser at 532 nm. The pulse- ulated high density argon plasmas. Journal of duration is about 8 ns and the repetition rate can be Vacuum Science & Technology A: Vacuum, Sur- faces, and Films, 13(5):2498, (1995).

T-3 Diagnostics for negative ion surface production in hydrogen plasmas

K. Achkasov 1, 2 *, A. Ahmad 1, A. Simonin 2 and G. Cartry 1

1 PIIM, UMR 6633—CNRS / Université d’Aix—Marseille, St. Jérôme, service 241, 13397 Marseille Cedex 20, France 2 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France *Contact e-mail: [email protected]

1. Introduction 1 distribution Negative ion surface production in plasmas function of f(E) has been studied [1-7], except in the context of f (E) backscattered - test fusion where H surface production in Cs seeded f '' (E) and sputtered test

plasmas is of a primary interest for neutral beam 0.1 particles, as injection devices [8]. Although surface calculated by intensity (arb.u.) intensity -

production is much lower in Cs free plasmas, it H SRIM may be non-negligible. Indeed it has been software, is - 0.01 observed that significant numbers of H ions can 0 10 20 30 used as the - be created on a HOPG (Highly Oriented Pyrolitic H energy (eV) test function Graphite) surface upon positive ion (blue). The choice of such a test function is bombardment in H 2 plasmas [1-5]. discussed here.

2. Experiments 4. Results In the experiment reported here, a HOPG Measurements and calculations show that sample was placed facing a mass spectrometer negative ions are produced from the central (MS) in the diffusion chamber of a helicon region of a sample (disc of diameter < 2 mm) plasma reactor. Measurements were performed at under chosen experimental conditions, and 2.0 Pa hydrogen gas pressure with an injected RF surrounding surfaces (clamp, sample holder…) power of 20 W in the capacitive coupling mode. do not contribute to the total yield of negative The sample was biased negatively with respect to ions. It is also shown that the measured NIDFs the plasma potential, this resulting in surface are significantly different from the NIDFs of the formation of H- ions upon positive ion particles emitted at the surface. This difference is bombardment. Surface produced H - ion attributed to the low acceptance angle of the MS distribution functions (NIDFs) were measured by which restricts the measurement to the particles means of the energy-resolved Hidden EQP mass emitted at low-energy and/or low-angle. The spectrometer. In order to obtain some insight into sputtered negative ions are emitted at a lower the surface production mechanisms, surface- angle and energy than backscattered ions and produced NIDFs had to be determined from the hence those are preferentially detected. The measured NIDFs. This is the aim of the work shapes of the measured NIDF are mainly presented here. determined by the proportion of sputtered and backscattered negative ions detected. 3. Measurement details Comparative studies between HOPG and Negative ions are emitted from a surface with BDD (boron-doped diamond) were performed a given energy and angle distribution function f using the present technique. At 400 °C the (E, θ). Due to acceleration and deflection of the negative ion yield on a BDD surface was about 5 ions in the sheaths and in the MS, the distribution times higher than for HOPG. This result could be function f” (E) at the MS detector surface differs θ θ explained by the previous study. from the original f (E, ). Unfortunately, f (E, ) cannot be obtained directly from f” (E) since the References information concerning angles, θ, is lost while [1] L Schiesko et al, PSST 17 (2008) 035023 performing the measurements. To derive f from [2] L Schiesko et al, APL 95 (2009) 191502 [3] L Schiesko et al, PSST 19 (2010) 045016 f”, a test function f test (E, θ) is assumed. From this test function, negative-ion trajectories in the [4] G Cartry et al, Phys Plasmas 19 (2012) 063503 sheaths and in the MS are computed to get f” [5] P Kumar et al, J. Phys. D: Appl. Phys. 44 (2011) test 372002 which is then compared to f”. Here, we show that [6] T Babkina et al, Europhys. Lett., 72 (2005) 235 good agreement can be obtained between f”test [7] H Toyoda et al, Appl Phys. Expr. 2 (2009) 126001 (see red curve in the figure) and f” (black) if the [8] U Fantz et al, Rev. Sci. Instr. 79 (2008) 02A511

T-4 Systematic measurements by ball-pen probe in magnetized low-temperature plasma

M. Peterka1), M. Zanáška1), P. Kudrna1), J. Adámek2), M. Tichý1)

1Charles University in Prague, Faculty of Mathematics and Physics, Ke Karlovu 3, 12116 Prague 2, Czech Republic 2Institute of Plasma Physics AS CR, v.v.i., Za Slovankou 3, 18200 Prague 8, Czech Republic *Contact e-mail: [email protected]

1. Introduction ball-pen probe would be an ideal diagnostic tool. The most widely used electric probes in low However, the typical values of the magnetic field temperature plasmas are the Langmuir probes. They used in such systems are by orders of magnitude are constructed of a simple and small electrodes of lower than in tokamaks. Moreover, the magnetron various shapes and inserted directly into the plasma operates with low-temperature plasma. as a floating or biased probes. From the probe's The first results were promising and published in current voltage characteristics many plasma [3]. Therefore, we would like to present further parameters can be found. If the plasma is systematic measurements of radial profiles of magnetized the interpretation of the Langmuir probe plasma potential with ball-pen probe. data becomes more complicated. Recently, the We show in our contribution the application of a specially designed probe so called ball-pen probe [1] ball-pen probe in a low-temperature experimental has been developed for measurements in magnetised system - in the cylindrical magnetron. The hot plasma because the conventional method of the magnetron consisted of cylindrical cathode mounted plasma potential determination using Langmuir coaxially inside of the cylindrical hollow anode. The probe must be combined with the electron diameters of the cathode and anode were 10 and 60 temperature measurements. mm respectively. The length of the discharge In tokamak edge plasma, a Langmuir probe is volume was 120 mm. The homogeneous magnetic routinely used for the direct floating potential Vfl field around 30 mT was parallel with the axis of the measurements. Then, the plasma potential  is system. During the discharge the working gas argon calculated of the floating potential Vfl and the flew through the system at a flow rate below 1 sccm. 3. Results and discussion electron temperature kT  e  We have used radially movable ball-pen probe Te determined of the Vfl     R)ln( (1) I-V characteristics of  e  with the movable collector within the ceramic the swept probe using the eq. (1). The coefficients k shielding tube. Therefore, we were able to reduce of and e represent the Boltzmann constant and the the electron current with the depth of collector elementary charge, respectively. The quantity retraction. The floating potential of the ball-pen - + R = Isat /Isat expresses the ratio of the electron and probe was measured either by scanning part of the ion saturation current, respectively. The ball-pen probe characteristic by high precision pA-meter or, probe can adjust the ratio R to be equal to one by a directly, using a high-input-impedance voltage proper experimental set-up of the probe and follower (1G). It is interesting to note that with therefore its I-V characteristics becomes symmetric. the retracted collector both the electron as well as If this is achieved, the floating potential of the probe the positive ion currents are substantially reduced. is equal to the plasma potential, as follows from The radial dependences of the plasma potential were equation (1). While the emissive probe increases compared with those measured by a Langmuir + - virtually the Isat up to the level of Isat [2], the ball- probe. The experimental results were in good pen probe utilizes the electron gyromotion to reduce agreement thus indicating that the ball-pen probe - + the Isat down to the level of Isat . might be applicable also for diagnostic of 2. Experimental magnetized low temperature plasma. The ball-pen probe consists of a metallic References collector, which is shielded by an insulating tube [1] J. Adamek, J. Stockel, M. Hron, et al., made usually of boron nitride (in our measurements Czech. J. Phys. 54, p. 95 (2004)  we used DEGUSIT ); the probe head itself must be [2] R. Schrittwieser, J. Adamek, P. Balan, et al., oriented perpendicular to magnetic field lines. Plasma Phys. Control. Fusion 44, p. 567 (2002) In the plasma-aided deposition systems, e.g. [3] J. Adamek, M. Peterka, T. Gyergyek, et al., magnetrons, it is often sufficient to know just the Contrib. Plasma Phys., 53, p. 39 (2013) spatial course of the plasma potential; for that the

T-5 Spectroscopic measurement of electric field in atmospheric pressure helium discharges

1 1 1 1 1 B. M. Obradović *, S. S. Ivković , G. B. Sretenović , V. V. Kovačević , I. B. Krstić , N. Cvetanović2 and M. M. Kuraica1

1 University of Belgrade, Faculty of Physics, Studentski trg 12, P.O. Box 44, 11000 Belgrade, Serbia 2Faculty of Transport and Traffic Engineering, University of Belgrade, Vojvode Stepe 305, Belgrade 11000, Serbia *Contact e-mail: [email protected]

1. Intoduction

Detailed knowledge of the electric field 45 distribution is necessary for better under- 40 ∆λ A standing of the processes in the discharges and 35 their practical applications. In this paper we 30 0.16 mm present optical spectroscopy technique firstly 0.38 mm 25 developed for the electric field measurement in the 0.58 mm low pressure discharge [1], and then extended to 20

atmospheric pressure helium discharges. Results of Intensity [arb. un.] 15 F electric field distributions measured in two different 10 types of discharges are presented. One discharge is a 5 homogeneous dielectric barrier discharge (DBD) 491.9 492.0 492.1 492.2 492.3 492.4 492.5 obtained between two parallel electrodes [2] and the ∆λ [nm] other is a helium plasma jet operating in the Fig. 1: He I 492.19 nm line recorded at several bullet/streamer mode [3]. Both discharges include a distances from cathode in DBD in helium. strong electric field region necessary for their This time, line is recorded from the plasma jet. maintenance. In the DBD, the strongest electric field According to [1], with the polarizer axis set parallel is located in the cathode fall region while the to electric field, three components are detected: strongest electric field in the jet is located in the allowed line, its forbidden counterpart and a field- streamer head. free component (ff) originating from the area where Electric field strength was measured using Stark the electric field is negligible, see Fig. 2. polarization emission spectroscopy based on shifting of helium line and its forbidden counterpart. Here a b we used polarization in the electric field direction (π ∆λ ∆λ polarization). Namely, the field strength is obtained 60 using wavelength distance between the HeI 492.19 nm line (2p1Po – 4d1Do) and its A 40 forbidden component (2p1Po – 4f1Fo) according to formula in Ref. [1]. A 20 ff F F ff 2. Results Intensity [arb. un.] Electric field influence on He I 492.19 nm line is presented in Fig. 1, where line profiles are recorded 0 491.2 491.6 492.0 492.4 492.8 493.2 492.0 492.2 at several distances from the cathode in the plan- λ [nm] λ [nm] parallel DBD in helium. As seen in the figure, the Fig. 2: He I 492.19 nm line recorded from (a) the plasma lines are broad and shifted in the electric field which jet and (b) low pressure DC discharge [3] increases towards the cathode. The line with the lower intensity is the forbidden (F) component of References the line and it is more shifted than the allowed (A) [1] M.M Kuraica and N. Konjević: Appl. Phys. component. The origin of line broadening is the Van Lett. 70, 1521 (1997) der Waals broadening together with overlapping of [2] S.S.Ivković et al.: J. Phys.D:Appl.Phys. 42, shifted spectral lines emitted by atoms placed at 2252062009 (2009) various positions in the discharge electric field. [3] G.B.Sretenović et al.: Appl.Phys Lett. 99, Another example of the electric field influence 1615022011 (2011) on the same helium line is presented in Fig. 2(a).

T-6 Analysis of plasmas by absolute emission spectroscopy and line analysis

A.R.J. Haenen 1, D.C. Schram 1*, R. Leyte Gonzales 1, R. Engeln 1

1Technische Universiteit Eindhoven, The Netherlands *Contact e-mail: [email protected]

1. Introduction radiation from the metastable 2s level. For high H 2 For plasma analysis knowledge of the plasma densities there may be a molecular continuum from state and thus measurement of electron density and the 3Σg+ state to the repulsive 3 Σu+ state. The fb and 2 1/2 temperature with (if possible time constants) is ff continuum is in first order proportional to n e /T e . necessary. An overview of plasma parameters can be For λ > 400 nm ff & fb dominate and measurement obtained by absolute spectroscopy of continuum and will yield electron density for higher n e and lower T e line emission. Knowledge of the plasma state is then plasmas. For recombining plasmas lower n e’s can be very helpful i.e. if the plasma is ionizing or measured as then line radiation is less strong. With recombining and how the level excitations react. In known data on radiative recombination rates, the the ionizing state fast electron excitation prevails, spectral form of continuum radiation can be whereas in recombining plasmas commonly constructed for given ne, Te, density of the n=2 level processes involving molecules, as dissociative n2, and H 2 density. recombination dominate. With time dependence As said, the populations of excited H levels give information of the populating mechanisms can be also information on n e and an indication of T e. The made visible. As example analysis of hydrogen latter can be deduced from the absolute value of the plasmas will be presented by analysis of atomic lines Fulcher band. Thus ne and T e, can be obtained from and continuum radiation by a simple Avantek a combined analysis of absolute continuum and line spectrometer. emission. The issue of ionizing and recombining state in In figure 1 a spectrum of a magnetized hydrogen molecular plasmas is more complicated. Even at low plasma is shown in which the several possible Te when direct excitation is absent, recombining analysis, as Fulcher, H lines and continuum (& plasmas can appear as ionizing, because molecular impurities as OH*), are indicated. assisted processes (MAR) can populate excited states. Thus though the system is recombining the atomic system may still have the characteristics of an ionizing system. Interpretation of absolute atomic line emission can thus reveal information on the importance of molecular processes and thus on the molecular assisted recombination in hydrogen plasmas [1]. There is an enormous advantage to take the relative small extra effort to calibrate the system in absolute signal strength. Then characteristics of Hn level populations can give electron density information and support electron temperature information. The latter can be obtained (if > 1 eV) from absolute Fulcher band emission, as H 2* can only arise by Fig. 1: Spectrum of a hydrogen plasma in which the direct excitation. Information on n=2 population by possibilities for analysis are indicated. e.g. diode laser absorption, may give more detail and permit also additional information from profile Conclusions analysis [2]. In this contribution we will focus on the With analysis of absolute continuum and line additional information from absolute continuum emission, with profile analysis determination of intensity [3]. This gives direct information on plasma parameters is possible. electron density and in some cases also on electron temperature. References

[1] W.J.F. Harskamp, thesis TU/e (2012)

2. Continuum radiation [2] W.J.F. Harskamp, et al, PSST 21 (2012) 024009

Continuum radiation is composed of four [3] R.F.G. Meulenbroeks, Phys. Rev. E. 49 (1994) contributions: free free, free bound and two photon 2272

T-7 Plasma Density Measurements by THz Time Domain Spectroscopy

St. M. Meier∗ , Ts. V. Tsankov , D. Luggenholscher¨ , U. Czarnetzki

Institute for Plasma and Atomic Physics, Ruhr-University Bochum, Germany ∗Contact e-mail: [email protected]

1. Introduction Terahertz Time Domain Spectroscopy (THz

Vacuum

TDS) is a non-invasive spectroscopic method which 4 combines the advantages of ps radiation pulses and High Plasma Density broad spectral width in the THz range. This method 2 is widely used in many fields of science, industry and security. In contrast to other optical diagnostics in the far-infrared (FIR), e.g., FIR interferometry, THz 0 TDS gives the opportunity to determine the com-

-2 plex dielectric function as well as the plasma density Detector Current [a.u.] and the collision frequency. In comparison to other diagnostic methods the ps radiation pulses used in 20 25 30 35 40 THz TDS provide a high temporal resolution in the Time [ps] sub-nano-second range. This opens possibilities for Fig. 1: THz pulses at different plasma densities detailled investigations of the ignition and the after- glow phases of plasmas. In spite of the great advan- tages of the THz TDS and especially its possibility 3. Plasma density measurements of measurements with very high temporal resolution Plasma densities in noble gas discharges (He, Ne, the method is still in its early development phase. Ar, Kr, Xe) are measured as a function of power in During the last ten years only the applicability of the a magnetic multi-pole ICP discharge by using THz TDS (Fig. 2). At a filling gas pressure of 20 Pa method for plasma investigations has been demon- 1014 −3 strated [1, 2]. plasma densities of up to cm are obtained. An analytical model was developed and compared with 2. Experimental realisation the measurements. The measurements are in a good Semiconductor dipole antennas with a dipole size agreement, indicating that considerable gas heating of 20 µm and 5 µm gap size are used both as THz and neutral gas depletion effects are responsible for source and detector. A fs laser beam is split and the observed trends. used to produce short living charge carriers in both

semiconductors. In the THz source antenna a bias 80

He ]

voltage is applied to accelerate the charges. Their -3

Ne

dipole radiation and short lifetime result in a short 60 Ar cm 12 electromagnetic pulse of ps length with a broad spec- Kr tral width in the THz range (≈ 0.2 - 4 THz). To detect Xe

40 the THz radiation the reverse effect is used. The elec- tric field of the wave accelerates the charges in the receiving semiconductor. This results in a short cur- 20 rent pulse. The current is proportional to the strength of the electric field of the THz pulse, which can be Plasma Density [10 0 determined in this way directly from the current mea- 0 200 400 600 800 1000 surements. By introducing a delay in the laser beam Power [W] which produces the charge carriers in the detector, Fig. 2: Plasma densities in noble gases in a magnetic the electric field of the THz wave can be probed at multi-pole discharge at 20 Pa different times (Fig. 1). Via Fourier transformation the amplitude and the phase of the pulse can be in- References fered. By comparing a measurement in a plasma with [1] S.P. Jamison et. al.: J. Appl. Phys. 93, pp 4334 a vacuum reference the plasma density and collision (2003) frequency can be extracted from the phase and am- plitude change. [2] A. Ando et. al.: J. Appl. Phys. 110, 073303 (2011)

T-8 Comparison of independent methods for the absolute calibration of the OH density in a plasma filament in atmospheric pressure He-H2O

1 1 1 1 2 T. Verreycken *, R. M. van der Horst , R. Mensink , E. M. van Veldhuizen , N. Sadeghi , P. J. Bruggeman1

1Technische Universiteit Eindhoven, PO Box 513, 5600 MB Eindhoven, The Netherlands 2LIPhy, Université de Grenoble 1/CNRS, UMR 5588, Grenoble F-38041, France *Contact e-mail: [email protected]

1. Introduction The determination of absolute OH radical densities is not a straightforward task, especially not when both a high time and spatial resolution is required as in atmospheric pressure filamentary plasmas. High temporal and spatial resolution is easily achieved by LIF although only relative densities are obtained and an additional calibration by e.g. Rayleigh or Raman scattering is necessary. Due to the importance of collisional induced processes during the LIF measurement at atmospheric pressure, a LIF model is needed which accurately describes collisional quenching and vibrational (VET) and rotational (RET) energy Fig. 1: Fractional absorption spectrum of OH(X) in a ns transfers. Often simplifying assumptions and pulsed discharge in He + 8400 ppm H2O at 7 kV. inaccuracies of some cross sections make it hard to assess the accuracy of the obtained OH density with To calibrate the LIF signal with Rayleigh this method. To this end, we present in this work the scattering, the density of the excited state of OH is absolute OH density of a stable plasma filament calculated with a detailed 6-level model that produced by a nanosecond voltage pulse in incorporates both RET and VET as well as a 4-level atmospheric He-H2O mixtures by 3 independent model where RET is assumed to be infinitely fast. methods: broadband UV absorption, LIF calibrated Table 1 shows an overview of the 4 obtained OH with Rayleigh scattering and relative LIF of the OH densities as described above. All 3 independent decay after the plasma pulse calibrated with a methods provide, within the experimental accuracy, chemical model. comparable OH densities. This validates, for the first time, all these 3 methods for measuring OH density 2. Methods and results at atmospheric pressure, including the LIF model. LIF is performed with a ns pulsed dye laser probing the P1(2) transition of OH(A-X) at 282.6 nm Tab. 1: OH density in a ns pulsed discharge in He + 8400 [1]. ppm H2O at 7 kV calibrated with 3 methods. The density Using a chemical model of the decay of the OH is averaged over 500 ns during the peak OH density. Calibration method OH density Accuracy density is straightforward in a He-H2O mixture since 22 -3 the number of reaction partners is limited and the OH absorption 1.5 10 m Factor 2 LIF with Rayleigh 3.4 1022 m-3 Factor 3 decay during the first few μs only depends on the (6-level model) volume recombination of the OH without diffusion. LIF with Rayleigh 3.1 1022 m-3 Factor 3 The broadband UV absorption is performed by (4-level model) using as light source a UV-LED with maximum Chemical model 3.4 1022 m-3 Factor 2 intensity around 312 nm, whose light is crossing the plasma filament [2]. An example of the fractional References absorption is shown in figure 1. The line of sight OH [1] T. Verreycken, R.M. van der Horst, A.H.F.M. density is calculated from the Beer-Lambert law and Baede, E.M. van Veldhuizen, P.J. Bruggeman: J. the absorption length is obtained from the spatial Phys. D: Appl. Phys. 45, 045205 (2012) profiles of the LIF intensity. The over 500 ns time [2] P. Bruggeman, G. Cunge, N. Sadeghi: Plasma averaged OH density during its maximum density is Sources Sci. Technol. 21, 035019 (2012) obtained.

T-9 Spatio-temporal resolved density measurements of helium metastable atoms by absorption spectroscopy in an atmospheric micro-plasma jet propagating in ambient air

C. Douat 1* , N. Sadeghi 2, G. Bauville 1, M. Fleury 1 and V. Puech 1

1Laboratoire de Physique des Gaz et des Plasmas, CNRS and Univ. Paris Sud, Orsay, France 2LIPhy (URA 5588), CNRS and Univ. Joseph Fourier, Grenoble, France * [email protected]

Recently, interest in plasma micro-jet at atmospheric the helium metastable atoms at different times after pressure has increased due to their unique the HV pulse is obtained by solving the Abel capabilities and novel applications, such as integral equation. biomedicine [1], thin film disposition [2] and chemical decontamination [3]. In this work, we report on the measurement, by laser absorption spectroscopy, of the radial and axial density distribution of helium metastable atoms inside micro-plasma jets propagating in free atmosphere.

Fig. 2: Radial distribution of the absolute density of He m at three distances from the dielectric outlet for an applied voltage of 6 kV. Helium gas fed at 4.5 slm It will be shown that, depending on the discharge geometry, applied voltage, and gas flow, the radial 3 distribution of He*( S1) metastable atoms can exhibit different shapes, evolving along the axis of Fig. 1: Time evolution of the percentage of absorption of m propagation of the plasma jet. In example shown in He at five radial distances at 500 µm from the dielectric 3 outlet and for an applied voltage of 6 kV. Helium gas fed Fig. 2, the radial profile of He*( S1) atoms density at 4.5 slm (standard liter per minute). evolves from hollow shape at the outlet of the tube to peaked one after 6 mm. The temporal dependence The discharge consists of concentric tubular of the absorption coefficient clearly shows that, in 3 electrodes separated by a dielectric cylindrical the core of the jet, the production of He*( S1) atoms structure. The device is made of a quartz tube is mainly due to other kinetic processes than the wrapped with a copper grounded electrode, while a direct excitation of helium ground state atoms by high voltage electrode is glued inside the tube. Pure electrons (probably e-ion recombination). These helium flows through the inner electrode at a flow studies should also help to better understand the rate in the range 3-6 L/min. High voltage pulses (3- complex interplay between the gas flow and the 6 kV) are applied between the electrodes at a discharge. repetition rate ranging from 100 Hz to 50 kHz. A laser diode emitting at 1083 nm is used as the References probing light source. The laser beam is focused by a [1] M. Laroussi, X. Lu: Appl. Phys. Lett. 87 , lens of f = 5 cm, giving a spatial resolution of about 112902 (2005) 20 µm. The plasma jet can be moved in two spatial [2] V. Rabbaland, J. Benedikt, S. Hoffmann, M. directions with electronically driven micro-stages. Zimmermann, A. Von Keudell: J. Appl. Phys. 105 , This allows a 2D mapping of the absorbance 083304 (2009) integrated along the line of sight. Plasma being [3] M. Laroussi, T. Akan, Plasma Proc. and pulsed, the time dependent absorbances at different Polymers 4, 777 (2007) radial distances are recorded (Fig. 1). Assuming an axially symmetrical profile, the radial distribution of

T-10 Spatio-temporal development of dielectric barrier micro-discharges: New insights by means of fast optical and spectroscopic methods

R. Brandenburg , H. Höft, M. Kettlitz, T. Hoder, K.-D. Weltmann

Leibniz Institute for Plasma Science and Technology - INP Greifswald, Greifswald, Germany *Contact e-mail: [email protected]

1. Introduction study is possible by simultaneous recording of The recording of the spatio-temporally resolved individual ICCD-photos and MD current signals [5]. development of filamentary plasmas at elevated Streak cameras transform the temporal profile of a pressures is a challenge for plasma diagnostic. This light pulse into a spatial profile on a detector (CCD) is due to its transient behavior, which requires high to reveal the MD development along the discharge time resolution and its small scale, requiring high axis, but limited to one spatial coordinate. spatial resolution. A profound knowledge on Spectrally, spatially and temporally resolved discharge development is necessary to get insights recording of MD development is possible by means on the elementary processes, to benchmark of Cross-Correlation Spectroscopy (CCS) which is simulation results of such plasmas and enable the based on a sensitive time-correlated single photon determination of basic plasma parameters. counting. However, the CCS method provides the Regarding dielectric barrier discharges (DBDs) the accumulation and thus averaging over a great study of single repetitive filaments or number of light pulses, which makes it very time microdischarges (MDs) is possible by means of consuming and requires long-time stability of the special electrode arrangements (see figure 1) [1-4]. MD.

3. Results Presented exemplary experimental results will cover volume and surface discharge arrangements supplied by ac or pulsed high voltages and with N2/O 2 mixtures or argon as discharge gases. A direct comparison of CCS, Streak and ICCD recordings and electrical measurements on the same discharge arrangement will be discussed. The plasma is a unipolar pulsed driven, symmetric volume DBD microdischarge (figure 1) in 0.1 vol.% O2 in N 2. The aim of the comparison is to show the peculiarities and limitations of the methods.

References Figure 1: Single filament (microdischarge) in volume DBD arrangement [1] G. J. Pietsch: Contr. Plas. Phys. 41 , 620-628 (2001)

[2] T. Hoder, R. Brandenburg, R. Basner, Intensified CCD cameras [5], Streak-cameras [1, K.-D. Weltmann, K.V. Kozlov, H.-E. Wagner: 6, 7] and the Cross-correlation spectroscopy [2-4] J. Phys. D: Appl. Phys. 43 , 123009 (2010) are optical diagnostics capable of recording the MD [3] T. Hoder, M. Sira, K.V. Kozlov, H.-E. Wagner: luminosity. The contribution will give an overview J. Phys. D: Appl. Phys. 42 , 035212 (2009) on these methods illustrated on selected [4] H. Grosch, T. Hoder, K.-D. Weltmann, experimental results. R. Brandenburg: Eur. Phys. J. D 60 , 547–553 (2010)

2. Methods [5] T. Hoder, D. Loffhagen, C. Wilke, H. Grosch, Intensified CCD cameras (ICCD) enable the J. Schäfer, K.-D. Weltmann, R. Brandenburg study of the spatial structure of individual MD in the 2011 Phys. Rev. E 84 , 046404 (2011) volume and on the dielectric surfaces. Although [6] M. Kettlitz, H. Höft, T. Hoder, S. Reuter, modern standard ICCD systems offer time K.-D. Weltmann, R. Brandenburg: J. Phys. D: resolutions of in the sub-ns range, time resolved Appl. Phys. 45 , 245201 (2012) studies are restricted mainly to pulsed driven [7] S. Müller, R.-J. Zahn, Proc. Int. Symp. Light discharges. A rough spatio-temporally resolved Sources, p. 171 (1995)

T-11 On the origin of hard X-rays in the growth of meter long sparks

P. Kochkin 1*, A.P.J. van Deursen 1, U. Ebert 2

1Technische Universiteit Eindhoven, The Netherlands 2Centre for Mathematics and Computer Science (CWI),Amsterdam, The Netherlands *Contact e-mail: [email protected]

1. General

Meter-long laboratory sparks generate high- energetic radiation in a similar way as lightning: Bremsstrahlung generated in collisions between high-energy electrons and air molecules. This study aims to localize and characterize the X-ray source and to visualize the relevant processes. A Marx generator delivers a standardized lightning impulse voltage pulse of 1.2/50 µs rise/fall time of positive or negative polarity. The generator was loaded by a spark gap formed by two conical electrodes at about 1 m distance; one of the electrodes was grounded. Applied voltages were 1 MV, which lead to breakdown of the gap. The voltage was measured by a high-voltage divider. Both electrodes were equipped with current probes to determine the electrical characteristics of the discharge. Two La(Ce)Br3 scintillation detectors measured the X-rays; different distances and angles gave information on the spatial distribution around the spark gap. Lead collimators limited the field of view. Lead attenuators of different thicknesses helped to determine the energy distribution. An intensified CCD camera allows us to capture images of pre-breakdown phenomena with ten-ns resolution. All diagnostics was synchronized to better than 1 ns. Many hundreds of discharges allowed statistical analysis. The X-ray emission area is concentrated in the vicinity of the cathode. The variation with detector position shows a 1/r2 dependence of the detection rate, characteristic of a point-like source of constant luminosity. The reduction with attenuators of variable thickness agrees with a characteristic X-ray energy of 200 keV. The X-rays never occur before there is any cathode current. The nanosecond-fast photography allowed us to follow all pre-breakdown stages of the discharge, from the formation of a first inception cloud, to the formation and propagation of streamers crossing the gap. At a later stage, some cold streamer channels developed into hot leaders which then lead to breakdown. For the X-ray production negative streamers were a necessary condition, for positive and for negative generator voltage.

T-12 Spectroscopic Characterization of the 400.9 nm Tungsten Inverse Photon Efficiency near the Ionization Threshold G.J. van Rooij *, N. den Harder, M.F. Graswinckel

Dutch institute for fundamental energy research, Nieuwegein, The Netherlands *Contact e-mail: [email protected]

1. Introduction The current design of ITER projects tungsten (W) as plasma-facing material in the divertor and beryllium (Be) in the main vessel for its active phase. Physical sputtering of W by impurities may compromise the life time of the plasma-facing components and deteriorate the fusion performance by unduly high W concentrations in the centre. Therefore, W sputtering is studied in situ in present day devices on basis of optical emission spectroscopy in combination with so-called inverse photon efficiencies (S/XB values) [1] to relate the Fig 1: Sputter yields of tungsten by argon measured in measured photon fluxes to particle fluxes. Pilot-PSI and compared TRIM.SP simulations[4].

The present contribution concerns an results is taken as proof that the argon flux and experimental determination of these S/XB values impact energy determinations are correct. Relative under detached plasma conditions as expected in measurements on basis of tungsten emission ITER on the basis of experiments in linear plasma provided the remaining data in Fig. 1. The data show generators, data that was lacking in the international a disagreement with the simulations towards lower database. We have measured the S/XB values for the impact energies, which is possibly explained by of neutral tungsten lines at 400.9, 429.5, 488.6, and the failing collision model in the TRIM.SP 505.3 nm in an argon plasma with an electron calculations at low energies – an aspect that is temperature between 1 and 3 eV. These plasma presently under further investigation. temperatures are near the ionization threshold of neutral tungsten, i.e. the transition from ionization as An example of a tungsten emission profile measured the main loss channel (prerequisite for the S/XB in these experiments is shown in Fig. 2. Relating the method) to particle escape from the plasma volume is covered.

2. Experimental approach Tungsten probes (1.6 mm diameter) were flush- mounted in a boron-nitride end plate that was terminating the ~2 cm diameter magnetized (0.4 T) argon plasma in the linear plasma generator Pilot- PSI [2]. Bias potentials (< 200 V w.r.t. earth potential) were applied to the probes. The probe current was measured to quantify the ion flux, probe 20 -3 weight losses were measured ex situ to Fig 2: Profile of the 400.9 nm line intensity in 6x10 m , independently verify the tungsten influxes. Various 1.5 eV (as measured with Thomson scattering at 2 cm in neutral tungsten emission profiles were spatially front of the surface) argon plasma. mapped (2D) with an in house constructed high integrated tungsten emission to the tungsten influx resolution imaging spectrometer [3]. yielded S/XB values of ~20 at 2 eV, increasing two

orders of magnitude to lower temperatures. 3. Results

Firstly, the tungsten sputtering yield was determined 4. References from weight loss measurements for experiments [1] A. Pospieszczyk et al., J. Phys. B 43 , 144017 (2010). with -100 V applied to the probe to benchmark the [2] G.J. van Rooij et al., Appl. Phys. Lett. 90 , 121501 (2007). experiment (Fig. 1). The agreement of the [3] A.E. Shumack et al., Phys. Rev. E 78 046405 (2008). experimental sputter yield with the simulation [4] W. Eckstein, Topics in Applied Physics 110, 33 (2007).

T-13 Vibrational relaxation of N2 on catalytic surfaces studied by infrared titration with time resolved Quantum Cascade Laser diagnostics

D Marinov1,2, O Guaitella1, D Lopatik3, M Hübner3, Y Ionikh2, J Röpcke3 and A Rousseau1

1LPP, Ecole Polytechnique, CNRS, UPMC, Université Paris Sud, 91128 Palaiseau, France 2St Petersburg State University, Institute of Physics, Ulianovskaya 1, 198904 St Petersburg, Russia 3INP Greifswald, Felix-Hausdorff-Str, 17489 Greifswald , Germany contact: [email protected]

1. Introduction Experimental results were interpreted in terms of a numerical model of non-equilibrium vibrational In nitrogen containing plasmas, vibrationally kinetics in N2.The result of the modeling for 0.2% excited N2(v) play a role of energy reservoir that CO2 is shown in Fig. 1. The relative uncertainty of affects electron kinetics, chemistry and  determination from fitting of experimental thermodynamic properties of the plasma. In low relaxation curves with the model was estimated to be pressure laboratory plasmas, relaxation on the 15%. reactor walls is the most efficient N2(v) loss mechanism. Therefore, the knowledge of the heterogeneous deactivation probability of N2(v) () is crucial for plasma modeling. The development of

] 0.33 % CO a simple and reliable technique for in-situ  14 2  -3 1x10

determination based on the titration with IR active cm

[ -3 molecules [1,2] was therefore the main motivation model  =1.6·10 ( ) 1 N2

0.2 % CO2 of the present study. N 13  5x10

- - 0.1 % CO2

2. Experimental 0 N Gas mixtures containing 0.05-1 % of titrating 0 plasma pulse molecules (CO2, N2O, CO) in N2 were excited by a 0 100 200 300 single DC discharge pulse (I=50 mA, =1-10 ms) at t [ms] a pressure of 133 Pa. The relaxation kinetics of CO2 (N2O, CO) was followed using a 3-channel quantum Fig. 1: Time evolution of after a I=50 cascade laser (QCL) spectrometer TRIPLE Q [3] mA, =5 ms pulse in a silica discharge tube. with time resolution up to 10 s. Experiments were done in a single pulse mode without accumulation. It was found that the value of depends on the partial pressure of titrating molecules, what suggests Due to a very efficient vibrational coupling a vibrational energy transfer mechanism between between N2 and CO2 (N2O, CO), the excitation of N2(v) and physisorbed CO2 (N2O, CO). Using the titrating molecules reflects the degree of vibrational described technique the value of was determined excitation of N2.A model of vibrational kinetics in for SiO2, TiO2, Al2O3, Pyrex and anodized N2 with CO2 (N2O, CO) admixtures was developed aluminum. The effect of plasma exposure on the and the value of  was determined from the best efficiency of vibrational N2(v) quenching on agreement between the model and the experiment. different materials was observed and studied for reactive (N2, O2) and non-reactive (Ar) plasma pre- 3. Results treatments.

With laser absorption spectroscopy a combination References of the populations of the lower 0 0 [1] Egorov et al.1973 Chem.Phys.Lett. 20 77-80 ([CO2(00 0)]≡N0) and the upper ([CO2(00 1)]≡N1) vibrational levels is actually measured. Figure 1 [2] Marinov D et al. Accepted to J.Phys. D: Appl. Phys. shows the time evolution of in a silica discharge tube for different initial concentration of [3] Hübner M et al. J 2011 Rev. Sci. Instr. 82 093102. CO2. One can see a depletion of the measured value of due to the vibrational excitation of CO2 upon the application of the discharge pulse.

T-14 Experimental Investigations on Ion Energies and the Bohm Criterion in Multi-Ion Species Plasma

Ts. V. Tsankov∗, U. Czarnetzki

Institute for Plasma and Atomic Physics, Ruhr-University Bochum, Germany ∗Contact e-mail: [email protected]

1. Introduction operated at 600 W power. Generally, the results from The generalization of the Bohm criterion for a all three diagnostic techniques agree well and allow multi-ion species plasma does not provide an unam- comparison with theoretical results. The discrepan- biguous value for the velocities of the individual ion cies and the limitations of the measurements and the species at the sheath edge. Analyzing the presheath theories will be discussed. region, Riemann [1] argues that each ion species

5

3.0 should attain its own Bohm velocity. The theory 10

= 26.43 eV

Ar of Baalrud et al [2] on the other hand suggests that Ar 2.5

= 22.19 eV

He

instability-enhanced friction in the presheath brings 4

10 all ion velocities to nearly the same value. Laser in- 2.0

duced fluorescence measurements of Hershkowitz et A/eV)

1.5 -7 al [3] support the latter hypothesis. Recently, based 3 10 on a minimization principle, a third possible solution 1.0

has been outlined [4]. In the present work the Bohm Countrate (counts/s) RFEA (10

0.5

2

He criterion in two component plasmas has been investi- 10 gated experimentally. Using a mass-resolved energy 30 0.0 analyzer, plasmas in binary noble gas mixtures are

Chamber axis studied and the results are compared with the theoret- 25 ical predictions.

20

2. Experimental 15

The measurements are performed in an induc- z (cm) tively coupled plasma produced in a chamber with a 10

radius of 25 cm and a height of 50 cm [5] at a pressure 5 PPM and RFEA

of 1.25 Pa. The mass resolved ion velocity distribu- position tion functions (IVDF) are measured with a Balzers 0 0 5 10 15 20 25 30 35 Plasma Process Monitor 421 (PPM). Relative cali-

U (V) bration of the individual mass channels is achieved pl by comparison of the IVDFs with the results from an Fig. 1: Measured IEDFs of Ar+ and He+ ions. The Impedans Retarding Field Energy Analyzer (RFEA). calibration curve of the RFEA is also shown together with The radial distribution of the plasma parameters (ef- the spatial variation of the plasma potential. The fective electron temperature Te, density ne, electron estimated mean ion energies are indicated by lines. energy probability functions (EEPF) and plasma po- tential Upl) are obtained by a Langmuir probe. References [1] K.-U. Riemann: J. Phys. D: Appl. Phys. 24, pp 3. Results and discussion 493 (1991) The ion fluxes for the two ion species are obtained from integration of their IVDF measured with the [2] S. D. Baalrud, C. C. Hegna, J. D. Callen: Phys. PPM. The ratio of the two fluxes, corrected with the Rev. Lett. 103, pp 205002 (2009) relative sensitivity of the mass channels, provides in- formation about the relative ion densities at the sheath [3] C.-S. Yip, N. Hershkowitz, G. Severn: Phys. edge. This is an important input parameter for the Rev. Lett. 104, pp 225003 (2010) theoretical predictions. The mean energies of the ion [4] U. Czarnetzki, Ts. V. Tsankov: Phys. Rev. Lett., species and the effective electron temperature are also submitted (2012) obtained from the measurements by taking the corre- sponding average. [5] Y. Celik, Ts. V. Tsankov, M. Aramaki, S. Figure 1 presents an example of the measured Yoshimura, D. Luggenholscher, U. Czarnetzki: IVDFs for the Ar+ and He+ ions in an Ar-He plasma Phys. Rev. E 85, pp 056401 (2012)

T-15 Species density oscillations launched in the reactor by pulsing the plasmas

1 1 1 1 2 G. Cunge, M. Brihoum, N. Sadeghi , E. Despiau-Pujo, N.St. Braithwaite

1Laboratoire des Technologies de la Microélectronique, CNRS, 38054, Grenoble, France *Contact e-mail: [email protected] 2Dept. Physical Sciences, The Open University, Walton Hall, MK7 6AA, UK

As the semiconductor industry continues to scale monitored by the MS follows the same behavior down the dimensions of IC circuits, the today than the ion flux. As we have previously shown [3], applied plasma etching processes are showing severe the observed phenomena result from the plasma limitations. Pulsing the plasma, is one of the new pressure generated on the top of the reactor which strategies to improve process control and suddenly pushes the neutral particles to the lower reproducibility. However, our ability to overcome part of the chamber. This triggers an acoustic wave, technological issues is limited by the lack of with gas density oscillations inside the chamber. understanding elementary mechanisms involved in Due to friction forces, ions also follow the these discharges. In recent years, we have oscillations of the neutrals. introduced several diagnostic techniques to Trig Pulse and delay characterize the plasma produced in complex A/D converter generator and PC chemistries used in etch reactors. By measuring the Multichannel absolute densities of different radicals and charged counter Transim particles generated in these plasmas and analyzing pedance LED or D2 Lamp their time variation when the plasma was pulsed, we M.S. could study different volume and surface reactions of these species (see [1] for more detail). In present Mono- chromator Chopper Trig +PM Driver work, we are combining three diagnostic methods to 10 Hz evidence the generation of density oscillations in the reactor volume when pulsing the plasma. Experiments are carried out in pure chlorine plasma using a commercial DPS reactor from Applied Material (50 cm diameter and 17 cm height) Fig. 1: Schematic of the plasma reactor and diagnostics. The ion flux probe (not shown) is located designed to etch 300 mm diameter wafers [1]. at the same position as the M.S. Density of Cl molecules is measured by optical 2 absorption of the light from a 365 nm UV-LED 40 mT / 200 Hz / 500; µs ON which crosses the reactor close to the quartz plate of RF ON the reactor roof, on which is seating the RF coil for 0.0065 0.0006 ion flux (/10) Cl2 density (absorption) the plasma generation. These Cl 2 molecules are also Cl2 (MS) detected with a differentially pumped mass spectrometer MS (Hiden EQP), whose sampling 0.0060 hole is located on the lower part of the reactor wall, 0.0004 see Fig. 1. The ion flux is measured by a newly

developed technique [2] at the same position as the Cl2 absorbance ionmA/cm-2 flux (/10) M.S. 0.0055 Results presented in figure 2 have been obtained 0.0002 in 40 mTorr Cl 2 plasma, pulsed at 200 Hz with 0.5 0 1000 2000 3000 4000 5000 ms RF on time, starting at t=0. To improve the time (µs) signal to noise ratio, all three signals have been averaged over many pulses. The ion flux increases Fig. 2: Time variations of ion flux to the bottom walls of during the plasma pulse and follows an oscillatory the reactor, of Cl 2 density on the top of the reactor (by behavior in the afterglow. Density of Cl 2 monitored UV-LED absorption) and on the bottom wall (by MS) by UV-LED absorption near the RF coil, where the plasma is mainly located, decreases during the RF References pulse because strong dissociation and gas heating in [1] G. Cunge, et al : PSST 21 , pp 024006 (2012) [2] M.Brihoum et al J. Vac. Sci. Technol.A 31 , 020604 this region. In the afterglow, this density has also an (2013) oscillatory shape, but in the phase opposition [3] G. Cunge, et al : Appl. Phys. Lett. 96 131501 (2010) compared to the ion flux. By contrast, Cl 2 density

T-16

Poster sessions First poster session

Presenting Title of contribution

1 Aranda Gonzalvo, Y Molecular Beam Mass Spectrometry in Atmospheric Pressure Plasmas

2 Balastikova, R PECVD characterization during the deposition of thin fluorocarbon films

Laser-spectroscopic electric field measurements in a DC-pulsed microplasma in 3 Böhm, P nitrogen Time resolved dust particles metrology by electrical characterization of a dusty 4 Boufendi, L plasma Tracking streamers: investigation of the sub-nanosecond light emission delays of 5 Brandenburg, R nitrogen radiative states in gas excited by streamer Excitation mechanisms in dielectric barrier discharges containing CO at 6 Brehmer, F 2 atmospheric pressure Thomson scattering and laser collisional induced fluorescence on argon 7 Carbone, E A D microwave discharges Characterization of the plasma structure of a Dielectric Barrier Discharge roller 8 Colombo, V plasma source for material treatment at atmospheric pressure

9 Danko, M Study of acetylene molecule fragmentation processes by electron impact

10 de Temmerman, G Diagnosing a fast pulse in a linear plasma device

11 den Harder, N Molecular spectroscopy on a magnetized hydrogen plasma

OH density by time-resolved broad band absorption spectroscopy in a He-H O 12 Dilecce, G 2 dielectric barrier discharge with small O2 addition

13 El Otell, Z Investigations of low-k dielectric damage in plasma etching environments

Advanced retarding field analyzer technology for ion energy measurements and 14 Gahan, D species identification in CW and pulsed plasma Electron Density and Temperature Measurements from Thomson Scattering in a 15 Graham, W G kHz driven Atmospheric Pressure Plasma Jet First Realistic validation of Plasma Air treatment with QCL-OFCEAS detection 16 Guaitella, O of formaldehyde below ppb range

17 Hamann, S On plasma chemistry in an industrial nitriding DC plasma reactor

Diaphragm discharge ignition supplied by DC non-pulsing voltage in electrolyte 18 Hlochova, L solutions with different conductivities Study of aluminium tri-isopropoxide (ATI) chemistry in an rf plasma by FTIR 19 Hübner, M spectroscopy Density of atoms in Ar ∗(3p54s) states and gas temperatures in an argon surfatron 20 Hübner, S plasma measured by tunable laser spectroscopy The memory effect on the breakdown of atmospheric pressure air studied on 21 Janda, M transient spark discharge using fast iCCD camera

22 Kempkes, P Investigations on the transient behavior of pulsed high-density discharges

Atmospheric pressure DC glow discharge in nitrogen-methane mixtures: 23 Krcma, F Analysis of the discharge products by PTR-MS

24 Krcma, F Optical emission spectroscopy of nitrogen post-discharge with mercury traces

Comparison of spectroscopic and catalytic probe characterization of afterglow 25 Kregar, Z oxygen and hydrogen plasma Quantitative and in-situ analysis of PECVD processes containing silane using a 26 Lang, N cw external cavity quantum cascade laser Removal of contaminants from EUV optics by means of an expanding hydrogen 27 Leyte-Gonzalez, R thermal plasma Spectroscopic measurement of characteristic electron energy in the dark phase of 28 Müller, A a combined RF and high-voltage nano pulse discharge Monitoring of electrical discharges for nanoparticle production: the transition 29 Palomares, J M between the spark and arc regimes

Second poster session

Presenting Title of contribution

An updated model of Ar/H gas dynamics and plasma in a microwave plasma 1 Obrusnik, A 2 torch A hybrid 2D/3D model of hydrogen plasma in a linear antenna microwave 2 Obrusnik, A device

3 Országh, J Excitation of Hydrogen by Impact of Monoenergetic Electrons

In situ diagnostics of hydrocarbon dusty plasmas using Quantum Cascade Laser 4 Ouaras, K Absorption Spectroscopy and Mass Spectrometry Shock waves and bubble evolution in low energy pulsed electric discharge in 5 Pinchuk, M E water Measurement of gas and discharge channel parameters by analysis of 6 Pinchuk, M E oscillations in high current discharge at superhigh pressure Influence of modulation regimes on longitudinal distribution of active species in 7 Poto čň áková, L atmospheric pressure plasma jet Influence of a high-voltage pulse on the steady-state radiofrequency plasma: 8 Pustylnik, M Y diagnostics and particle-in-cell simulations

9 Pustylnik, M Y Controlling and understanding the heartbeat instability in dusty plasmas

Development of plasma and beam diagnostics for the PEGASES thruster 10 Rafalskyi, D experiment

11 Reuter, S Absorption Spectroscopy on Plasma Jets Interacting with Liquids

Characterization of a plasma jet for biomedical applications: composition, 12 Sanibondi, P temperature, fluid dynamics and plasma structure The OES Line-Ratio Technique for Discharges in Pure Argon and in Argon- 13 Siepa, S Hydrogen Mixtures Nitric oxide detection in atmospheric pressure NRP discharges by Quantum 14 Simeni, M Cascade Laser Absorption Spectroscopy

15 Sobota, A Breakdown regimes in temperature-dependent mixtures of Ar and Hg

Pump-probe experiments at a microplasma jet using supercontinuum radiation 16 Spiekermeier, S for broadband-absorption spectroscopy Characterization of a low pressure RF plasma jet generated in Ar/H /C H 17 Stoica, S D 2 2 2 admixture utilized for carbon nanowalls synthesis

Pre-breakdown emission of triggered streamer micro-discharge developing in 18 Šimek, M surface coplanar DBD geometry in argon at atmospheric pressure

19 Šperka, J Diagnostics of the glide arc under varying gravity conditions Investigations of a long and stable filamentary plasma jet generated at 20 Teodorescu, M atmospheric pressure Examination of time-varying electron properties in the plasma plume of a Hall 21 Tsikata, S thruster Thomson scattering at the high flux linear plasma generator Magnum-PSI for 22 van der Meiden, H J the determination of electron and ion properties Excitation kinetics and NO production in a cold RF atmospheric pressure 23 van Gessel, A F H plasma jet

24 van Helden, J H Optical cavity based infrared spectroscopy of plasma using QCLs

25 Vayner, B Far Field Plasma Parameters in the Plume of a Hall Thruster

Detection of Hydrogen Atoms by Two Photons Absorption Laser Induced 26 Wartel, M Fluorescence in a High Power Density H 2/CH 4 Microwave Plasma Time-resolved quantum cascade laser based in-situ diagnostics applied to 27 Welzel, S dielectric barrier discharges Scaling parameter determined in high-current DBDs used for plasma-enhanced 28 Welzel, S CVD of SiO 2 thin films

Molecular Beam Mass Spectrometry in Atmospheric Pressure Plasmas

Y. Aranda Gonzalvo1* and P. Hatton1

1Plasma & Surface Analysis Division, Hiden Analytical Ltd., 420 Europa Boulevard, Warrington, WA5 7UN,UK *Contact e-mail: [email protected]

1. Introduction Atmospheric pressure plasmas are becoming an important research field for its interest in different kind of applications from material processing up to biomedical treatment. Non-thermal plasmas can have additional benefits compared to conventional methods for many applications including purification of water, the sterilization of surgical instruments, surface activation of plastics and polymers including woven and unwoven textiles, removal of pollutant and hazardous components, combustion enhancement and treatment of biological samples. There exist many plasma diagnostics but the Fig. 1: Schematics of the MBMS Analyser. most straightforward technique to determine fluxes of ions and neutral species is molecular beam mass References spectrometry. It can be used to measure both [1] Jun-Seok Oh, Yolanda Aranda-Gonzalvo and negative and positive ions including short lived James W. Bradley, J .Phys. D: Appl. Phys, Vol. 44 radical species formed in the atmospheric pressure (36), pp 92-101 (2011). plasmas. [2] P. Bruggeman, F. Iza, D. Lauwers and Y. An overview of different source configurations of atmospheric plasma discharges studied with a Gonzalvo Aranda, J.Phys.D: Appl. Phys. 43, molecular beam mass spectrometer (MBMS) will be 012003, (2010). presented. The MBMS used was a quadrupole-based [3] G. Horvath, Y. Aranda-Gonzalvo, N.J. Mason, mass/energy resolved spectrometer (EQP) system, M. Zahoran and S. Matejcik, Eur. Phys. J. Appl. the HPR-60 MBMS (from Hiden Analytical Ltd) Phys. 49, 13105 (2010). having a three stage differentially pumped inlet [4] J.D. SKalny et al. Journal of Physics D: Applied system separated by aligned skimmer cones and Physics 41, (2008). turbomolecular pumps as shown in figure 1. The sampling orifices/skimmer cones are carefully [5] Lucy V. Ratcliffe et al., Anal. Chem. Vol. 79 aligned to produce a molecular beam which (16), pp 6094-6101 (2007). minimizes the collisions of the sampled particles [6] Alison J. Beck et al., Plasma Processes and with each other and with surfaces. Polymers 6, Issue8 pp521-529, (2009).

2. Experiments The studies presented by means of MBMS includes time- resolved measurements of the ionic species in the plasma plume (“bullet” formation) of an atmospheric pressure helium microplasma jet [1], investigation of a capacitively coupled atmospheric pressure RF excited glow discharge in He-water mixtures [2], ion measurements in a gas composition corresponding to Titan’s atmosphere [3], reaction kinetics studies of ions produced in a N2-O2 mixture in a corona discharge [4] and plasma-assisted desorption/ionization method (PADI) based in non- thermal plasma discharge (DBD) interacting with the surface of the analyte to investigate the surface composition under ambient conditions [5-6].

P1-1 PECVD characterization during the deposition of thin fluorocarbon films

1 2 2 1 R. Balastikova *, S. Massey , M. Tatoulian , F. Krcma

1Brno University of Technology, The Czech Republic 2Ecole Nationale Supérieure de Chimie de Paris, France *Contact e-mail: [email protected]

1. Introduction totally fragmented and several reactive species are Deposition of thin films is one of the most formed. widespread applications used for the modification of This spectrum is typical for all depositions but its surface properties of various materials. This method intensity was changed with different conditions. doesn´t influence the bulk properties, but thin films can enhance for example surface adhesion, hydrophobicity, hydrophilicity, etc. The most frequently used method for the deposition of thin films is the plasma enhanced chemical vapour deposition (PECVD). The main technological product of this method is a well-adhering polymer thin film [1]. This study focuses on plasma diagnostic of the deposition process during the preparation of the thin film prepared by a PECVD technique. The discharge was monitored using optical emission spectroscopy and in situ mass spectrometry. Fig. 1: In situ mass spectrum with identified species (100 % DC, 35 W, 6 % H2) 2. Experimental part The capacitively coupled RF discharge at low A typical emission spectrum is presented in Figure 2. It shows the position of H α at 655 nm and pressure (Plasmionique, type FLR 300 – H) was β used for the thin films deposition using the position of H at 486 nm. It´s clear that intensity of the peaks increases with increasing power. The tetrafluoromethane (CF 4) with addition of hydrogen detailed dependences of selected peaks will be (H2) as a precursor. As a substrate, polymer NOA (Norland Optical Adhesive, commercial presented on poster as functions of deposition photosensitive resin) was used. parameters. Influence of varying power, gas mixture 9000 composition and a discharge mode on the deposition 35 W process was investigated. We used three different 8000 75 W 7000 150 W applied powers: 35 W, 75 W and 150 W. The 6000 depositions were performed in the pulsed mode with 5000 a different duty cycle (DC 50% or 5%) and in the 4000 continuous mode (DC 100%). As a gas mixture, we 3000

used a constant flow of CF 4 (42 sccm) and we intensity Relative 2000 changed the hydrogen flow (6 %, 17 % and 33 %). 1000 Precursor fragmentation in plasma was observed by 0 TM mass spectrometry (Pfeiffer vacuum Prisma Plus -1000 with quadrupole analyzer, model QME 220) and 300 400 500 600 700 800 900 1000 optical emission spectroscopy (spectrometer Spectra Wavelength (nm) Pro ® - 500i, Acton Research company). Deposition time was the same during all experiments (30 min) Fig. 2: Emission spectra as a function of the applied power (DC 5 % and gas mixture CF + 17 % H ) as well as pressure (26 Pa). 4 2

Acknowledgment 3. Conclusion This work was supported by Erasmus program. A typical mass spectrum obtained during the deposition process is given in Figure 1. There are no References peaks of CF 4 which means that this molecule is [1] R.d´Agostino, P.Favia, F.Francassi: Plasma processing of Polymers, pp 532 (1997)

P1-2 Laser-spectroscopic electric field measurements in a DC-pulsed microplasma in nitrogen

P. Böhm1*, D. Luggenhölscher1, U. Czarnetzki1

1Institute for Plasma and Atomic Physics, Ruhr-Universität Bochum, Germany *Contact e-mail: [email protected]

1. Introduction Atmospheric microplasmas are a challenge for plasma diagnostics due to their small spatial dimensions, high pressure, and often very short time scales. Here ns-pulsed discharges in nitrogen are investigated by laser-spectroscopic electric field measurements [1, 2], ultra-fast optical emission spectroscopy, and current and voltage measurements. This kind of discharge offers Fig. 1: the CARS-scheme. interesting opportunities for application as 2.2. Results atmospheric pressure plasma jets [3]. In particular A sensitivity of around 50 - 100 V/mm in a operation in pure nitrogen or nitrogen dominated pressure-range of 0.4 – 1 bar in pure nitrogen is mixtures is of interest. In the present investigations achieved (Fig. 2). At higher pressures the discharge the discharge is operated with kV-pulses of about 10 starts arcing which limits the pressure range ns duration between two parallel plate electrodes presently. Field-measurements are accompanied by with a 1 mm gap. emission measurements using a streak-camera with sub-ns resolutions. Further, current and voltage 2. Electric field measurements measurements in combination with the electric field 2.1. CARS process measurements allow determination of the plasma The laser technique for electric field measurement is density. Combining all diagnostics a detailed picture based on a four-wave mixing process similar to of the discharge dynamics can be developed. CARS (Coherent anti-Stokes Raman Scattering). This technique works in diatomic gases like hydrogen or nitrogen especially at higher pressures. In the classical CARS scheme, three waves provided by two lasers (pump: second harmonic of Nd:YAG at 532 nm, Stokes: tunable dye laser) generate a fourth coherent wave in the UV, the so called anti- Stokes component. The general scheme is depicted in Fig. 1. The two energy states shown there are the vibrational ground and first excited state. For Raman active levels no dipole transitions are allowed. The Intensity of the anti-Stokes wave is proportional to the intensity of the Stokes wave, i.e. the square of Fig. 2: Field measurement in 0.35 bar of nitrogen. the field amplitude. If now the frequency of the third wave is reduced to zero, the process still works but References the frequency of the anti-Stokes wave is drastically [1] Tsuyohito Ito, Kazunobu Kobayashi, Sarah reduced to the energy difference between the two Müller, Dirk Luggenhölscher, Uwe Czarnetzki and vibrational states, i.e. a wave in the IR regime. In Satoshi Hamaguchi: Journal of Physics D: Applied this case the substitute of the third wave is the static Physics 42, 092003 (2009) electric field. Similar to the CARS case, the signal is proportional to the square of the static electric field. [2] Sarah Müller, Dirk Luggenhölscher, and Uwe By measuring the intensity of this infrared signal Czarnetzki: Journal Physics D: Applied Physics 44, and the CARS-signal, which is generated in parallel, 165202 (2011) it is now possible to calculate the static electric field. Due to the short pulse-length of the lasers (about 5 [3] K.Niemi, St.Reuter, L.Schaper, N.Knake, ns) a high temporal resolution can be achieved. V.Schulz-von der Gathen, T.Gans: J.Phys.: Conf. Ser. 71, 012012 (2007)

P1-3 Time resolved dust particles metrology by electrical characterization of a dusty plasma. M. Henault1, G. Wattieaux2, L. Boufendi1* 1GREMI, Orleans university, 14 rue d’Issoudun BP 6744 45067 Orleans cedex 2, France 2LAPLACE - Université de Toulouse III, 118 route de Narbonne 31062 TOULOUSE CEDEX 9 *[email protected]

measurement, could be appropriate to monitor Dust particles growing or injected in in real time the plasma coupled power in any plasma modify significantly the impedance of CCRF discharge with a very good accuracy. capacitively coupled radiofrequency (CCRF) Moreover, the underlined relationship between discharges. The principal modifications are the the plasma/electrode sheath impedance and the increase of the plasma bulk resistance and of dust particle size could be used to follow in the plasma sheath capacitance. In this work, real time the evolution of the size of the dust we propose a method to evaluate the particles using a plasma [2]. Diagnostic"plasma"à"partir"de"la"mesure"de"l’efficacité"du"couplage"d’une"décharge" 29" impedance of the discharge (sheath + plasma Determiningcapacitive"radiofréquence"(Grémi,"Polytech’Orléans) the power by measuring " bulk) during the growth of dust particles in a ! the current/voltage phase shift then completes plasma without measuring any current/voltage 4.3.1.this Ré studysultats"obtenus"à"partir"de"la"mesure"de"UIcos(φ) and then the effective power coupled" ! phase shift. Then the evolution of the power Nous! avons!to the donc! plasma dans! un! premier!is evaluated temps! déduit! and la!compared densité! électronique! to the à! partir! de! la! coupled into the plasma as well as the voltage mesure!de!UIone!UIcos(φ).!Voici!les!résultats!que!nous!obtenons given by the sous tractive method.!:! This drop across the plasma bulk are derived. ! last results allow the determination of the It follows that the plasma coupled electron4.3.1.1. Pour)une)pression)de)1)mbar density (Fig.2). Thus):) the variations ! induced by the presence of dust due to electron power and the voltage drop across the plasma ! bulk increase by a factor of five during the dust attachment can be evaluated and consequentely growth. Moreover, the effect of the reactor the particle size Densité'électronique'and the concentration [1]. stray capacitance on the power coupled to the 4E+15! plasma is underlined. Finally, a perfect 3,5E+15! correlation between the evolution of the size of 3E+15! 2,5E+15! the dust particles in the plasma and the 2E+15! 25=janv! increase of the plasma/electrode sheath 1,5E+15! ne'en'm^;3' capacitance (fig. 1) suggests that charged dust 1E+15! 27=janv! particles induce an electrostatic force on the 5E+14! plasma sheath. An analytical model is 0! 10! 15! 20! 25! 30! proposed in order to take this phenomenon into Fig.2 : Electron densityPuissance'injectée'en'W' evolution with the account in future dusty plasma electrical ! Figure'24:'Densité'électronique'en'fonction'de'la'puissance'injectée'pour'deux'séries'de'mesure,'une'réalisé'injected power. modelling [1]. le'25'janvier'et'la'seconde'réalisé'le'27'janvier'à'une'pression'de'1'mbar' Nous! pouvons! observer! que! les! deux! courbes! ont! la! même! tendance.! Nous! avons,! de! plus,!une!augmentation!de!la!densité!électronique!en!fonction!de!l’augmentation!de!la! puissance!injectée.!La!densité!électronique!moyenne!reste!dans!l’ordre!de!grandeur!de!References 1015!m=3.![1] G. Wattieaux and L. Boufendi, “Discharge ! ! impedance evolution, stray capacitance effect ! and corre- lation with the particles size in a ! ! dusty plasma,” Physics of Plasmas, vol. 20, p. ! in press, 2012. ! [2]G.Wattieaux, A.Mezeghrane, and L. ! ! Boufendi,“Electricaltimeresolvedmetrologyofd ! ustparticles growing in low pressure cold ! ! plasmas,” Physics of Plasmas, vol. 18, no. 9, p. ! 093701, 2011. Fig. 1: Comparison between sheath ! capacitance variation and particle size ! ! evolution. ! The presented method, which does not "! " Hénault!Marie,!Polytech’Orléans,!2012! require any current/voltage phase shift " "

P1-4 Tracking streamers: investigation of the sub-nanosecond light emission delays of nitrogen radiative states in gas excited by streamer

1 2 1 3 T. Hoder *, Z. Bonaventura , R. Brandenburg and A. Bourdon

1Leibniz Institute for Plasma Science and Technology - INP Greifswald, Greifswald, Germany 2Department of physical electronics, Faculty of science,Masaryk University, Brno, Czech Republic 3EM2C Laboratory, Ecole Centrale Paris, CNRS, Grande voie des vignes, Chatenay-Malabry Cedex, France *Contact e-mail: [email protected]

1. Introduction means that in the moment the emission is observed, In atmospheric pressure air microplasmas the the streamer is already 0.2 ns away. This fact is discharge usually takes a form of thin filaments of a important for exact analysis of any streamer-based streamer nature. The same mechanism rules the system where for streamer propagating with velocity lightning and transient luminous events in the of 10 6 m/s this delay corresponds to 0.2 mm of Earth’s atmosphere. In last years, the interest to actual streamer misplacement. This effect can cause investigate these phenomena experimentally was significant errors, e.g. in power balance estimation raised by increased accessibility of fast-gating by correlating optical observations with current and intensified CCD cameras. Such a boom of voltage measurements. automatized ICCD camera investigations however, The presented work emphasizes the necessity of is neglecting one important fact: by using an ICCD inclusion of highly-spatial and highly-temporal camera with nanosecond temporal resolution one resolved measurements in streamer-based discharge gets only very rough insight into the streamer analysis. processes happening in the scales of tens of picoseconds. Recently, one of the complications was pointed out for electric field estimation in [1, 2]. In this contribution, we follow the direction of preceding efforts [1, 2, 3, 4] towards a better understanding of ultra-fast streamer processes and we point out some other issues which should be not neglected. Both experimental and theoretical analysis of an ultra-short effect during the streamer propagation in atmospheric pressure air discharges is presented.

2. Experiment and results Fig. 1: Electric field and synchronous FNS intensity The measurements on positive and negative development. Signal maxima are denoted. streamers were conducted on Trichel pulses in negative corona discharge in atmospheric pressure References air using cross-correlation spectroscopy. The [1] G.V.Naidis: Phys.Rev.E 79 , 057401 (2009) achieved resolution was 10 microns in space and [2] Z.Bonaventura, A.Bourdon, S.Celestin, almost 10 picoseconds in time [5]. For each spatial V.P.Pasko: Plasma Sources Sci. Technol. 20 , coordinate the temporal development of the 035012 (2011) radiation of different spectral bands of molecular [3] Yu.V.Shcherbakov, R.S.Sigmond: J.Phys.D: nitrogen together with synchronous development of Appl.Phys. 40 , 460-473 (2007) the electric field was recorded [6], see Fig.1. [4] Yu.V.Shcherbakov, R.S.Sigmond: J.Phys.D: It is shown that as the streamer head (i.e. the Appl.Phys. 40 , 474-487 (2007) maximum of the electric field) passes a spatial [5] T.Hoder, R.Brandenburg, R.Basner, K.D. coordinate the emission of radiative states with Weltmann, K.V.Kozlov, H.E.Wagner: J.Phys.D: different excitation energies follows with different Appl.Phys. 43 , 123009 (2010) delays. This is shown for positive as well as negative [6] T.Hoder, M.Cernak, J.Paillol, D.Loffhagen, streamers. The maximum delay of about 0.2 ns was R.Brandenburg: Phys.Rev.E 86 , 055401(R) found experimentally for the emission of the first (2012) negative system of molecular nitrogen (FNS, 0-0 vibrational transition at wavelength 391.5 nm) behind the positive streamer. This finding actually

P1-5 Excitation mechanisms in dielectric barrier discharges containing CO2 at atmospheric pressure

F. Brehmer1,2*, S. Welzel1, H.J. van der Meiden3, M.C.M. van de Sanden1,3, R. Engeln1

1Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands 2AFS GmbH, Von-Holzapfel-Straße 10, 86497 Horgau, Germany 2Dutch Institute for Fundamental Energy Research, P.O. Box 1207, 3430 BE Nieuwegein, The Netherlands *Contact e-mail: [email protected]

19 -3 1. Introduction input gas is n0 = 2.4 x 10 cm ). Mixing ratios of In any scenario for storing renewable energy in CO and O3 were below 4.3% and below 0.1%, value-added hydrocarbons produced from CO2, the respectively. A monotonic trend with the injected dissociation into CO is known as the process specific energy was observed (fig. 2) at 1 atm. limiting step. To tackle the challenges in Deviations of this trend could be attributed to conventional production routes, non-equilibrium changes in temperature of the reactor. plasma processing is considered as an alternative approach. We report on a dielectric barrier discharge (DBD) that provides a convenient basis for fundamental studies of the plasma physics in pure CO2 plasmas at atmospheric pressure.

2. Experimental Setup The DBD was designed in parallel plate configuration using a discharge gap of 1 mm. Quartz barriers enclose the flow-tube. This specific design (fig. 1) allows active and passive optical (in-situ) diagnostics. The reactor itself is readily Fig. 2: Number densities of CO (full symbols) and O3 exchangeable, which enables comparison of (open symbols) vs. specific injected energy measured at different hardware parameters such as dielectric different excitation frequencies (60 kHz = triangles, 90 materials, their thicknesses and gap sizes. A kHz = circles) and residence times via ex-situ FT-IR absorption spectroscopy. matching circuit allows step-less tuning of the excitation frequency (30 … 130 kHz) which in turn Thomson scattering was applied to estimate the enables the resonant power injection to be adjusted. time-averaged electron temperature, t, which A careful electrical characterization was carried was of the order of 1.5 eV. This suggests high out to specify the energy efficiency and the relevant electron energies in the single microdischarges. capacities of the flow-tubes. The injected energy Time-resolved optical emission spectroscopy was was recorded directly via voltage and current used as complimentary diagnostic tool. The spectra measurements as well as using Lissajous figures. + mainly contain electronic transitions of the CO2 (A) and (B) states, which require excitation energies of ~20 eV per electron. Metastable CO could usually not be detected. The intensity of the spectra was correlated in time with the current peaks, again suggesting that single microdischarges are characterized by high electron energies which may also govern the CO2 conversion processes. CO2 excitation at high electron energies is mainly determined by significant electron impact excitation

Fig. 1: Schematic diagram of the setup used to and ionization. However, to achieve high CO2 perform optical emission and IR absorption spectroscopy. dissociation efficiencies, excitation of the asymmetric stretch mode would be beneficial. This 3. Results & Discussion requires electron energies of about 1 eV, i.e. far FT-IR absorption spectroscopy was used to below those present in the active plasma. detect stable species in the exhaust of the flow-tube. Additionally, quenching of electron impact The gas in the absorption cell can be assumed to be excitation of the vibrational modes is fast under fully relaxed (i.e. the neutral particle density of the atmospheric pressure conditions.

P1-6 Thomson scattering and laser collisional induced fluorescence on argon microwave discharges

E. A. D. Carbone∗, S. Hubner,¨ W. A. A. D. Graef, M. Jimenez Diaz, J. M. Palomares, J. van Dijk, J. J. A. M. van der Mullen, G. M. W. Kroesen

1 Technische Universiteit Eindhoven, The Netherlands ∗Contact e-mail: [email protected]

Microwave induced plasmas are applied in many particles kinetics [4]. The method is applied, for the fabrication processes such as the deposition of SiO2 first time, to a pure argon plasma. The results are for the production of optical fibers and the deposition compared with a time-dependent collisional radiative of Si to make solar cells. To control these deposition model (CRM) simulating the LCIF experiment. The processes a good understanding of the plasma kinet- argon CRM is found to give relatively good results for ics is required. steady state but significant discrepancies are found In this study, the surfatron source is chosen as a in the case of fast relaxation processes. Based on model system for the validation of different diagnos- the experimental results, a path for improvements of tic techniques and models [1]. One of its main advan- the CRM is given. LCIF is used to probe quenching tages is its flexible operation range and stability when mechanisms in the case of an argon-hydrogen plasma. operated in complex gases. Significant quenching by atomic hydrogen of argon Various experimental techniques, such as Thom- 4p states is demonstrated. son scattering, laser (collisional) induced fluores- In resume, advanced (time-resolved) diagnostic cence and optical emission spectrometry, are used to techniques and modelling tools are combined to ob- investigate the plasma properties as a function of ex- tain a complete picture of the plasma dynamics. The ternal parameters (e.g. the pressure and the gas com- surfatron source is shown to be a flexible and rel- position). atively simple tool for the investigation of plasma The radial electron density and temperature pro- chemistry. Although argon plasmas are usually con- files of the surfatron are measured by Thomson scat- sidered to be rather simple, if not trivial, the extensive tering for various pressures [2]. Radial contraction comparison between experimental results and state- is observed for pure argon plasmas above 20 mbar. of-the-art modelling shows that significant improve- Molecular ions are found to be partially responsi- ments can still be achieved in our understanding of ble for that trend but other effects such as Maxwell (microwave) argon plasmas. deviations cannot be neglected either. Deviations from maxwellian equilibrium are investigated as well References along the plasma column by a combination of exper- imental and modelling methods [3]. It is found that [1] M. Jimenez Diaz, et al. Journal of Physics D: the tail of the electron energy distribution function is Applied Physics, 45(33):335204, (2012). increasingly depleted for lower ionization degrees. [2] E.A.D. Carbone et al. Journal of Physics D: Ap- Electron and heavy particles kinetics are an im- plied Physics, 45(34):1–9, (2012). portant part of plasma dynamics and need to be in- cluded in any plasma model. In combination with [3] E.A.D. Carbone et al. Journal of Physics D: Ap- different diagnostic techniques, plasma sources can plied Physics, 45(47):475202, (2012). be used for the determination of rate coefficients as well. Pulsed laser collisional induced fluorescence [4] J.J.A.M. van der Mullen et al. Journal of Instru- (LCIF) can be used for studying electron and heavy mentation, 7, C05016, (2012).

P1-7 Characterization of the plasma structure of a Dielectric Barrier Discharge roller plasma source for material treatment at atmospheric pressure

1,2 1,2 1,2 1 M. Boselli , V. Colombo *, E. Ghedini , M. Gherardi , R. Laurita1, A. Liguori1, P. Sanibondi1 and A. Stancampiano1

Alma Mater Studiorum – Università of Bologna 1 Department of industrial engineering (DIN) 2 Industrial Research Center for Advanced Mechanics and Materials (C.I.R.I.-M.A.M.) Via Saragozza 8-10, 40123 Bologna, Italy

*Contact e-mail: [email protected]

1. Introduction maximum peak voltage some extremely luminous In the present study we investigate the structure filaments are visible in the acquired images. In the of the plasma generated by a Dielectric Barrier same acquisition several regions of apparently Discharge (DBD) roller plasma source operating at diffuse plasma condition are visible. Near the center atmospheric pressure in ambient air. This type of of the gap the plasma appears less intense than in source is particularly fit for treating heat sensitive proximity of the dielectric surface of both electrodes materials processed on rotating shafts (for example where it seems that a layer of plasma is formed. The polymers for biomedical or packaging applications), intensity and uniformity of these plasma layers however too aggressive treatments may induce increase with the peak voltage and the repetition damage on the processed material. The scope of this rate. Moreover, selected results of the treatment of work is to determine which geometrical and polymeric materials for packaging and biomedical operating conditions (gap distance, dielectric layer applications will be presented to correlate eventual width, peak voltage and pulse repetition frequency) treatment non-uniformities or damages to the plasma of the DBD roller result in a filamentary structure, structure. possibly causing treatment disuniformities and material damage, with the final aim of process optimization.

2. Method The DBD Roller plasma source is composed of two electrodes made of metallic rods covered by a dielectric layer and separated by a gap of a few millimeters (Fig. 1). One of the electrodes is grounded while the other is electrically connected to a high voltage pulse generator with nano-second rise time. An intensified Charge Couple Device (iCCD) camera with exposure time down to 3 ns, in some Fig. 1: Picture of the DBD roller setup and 50 ms cases implemented with High Speed Imaging (HSI) exposure time photograph of the inter-electrode region informations, has been adopted to characterize the plasma source in different geometrical and operating conditions.

3. Results A small selection of the acquired images for different operating conditions is shown in Fig. 2. In all the presented condition the plasma appears diffuse and uniform to the naked eye, but always presents at least a partial filamentary structure if observed in a nanosecond time scale. The overall light emission and the number of filaments increase Fig. 2: iCCD imaging of the inter-electrode region in the with the increase of the peak voltage and/or the DBD roller plasma source increase of the repetition rate of the pulse. At the

P1-8 Study of acetylene molecule fragmentation processes by electron impact

M. Danko , J. Országh, P. Čechvala, M. Ďurian, Š. Matej čík

Department of Experimental Physics, Comenius University, Slovakia *Contact e-mail: [email protected]

1. Introduction molecular fragment of CH emission, Mulliken 1 + 1 + 3 3 Acetylene is a gas used in such applications as (D Su →X Sg ) and Swan (d Pg→a Pu) bands of C 2. welding, polymer production [1] and artificial The thresholds for dissociative excitation reactions diamond growth [2]. It can be traced as well in the were evaluated on the basis of relative cross sections emission spectra of stars, nebulas and comets [3]. in the threshold region. The dissociative channels This simplest unsaturated hydrocarbon with a triple responsible for the formation of the excited states bond is studied to obtain a fundamental knowledge were proposed, and threshold energies based on about this group of molecules. The molecule enthalpies of formation of fragments for each dissociates upon electron impact excitation, leaving channel were calculated. excited fragments, which can be observed by optical

emission spectroscopy, in UV/VIS spectral range N 3.0 2 C H , 50 eV, 100 µm slits 2 2 namely H, CH, and C 2 [4]. 2 2 CH (A ∆-X Π) 2.5 + 1 1 + CH CH (A Π-X Σ ) 2. Experiment 2.0 2 - 2 N (B Σ -X Π) 2

The electron fluorescence spectroscopy was Hβ 1.5 Hζ Ηγ C (d 3Π -a 3Π ) applied to study fragmentation and excitation 2 g u Intensity [cps] 3 3 Hδ Swan system C (d Π -a Π ) processes of acetylene and to estimate the 1.0 Hε 2 g u Swan system corresponding threshold energies. The processes 0.5 were induced by impact of electrons with narrow 370 380 390 400 410 420 430 440 450 460 470 480 490 500 510 520 530 energy distribution of approximately 200 meV. The Wavelength [nm] experiment was conducted on an apparatus of crossed electron and molecular beams with Fig. 2: Fluorescence spectrum of acetylene induced by trochoidal electron monochromator [5]. The vacuum electron impact dissociative excitation process. chamber was pumped to 10 -8 mbar and filled with sample gas up to 10 -4 mbar. The fluorescence The relative emission cross section curves radiation was partially reflected by a mirror, and demonstrated a competition of more than one focused using a set of lenses onto the entrance slit of fragmentation channel for each dissociative an optical ¼ m Czerny-Turner monochromator and excitation channels of acetylene. This corresponds to the signal was detected by R4220P Hamamatsu the complexity of measured functions. Not all photomultiplier working in spectral region 185-710 proposed channels were observed though and their nm. inactivity was proposed.

Acknowledgments This work was supported by the projects Nr. APVV- 0733-11, SK-SRB-0026-11, DO7RP-0025-11 and VEGA- 1/0379/11.

References [1] H.Lischka, A.Karpfen: Chem. Phys. 102, pp 77 (1986) [2] J.A.Smith, E.Cameron, M.N.R.Ashfold, Y.A.Mankelevich, N.V.Suetin: Diamond and Fig. 1: Cross beam apparatus used for study of electron Related Materials 10, pp 358 (2001) induced fluorescence processes. [3] A.Tanabashi, T.Amano: Journal of Molecular Spectroscopy 215, pp 285 (2002) 3. Results and discussion [4] C.I.M.Beenakker, F.J.De Heer: Chem. Phys. Fluorescence spectrum in UV/VIS range was 6, pp 291 (1974) measured and the relative dissociative excitation [5] J.Matuska, D.Kubala, S.Matejcik: Meas. Sci. cross sections determined, leading to emission of Technol. 20, pp 015901 (2009) hydrogen atomic Balmer series lines (H(n→2)),

P1-9 Diagnosing a fast pulse in a linear plasma device

T. Morgan1, H.J. van der Meiden1, J. Scholten1, J.J. Zielinski1, T. de Kruif1, G. De 1* Temmerman

1Dutch Institute for Fundamental Energy Research, Association EURATOM-FOM, Trilateral Euregio Cluster, Nieuwegein, The Netherlands *Contact e-mail:[email protected]

1. Introduction The linear plasma devices Magnum-PSI [1] and Pilot-PSI [2] produce high density (~1020-1021 m-3) low temperature (<5 eV) plasmas which well reproduce the divertor conditions expected in the ITER tokamak. In combination with these continuous plasma conditions a millisecond length pulse of increased density (~1021-1022 m-3) and temperature (6-15 eV) can be superimposed by dischargi a capacitor bank system through the plasma source [3]. This can be used to replicate the effect of ELM transients on the plasma facing surface to determine the combined effects of transient and steady plasma exposure on both Fig. 1: Schematic drawing of the Pilot-PSI linear device erosion and retention of plasma facing materials. and the optical emission spectroscopy diagnostic

To assess the performance of this pulse two beam (see figure 1). Using this Hβ emission from diagnostic systems have been utilised and are the plasma can be used to determine the rotational presented here. and axial velocities of the hydrogen ions [5]. By attaching a fast visible CCD camera to the Littrow spectrometer, time-resolved measurements (of up to 2. 3D Thomson Scattering 0.1 ms for axial measurements and 1 ms for In Magnum-PSI a high resolution Thomson rotational measurements) of the pulse can now be scattering diagnostic is routinely used to assess the observed both close to the source and close to the radial distribution of electron temperatures and target. Furthermore electron density can be densities across the plasma column with a high determined through the Stark broadening of the spatial resolution of ~2 mm [4]. Unlike in normal lines. operation the increased plasma density during a pulse permits ne and Te to be determined from a By combining these diagnostics a full picture of the single laser pulse rather than statistically summed plasma conditions during a pulse can be determined. from many laser pulses. The capacitor bank system Techniques and data analysis will be presented for possesses a high repetition rate of up to 70 Hz. This both diagnostic systems. permits the same pulse to be applied many times during a single discharge. By incrementally References increasing the delay time between the Thomson [1] J. Rapp et al, Fusion Eng. Des. 85, pp1455 scattering system and the capacitor bank discharge (2010) time a full 3D picture of the pulse can be built in [2] G.J. van Rooij et. al. Appl. Phys. Lett. 90 time and radial directions. pp121501 (2007) [3] J.J. Zielinski et. al. Plasma Sources Sci. Technol. 21 pp065003 (2012) 3. OES velocity and density measurements [4] H.J. van der Meiden et. al., Rev. Sci. Instrum. 83 In Pilot-PSI the plasma emission is observed by a set pp123505 (2012) of 40 optical-fibre chords with a spatial resolution [5] A.E. Shumack et. al., Phys. Rev. E 78(4) pp of 1 mm in radial cross section across the plasma. 046405 (2008) These can be arranged to observe in both tangential and (approximately) normal directions to the plasma

P1-10 Molecular spectroscopy on a magnetized hydrogen plasma

N. Den Harder1∗ G. J. Van Rooij1

1FOM Institute DIFFER - Dutch Institute for Fundamental Energy Research, Association EURATOM-FOM, Trilateral Euregio Cluster, Nieuwegein, The Netherlands ∗Contact e-mail: [email protected]

1. Introduction The linear plasma generator Pilot-PSI at the FOM 12000 Institute DIFFER is used to study Plasma Surface 10000 Interaction[1]. In order to reach the high particle fluxes expected in the ITER divertor, a high density 8000 (1020 m−3), low temperature (1 eV) plasma is created using a cascaded arc source. The plasma is guided 6000 towards a target by a magnetic field. Background hy- Trot (K) drogen molecules diffuse into the plasma beam, par- 4000 ticipate in various Molecular Assisted Recombina- 2000 tion channels, and determine the overall plasma en- ergy losses[2]. The kinetics of these processes are 0 0 2000 4000 6000 8000 10000 12000 highly dependent on the internal energy of the hydro- Tgas (K) gen molecules. The present work concerns a spectroscopic study Fig. 1: Molecular rotational temperatures compared with of the internal energy of the hydrogen molecules via gas temperatures. the Fulcher-α band to yield insight in recombination 3. Conclusion rates and molecular densities and temperatures. Optical Emission Spectroscopy on the Fulcher 2. Results band was used to determine the vibrational, ro- The vibrational temperature of the molecules was tational and translational temperature of hydrogen determined by comparing measured emission line molecules surrounding the high-density magnetized intensities to calculated intensities using a simple plasma beam in the linear plasma generator Pilot- model[3]. The electron temperature needed as in- PSI. At electron temperatures of 3 eV, a vibrational put for the model was taken from Thomson Scatter- temperature of 1 eV was measured. At these con- ing measurements. A vibrational temperature of 1 eV ditions, the rate for negative-ion-mediated MAR and was found at an electron temperature of 3 eV. Using ion-conversion MAR are 1.7 · 10−16 m3s−1 and 9.5 · vibrationally resolved reaction rates and the measured 10−16 m3s−1 respectively. Rotational temperatures Tvib and Te, effective rates for negative-ion-mediated obtained from the Fulcher band were compared with MAR and ion-conversion MAR were estimated. the gas temperature obtained from line shape analy- The rotational temperature of the hydrogen sis. Rotational temperatures obtained from the Q(0- molecules was determined from the relative line in- 0) branch scale with the translational temperature. tensities in the Q(0-0) branch of the Fulcher band[4]. Molecular densities were computed from temperature Rotational temperatures were compared with trans- and pressure measurements. Molecular densities be- lational temperatures as determined from line shape tween 0.1 to 1 x 1020m−3 were found, which is of analysis. As shown in Fig. 1, the rotational tem- the same order as the plasma density. Lateral molec- perature scales with the translational temperature. ular velocity profiles were obtained. Typical speeds However, rotational temperatures were systemati- ranged from 500 to 1500 m/s. cally lower than the translational temperature. Mech- anisms to explain this discrepancy are currently under References investigation. Molecular densities were estimated us- [1] G.J. van Rooij, Applied Physics Letters 90, pp ing the gas temperature and pressure. 121501 (2007) Lateral velocity profiles of the hydrogen molecules were constructed from the Doppler shift [2] R.K. Janev, Physica Scripta 2002, pp 94 (2002) of the emission lines. The molecules were found to [3] U. Fantz, Plasma Physics and Controlled Fusion co-rotate with the ions at a small fraction of the ion 40, pp 2023 (1998) velocity. High temperatures were interpreted as the result of coupling to the magnetized plasma, further [4] G. Herzberg, Molecular spectra and molecular supported by the velocity profile of the molecules. structure, Vol. I. (Krieger publishing company, 1989) P1-11 OH density by time-resolved broad band absorption spectroscopy in a He-H2O dielectric barrier discharge with small O2 addition L. M. Martini1, G. Dilecce2,3, M. Scotoni1 and P. Tosi1

1Dipartimento di Fisica Universita` di Trento, via Sommarive 14, - 38123 Povo-Trento, Italy 2Istituto di Metodologie Inorganiche e dei Plasmi - CNR - UOS di Bari, via Orabona, 4 - 70125 Bari, Italy 3Istituto dei Materiali per l’Elettronica ed il Magnetismo - CNR - sede di Trento, via alla Cascata, 56/C - 38100 Povo-Trento, Italy ∗Contact e-mail: [email protected]

1. Introduction electrode area). Technical changes of the BBAS tech- The importance of the hydroxyl radical as an nique concern both the collimation of the light source oxidation agent in many atmospheric pressure dis- and the detection. We recall that the light source ia charge applications is well known, so that its local a UV LED, that is an extended source. To improve measurement in real operating conditions is desir- collimation we have reduced the source size by canal- able. Laser Induced Fluorescence (LIF) is the tech- izing the light into a nozzle with 100 µm exit bore. nique of choice for application to a wide variety of After collimation by a lens, the resulting beam re- discharge configurations [1], due to its unique com- mains well collimated for distances up to about 50 bination of time/space resolution and sensitivity, but cm from the source. The change in the detection sys- it requires a calibration. We have recently developed tem consists in the use of a modern cooled ICCD, a time-resolved broad-band absorption spectroscopy compared to the previous non-cooled linear CCD ar- (TR-BBAS) set-up [2] with the aim of calibrating a ray. We shall discuss the effects of these changes in LIF measurement, but its utility as a stand-alone tech- the performance of the technique. nique soon came out. Although not much sensitive (lower detection limit about 5 × 1012cm−3) and lim- 3. Results ited to relatively large discharges (for an absorption Results show a measurable dependence of OH length of some cm with single/double-pass path), it concentration on small O2 additions, but less marked is simple and low cost, it gives absolute density val- than that reported in [3]. Densities are in the ues and a simultaneous measurement of the ground range (2-6)×1013cm−3, lower than those, about (1- state rotational temperature. In [2] we also discussed 3)×1014cm−3, calculated in [3]. We recall that possible technical improvements to enlarge BBAS model results refer to a RF discharge at constant sensitivity and flexibility. power density of 10 W/cm3 (1 W/cm2 with 1 mm OH concentration measurements in test cases is also inter-electrode gap). In addition to the absolute value of interest for comparison to model calculation out- difference, that might be ascribed to the different ge- comes. The hydroxyl radical is one of many reactive ometry, we observe a striking difference in the be- oxygen species (ROS) that can contribute to oxida- haviour at very low oxygen addition. In particular a tion processes, the others being O, O3,H2O2, HO2, sudden decrease of OH concentration followed by a 1 O2(a ∆g). Understanding and improving processes smooth increase, in contrast to the calculated contin- then requires both the knowledge of single species uous increase up to 1 % of O2. In the paper we shall concentration and the possibility to change their rel- discuss the discrepancies, but we believe that, in real ative amount by changing external parameters. One discharge systems, the electrical power is not a good such possibility is by addition of small O2 quantities parameter, i.e. its constancy does not ensure the in- to He-H2O mixture in a discharge. Recent model cal- variance of electron impact processes. culations have shown interesting results [3]. In this contribution we present our newest attempts References to improve the TR-BBAS technique applied to a He- [1] G. Dilecce and S. De Benedictis: Plasma Phys. H2O-O2 dielectric barrier discharge aimed at a com- Controlled Fusion 3, p. 124006 (2011) parison to model calculations. [2] G. Dilecce, P.F. Ambrico, M. Simekˇ and S. 2. Experimental De Benedictis: J. Phys. D: Appl. Phys. 45, p. The discharge is made of two 35 × 35 mm par- 125203 (2012) allel plates covered by 0.7 mm thick alumina, with 5 mm gap. It is operated at a frequency of 20 KHz in [3] K McKay, D X Liu, M Z Rong, F Iza and M a power range of 11.5-13 W, i.e. around 8 W/cm3 G Kong, J. Phys. D: Appl. Phys. 45, p. 172001 and 4 W/cm2 (the surface density is referred to the (2012)

P1-12 Investigations of low-k dielectric damage in plasma etching environments

1 2 1 1 Z. El Otell , P. Verdonck , M. Bowden , N.St.J. Braithwaite * *Contact e-mail: [email protected]

1 Dept. Physical Sciences, The Open University, Walton Hall, MK7 6AA, UK 2 IMEC, Kapeldreef 75 3001 Leuven, Belgium

Plasma-based processing continues to provide The conductor-semiconductor junction hosts a many of the solutions to the challenges of depletion region with comparable nonlinearities to a manufacturing of electronic components on single plasma boundary sheath. chips. As substrates have become larger, a key challenge has emerged relating to the need to use low-k dielectrics between interconnects on a chip to minimize RC time constant effects. Open-structured materials are used but these are themselves susceptible to inadvertent damage during the manufacturing sequence, caused by exposure to etching and deposition plasmas.

To provide insight into plasma-induced degradation of low-k dielectric an ‘in-plasma’ monitor, of a thin layer of low-k dielectric, has been developed. The method is an adaptation a planar, surface-mounted ‘ion flux’ probe. This probe uses Fig. 1: Transient discharge of a 22 nF external bursts of RF (or pulsed DC) in conjunction with the capacitance coupled to a tile of bare TiN (solid line) and nonlinear sheath that forms at plasma boundaries to a tile of TiN with a 100 nm coating of SiO2 (broken line), provide transient DC bias. Since it uses RF to in almost identical plasmas. generate its bias potentials this probe design is tolerant of insulating surface films. The transient Experiments and models are underway to behaviour of the probe is determined in part by a decouple the effects of the substrate from the effects selected external capacitance that sets the timescale of the plasma. This is necessary for the method to for the measurement; typically this timescale is a provide a quantitative diagnostic of plasma-induced few hundred microseconds. The response to bursts dielectric damage. of RF (or pulsed DC) is also determined in part by the capacitance of any dielectric coating on the References probe surface. In this case that dielectric coating is a [1] N. S. J. Braithwaite, J. Booth, and G. Cunge, Plasma thin layer of low-k dielectric. Sources Sci. Technol. 5, 677 (1996).

[2] V. Šamara, J.-P. Booth, J.-F. De Marneffe, A P. The effect of plasma exposure on dielectric Milenin, M. Brouri, and W. Boullart, Plasma Sources Science and Technology 21 , 065004 properties is studied in the following manner. A (2012). planar, surface-mounted probe has been formed from an isolated 1.4 x 1.4 cm tile of semiconductor wafer, coated with several nm of titanium nitride conductor (the primary probe surface), which is in turn coated with about 100 nm of test dielectric. The probe is placed behind a 1.0 x 1.0 cm opening in an alumina wafer that makes shielded electrical contact with a circumferential strip of exposed titanium nitride. The feasibility of the method has been demonstrated using a simple silicon dioxide dielectric (Figure 1). The presence of these coatings can be easily detected in situ. Interestingly the silicon substrate on which the first designs of this dielectric monitor have been based provides in effect a solid-state plasma on the back side of the probe.

P1-13 Advanced retarding field analyzer technology for ion energy measurements and species identification in CW and pulsed plasma

David Gahan 1*, Gilles Cunge 2 and M. B. Hopkins 1

1Plasma Research Group, Impedans Ltd, Woodford Business Park, Santry, Dublin 17, Ireland 2 Laboratoire des Technologies de la Microelectronique, CNRS, Grenoble Cedex 9, Isere 38054, France *Contact e-mail: [email protected]

1. Introduction and thus allowing the RFA to operate under p-RF Retarding field analyzers (RFAs) have been used bias conditions. for many decades to measure the energy of ions at various locations in plasma discharges. In general, the most important location at which to measure ion energies is at the substrate location. Electrical bias signals are commonly applied to the substrate holder to enhance the substrate processing. The application of bias signals complicates the measurement of the ion energy at the substrate location. Previously, RFA technology has been developed [1], which is suitable for time averaged ion energy measurements at direct current (DC) biased and continuous-wave (CW) radio-frequency (RF) biased substrates. There are, however, myriad other types of bias signals used to process substrates. These Fig. 1: Time resolved ion energy distributions in a p-DC include pulsed direct-current (p-DC), pulsed RF (p- magnetron sputtering reactor. RF) and ‘tailored’ waveform bias signals. Process engineers and researchers have a host of other requirements of the RFA technology including time resolved capabilities, spatial mapping of the ion energy across the substrate and species identification. In this paper a number of advances to the standard RFA technology are discussed.

2. Results 2.1. p-DC - time resolved capability In order to make time resolved ion energy measurements with 100ns time resolution the ion current detector must to able to float at the bias potential applied to the substrate holder and must be Tab. 1: Time averaged ion energy distributions in a p-RF completely isolated from ground. This provides a plasma [2]. considerable technical challenge. The circuitry was developed and 100ns time resolution was achieved 2.3. Spatial mapping and species discrimination with an upper frequency limit of 350 kHz. A typical The first results of ion energy measurements made at measurement in a p-DC magnetron sputtering 13 locations simultaneously, across a 300mm reactor is shown in figure 1. substrate holder, are presented showing the spatial variation of ion energy and ion flux during plasma 2.2. p-RF time averaged capability processing. Initial measurements are also presented p-RF processes use repetitive pulsing of the RF which illustrate the potential for the RFA to be used power source and/or bias to achieve plasma to discriminate between ion species. properties that are not possible in CW mode. The repetition frequency is typically in the range 1 – 20 References kHz. The standard RFA technology incorporates RF [1] D. Gahan, B. Dolinaj and M. B. Hopkins: Rev. low pass filters which work in the range 400 kHz to Sci. Instrum. 79 (3) (2008). 100MHz. Advance filtering techniques were used to [2] M. Brihoum et al : J. Vac. Sci. Technol. A 31 (2) extend the operating range from 1 kHz to 100 MHz (2013).

P1-14 Electron Density and Temperature Measurements from Thomson Scattering in a kHz driven Atmospheric Pressure Plasma Jet.

W. Adress, E. Nedanovska, G. Nersisyan, D. Riley and W. G. Graham*

Centre for Plasma Physics, Queen’s University Belfast, BT71NN, United Kingdom *Contact e-mail: [email protected]

1. Introduction arrangements ensure that the laser and camera are Atmospheric pressure plasma jets, APPJs triggered so as simultaneously intercept and observe are attracting substantial interest because of their the plasma bullet. The plasma jet can be moved capability to deliver significant densities of reactive axially and radially with respect to the intersection species remote from the discharge region. While the point. Various corrections and calibrations were optical and chemical properties of such systems required to extract the Thomson signal and to have received significant attention, there is still a determine the plasma properties. lack of experimental data on the electron densities and electron temperatures. Here Thomson 3. Results Scattering is used measure the temporal and Along the central axis in the axial direction spatially resolved properties of the electrons in a (distance from the exit of the tube), the electron kHz-driven, APPJ operating in helium. Since the jet density decreases from 6 x 1013 cm-3, at 1.25 mm propagates into air a key aspect of this approach is to from the exit of the quartz tube to 1 x 1013 cm-3 at distinguish the three types of laser scattering 4.25 mm, while at the same positions the electron Rayleigh, Thomson and Raman [1]. temperature remains essentially constant at 0.1 eV. In the radial direction the measured electron 2. Experimental Details densities and the electron temperatures are both The APPJ is based on that first described by found to increase towards the outer edge of the Teschke et al [2]. It consists of a cylindrical quartz plume. For example both the electron density and tube of 4mm inner and 6mm outer diameter with temperature increase by a factor of about three at 2 helium gas flowing at 2 slm. Two copper electrodes, mm, at an axial distance of 1.25 mm. Smaller radial 2.5cm apart, surround the quartz tube. The upstream changes are seen further from the exit of the tube. electrode is grounded and the downstream, 4 mm The magnitude of the increases is not symmetric from the end of the tube, is connected to a power about the axial direction. Both these observation are supply which generates a 50µs long, 6 kV bipolar consistent with previous radial light emission pulse at 20 kHz. As described previously, an intense measurements [4]. The measured electron density streamer discharge is created inside the tube, and temperatures are consistent with the recent between the two electrodes [3]. A plasma plume, ~ computational study by Breden et al [5]. 3 cm long, propagates into the surrounding air in the helium gas channel. It is well established that the 4. References plume is an ionization streamer consisting of [1] A. F. H. van Gessel, E. A. D. Carbone, P. J. “plasma bullets” [3]. Bruggeman, and J. J. A. M. van der Mullen: Plasma A 10 cm focal length lens focuses the Sources Sci. and Technol. 21, 015003 (2012) second harmonic of a 10 Hz Nd:YAG laser (532nm) [2] M. Teschke, J. Kedzierski, E. G. Finan-Dinu, D. Korzec, and J. Engemann: IEEE Trans. Plasma Sci. onto the radial centre of the plume. The scattered o 33, 310 (2005) laser light is collected at 90 to the direction of both [3] X.P. Lu and M. Laroussi: J. Appl. Phys. 100, the probing laser beam and plasma plume and 063302 (2006) focused onto the entrance slit of an imaging double [4] Q.T. Algwari and D. O’Connell: Appl Phys Lett. 99 grating spectrometer SPEX 750, with two 1200 121501 (2011) l/mm gratings which provides 5.7Å/mm dispersion [5] D.Breden, K.Miki, and L.Raja: Appl Phys Lett. 99, 111501 (2011) at a gated ICCD camera. Timing and triggering P1-15 First Realistic validation of Plasma Air treatment with QCL-OFCEAS detection of formaldehyde below ppb range

O. Guaitella1*, C. Barakat1, E.Fasci1, A. Rousseau1, P. Gorrotxategi Carbajo2, I.Ventrillard2, M. Carras3, G. Maisons3, D. Romanini2

1LPP, Ecole Polytechnique, UPMC, Université Paris Sud-11, CNRS, Palaiseau, France 2 Laboratoire Interdisciplinaire de Physique (LIPhy), CNRS UMR 5588, Université J. Fourier de Grenoble, 38402 St Martin d'Hères, France 3 Alcatel Thales III-V lab, Av. Augustin Fresnel, Campus Polytechnique, Palaiseau, France (*) [email protected]

1. Introduction measurements of H2CO, which will be applied both One of the most advanced applications of NTP in plasma diagnostic and environmental (especially for environment is the abatement of diluted indoor) concentration monitoring of this specie. pollutant, especially for indoor air treatment. The laser radiation, which can be turned over Dielectric Barrier Discharge (DBD) and Corona about 7 cm-1 by temperature, is directly coupled to a discharges in air are the most frequently used high finesse (HF) V-shaped cavity, by means of an discharges for volatile organic compounds removal aspheric lens of 1.87 mm focal length. Spectral data [1]. Plasma is very often coupled with adsorbent points correspond to cavity modes, which are and/or catalytic materials. Several systems are uniformly spaced and offer a spectral resolution of already on the market in spite of the lack of 150 MHz (0.005 cm-1) for a 1m long V-shape cavity validation of such systems at low concentration of with a spectral definition in the 10 kHz range. In pollutant. Indeed, odours usually correspond to VOC addition the high reflectivity of the mirrors provides concentration below ppm level. The sensitivity of an optical interaction path of about 10 km. the diagnostics the most commonly used for A minimum detectable absorption coefficient of studying the efficiency of plasma/catalyst coupling 1 x 10-9 cm-1 was demonstrated in 100 ms of such as FTIR or gas chromatograph does not provide integration time (single laser scan) which for CH2O sensitivity high enough to validate the destruction of corresponds to a detection limit of 120 ppt. A a pollutant with an initial concentration of less than preliminary study of the Allan Variance of the 1 ppm. Therefore, we have developed a new system measured data shows that averaging over 10 seconds capable to detect formaldehyde in ppt range. yields an improvement of 10 times, leading to a The aim of this work was then to develop a detection limit down to the 10 ppt range. sensor based on cavity enhance absorption Thanks to this very sensitive tool a packed bed spectroscopy with optical feedback in order to like DBD reactor was evaluated in terms of validate the efficiency of our plasma/catalyst formaldehyde destruction. coupled reactor for the destruction of VOCs at realistic concentration of pollutant. 3. Conclusion For the first time a detection system with 2. Principle of the QCL-OFCEAS system sensitivity compatible with concentration level of The detection system is based on a continuous odours has been developed and then used for the wave Distributed Feed Back Quantum Cascade validation online of plasma/catalytic reactor. The Laser (DFB-QCL), realized at Thales-III-V lab [1]. good results obtained on formaldehyde destruction This single mode laser emits at a wavelength of in ppb range represent an important step forward the 5.65 µm at room temperature. It has been employed development of really efficient indoor air treatment to match molecular fundamental vibration devices. transitions of formaldehyde (H2CO). OF-CEAS is a very sensitive technique, which References combines absolute calibration performed by Cavity [1] O. Guaitella, F. Thevenet, E. Puzenat, C. Ring Down Spectroscopy together with the fast Guillard, A.Rousseau Applied Cata. B. 80 response time of Cavity Enhanced Absorption (2008) 296–305 Spectroscopy. It has been largely used until now, [2] M.Carras et al., App. Phys. Letters, 96 (2010) above all, in the near infrared region, in medical 161 diagnosis [2], as well as in atmospheric gas analysis. [3] I. Ventrillard-Courtillot et al., J. Biomed. Opt., After only one year of the first demonstration of 14 (2009) 6 QCL based OF-CEAS [3], we have built a compact [4] G.Maison et at., Opt Lett., 35 (2011) 21 and robust instrument capable to perform fast

P1-16 On plasma chemistry in an industrial nitriding DC plasma reactor

S. Hamann 1*, K. Börner 2, I. Burlacov 2, H.-J. Spies 2, J. Röpcke 1

1INP Greifswald, Felix-Hausdorff-Str. 2, 17489 Greifswald, Germany 2TU Bergakademie Freiberg, Gustav-Zeuner-Str. 5, 09599 Freiberg, Germany *Contact e-mail: [email protected]

1. Introduction Furthermore other dependencies were studied in a The active screen plasma nitriding (ASPN) is an wide parameter range of the applied screen power, advanced technology for the plasma nitriding of the total pressure, the partial pressure of the steel components. The advantages of this technique precursors, and the variation of the N 2-H2 mixture. over conventional plasma nitriding are (i) a homoge- From the measured absolute concentrations of neous temperature distribution and (ii) the non- CH 4 and CO 2 the degree of dissociation of the appearance of arcing damages [1]. Meanwhile precursors and the fragmentation rate were ASPN has been proven its industrial applicability, calculated. but however the treatment processes and, in particular, plasma chemical phenomena are far from being completely understood [2]. Recent studies showed the high applicability of IR-laser absorption spectroscopy as a powerful tool for diagnostics of technological plasma processes [3-4].

2. Experimental setup This study presents the results of spectroscopic investigations of a N 2-H2 containing pulsed DC plasma in an industrial-scale reactor with an inner volume of about 1 m3. The model probe (horizontal arranged, 26 punched discs with 65 mm in diameter on a length of 480 mm) – which simulated the Fig. 1: The concentrations of the detected species treated workload – in the middle of the reactor was depending on the CH 4 admixture measured by TDLAS in surrounded by the cylindrical active screen – a the plasma of the biased probe (P = 1 kW, p = 2 mbar) double wall metal mesh with 800 mm in diameter Using (i) the Doppler broadening of the Q(3,3) and 750 mm in height. Two separate generators absorption line of the CH radical and (ii) the supplied the active screen at P = 10 kW 3 max (0-0) band of the first negative system of the N +-ion (f = 1 kHz, 60% duty cycle) and the negative biased 2 recorded by OES the gas temperature in the plasma model probe at P = 1 kW (f = 10 kHz, 50% duty near to the model probe and near to the screen was cycle). CH and CO have acted as precursors. 4 2 found to be up to 850 K. Using in-situ tunable diode laser absorption spectroscopy in the mid-infrared spectral range References (TDLAS) the concentration of the precursors, CH 4 [1] C.Zhao, C.X.Li, H.Dong, T.Bell: Surf. Coat. and CO , of NH , of the hydrocarbon byproducts 2 3 Technol. 201 (2006) 2320 (C H , C H , CO) and the CH radical near the 2 2 2 4 3 [2] I.Burlacov, K.Börner, H.-J.Spies, H.Biermann, treated components could be determined. Using D.Lopatik, H.Zimmermann, J.Röpcke: Surf. optical emission spectroscopy (OES) the trends of Coat. Technol. 206 (2012) 3955 atomic hydrogen and atomic and molecular nitrogen [3] F.Hempel, N.Lang, H.Zimmermann, S.Strämke, emissions near the screen plasma were qualitatively J.Röpcke: Meas. Sci. Technol. 21 (2010) 085703 monitored. [4] N.Lang, F.Hempel, S.Strämke, J.Röpcke: Jpn. J.

Appl. Phys. 50 (2011) 08JB04 3. Results Fig. 1 shows the dependencies of the concentration of the detected species monitored by TDLAS on the CH 4 admixture which were found to be in the range of 10 12 to 10 15 molecules cm -3.

P1-17 Diaphragm discharge ignition supplied by DC non-pulsing voltage in electrolyte solutions with different conductivities

L. Hlochova*, M. Vasicek, Z. Kozakova, F. Krcma

Brno University of Technology, Faculty of Chemistry, Purkynova 118, 612 00 Brno, Czech Republic *Contact e-mail: [email protected]

1. Introduction increases with the solution conductivity increase. Electrical discharges generated directly in liquids The breakdown voltage as well as breakdown or direct plasma interaction with liquid phase is one current is higher in the case of thicker dielectric of the hot topics of the contemporary plasma barrier (i.e. in capillary configuration) because of the research. The plasma in water solutions can be higher resistivity at capillary part of the whole generated by various electrode configurations, and it discharge-solution interelectrode system. The lower can be supplied by many kinds of the applied stability of the thinner diaphragm system is due to voltage from DC up to MW frequencies using rapid movement of the microbubbles out of pin-hole. pulsed as well as non-pulsed regimes [1, 2]. 120 The presented contribution deals with the direct 275 S/cm 400 S/cm observation of the pin-hole discharge breakdown in 100 550 S/cm water solutions. In this case, both electrodes are 750 S/cm 980 S/cm immersed inside the liquid phase, and the electrodes 80 are separated by a dielectric barrier with a small 60

orifice. If the aspect ratio (thickness/diameter) is [mA] I about 1 (thin barrier with a relatively big orifice), the 40 discharge is called the diaphragm discharge; if the 20 aspect ratio is much higher than 1, the discharge is 0 called the capillary discharge. The non-pulsing DC 200 400 600 800 1000 1200 1400 1600 voltage was used for presented study. The time U [V] resolved current-voltage characteristics were applied Fig. 1. Mean current-voltage characteristics (pin-hole for the discharge breakdown determination [3, 4]. diameter of 0.3 mm, thickness of 0.6 mm).

275 S/cm 600 2. Experiment 400 S/cm 550 S/cm The batch discharge reactor (volume of 110 ml) 500 750 S/cm was used for this study. The stainless steel electrodes 980 S/cm were separated by the Shapal-MTM ceramics. Two 400

diaphragms with one central orifice (diameter of 300 I [mA] I 0.3 mm) with thickness of 0.6 and 1.5 mm were 200 used for the contemporary experiments. NaCl solutions with conductivity of 275, 400, 550, 750, 100 −1 980 μS∙cm were prepared. The discharge ignition 0 200 400 600 800 1000 1200 1400 1600 1800 arises in the middle of the reactor at the edge of the U [V] diaphragm. Fig. 2. Mean current-voltage characteristics (pin-hole Diagnostics of the system were performed by a diameter of 0.3 mm, thickness of 1.5 mm). two channels Tektronix TDS 1012B oscilloscope. The high voltage was measure between electrodes, Acknowledgement the currents was measured from voltage drop on This research was done under project of Czech ballast resistor (5 Ω). Ministry of Culture No. DF11P01OVV004. References 3. Results [1] A.T. Sugiarto, S. Ito, T. Ohshima, M. Sato, J.D. The measured mean current-voltage characteris- Skalný: J. Electrostatics 58, pp. 135 (2003) tics are given in Figs. 1 and 2. The current density [2] S.M. Thagard, K. Takashima, A. Mizuno: increases inside the pin hole and thus the Plasma Process. Polym. 6, pp. 741 (2009) microbubbles are generated, here. The discharge is [3] F. Krčma, L. Hlavatá, L. Hlochová: Proc. ICPIG consequently ignited in these microbubbles. Due to XXX, C10-164, 4 pp. (2011) the fact that resistivity (and thus Joule heating) is [4] L. Hlochová, L. Hlavatá, Z. Kozáková, F. indirectly proportional to the conductivity the Krčma: J. Phys. Conf. Ser. - submitted breakdown voltage decreases and breakdown current

P1-18 Study of aluminium tri-isopropoxide (ATI) chemistry in an rf plasma by FTIR spectroscopy

M. Hübner 1* , M. Fröhlich 2, H. Tawidian 3, M. Mikikian 3, H. Kersten 2, J. Röpcke 1

1Leibniz Institute for Plasma Science and Technology e.V. (INP), D-17489 Greifswald, Germany 2Institute of Experimental and Applied Physics, Kiel University, D-24098 Kiel, Germany 3GREMI, UMR 7344, CNRS/Université d’Orléans, 45067 Orléans Cedex 2, France *Contact e-mail: [email protected]

1. Introduction sensitivity has been in the order of The deposition of metal oxide layers is of 10 13 molecules cm -3. Altogether, seven species have increasing interest. Their properties open up a large been detected during the plasma process, i.e. ATI, field of applications. E. g. Al 2O3 layers on cutting CH 4, C 2H2, C 2H4, C 2H6, CO and HCN. tools provide hardened surfaces with increased resistance functionality. Furthermore, the density, 3. Experiment / Results adhesion and diffusion barrier properties of alumina For the characterisation of the complex plasma, coatings make them quite valuable for aerospace several important parameters have been calculated, propulsion applications. The Al 2O3 film can be i.e. degree of dissociation D ATI [%], fragmentation -1 deposited using plasma-enhanced chemical vapour efficiency F E [molecules J ] and fragmentation rate -1 deposition (PECVD) with aluminum tri- FR [molecules s ]. Additionally, in order to study the isopropoxide (ATI) as precursor gas. That means the deposition, the carbon balance B Carbon [%] has been properties of the layer are strongly influenced by the calculated and analysed. ATI-containing plasma. Thus, a better understanding As an example, in figure 1 the concentration n ATI is needed in order to further improve the deposition of ATI and the degree of dissociation D ATI at a of alumina. pressure of p=6 Pa and a gas mixture of The aim of the work is to obtain general Ar/N 2/ATI=1/1/1 is shown. information about the ATI formation and to study its ] conversion into by-products using FTIR diagnostic. -3 100 10 These tasks have been investigated by studying the n ATI 80 influence of the variation of several parameters, i.e. D 8 ATI gas mixing ratio, pressure and power. 60 molecules cm 6 14 40 2. Experimental setup 4 The experiments have been carried out in an 20 asymmetric coupled RF discharge at a frequency of 2

13.56 MHz working at pressures in the Pa-range. 0 0 Degree dissociation of[%] ATI More details are given in [1, 2]. The gas mixtures 0 20 40 60 80 100 ATI concentration[10 ATI power [W] consist of Ar, N 2 and ATI. While Ar and N 2 have Fig. 1: Concentration of ATI and degree of dissociation been controlled by mass flow controllers, ATI, in dependence on the discharge power in an Ar/N 2/ATI usually present as a powder, has been heated above plasma, p = 6 Pa, gas ratio Ar/N 2/ATI=1/1/1 [3]. the boiling point. Consequently, the vapour pressure has initiated the ATI flow. Acknowledgements In order to determine the ATI flow, a needle The work was supported by Deutsche valve has been used to set a constant flow which was Forschungsgemeinschaft SFB-TR 24, Projects B2, calculated by measuring the increase of pressure B13. The authors thank F. Weichbrodt and V. after turning of the pumping system. Rohwer for technical support. H.T. and M.M. would The gas composition has been determined using like to thank the financial support of ANR, project Fourier Transform Infrared, FTIR, spectroscopy INDIGO, ANR-11-JS09-010-01. combined with an optical long pass cell which increases the absorption length to 17.2 m. The References identification and quantification of the species have [1] D. Lopatik et al.: Contrib. Plasma Phys., 2012 been performed with the help of spectral databases. [2] S. Niemietz et al.: Plasma Process. Polym. For ATI, a calibration has been done prior to the 9(2012), 904-910 measurements. Depending on the species, the [3] M. Hübner et al.: to be submitted, 2013

P1-19 ∗ Density of atoms in Ar (3p54s) states and gas temperatures in an argon surfatron plasma measured by tunable laser spectroscopy

S. Hubner¨ 1∗ , N. Sadeghi2 , E.A.D. Carbone1 and J.J.A.M. vd Mullen1

1Department of Applied Physics, Technische Universiteit Eindhoven, The Netherlands 2LIPhy, Universite´ Joseph Fourier-Grenoble & CNRS(UMR5588), France ∗Contact e-mail: [email protected]

1. Introduction good agreement is found. Argon atoms excited into the 4s(1s) levels-group The absolute Ar(4s) densities are in the order of are often the most abundant energy carrying atoms in 1016 − 1018 m−3, decreasing sharply with pressure argon plasmas. This is the basic mechanism of re- before reaching a plateau around 20 mbar and subse- mote plasma applications where the efflux of Ar(4s) quently increasing. It also increases slightly along the from the plasma can be used to generate excimers or plasma column. other active species for various applications [1] by ex- Measured Ar(4s) densities are compared to a Col- citation transfer or by Penning ionization. lisional Radiative Model, by using previous Thomson To determine the absolute number densities of Ar scattering results on ne and Te as input parameters for atoms in the 4s levels, the optical absorption spec- the CRM. Presented in figure 1, the simulated densi- troscopy on Ar(4p)-Ar(4s) transitions is the most ap- ties are in good agreement with the experiments. The propriate method. Ar(4s) densities seem to scale with Te of which its In this study, we use a narrow band tunable diode pressure dependence is also shown. An increase from laser (TDL) as light source. The spectral profile of 1 to 2 eV results in 2 orders of magnitude higher den- the line absorbed by atoms in one of the Ar(4s) states sities. That can be understood intuitively by the ex- is recorded by scanning the wavelength of the TDL ponential dependence on Te of the excitation rate of across the atomic line shape. The main advantage of these atoms k0−>4s exp (−E4s/kBTe). this method, compared to the broadband absorption is, that, because of the fact that ∆νlaser << ∆ν2p−1s, the density of the absorbing atoms and separately the gas temperature Tg can be determined without any

-4

10

deconvolution procedure [2] from the width of the 2.0 n(1s5) recorded line profile, see e.g.[3]. n(1s4)

n(1s3)

-5

10 The plasma source is a microwave driven surface T (TS) e 1.5 wave discharge, launched by a surfatron configura- a

-6

10 tion. The pressure range of this study is 0.65 < p < (eV) e 1.0 n(1s) / n 100 mbar and the plasma source allows a (quite) in- T

dependent tuning of the electron density (ne) while -7 10 0.5 maintaining the electron temperature (Te) to more or less the same value.

-8

0.0 10

With two diode lasers used in this work, den- 1 10 100 sities of atoms in 1s3, 1s4 and 1s5 levels could be pressure (mbar) probed from absorption signals on 2p2-1s3, 2p7-1s5, 2p7-1s4 and 2p9-1s5 (Paschen notation) transitions. Fig. 1: Pressure dependence of measured and simulated At gas pressures of p < 10 mbar, the line profile is Ar(4s) densities, normalized to the ground state density. mainly Doppler broadened. For higher pressures, the Te is also shown to illustrate its influence. pressure broadening is no more negligible and Tg is deduced by fitting the line profile with a Voigt func- References tion. [1] M.E. Bannister J.L. Cecchi: J. Vac. Sci. Tech- 2. Results nol. A 12, pp 106 (1994) Scanning the mentioned pressure range, gas tem- peratures in the range of 480-750 K are measured, in- [2] M. Kogelschatz , G. Cunge and N. Sadeghi: J. creasing with the pressure. Tg was compared to pre- Phys. D 37, pp 1954 (2004) vious Rayleigh scattering measurements. Taking into account the non radial-homogeneity of Tg and the fact [3] J.M. de Regt, R.D. Tas, J.J.A.M. vd Mullen: J. that laser absorption is a line of sight measurement, a Phys. D 29, pp 2404 (1996)

P1-20 The memory effect on the breakdown of atmospheric pressure air studied on transient spark discharge using fast iCCD camera

M. Janda 1*, V. Martišovitš 1, Z. Machala 1

1Faculty of Mathematics, Physics and Informatics, Comenius University Bratislava, Slovakia *Contact e-mail: [email protected]

1. Introduction density during the spark phase of TS (Stark Transient spark (TS) is a streamer-to-spark broadening). Finally, the imaging of TS was used to transition type discharge initiated by a streamer observe the influence of f on the propagation of the followed by the gas breakdown and a short (~10 ns) streamer, and the evolution of the plasma channel spark current pulse (~ 1 A) [1-3]. We studied this diameter. discharge of positive polarity in atmospheric Both electrical and optical data showed pressure air in point-to-plane geometry. Despite differences between TS at ‘low’ f (below ~3 kHz) using DC high voltage (HV) power, TS has a and at ‘high’ f (~6 kHz). There was almost no delay repetitively pulsed character: and the streamer-to- between the streamer and the spark at ~6 kHz. The spark transition repeats in the kHz frequency range. OES and imaging showed disappearance of atomic It is due to periodical charging and discharging of lines and no constriction of plasma channel during the internal capacity C of the used electric circuit. the spark phase at ~6 kHz. Thanks to the small value of C (~10-40 pF), the The increase of Tstreamer with growing f explains the plasma formed during the short spark pulse of TS observed decrease of the breakdown voltage, while cannot reach LTE conditions and so differs from a the reduced electric field E/N, at which streamer classical spark. TS generates highly reactive non- initiating TS starts, does not change with f. We equilibrium plasma, as indicated by optical emission suppose that for TS below ~3 kHz, the breakdown spectroscopy (OES). Several excited species, such as mechanism suggested by Marode [4] is crucial, i.e. + N2(C), N 2(B), O*, N* or N 2 (B) were observed [1]. heating of the channel → increase of the pressure → Transition to an arc and generation of thermal hydrodynamic expansion → decrease of N in the plasma is also prevented by a large external resistor core of the channel → increase of E/N → R (5-10 M Ω) placed between the HV power supply acceleration of ionization processes. The ‘memory’ and the needle HV electrode. The product of R and effect on UTS can be thus reduced on the influence of C determines the repetition frequency f that can be pre-heating. However, we assume that pre-ionization controlled by the onset voltage Uoo [2]: or accumulation of reactive species can play   important role on TS characteristics and breakdown U oo f = 1 RC ln   . processes at higher f (~6 kHz). Under these U −U  oo TS  conditions, the chemical and stepwise ionization [5] Here, UTS represents breakdown voltage at which or accumulation of metastable species influence the streamer initiating the transient spark appears. breakdown significantly. The UTS was found to decrease with the growing f. It was attributed to the influence of a ‘memory’ Acknowledgement effect [2]. We performed time resolved OES study Effort sponsored by the Slovak Research using a fast photomultiplier tube and a fast and Development Agency APVV SK-FR-0038-09, intensified CCD camera coupled with high and Slovak grant agency VEGA 1/0668/11 and resolution spectrometer in order to find more about 1/0998/12. the role of the increasing f and the induced ‘memory’ effect on TS and the breakdown References processes. [1] Z. Machala, M. Janda et al.: J. Molec. Spectrosc. 243 , pp 194 (2007) 2. Results and Discussion [2] M. Janda, V. Martišovitš, Z. Machala: Plasma nd Time resolved emission spectra of the N 2 2 Sources Sci. Technol. 20 035015 (2011) positive system were used to estimate time evolution [3] M. Janda, Z. Machala et al.: Plasma Sources Sci. of the gas temperature T during the streamer-to- Technol. 21 045006 (2012) spark transition [3]. The value of T at the beginning [4] E. Marode, F. Bastien, M. Bakker: J. Appl. of the streamer Tstreamer was used to estimate the pre- Phys. 50 pp 141 (1979) heating effect of increasing f. Next, the emission [5] G.V. Naidis: J. Phys. D: Appl. Phys. 32 , spectra of H α line were used to calculate the electron pp 2649 (1999)

P1-21 Investigations on the transient behavior of pulsed high-density discharges

P. Kempkes1∗ , B. Buttenschon¨ 2 , O. Grulke3, T. Klinger3, F. Mackel4, S. Ridder4, J. Tenfelde4, H. Soltwisch4

1Ernst-Moritz-Arndt University, MPI for Plasma Physics, Greifswald 2MPI for Physics, Munich 3MPI for Plasma Physics, Greifswald 4Ruhr University Bochum ∗Contact e-mail: [email protected]

Abstract applying a high voltage (up to 6 kV) between the elec- The transient evolution of pulsed magnetized trodes. The arch-shaped plasma structure forms in high density plasmas requires diagnostics with a tem- less than one microsecond after ignition, followed by poral resolution in the microsecond range. A set of a rapid expansion into the vessel, driven by the elec- diagnostics for different plasma quantities has been tromagnetic hoop force. developed in the framework of two different plasma experiments: the FlareLab project aims at the experi- mental investigation of arched, twisted magnetic flux Electrodes ropes. These structures are frequently utilized as a de- Expanding scriptive model for arched solar prominences. Flare- plasma Lab is a classical pulsed-power plasma experiment, in which discharge currents ≈10kA form a magnetized plasma arch with electron densities up to 1023m−3, ~3 mm developing on a microsecond timescale. The sec- Probe ond experiment is a high-density helicon plasma cell, which is developed as plasma source for proton driven plasma wakefield accelerators. As a first stage, this experiment is equipped with a 12 kW rf power Interferometer laser beam supply and operated in a pulsed fashion, in order to explore the density limits of helicon discharges. The chief diagnostic tool for both experiments is a CO2 Fig. 2: Diagnostics setup at FlareLab. laser interferometer. This line-integrated diagnostic is complemented with sets of electrostatic and elec- Figure 2 shows the diagnostic arrangement for tromagnetic probes and spectroscopy / imaging tech- FlareLab which utilizes the movement of the plasma niques to obtain information on the spatial evolution. arch, scanning it radially while it passes. Figure 3 shows an example of a density measurement, per- formed with the interferometer and a triple probe for a ±2 kV hydrogen discharge.

3

Discharge current (I = 21.5 kA)

max

8

Interf erom eter ) -2 m ) 19

6 2 -3 m (10 e 21

4

1

2 Density (x10

Triple probe

Fig. 1: ICCD camera images of a typical discharge Line-integrated n

evolution in FlareLab. 0 0

0 2 4 6 8 10 12 14 16 18 As an example, a typical evolution of the dis- Time (µs) charge in FlareLab is shown in figure 1. The plasma is Fig. 2: Temporal evolution of the line-integrated density ignited by puffing a small amount of neutral gas into a measured by the laser interferometer (black) and local vacuum vessel through orifices in two electrodes and density, measured by a triple probe (red).

P1-22 Optical emission spectroscopy of nitrogen post-discharge with mercury traces

1 1 2 V.Mazankova *, F. Krcma , D. Trunec

1BrnoUniversity of Technology, Faculty of Chemistry, Brno, Czech Republic 2Masaryk University, Faculty of Science, Brno, Czech Republic *Contact e-mail: [email protected]

1. Introduction The fourth part corresponds to an equilibrium in Nitrogen post-discharges in various configurations population and depopulation processes of vibration have been subjects of many studies during last fifty level v = 19 by another kinetic processes and line years. Despite this long interest there are still various intensity is nearly constant. The most important is open problems in the understanding of N 2 kinetics the second part because the exponential decrease can [1]. It was pointed more times that nitrogen post- be used for the calculation of rate coefficient of discharge is very sensitive to various impurities. The reaction (1). From Fig. 2 is visible, that the reaction presented work extends our recent research of time of part II for these experimental conditions is nitrogen DC flowing post-discharge containing 4 ms. mercury traces [2].

2. Experiment The pure nitrogen (99.9999%) DC discharge was created in a quartz tube of 12 mm inner diameter at current of 100 mA at pressure of 1000 Pa. Mercury was added into the nitrogen post-discharge through the movable capillary tube immersed upstream from the discharge into the quartz tube at its axis. The position of the output end of capillary tube was fixed at 330 mm from the active discharge and it Fig. 1: Overview spectrum of nitrogen post-discharge corresponds to the decay time of 22 ms. The gas with mercury titration. velocity was 15 ms -1 in the mainstream and 400 ms -1 in the capillary tube. Spectra of light emitted during the post-discharge were measured by Jobin Yvon TRIAX 550 spectrometer with CCD detector in the wavelength range of 300–800 nm.

3. Results The example of recorded spectra during the post- discharge with mercury 254 nm line in the second order spectrum is shown in Fig. 1. As we proposed in paper [3], the mercury excitation under post- discharge conditions can be described by the reaction: 1 + 1 1 + N2 (X Σg , v = 19) + Hg ( S0) → N2 (X Σg , v = 0) + 3 Hg ( P1) (1) Fig. 2: The dependence of mercury spectral line intensity The mercury line was identified a few ms before on decay time. the titration point and the dependence of its intensity on the decay time is shown in Fig.2. This References dependence can be divided into the four parts. The [1] V.Guerra, P.A.Sa, J.Loureiro: J. Phys. D, Appl. first part represents the rapid increase of mercury Phys 34, pp 1745 (2001) line intensity to the maximal value due to the mixing [2] V.Mazankova, F.Krcma, M.Zakova, Proc. 18 th of mercury vapor with nitrogen post-discharge. Then Symposium on Physics of Switching Arc, pp only the reaction (1) takes place and the exponential 250 (2009) decrease of line intensity can be observed in the [3] V.Kanicky, V.Otruba, A.Hrdlicka, P.Krasensky, second part. In the third part there is a fast decrease F. Krcma: J. Anal. At. Spectrom. 22 , pp 754 of intensity due to the widening of capillary tube. (2007).

P1-23 Atmospheric pressure DC glow discharge in nitrogen-methane mixtures: Analysis of the discharge products by PTR-MS

L. Torokova, F. Krcma *, M. Prochazka

Brno University of Technology, Faculty of Chemistry, Purkynova 118, 612 00 Brno, Czech Republic *Contact e-mail: [email protected]

1. Introduction Titan is the largest moon in Saturn’s lunar system and it has been a subject of interest to astronomers, planetary scientists as well as chemists because its atmospheric conditions are thought to have resembled to those conditions on the Earth several billion years ago [1]. Many organic compounds as hydrocarbons [2] and nitriles [3, 4] were confirmed in its atmosphere. In order to understand the physical and chemical processes leading to constitution of these compounds many studies using various discharges in nitrogen-methane mixtures were carried out. These laboratory experiments shown that various complex compounds can be Fig. 1. An example of exhaust gas mass spectrum in formed, for example the higher hydrocarbons, CH 4-N2 gas mixture (1:99) at power of 11 W. nitriles or even amino acids. The FTIR and GC-MS Tab. 1. The main determined compounds. techniques are frequently used for these compounds Experiment Formula Protonated Mass determination. This contribution presents the first hydrogencyanide HCN 28 results obtained by Proton-Transfer-Reaction Mass methanimine CH N 30 Spectrometry (PTR-MS) of discharge exhaust gas 3 amino-methyl CH 2NH 2 31 2. Experiment diimine H2N2 31 Atmospheric pressure DC glow discharge was hydrazine H4N2 33 created at atmospheric pressure between stainless acetonitrile C2H3N 42 steel electrodes with 2 mm gap. The stainless steel isocyano-methane C2H3N 42 vacuum chamber (volume of 1 liter) was pre- methyldiazene CH 4N2 45 vacuated by rotary oil pump to keep oxygen free ethylamine C2H7N 46 system. The discharge was operated at applied dimethyl-diazene C2H6N2 59 power from 4 to 15 W in pure nitrogen enriched by cyclohexadiene C6H8 81 pyrazine C H N 81 1-4 % of methane with total flow rate of 200 sccm. 4 4 2 The exhaust gas was in situ analyzed by PTR-MS The main identified compounds are given in + using H 3O ions. This technique allows very fast Table 1 with their masses. The peaks at masses 21 analyzis of compounds with proton affinity higher and 37 are not listed there because they correspond + + than 165 kcal without any sampling and nearly to D 2HO , and H 3O -H2O ions originating in the without fragmentation of the analyzed species. ionization source. All detected compounds and their Unfortunately, this method is very difficult to use relative abundances are determined with respect to for the absolute measurements due to necessity of the experimental conditions (gas composition and detailed calibration. So, the presented results are applied power). relative, only. Moreover, there is nearly impossible Acknowledgement to distinguish different isomers so further This research was done under project of Czech experiments using GC-MS are necessary. Science Foundation No. 104/09/H080. The PTR-MS results were compared to results obtained by classical GC-MS (sampling using gas References syringes) and in situ FTIR. [1] K.L.Aplin, Surv. Geophys. 27 , pp 63 (2006). [2] S.Vinatier, B. Bézard, C. Nixon et all, Icarus, 188 , pp 3. Results 120 (2007). An example of mass spectrum is given in Fig. 1. [3] T. Gautier, N. Carrasco et all, Icarus, 213 , pp 625 (2011). [4] V. Vuitton, R. V. Yelle, M. J. McEwan, Icarus, 191 , pp 722 (2007).

P1-24 Comparison of spectroscopic and catalytic probe characterization of afterglow oxygen and hydrogen plasma

Z. Kregar1*, M. Bišćan1, R. Zaplotnik2, S. Milošević1

1Institute of Physics, Bijenička 46, 10000 Zagreb, Croatia 2Josef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia *Contact e-mail: [email protected]

Inductively coupled plasma modification of Both the spectral features and the O and H atom surface is a well-established technique used in a concentrations are spatially resolved. Oxygen wide variety of applications [1, 2]. Reactive and fast spectrum (with the 2% of added argon for interaction between the plasma and sample show the actinometry) is shown on Fig. 1. It is characterized need for real-time plasma diagnostics. Optical by oxygen lines (stronger ones are 777 and 844 nm), emission spectroscopy and actinometry combined as well as with the argon line at 750 nm. with the measurement of oxygen atom concentrations by the catalytic probe offer a Oxygen atom concentrations were measured to relatively simple and efficient solution for that need. be in the range from 5·1018 m-3 (lowest pressure, The combination of these methods was used for furthest position) to 2·1021 m-3 (70 Pa, near the coil). characterization of low pressure inductively coupled Significant concentrations of oxygen atoms were oxygen plasma in an afterglow chamber. The measured even in the “dark” parts of the afterglow chamber enables real-time monitoring of chamber. Spatial distribution of concentration (Fig. modification of samples (via 12 windows/inputs). 2) shows two distinct areas: inside the afterglow Plasma was created in a linear borosilicate glass chamber (from -4 cm to 8 cm), and near the coil in tube by a 6 turn coil with an EM field oscillating at the tube (10 cm to 27 cm). 13.56 MHz at the distance of 30 cm from the center of the afterglow chamber. Various plasma conditions were used: oxygen and hydrogen gas pressure (20-90 Pa), and discharge powers (up to 260 W of applied power). Real-time spectral analysis was performed by a LIBS2000+ spectrometer system from Ocean Optics, which consists of seven miniature spectrometers (resolution 0.1 nm in the range 200-980 nm). The spectrometer is calibrated for the spectral response. Ni-plated catalytic probe was used for measuring neutral oxygen atom concentrations, while Au probe was used for neutral hydrogen atoms.

Fig. 2: O atom concentration as a function of position and applied power inside the chamber and the tube.

Actinometric concentrations will be compared with the catalytic probe measurements (for all positions in the chamber) which will allow a complete picture for the future material processing.

References [1] Z. Kregar, M. Bišćan, S. Milošević, M. Mozetič, A. Vesel, Plasma Process. Polym. 9, pp 1020 (2012)

Fig. 1: Spectrum of oxygen-argon plasma mixture (for [2] O. Grulich, Z. Kregar, M. Modic, A. Vesel, U. actinometry) at 29 Pa and 260 W. Cvelbar, A. Mraček, P. Ponizil, Plasma Chem. Plasma P. 32, pp 1075 (2012)

P1-25 Quantitative and in-situ analysis of PECVD processes containing silane using a cw external cavity quantum cascade laser

N. Lang 1*, S. Hamann 1, A. Salabas 2, J. Röpcke 1

1 INP Greifswald, Felix-Hausdorff-Str. 2, 17489 Greifswald, Germany 2TEL Solar AG, Hauptstr. 1a, P. O. Box 124, 9477 Trübbach, Switzerland *Contact e-mail: [email protected]

1. Introduction a wide parameter range of the applied RF power, the We report on in-situ measurements of absolute total and partial pressures, as well as the total gas concentrations of the precursor silane for PECVD of flow at stationary plasma conditions. thin film silicon photovoltaic modules using infrared laser absorption spectroscopy. Recent studies have proven that quantum cascade laser absorption spectroscopy (QCLAS) is a powerful technique for online and in-situ monitoring of technological plasma processes with high sensitivity and time resolution [1-3]. For the first time a cw external-cavity quantum cascade laser (EC-QCL) was used to investigate such PECVD processes containing silane in an industrial test bench reactor. This broadly tunable mid-infrared laser source allows measurements of transitions in the v3 band of silane in the range of 2085 – 2175 cm -1 with a spectral resolution of 10 -3 -1 cm [4]. Fig. 1: Time-resolved development of the SiH 4 For calibration purposes a two-beam setup was concentration during a typical a-Si:H deposition process: implemented enabling the simultaneous detection of p = 0.3 mbar, P RF = 32 W, Φ = 104 sccm, 50% SiH 4 in silane and reference gas absorption lines, e.g. CO H2. (a) gas inlet, (b) plasma on, (c) plasma off, (d) purge and N O. To enhance the sensitivity the absorption and pump. Time resolution is 0.11 s with additional FFT 2 smoothing of the data (f = 0.8 Hz) length was doubled with the help of an external cutoff mirror. With this the effective absorption length was It is demonstrated that QCLAS using an EC-QCL about 90 cm resulting in a detection limit for silane 13 -3 -1/2 enables in-situ and time-resolved insight into of about 3 ×10 molecules cm Hz . PECVD processes for Si:H layers. The experiments performed under industrial conditions allow for a 2. Results quantitative analysis of the different deposition In fig. 1 the time-resolved development of the process regimes, like amorphous and SiH 4 concentration is shown measured in-situ during microcrystalline silicon layers. a typical PECVD process to deposit amorphous silicon layers (a-Si:H). The achieved time resolution References was 0.11 s, the data shown in fig. 1 were [1] S. Welzel, F. Hempel, M. Hübner, N. Lang, P. additionally smoothed by a FFT filter with a cut-off B. Davies, J. Röpcke: Sensors 10 , pp. 6861 frequency of 0.8 Hz. For the determination of the (2010) absolute silane concentration an absorption line at -1 [2] N. Lang, F. Hempel, S. Strämke, J. Röpcke: Jpn. 2156.4 cm was used. Beforehand the required line J. Appl. Phys. 50 , pp. 08JB04 (2011) strength of this transition was determined in a gas -21 2 -1 [3] J. Röpcke, P. B. Davies, N. Lang, A. Rousseau, phase experiment to be S = 5.392 ×10 cm cm S. Welzel: J. Phys. D: Appl. Phys 45 , 423001 independent on the gas temperature. (2012) From the measured absolute SiH 4 concentrations, [4] D. Lopatik, N. Lang, U. Macherius, H. the degree of dissociation of the precursor and the Zimmermann, J. Röpcke: Meas. Sci. Technol. fragmentation rate was calculated for two different 23 , 115501 (2012) deposition regimes: amorphous ( a-Si:H) and micro crystalline ( µc -Si:H) silicon layers. The dependencies of these measures characterizing the deposition process were studied in

P1-26 Removal of contaminants from EUV optics by means of an expanding hydrogen thermal plasma

R. Leyte-Gonzalez 1* , A.R.J. Haenen, D.C. Schram, R. Engeln.

1Technische Universiteit Eindhoven, The Netherlands *Contact e-mail: [email protected]

1. Introduction

Extreme ultraviolet lithography (EUVL) is one of to H2/Ar and pure H2 plasmas. Since we want to the most promising lithography technologies for the understand the mechanisms involved on the carbon fabrication of the next generation Ultra Large Scale removal, the next step is the monitoring of the CH Integration systems (ULSIs). This technique uses molecule production near the surface. Laser induced radiation with wavelength of 13.5 nm (92 eV) for fluorescence (LIF) is a suitable technique for this imprint of patterns onto silicon wafers. For EUV purpose, due to the fact that is a selective species radiation transmissive optics cannot be used, detection technique and also allows performing because EUV radiation is strongly absorbed by any concentration measurements. material. Therefore multilayer reflective optics (mirrors) are used.

These Multilayer mirrors (MLM) consist of a stack of about 50 Mo/Si bi-layers deposited on substrates capped with a thin film of Ru ( ≈ 3nm). MLMs are key elements in the collection and imaging optics for EUVL machines. Contamination by photo-decomposed back-ground molecules lowers the reflectivity of these mirrors. Carbon is one of the main contaminants; 2nm of graphite reduces the reflectivity with about 1.5% per mirror (10 MLMs in the machine) [1]. Extending the life time of MLMs is of crucial importance for the successful introduction of EUVL.

2 Removal of contaminants with an expanding Fig. 1 OES spectrum from the H 2/Ar plasma interaction hydrogen plasma with a carbon sample.

Studies have shown that atomic hydrogen can remove carbon from MLMs [2]. But the mechanisms References are not fully understood. We study the removal of [1] B.Mertens, et al.: Micro Electronic Engineering carbon contaminants and the involved processes by 73-74 (2004) 16-22. means of an expanding thermal hydrogen plasma [2] K.Motai, et al.: Thin Solid Films 516 (2008) produced by a cascaded arc [3]. 839-843. Optical emission spectroscopy (OES) allowed us [3] M.C.M. van de Sanden, et al.: Plasma Sources to identify the production of CH molecules from the Sci. Technol. 3 (1994) 501. interaction of the hydrogen plasma with a carbon sample Fig. 1. With a quadrupole mass spectrometer we have detected the formation of diverse CxHy molecules formed from carboneous layers exposed

P1-27 Spectroscopic measurement of characteristic electron energy in the dark phase of a combined RF and high-voltage nano pulse discharge

A. Muller¨ 1∗ , M. Pustylnik1 , L. M. Vasilyak3, H. M. Thomas1, G. E. Morfill1

1Max-Planck-Institut fur¨ extraterrestrische Physik, Garching, Germany 3Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow, Russia ∗Contact e-mail: [email protected]

Measurements of characteristic electron energy is synchronized with the pulse generator. To analyse in a combined radio-frequency and high-voltage the data, a combination of two diagnostic techniques nanosecond pulse discharge are reported. is used. The experiments are performed in a parallel-plate First the argon metastable density is measured us- reactor chamber with electrodes of 150 mm diame- ing the ratios of intensities of spectral lines with com- ter and an inter-electrode distance of 54 mm. The mon upper level [1]. These ratios depend solely on chamber is filled with argon gas at pressures ranging the optical depth of the plasma and allow us to calcu- from 0.1 - 10 Pa. A RF- discharge is sustained by late the densities of the correspondent lower 1s states. a sinusoidal voltage of 13.56 MHz and peak to peak Then the results are used to calculate the electron voltage of 40 - 100 V. This steady state capacitively temperature from the line ratio of the 420 nm to the coupled plasma is then combined with high voltage (3 419 nm spectral lines of argon [2], which depends on - 17 kV) pulses of 20 ns length and a repetition fre- the density of the argon metastable states. quency of 20 Hz. As a result a bright flash is observed The measurement procedure was tested on the shortly after a pulse followed by a dark phase lasting steady-state parallel-plate RF discharge. Discussion up to a few hundreds µs. Microwave interferometry of the time resolved measurement results based on the measurements and additionally performed particles in comparison with simulations is given. cell simulations show that during the flash a high den- sity plasma is formed which screens the RF field and allows for a drop in electron temperature during the References subsequent dark phase. To experimentally measure how characteristic [1] M. Schulze, et al., Journal of Physics D: Applied electron energy in the plasma evolves, optical emis- Physics 41, 065206 (2008). sion spectroscopy (OES) is employed. For this pur- pose an ICCD camera installed on the output of a 550 [2] J. B. Boffard, et al., Journal of Physics D: Ap- mm focal distance spectrometer is used. The camera plied Physics 45, 045201 (2012).

P1-28 Monitoring of electrical discharges for nanoparticle production: the transition between the spark and arc regimes

J M Palomares1*, E Hontañon2, M Stein2, E Kruis2 and R Engeln1

1Technische Universiteit Eindhoven, The Netherlands 2University of Duisburg-Essen, Germany *Contact e-mail: [email protected]

1. Introduction behavior of the light emitted is measured with a Electrical discharges are reliable method for photodiode, Thorlabs-PDA36A. The spectral production of metallic nanoparticles [1, 2]. By information in the range 300nm – 1100nm is means of high intensity sparks or arcs sustained at collected with an Avantes spectrometer, AvaSpec atmospheric pressure a relatively large production of 2048-4-DT (with no temporal or spatial resolution). nanoparticles is achieved. The particles are formed out of the electro material after it is evaporated by 3. Results the high temperature of the discharge, or extracted The I-V curves for the spark discharges show a by ion sputtering. This process has a relatively low ringing behavior typical of an under-damped cost and it can be easily upscaled for greater oscillator. The photodiode measurements show production, making it a good candidate for industrial sparks durations in the order of 10µs what is in applications. In the present contribution we present agreement with the I-V curves. Depending on the results on the monitoring and characterization of the spark gap peak currents of 400A can be reached electrical discharges used for nanoparticle after the breakdown. It is observed how the production. breakdown voltage is reduced when the spark frequency rises indicating that the subsequent sparks 2. Experimental setup are no longer independent. Since this effect is The process takes place inside a vacuum chamber observed for frequencies as low as 100 Hz is most with a control atmosphere. Different electrode likely due to an increase of the gas temperature in arrangements can be used in order to work with the spark gap, with increases the reduced electric different types of sparks or arcs. The chamber is field E/N and therefore the breakdown voltage. filled with an inert gas for the electrode material, At certain frequency the system moves from a normally N2, Ar, He or H2. The pressure is kept high current spark to a low current continuous glow atmospheric to reduce the costs related to a vacuum discharge. The spark case shows a purely atomic system. emission of N and Cu species, indicating a high In the spark arrangement the spark gap is dissociation degree of the N2 gas. On the contrary connected in parallel with a capacitor box and to the the glow regime shows a spectrum dominated by the power supply, working in a positive configuration molecular emission of N2 what indicates a lower (cathode is grounded). The box has a capacitance in temperature. When the current passing through the the order of 30 pF. Cu electrodes are used with glow is increases the discharges gets progressively diameter within 6,5mm – 9,5mm. In some hotter. At some point the cathode starts glowing and conditions of high current a thin Tungsten anode the discharge properties resemble those of an arc. In (1,5mm) is used. The power supply can provide this sense the glow regime works as a bridge voltages up to 10KV what is enough to ignite sparks between two extreme modes of operation: the spark with electrode gaps between 0,5mm – 10mm. The and arc regimes. gas flow is kept constant at 10slm. In the arc setup the gap is directly connected to wielding power References supply that can provide currents in the order of 1A – [1] N.S. Tabrizi, M. Ullmann, V.A. Vons, U. 45A. Lafont, A. Schimidt-Ott: J Nanopart Res 11, pp The temporal evolution of the voltage over the 315 (2009) spark gap is monitored with a homemade voltage [2] M. Stein, D. Kiesler, F.E. Kruis: J Nanopart Res divider 1000:1. The current curve is measured with 15, pp 1400 (2013) Pearson current probe (model 110). Both curves are recorded on a digital scope. The light emitted by the spark is collected with an optical fiber, integrating all the light emitted by the discharge, with no spatial resolution. The time

P1-29 An updated model of Ar/H2 gas dynamics and plasma in a microwave plasma torch

A. Obrusn´ık1 , P. Synek1 , L. Zaj´ıckovˇ a´1∗

1Dept Phys Electronics at the Faculty of Science and Plasma Technologies at the Central European Institute of Technology (CEITEC), Masaryk University, Brno, Czech Republic, ∗Contact e-mail: [email protected]

1. Introduction We have previously presented a fluid plasma model of an atmospheric pressure microwave plasma torch (MPT). The torch has been used at the Depart- ment of Physical Electronics for nanotube [1] and nanoparticle [2] synthesis. Simulating such device is, however, a complex task since the gas mixture in the discharge chamber is strongly inhomogeneous Fig. 1: Neutral gas flow results showing velocity (separate Ar/H2 inlets), strongly non-isothermal and magnitude in [m/s] (log10), temperature in [K] and Ar the flow regime is turbulent. Since the previously 3 and H2 number densities in [1/m ] (log ) presented model suffered from quite slow conver- 10 gence and a few inconsistencies, the kinetic scheme 2.3. Plasma model was strongly revised and updated, several new reac- The plasma model solves in total 9 continu- tions were added, neutral gas flow was included in ity equations for electrons, ions and excited atoms the model and the code was strongly optimized. This along with the electron energy equation. In to- contribution will present the new model and its re- tal, 31 electron-heavy particle reactions and 9 heavy sults. particle-heavy particle reactions were considered. The plasma model uses BOLSIG+ software to cal- 2. The model and results culate the electron energy distribution functions [3]. The whole iterative loop is implemented in Matlab The model consists of three relatively separate with COMSOL Multiphyisics API. parts (sets of equations) that are solved iteratively and the relevant parameters are passed between indi- vidual solutions.

2.1. Electromagnetic field model The EM field model solves the wave equation in the time-harmonic form with plasma being treated as a dielectric with complex permittivity depending on the plasma frequency, ωpe, and the electron-neutral collision frequency, νen. In order to calculate the per- mittivity, the electron density and temperature must Fig. 2: Electron density [1/m3] and temperature [eV] be known from the plasma model described below.

2.2. Gas dynamics model References The gas flow regime in the discharge chamber [1] L. Zajickova et al. Pure Appl. Chem 82 (2010) must be considered turbulent since the Reynolds 1259-1272 number near the argon inlet can get as high as [2] P. Synek et. al. Materials Letters 65 (2011) 982- 60 000. The gas flow model solves self-consistently 984 the Reynolds-Averaged Navier-Stokes equations with the k-ε turbulence model, the heat equation for the [3] G. J, M. Haagelaar, L. C. Pitchford, Plasma Sources Sci. Technol. 14 (2005) 722–733. Ar/H2 mixture and the diffusion equation. Fig. 1 shows an example of neutral gas characteristics ob- This work was supported by the projects tained from the gas dynamics model. The neutral gas ‘CEITEC Central European Institute of Technology’ flow influences the plasma since the varying gas den- (CZ.1.05/1.1.00/02.0068) and ‘R&D center for low- sity and composition at different positions leads to cost plasma and nanotechnology surface modifica- different ion production and collisional damping. tions’ (CZ.1.05/2.1.00/03.0086) from European Re- gional Development Fund. P2-1 A hybrid 2D/3D model of hydrogen plasma in a linear antenna microwave device

A. Obrusnk1 , Z. Bonaventura1,2∗ , S.ˇ Potocky´3, A. Kromka3

1Department of Physical Electronics, Faculty of Science, Masaryk University, Kotla´rskˇ a´ 2, CZ-61137 Brno, Czech Republic 2R&D Center for Low-cost Plasma and Nanotechnology Surface Modifications, Masaryk University, Kotla´rskˇ a´ 2, CZ-61137 Brno, Czech Republic 3Institute of Physics of the ASCR, v.v.i., Cukrovarnicka 10, CZ-16253 Prague, Czech Republic ∗Contact e-mail: [email protected]

1. Introduction the plasma and neutral gas dynamics model. The EM The linear antenna microwave reactor has been field model solves the time-harmonic wave equation used at the Institure of Physics for nanocrystalline di- in 3D geometry while the plasma model includes 7 amond synthesis. The device operates at relatively continuity eqs. for electrons, ions and excited species, low pressure (around 100 Pa) and the plasma is usu- the electron energy equation and neutral gas heat ally ignited in hydrogen with a small admixture of equation. These are solved in 2D in one or more methane as the precursor gas. We have previously de- transverse cross sections of the 3D geometry (shown veloped a model that simulates the hydrogen plasma in fig. 3), neglecting out-of-plane particle flux. The in the device in a simplified 2D axisymmetrical ge- plasma model uses a pre-calculated set of rate coef- ometry even though the device possesses no actual ficients of the 32 reactions that are considered (incl. 2D symmetry. Example results from the simplified H2 rot. and vib. excitations). The electron energy model (100 Pa and 660 W of input power) are shown distribution function (EEDF) necessary for the calcu- in figs. 1 and 2. The results are in good qualitative lation of rate coefficients was calculated using BOL- agreement with values measured by other authors on SIG+ software [3]. The model itself is implemented similar devices [1]. in Matlab with COMSOL Multiphysics API.

Fig. 1: Calculated electron density (simplified axisymmetrical model)

Fig. 3: A 3D view of the device

This contribution will present the first results ob- tained from the 2D/3D hybrid model. These results Fig. 2: Calculated electron temperature (simplified are very important since they will allow us to calcu- axisymmetrical model) late the relevant plasma properties near the substrate (as opposed to the previous model which provides Having obtained satisfying results from the simpli- values only near the antenna). fied geometry model, the principal problem of the lack of 2D symmetry has to be tackled. Since solving References the equations (as specified below) in 3D would be too demanding in terms of computational power, we [1] K. Tsugawa et al. Diam. Rel. Mat. 20 (2011) propose a novel 2D/3D hybrid model. [2] K. Hassouni , F. Silva and A. Gicquel, J. Phys. D: Appl. Phys. 43 (2010) 2. The New hybrid model The model consists of two parts that are solved [3] G. J, M. Haagelaar, L. C. Pitchford, Plasma iteratively, the electromagnetic (EM) field model and Sources Sci. Technol. 14 (2005) 722–733.

P2-2 Excitation of Hydrogen by Impact of Monoenergetic Electrons

J. Országh*, A. Ribar, M. Danko, Š. Matejčík

Department of Experimental Physics, Comenius University, Bratislava, Slovakia *Contact e-mail: [email protected]

1. Introduction Hydrogen is the simplest molecule and at the 16 H Blamer and continuum  same time its importance in different fields of 14 continuum science and technology is very high. This gas is used 12 in many applications of low and high temperature plasma physics as well. This results in a great 10 interest in the spectrum of this gas. The spectra of 8 molecular hydrogen are studied from beginning of 6 th [cps] Intensity the 20 century [1, 2]. The spectrum is very rich 4 containing more than 3000 rotational lines. 2 The excitation and dissociative excitation of H2 0 by electron impact started early [3], followed by 0 20 40 60 80 100 studies Lyman and Balmer’s emission studies [4], Electron energy [eV] Fulcher bands [5], VUV continua studies [6] and UV-NIR spectra of H2 to mentions just several of the large number of studies. Fig. 1: Excitation curve at the wavelength corresponding to H (black) and continuum excitation curve measured at In this work we present the results concerning α 230 nm (red). the electron impact excitation and dissociative excitation of hydrogen molecule. We present the At this wavelength the continuum and Balmer’s line emission spectra induced by 50 eV monochromatic are superimposed and the continuum excitation electrons in the spectral range 200 - 700 nm. For curve measured at different wavelength had to be several emission lines we present excitation curves subtracted to determine the Hα threshold. with determined threshold values. Acknowledgments 2. Experiment This work was supported by the projects Nr. APVV- 2.1. Apparatus 0733-11, SK-SRB-0026-11, DO7RP-0025-11 and Nearly monoenergetic electrons form a beam in VEGA- 1/0379/11. trochoidal electron monochromator (TEM). The effusive molecular beam and the electron beams References collide in the collision chamber producing excited [1] O.W.Richardson, T.B. Rymer: Proc. R. Soc. molecules and atoms emitting photons. These Lond. A 147, pp 24 (1934) photons are analysed using Czerny-Turner optical monochromator and later detected by Hamamatsu [2] H.G. Gale, G.S. Monk, K.O. Lee: The photomultiplier working in photon-counting regime. Astrophysical Journal 2, pp 89 (1928) The experimental measurements have two [3] P. M. S. Blackett and J. Franck: Z. Physik 34, modes: i) spectrum mode at fixed electron energy pp 389 (1925) and ii) excitation curve mode at wavelength set to a [4] D. A. Vroom, F. J. De Heer: J. Chem. Phys. 50, particular emission line or band and the electron pp 580 (1969) energy is increased from in 0.1 eV steps. [5] G.R. Möhlmann, F.J. De Heer: Chem. Phys.

2.2. Results Lett. 43, pp 240 (1976) The hydrogen spectrum was detected at the [6] H. Abgraall, E. Roueff, X. Liu, D.E. electron energy of 50 eV. In the spectrum the Schemansky: Astrophys. J. 481, pp 557 (1997) Balmer’s series lines (Hα - Hζ) and Fulcher systems [7] A. Aguilar, J. M. Ajello, R.S. Mangina, G. K. (α – δ) were identified. Apart from them the James, H. Abgrall, E. Roueff: Astrophys. J. continuum H (a3Σ+ → b3Σ+ ) was identified as well. 2 g u Suppl. Ser. 177, pp 388 (2008) The excitation curves were measured at the wavelengths corresponding to the Balmer’s series lines. The example for Hα is shown in the figure 1.

P2-3 In situ diagnostics of hydrocarbon dusty plasmas using Quantum Cascade Laser Absorption Spectroscopy and Mass Spectrometry K. Ouaras 1*, L. Colina Delaqua 1, G. Lombardi 1, M. Redolfi 1, M. Wartel 1, J. Röpcke 2, H. Zimmermann2, X. Bonnin 1

1LSPM-CNRS, Université Paris 13, Sorbonne Paris Cité, 99 av. Jean-Baptiste Clément, 93430 Villetaneuse, France 2INP Greifswald, Felix-Hausdorff-Str. 2, 17489 Greifswald, Germany *Contact e-mail: [email protected]

To investigate nano-particle formation in plasmas, an ECR microwave discharge [1] was used for simulating basic kinetic reactions. The dynamic of dust precursors C 2H2, CH 4 and H 2 in different mixtures with a carbon target has been studied under low pressure (10 -2 mbar) and high density. In the present study the combination of an in situ quantum cascade laser (QCL) absorption spectrometer with a mass spectrometer gives us the tools to study the kinetics of plasma processes. In this way both qualitative and quantitative characteristics could be obtained. The QCL Fig. 2 : Mass spectrum of positive ions in C2H2 discharge absorption spectrometer detects specific absorptions of C 2H2 and CH 4 molecules inside the process chamber and determines the concentrations online by means of the Lambert-Beer law (Fig. 1). This provides the opportunity to monitor the degree of dissociation for these species as well as the recombination of hydrogen with erosion products emanating from the carbon target exposed to plasma. Synchronously, the mass spectrometer is used to keep track of all species playing a role in the formation of dust. Thus, supplemented by SEM micrographs showing nanoscale dust after 30 Fig. 3: Mass spectrum of negative ions in C 2H2 discharge seconds of discharge (Fig. 4), an outstanding role can be attributed to the positive ions in the monitored magnetized plasmas (Fig. 2 and 3). This result is contrary to former studies [2] made on the formation of dust driven by negative ions.

1,0

0,8

: 1313.788 : : 1313.903 : 4 : 1313.722 : 4 0,6 4 CH CH CH Fig. 4: SEM micrograph of dust after 30 s of discharge 0,4 Transmittance

0,2 1314.068 : References 2 H 2 [1] J.Pelletier, “ Distributed ECR Plasma Source ” 0 C 1313,7 1313,8 1313,9 1314,0 1314,1 High Density Plasma Sources, 1996, Pages 380-425 -1 wavenumber [cm ] [2] Ch.Hollenstein, "The physics and chemistry of dusty plasmas" , Plasma Physics and Controlled Fig. 1 : Conversion of C 2H2 into CH 4 by the plasma discharge Fusion, 2000. 42 (10): p. R93.

P2-4 Shock waves and bubble evolution in low energy pulsed electric discharge in water

M.E. Pinchuk1,2∗ , V.A. Kolikov1 , A.G. Leks1 , V.N. Snetov1 , A.Yu. Stogov 1 , Ph.G. Rutberg1

1Institute for Electrophysics and Electric Power of Russian Academy of Sciences (IEE RAS), St.Petersburg, Russia 2St.Petersburg State Polytechnical University (SPbSPU), St.Petersburg, Russia ∗Contact e-mail: [email protected]

UV radiation and shock waves play main roles distance were varied from 2 to 10 mm. for water disinfection by pulsed electrical dis- Velocity of bubble expansion and collapse is charges among the direct action factors affecting on about several hundred meters per second at early pathogenic bacteria. The mechanism of bacterial de- stage of discharge. Bubble pulsation period is 0.5- struction by shock wave is caused by destruction of 1 ms. Increasing of energy released in the discharge its membrane due to the pressure drop with ampli- gap will increase bubble pulsation period. Collaps- tude > 2 MPa in the shock front. A study of energy ing bubble also produces shock waves. And its am- transfer mechanisms from expanding discharge chan- plitudes can be higher then ones are after discharge nel to shock wave is a promising and under-studied channel expansion. area of researches. Other source of shock waves is Pictures of a streamer bush with different struc- collapsing bubble. tures of the discharge gap breakdown are observed. Input energy increasing into discharge channel Analysis of the images showed that two shock waves does not lead to pressure amplitude increase in shock are formed near the ends of the electrodes and at an front. And from economic and technological points early stage expand with the speed of ∼ 2 × 104m/s. of view it is advantageous to use the lowest power After about 500 ns in the far Fraunhofer zone both setting. waves merge into one in the form close to spherical, To study the hydrodynamic structure of shock spreading with a rate of ∼ 2 × 103 m/s. waves [1] and bubble evolution [2] in water discharge Numerical simulations of bubble dynamic and system the direct shadow optical diagnostic installa- shock wave propagation in water under various con- tion with a time resolution of 5 ns and a spatial res- ditions of energy input were made. Based on the re- olution of 0.1 mm was designed. Synchronization search results some recommendations for adjustment of diagnostic system was carried out by original sys- of the system power supply and load parameters were tem based on fast optocouplers. Also pulsed pressure suggested. measurements on discharge chamber wall were made. This work was partially supported by the Russian Velocity of bubble growth and shock wave prop- Foundation for Basic Research, project nos. 11-08- agation was measured for several power sources. The 00674-a. first one is with voltage up to 70 kV, pulse duration of 20 s. The second one is capacitor storage with a volt- References age up to 50 kV and changeable capacity for varying [1] Ph.G.Rutberg, M.E.Pinchuk, V.A.Kolikov et al.: input energy into discharge gap and pulse duration. J. Phys.: Conf. Ser. 406 012034 (2012) And the last power supply is power supply with en- ergy recuperation was specially designed and made [2] Ph.G.Rutberg, M.E.Pinchuk, V.A.Kolikov et al.: for intelligent regulation of input energy level into the J. Phys.: Conf. Ser. 406 012035 (2012) discharge gap [3]. In all cases the energy in pulse was of ∼ 1 J. Axisymmetric electrodes of tip-tip con- [3] S.V. Korotkov, Yu.V. Aristov, A.K. Kozlov et figuration were made from copper and interelectrode al.: Instrum. Exp. Tech. 54 n2 190 (2011)

P2-5 Measurement of gas and discharge channel parameters by analysis of oscillations in high current discharge at superhigh pressure

M.E. Pinchuk1,2∗ , A.A. Bogomaz1 , A.V. Budin1 , A.G. Leks1 , A.A. Pozubenkov1 , Ph.G. Rutberg1

1Institute for Electrophysics and Electric Power of Russian Academy of Sciences (IEE RAS), St.Petersburg, Russia 2St.Petersburg State Polytechnical University (SpbSPU), St.Petersburg, Russia ∗Contact e-mail: [email protected]

Discharges in hydrogen, ignited by wire explo- oscillations analysis. By frequency of first branch os- sion, with current amplitude up to 500 kA and ini- cillation it is possible measure temperature of plasma tial gas pressure of 80 − 160 MPa were investigated channel. Gas temperature in discharge chamber are [1][2]. Detailed description of the experimental in- mesured by the second branch oscillation frequen- stallation can be found in [3]. Two types of chan- cies. The registered values correspond to values mea- nel diameter oscillations are registered. It was estab- sured by other methods of diagnostic and obtained lished that this oscillations were responsible for volt- from math simulations. age pulsations on discharge gap and pulsed pressure The work is partially supported by Russian Foun- oscillations on discharge chamber wall by correlation dation for Basic Research (grant 12-08-01062-a). analysis. In the work a dependency each type of oscil- References lations depending on the pressure in the discharge [1] M.E. Pinchuk, A.A. Bogomaz, A.V. chamber are considered. A comparison with results Budin et al.: Proceedings of ICPIG- of study of MHD instabilities in dense gas environ- 2011, Belfast, NI UK, paper D17-077, ment uses for confirmation the hypothesis that one of http://www.qub.ac.uk/sites/icpig2011/abstractlist/ the branches of the oscillations was connected with (2011) the alignment of the magnetic and gas pressures. It was justified a assumption that at super-high gas pres- [2] A.V. Budin, A.A. Bogomaz, M.E. sures the most part of the current flows in vapour of Pinchuk et al.: Proceedings of ICPIG- initiating wire. The second branch of the oscillations 2011, Belfast, NI UK, paper D17-078, is analyzed on the basis of calculation of the acous- http://www.qub.ac.uk/sites/icpig2011/abstractlist/ tic oscillations that occur in the whole volume of the (2011) discharge chamber. Two methods of measuring of channel parameters [3] A.V. Budin , A.F. Savvateev, and F.G. Rutberg: and gas in discharge chamber were designed by this Instrum. Exp. Tech. 47 n4 534 (2004)

P2-6 Influence of modulation regimes on longitudinal distribution of active species in atmospheric pressure plasma jet

L. Poto čň áková*, J. Hnilica and V. Kudrle

Masaryk University, Brno, Czech Republic *Contact e-mail: [email protected]

1. Introduction 3. Results Nowadays, atmospheric pressure plasma jets are We plotted the relative intensities of four most used in variety of industrial applications [1]. The jets essential spectral ranges [3] along the axis of the can operate in broad range of operating parameters luminous flame and plasma afterglow. As can be that can be adjusted to achieve the best performance seen in Fig. 2, argon line intensity outside the tube for desired outcome. As the plasma is blown out of a decreases continuously. All the admixtures from air discharge tube, it reacts with surrounding (OH, N 2, O) have a common maximum that in CW atmosphere. Consequently, the plasma properties mode coincides with the position of flame end. In differ significantly along the plasma flame axis with AM mode, the maximum intensity is observed at pronounced effects for e.g. plasma surface approximately the same position, although the treatment. visible flame in this mode is longer. Also, the Modulating the microwave power can be maximum in CW mode is sharper. In the afterglow, interesting tuning parameter. Using optical emission admixtures from air dominate the spectrum over spectroscopy (OES) we carried out the spatially argon lines. resolved diagnostics of microwave plasma jet with focus on various plasma species. 4000 6000 308 nm 357 nm AM 5000 2. Experimental setup 3000 CW Schematic drawing of the experimental setup is 4000 shown in Fig. 1. As a plasma source, surfatron [2] 2000 3000 2000 was used. For the generation of plasma, surfatron 1000 uses a surface wave propagating along the interface 1000 0 0 between plasma and dielectric tube wall. As for 0 2 4 6 8 10 12 14 16 18 0 2 4 6 8 10 12 14 16 18 16000 5000 777 nm 842 nm other discharges with surface wave, also the 14000 4000 12000 surfatron plasma exhibits typical elongated plasma [rel.u.] intensity 10000 3000 form with slow decrease of plasma density towards 8000 the discharge end. Power was supplied by 2000 6000 4000 1000 microwave (2.45 GHz) generator, either in 2000

0 0 continuous wave (CW) or amplitude modulated 0 2 4 6 8 10 12 14 16 18 0 2 4 6 8 10 12 14 16 18 (AM) mode. We worked with argon as working gas, distance from the end of discharge tube [mm] without any intentional admixtures, except for Fig. 2: Relative intensity of spectral lines and band for admixtures coming from surrounding air at the open nd end of the discharge tube. OH, 2 positive system of N2, atomic O and Ar in AM and CW mode. Vertical lines indicate the apparent plasma flame end (AM - 12mm, CW - 6mm).

Acknowledgement This work was supported by the project CZ.1.05/2.1.00/03.0086 funded by the European Regional Development Fund.

References [1] M. Laroussi, T. Akan: Plasma Processes and Polymers 4, pp. 777 (2007) [2] M. Moisan, C. Beaudry, P. Leprince: Physical Fig. 1: Schematic drawing of the experimental setup. Letters A 50 , pp. 125 (1974) [3] J. Hnilica, V. Kudrle, L. Poto čň áková: IEEE Trans. on Plasma Science 40 , pp. 2925 (2012)

P2-7 Influence of a high-voltage pulse on the steady-state radiofrequency plasma: diagnostics and particle-in-cell simulations

M.Y. Pustylnik1∗ , L. Hou1, A.V. Ivlev1 , L.M. Vasilyak2, L. Couedel¨ 3, H.M. Thomas1, G.E. Morfill1, V.E. Fortov2

1Max-Planck-Institut fur¨ extraterrestrische Physik, Garching, Germany 2Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow, Russia 3Laboratoire de Physique des Interactions Ioniques et Moleculaires,´ Centre National de la Recherche Scientifique, Aix-Marseille-Universite,´ Marseille, France ∗Contact e-mail: [email protected]

The high-voltage nanosecond pulses (HVNP) are ported by 1D3V particle-in-cell simulations. widely used in modern low-temperature plasma re- Both experiment and simulations showed two search and technology [1]. They are mainly ap- main regimes, through which the plasma was evolv- plied under relatively high-pressure conditions (102 − ing after the application of HVNP: the bright flash 105 Pa). Recently, there is a growing interest in ap- (Fig. 1a) and dark phase (Fig. 1b). It was shown, that plying similar pulses at significantly lower pressures, the HVNP is capable of removing a significant frac- i.e. 10−1 − 102 Pa and in combination with other tion of electrons from the discharge gap. The flash discharge types (e.g. [2, 3]). Therefore, the problem is therefore the result of acceleration of electrons in of interaction of a HVNP with a low-pressure plasma the residual electric field of the immobile ions. High- has to be studied at a very basic level. density plasma generated during the flash screens the The experiments were performed in a parallel- RF electric field, which leads to the rapid cooling of plate geometry with disc-shaped electrodes of electrons and therefore dark phase. Comparison of 150 mm diameter and interelectrode gap of 54 mm experimental and simulation results allows for the de- filled with argon at 0.1 − 10 Pa pressure. One of the tailed discussion of these mechanisms. electrodes was powered with a sinusoidal RF signal to sustain weak steady-state plasma. HVNP (3 − 17 kV amplitude and fixed duration of 20 ns) was guided via References a long 50 Ω coaxial cable to the opposite electrode. [1] Yu.D. Korolev, G.A. Mesyats, Physics of Pulsed Pulse repetition rate was as low as 20 Hz. The dis- Breakdown in Gases (URO-Press, Ekaterinburg, charge was imaged with the ICCD camera with the 1998) minimal gate width of 10 ns. In addition to that we could measure the electron density by microwave in- [2] M.Y. Pustylnik et.al. Phys. Plasmas 16, 113705 terferometry at 26.5 GHz with the time resolution of (2009) 10 µs. By these means the multitimescale evolution of the plasma was observed. Observations were sup- [3] J. Sun et.al. Phys. Plasmas 17, 103505 (2010)

Fig. 1: Space-time diagrams of (a) flash and (b) dark phase regimes of the plasma, measured by the ICCD camera. Black curve in panel (a) shows the evolution of the voltage on the high-voltage electrode.

P2-8 Controlling and understanding the heartbeat instability in dusty plasmas

M.Y. Pustylnik1, A.V. Ivlev1, N. Sadeghi2, R. Heidemann1, S. Mitic1, H.M. Thomas1, G.E. Morfill1

1 Max-Planck-Institut fur¨ Extraterrestrische Physik, Garching, Germany 2Laboratoire Interdisciplinaire de Physique, CNRS - Universite´ Joseph Fourier, Saint-Martin-D’Heres, France ∗Contact e-mail: [email protected]

The heartbeat instability reveals itself in periodic bility was the strongest when the laser beam passed contractions of the boundary of a microparticle-free through the void center and was getting weaker as it area (the so-called ”void”), normally formed in the was moved out to the periphery. In addition using center of the complex plasma in the rf discharge. First the photomultiplyer modules with the bandwidth of discovered in the microgravity experiments [1], it still 200 kHz we measured the temporal evolution of the remains one of the big mysteries in the entire com- emission intensity of the plasma inside and outside plex (dusty) plasma field. Thorough laboratory in- the void during the heartbeat instability. We showed, vestigation of the phenomenon [2] showed, that the that the emission intensity inside and outside the void instability is not a simple dynamical phenomenon in oscillate remarkably in opposite phases (Fig. 2). the microparticle component. Electrical as well as the optical characteristics of the plasma were found (a) to undergo significant modulation during the cycle of 1.7 the instability. 1.6

1.5

1.4 5.5 (b) 5.0 Integral intensity [a.u.] intensity Integral 4.5

4.0 -5 0 5 10 15 20 25 30 t [ms]

Fig. 2: Temporal evolution of the plasma emission intensity (a) outside and (b) inside the void during the self-excited heartbeat instability.

Both experiments suggest, that the heartbeat in- Fig. 1: Experimental setup for the tunable-laser control of the heartbeat instabilty. stability is a heterogeneous phenomenon. Our hy- pothesis is that the heartbeat instability occurs due to In our recent ground-based experiments [3], con- the formation of a sheath on the void boundary. We ducted in a PK-3 plus chamber, we could excite the demonstrate, that this can qualitatively explain the be- heartbeat instability intentionally by a periodic illu- havior of the plasma glow and dynamics of the mi- mination of the microparticle cloud (1.95 µm MF croparticles during the instability. spheres, 20 Pa of argon, ∼ 0.5 W power) by a beam of a tunable diode laser with the wavelength of 772.38 References nm (Fig. 1). This laser pumped the 1s metastable ar- 5 [1] J. Goree, G.E. Morfill, V.N. Tsytovich, S.V. gon atoms to upper radiative 2p state. The pumping 7 Vladimirov, Phys. Rev. E, 59, 7055 (1999) rate considerably exceeded the excitation rate of the 1s5 state. Therefore, the laser was significantly reduc- [2] M. Mikikian, L. Couedel,¨ M. Cavarroc, Y. ing the number density of metastable states, leading Tessier, L. Boufendi, New J. Phys. 9, 268 (2007) to the modulation of the ionization rate with the depth of the order of 10−3. Excitation had a resonance [3] M.Y. Pustylnik, A.V. Ivlev, N. Sadeghi, R. Hei- character. The frequency of the heartbeat increased demann, S. Mitic, H.M. Thomas, G.E. Morfill, with the increase of the laser power. Also, the insta- Phys. Plasmas 19, 103701 (2012)

P2-9 Development of plasma and beam diagnostics for the PEGASES thruster experiment

D. Rafalskyi*, A. Aanesland

Laboratoire de Physique des Plasmas, CNRS-Ecole Polytechnique, Palaiseau CEDEX 91128, France *Contact e-mail: [email protected]

The PEGASES thruster, acronym for Plasma The resistor Rmeas (see Fig.1) is used for extracted Propulsion with Electronegative GASES, accelerates positive ion current density measurements as well as alternately positive and negative ions for thrust [1]. for circuit and probe protection (from arcing, short This is obtained by a set of grids placed in an ion- circuits due to conductive film deposition, etc.). Its ion plasma and biased with square voltage value is adjusted with the probe current and usually waveforms. Several PEGASES prototypes have equal to 1 kOhm. been developed in recent years, however an open The Langmuir probe located in the IBP volume is question is still how the secondary downstream driven by the system from Impedance Inc. The plasma is formed and how it interact with the target is connected to a DC source. In order to upstream ion-ion plasma. analyze positive and negative ion flows we currently The PEGASES experimental setup contains two develop also different electrostatic and magnetic plasmas (see Fig.1): i) a primary ICP plasma where energy analyzers, which will be placed on the target ionization and depending on the gas dissociate (not shown on the Fig.1). attachment occur, and ii) a secondary plasma, or ion- PEGASES beam plasma (IBP) created in the beam transport nd chamber by extracted ion-ion flow (at alternate 2 prototype extraction) or due to charge-exchange collisions and S beam interaction with surfaces at continuous positive or negative ion extraction [2]. For a Extrac ICP -tion IBP Target complete understanding of the processes in such a region system, both plasmas should be particularly N HV DC Rballast analyzed. The main challenges for such study are: i) source the primary plasma might have a potential (positive “RelRamp” or negative) exceeding 1 kV relative to ground, so R DC source all measurements in this plasma should be Floating meas “Impedance” DC source performed with floating diagnostics; ii) both the positive and negative ion beams, as well as the two Fig. 1: Experimental setup. plasmas should be analyzed simultaneously; iii) due The developed system has been successfully tested at operation with Ar and SF 6. Preliminary to operation with SF 6 gas fast film deposition complicates probes measurements; some can be results show that positive ion beam formation starts done just during short interval after cleaning by form 120-150 V of acceleration voltage (depending negative potential (with respect to the biased grid or on RF power, gas pressure etc.) for the chosen grids grounded transport chamber, depending on the geometry. The estimated from target current- probe). distance traces beam divergence does not exceed 20 degrees. The measured density of the ion-beam In order to overcome such challenges we have 14 -3 developed a system of plasma and beam diagnostics plasma is about 10 m in the regime of positive ion shown in Fig.1. Langmuir probes are introduced in beam extraction. This is about 2 orders of magnitude both the ICP and IBP volumes, a planar probe in the lower than the plasma density in the extraction ICP volume for measurement of positive ion flux to region. The measured efficiency of positive ion the grids, and a big target intercepting the ion beam beam extraction is about 50 % at 300 V acceleration in the IBP volume. The two probes placed in the ICP voltage and increase with increasing voltage. were mounted through the acceleration grids as also shown on the Fig.1. The Langmuir probe in the ICP References region is driven by an original floating measuring [1] A. Aanesland, A. Meige, and P. Chabert, J. system “RelRamp”. This system provides fast Phys.: Conf. Ser. 162, 012009 (2009). current-voltage (IV) scans (10ms) and then switches [2] 7S. V. Dudin and D. V. Rafalskyi, Eur. Phys. J. to the cleaning regime until the next scan. The D 65 , pp 475–479 (2011). planar probe is biased to -25 V versus the potential of the first grid by a low-leakage floating DC source.

P2-10 Absorption Spectroscopy on Plasma Jets Interacting with Liquids

S. Reuter1,2*, J. Winter1,2, M. Hammer1,2, S. Iseni1,2, H. Tresp1,2, A. Schmidt-Bleker1,2, M. Dünnbier1,2, K.-D. Weltmann2

1Centre for Innovation Competence plasmatis, Greifswald, Germany 2INP Greifswald e.V., Greifswald, Germany *Contact e-mail: [email protected]

1. Introduction by calculating the production rates also from the The advances in atmospheric pressure plasmas ozone map via flow profiles determined from fluid have led to the new field of plasma medicine - a modelling. field where in many cases plasma directly interacts In order to determine reactive species generation with liquid media. To gain an understanding of the dynamics, a variation of the shielding gas transport and reactive species generation composition of oxygen, nitrogen and water was mechanisms, quantitative data is essential. This data performed. The RONS generation dynamics was can best be obtained by non-invasive optical monitored by FTIR-absorption spectroscopy. Finally diagnostic methods. The presentation will focus on plasma treated water was investigated quantitatively absorption spectroscopic diagnostic techniques. by EPR-spectroscopy (absorption of microwave These methods yield absolute values without the radiation in a varying magnetic field). OH-radical necessity of calibration. The effect of ambient and superoxide anion formation dynamics as a species diffusion on the generation mechanisms of function of diffusion ambient species composition reactive oxygen and nitrogen species (RONS) in the into the active effluent showed the importance of gas- as well as the liquid phase is studied and oxygen dissociation and excitation in the plasma presented. zone for a tailoring of reactive species within treated Plasma Sources Sci. Technol. 21 (2012) 034015 S Reuter et al liquids. 2. Experiments 2.1. Plasma source For our study an atmospheric pressure plasma jet – the kinpen (neoplas GmbH, Germany) – was used. rf voltage The plasma jet consists of a centered rod electrode 0 inside a ceramic capillary and a grounded ring electrode. The jet is operated at 1 MHz frequency Figure 1. Schematics of the argon plasma jet (kINPen09). with argon and small quantities of molecular admixture.(0.5 mm radius) In is order mounted to (see investigate figure 1). In the the continuous effect of ambient species diffusion, an additional glas hull is working mode, a high-frequency sinusoidal voltage (1 MHz, delay period 1µs gate width 1ns time c2–6onstructe kVpp) isd coupled around to the the pin-typeplasma electrodejet. As [shielding6]. The plasma gas nitrogenjet is operated (N2 purity with a 99.999 dry argon %) flux and of oxygen 5 standard (O liters2 purity per Figure 2. Principle of phase-resolved optical emission spectroscopy. 99.995minute (slm) %) andin varying in this work ratios with up with to 2% water molecular admixtures oxygen admixture. Additional technical details about the working was applied. conditions and the design of the jet have been presented in previous papers [7]. 2.3. Diagnostics and Results

3. Phase-resolvedFor the characterization optical emission of the measurements reactive oxygen and reactive nitrogen species the following FigureFig. 3. Space-resolved1: On-axis density wavelength of ambient integrated oxygen emission in profile.the jet Phase-resolved optical emission measurements can image Theeffluent image ismeasured false color-coded. with VUV Zero absorption denotes the tipspectroscopy of the nozzle. for absorption spectroscopic methods were applied: The jet is operated with 5 slm argon and no oxygen admixture. VUVcomplex spectroscopy plasma dynamics along in thewith ns rangean analytic and yield mod valuableel of the case of shielded and non-shielded plasma jet information about the plasma chemistry [8]. As non-intrusive Integration time is 700 ms. [4](below: false color emission map of the effluent [2]) diffusionplasma diagnostic analyzed this technique the on-axis can also molecular provide access oxygen to speciesquenching density coefficients with and and excitation without processes gas shielding [9]. (see dischargeReferences dynamics. The transition from the illuminated tip of fig. 1). For this, the VUV Ar-excimer radiation the[1] outer S. ceramicReuter, capillaryJ. Winter, (z-positions A. Schmidt below- 0Bleker, mm) and et. the al. free effluent can clearly be observed in all contour plots as a 3.1. Experimental setup PSST 21 pp 024005 (2012) emitted from the jet was utilized as background stepwise increase of intensity. The remarkable characteristic, [2] S. Reuter, J. Winter, S. Iseni, et. al.: PSST 21 pp radiationThe experimental [1]. setup Quantum consists of cascade a high-repetition laser rate(QCL) gated however, is the discontinuous effluent, indicating the presence absorptioniCCD camera spectroscopy (LaVision PicoStar was HR12) used with to 1370 determine1040 of so-called034015 plasma (2012) bullets, known in the literature for the ozonepixels and production a mounted rates macro-objective, as well as 25 nitrogen cm in front oxygen× of the case[3] of J. kHz Winter, excitation M. [ Dünnbie10–12]. Theser, A. bullets Schmidt become-Bleker, more et compoundsplasma jet. The with trigger high of accuracy the camera’s (50 gateppb) is—via [1, 2]. a delay pronouncedal.: J. Phys. for higher D 45 oxygen 385201 admixtures. (2012) The emission generator—connected to the trigger output of the plasma jet’s intensities[4] S. Reuter, in the first J. andWinter, second A. half-wave Schmidt of-Bleker, the excitation et al.: The high sensitivity of the space averaged QCL cycle decrease dramatically to zero with increasing oxygen 1 MHz power supply. Because of the setup’s simplicity, a IEEE TPS 40 2788 (2012) methodschematic wasis not shown. compared The system to space has a spatial resolved resolution O3- admixture in the case of the first half-wave. measurementsof approximately by 30 µ UVm. For absorption phase-resolved spectroscopy measurements [3], For pure argon the plasma bullet evolves between 0.4 and the iCCD camera is triggered synchronously to the excitation 0.6 µs and detaches from the effluent. The black dashed line in signal of the plasma jet. At a fixed phase position of the figure 4 indicates the spatio-temporal development of the bullet excitation signal, the light emission from the visible effluentP2-11 is and the lines slope represents the bullet velocity. The temporal t1 position of the bullet tb(z) dttIz(t) with t0 T/4 and acquired with a gate width of 1 ns, as shown in figure 2. The t0 3 = = emission from all cycles within a time frame of 700 ms was t1 T is calculated for z 4 mm. Iz(t) is the emission = 4 !! integrated. intensity normalized to unity. This yields the bullet trajectory After this time integration the phase is shifted by a defined z(tb) from which the bullet velocity can be derived via linear time step of 25 ns with respect to the phase-locked trigger, so regression. Bullet velocities for different oxygen admixtures that one full cycle with a period of 1 µs is resolved into 41 are shown in figure 5. equidistant time intervals. In pure argon the bullet velocity reaches up to 7 4 1 × 10 ms− . Admixing only 5 standard cubic centimeter (sccm) 3.2. MHz plasma bullets oxygen, the bullet velocity is almost reduced to half of the initial value. With an oxygen admixture of 20 sccm the Figure 3 shows a side view of the propagating argon effluent as bullet velocity is reduced by about 80%. Toward higher spatial intensity distribution at a specific time of the excitation oxygen admixtures, the bullet velocity converges to a level 4 1 cycle. The tip of the outer ceramic capillary is illuminated by of approximately 1.1 10 ms− . These results agree with × 3 5 1 the discharge and the horizontal white dotted line indicates the reported bullet velocities ranging from 10 up to 10 ms− for position where the emission of the effluent is analyzed phase ‘bullet-like’ structures in other discharges [13–17]. Moreover, resolved. Accordingly, all deduced axial intensity profiles of the velocity is not constant for the case of no oxygen admixture the emission are arranged as color-coded 2D plots over time, and for 5 sccm O2 admixture at the end of the effluent, in shown in figure 4. These non-interpolated raw data reveal the contrast to the other slopes for higher oxygen admixtures.

2 Characterization of a plasma jet for biomedical applications: composition, temperature, fluid dynamics and plasma structure

M. Boselli1,2, V. Colombo1,2*, E. Ghedini1,2, M. Gherardi1, R. Laurita1, A. Liguori1, P. Sanibondi1 and A. Stancampiano1

Alma Mater Studiorum-Università di Bologna 1 Department of Industrial Engineering (D.I.N.) 2 Industrial Research Centre for Advanced Mechanics and Materials (C.I.R.I.-M.A.M.) Via Saragozza 8, 40123 Bologna, Italy

*Contact e-mail: [email protected]

In recent years, atmospheric pressure non- Schlieren imaging was adopted to investigate the equilibrium plasmas have been proven to be viable fluid-dynamics of the afterglow region; flow tools for decontamination and sterilization of fluctuations generated by the effluent when surfaces and living tissues; currently, exploration of impinging on substrates of different geometries the feasibility of plasma aided medical therapies, (plain substrate, Petri dishes, etc.) were investigated such as blood coagulation, chronic wound by means of a Schlieren high speed imaging (CMOS remediation and cancer treatment are at the forefront camera up to 200,000 fps) and subsequent statistical of research in cold plasma applications. This elaboration of high-speed recordings. exciting field poses the challenge for deeper understanding of plasma interaction with biological matter and puts a premium on diagnostics as a mean to investigate process feasibility and to develop plasma sources tailored for specific applications. Consequently, the plasma community has dedicated large efforts to characterize plasma sources for biomedical applications and to identify the most suitable diagnostic techniques [1,2]. In this work a set of diagnostic methods have been used to investigate plasma behavior (gas temperature, heat flux, effluent composition, fluid- dynamics and plasma discrete structure) in a nanosecond pulsed multi-gas plasma jet developed by the authors and based on the plasma needle concept [3]. The behavior of emitting reactive species in the effluent was analyzed at different axial positions, downstream the needle, by means of time-resolved optical emission spectroscopy (OES) in the ultraviolet, visible and near-infrared region, comparing results obtained at different operative conditions. Emission spectra of the plasma source Fig. 1: iCCD image of the structure of the plasma jet were collected using a 500mm spectrometer synchronized with an iCCD camera, while voltage References and current signals were recorded by means of an [1] Weltmann K.-D., Kindel E., Brandenburg R., oscilloscope. Time-resolved recordings of selected Meyer C., Bussiahn R., Wilke C. and von spectral regions have been carried out using a Woedtke T., Contributions to Plasma Physics photomultiplier tube (PMT) coupled with an (2009), 49(9), 631–640 oscilloscope. iCCD imaging of the plasma plume [2] Hofmann S., van Gessel A. F. H., Verreycken T. has been adopted to investigate the structure of the and Bruggeman P., Plasma Sources Science and plasma. Technology (2011), 20, 065010 Axial temperature and heat flux profiles of the [3] Stoffels E., Elikweert A. J., Stoffels W. W. and afterglow region were obtained by means of a highly Kroesen G. M. W., Plasma Sources Science and accurate optical fiber temperature sensor; while Technology (2002), 11, 383.

P2-12 The OES Line-Ratio Technique for Discharges in Pure Argon and in Argon-Hydrogen Mixtures

S. Siepa1*, S. Danko2, Ts. V. Tsankov1, U. Czarnetzki1

1Institute for Plasma and Atomic Physics, Ruhr-University Bochum, Germany 2Dept. for Coating Technol. and Surface Engineering, Robert Bosch GmbH, Gerlingen-Schillerhöhe, Germany *Contact e-mail: [email protected]

1. Introduction 5. Results and Discussion Electron density and temperature are determined Measurements in a pure argon capacitively by optical emission spectroscopy (OES) in coupled plasma in a wide pressure range have been discharges operated in pure argon and argon- performed in order to determine the most suitable hydrogen mixtures. In the former case the model of line-ratios. Electron density and temperature have Koleva et al. [1] using line intensity ratios is applied been obtained using these ratios. with certain modifications. In the latter case the Absolute line intensity calibration has been direct intensities of selected lines in argon are performed by using the former results in order to analyzed. For both cases collisional-radiative models enable determination of plasma parameters in are developed. discharges in argon-hydrogen mixtures. The choice of suitable line pairs, the limitations of the model 2. Line -ratio technique (pure argon) and the absolute calibration technique are discussed. The determination of electron density and temperature requires at least two line intensity ratios. 696.5 / 750.4 (Koleva [1]) The technique is most accurate if one line-ratio is 1.0 706.7 / 750.4 only sensitive to the electron density while the other is only sensitive to the electron temperature. Up to 0.8 now the lines have been chosen mostly based on their calculated ne- and Te-dependencies [1,2]. This

can be done also experimentally, which is norm. intensity 0.6 independent from the assumptions in the model. Fig. 1 shows that the new line-ratios of this work 0.4 show better performance for diagnostics. 0 100 200 300 400 power [W]

3. Line -intensity technique (argon mixtures) 1.2 In gas mixtures the line-ratio technique looses its ne-sensitivity due to strong collisional de-excitation of the low-lying excited levels of the modelled gas 1.0 by the other gases in the mixture. In this case single emission lines can be applied, using the pure argon 0.8 line-ratio measurements as an absolute calibration tool. norm. intensity 0.6 763.5 / 738.4 801.5 / 794.8 (Koleva [1]) 4. Models 0.4 The collisional-radiative model used in this work 0 100 200 300 400 is based on the model of Koleva et al. [1]. Their power [W] extended corona model considers the first 14 excited Fig. 1: Variation of an ne-sensitive and insensitive levels of argon (1s- and 2p-levels in Paschen’s line-ratio with power at a pressure of 200 Pa in notation) , including electron impact transitions comparision with the line-ratios used by Koleva et al [1]. between the 1s- and 2p-states as well as radiation The electron density increases with power while the trapping. The modifications made concern the temperature stays approximately constant. choice of cross sections and escape factor. In case of mixtures, all 1s states are totally quenched and References excitation is only from the ground state which [1] S. Iordanova, I. Koleva, Spectrochimica Acta drastically simplifies the model. Part B 62, pp 344 (2007) [2] X.-M. Zhu, Y.-K. Pu, J. Phys. D: Appl. Phys. 40,

pp 2533 (2007)

P2-13 Nitric oxide detection in atmospheric pressure NRP discharges by Quantum Cascade Laser Absorption Spectroscopy

1,2 1,2* 1,2 M. Simeni Simeni , G.D. Stancu , C.O. Laux

1CNRS-UPR 288, Laboratoire E.M2.C, Grande Voie des Vignes, 92295 Châtenay-Malabry, France 2Ecole Centrale Paris, Grande Voie des Vignes, 92295 Châtenay-Malabry, France *Contact e-mail: [email protected]

Nitric oxide (NO) is a free radical, a by-product shown in figure 2. The variation of NO density as of combustion of fuels in air and a major pollutant. function of the measured energy per discharge pulse There is a large interest for combustion engine exhibits a linear dependency. The energy per makers for pollutants emission reduction. discharge pulse was driven from ns-time resolved The use of nanosecond repetitively pulsed voltage and current measurements. (NRP) discharges is a very promising approach for application in fields of flame ignition and stabilization, particularly for stabilization of lean flames which are known to produce less NOx [1]. However the NRP discharge emissions of NO in air and in NRP assisted combustion is unknown. The purpose of this study was to quantify the amount of NO produced by the NRP discharge as function of different discharge parameters. NO was measured in a combustion set-up where only NRP discharges were generated by 10 ns short high voltage pulses (5-8 kV), at pulse repetition frequency of 1-30 kHz, Fig. 1: A sample of NO absorbance measurements in air at flow rates of 8-12.5 m/s, and in a pin-to-pin electrode configuration (gap distance 4 mm). The small amount of particles to detect, the large broadening of spectral lines at atmospheric pressure, the high temperature environment, the presence of other plasma and flame species, and the quenching uncertainties (for fluorescence based methods) make the NO detection challenging [2], [3]. Measurements by Mid-IR Quantum Cascade Laser Absorption Spectroscopy (QMACS laser) of NO absolute densities as function of NRP discharge parameters were carried out. To increase the sensitivity the laser was coupled into a White multi-pass cell (20 passes) made of two mirrors separated by 50 cm. The beam Fig. 2: NO density as function of discharge pulse energy at the exit of the multi-pass unit was focused on an The QCLAS was proven to be a suitable indium antimonide thermoelectrically cooled diagnostic for atmospheric pressure detection of NO detector. Particular care was taken for the choice of produced by NRP plasma. The obtained results are the NO spectral line. The rotational-vibrational -1 of interest for the understanding of plasma-assisted transition at 1900.076 cm presents a negligible combustion. overlapping with water lines and others combustion species in a large temperature range and it has large line strength. References The measurements were made at the output of a [1] G.Pilla, D.Galley, D.A.Lacoste, F.Lacas, steal tube of 50 cm length and 8 cm diameter. The D.Veynante, and C.O.Laux: IEEE Trans. On discharge was placed at the base of the tube as for Plasma Sci. 34, (6) pp 2471 (2006) the typical NRP combustion assisted experiments. [2] G.D.Stancu, D.A. Lacoste, C.O. Laux: Figure 1 shows a sample of NO absorbance. A ESCAMPIG 21, Viana do Castelo, 272 (2012) good signal to noise ratio was obtained using the [3] W. Kim, H. Do, M.G. Mungal, M.A. Cappelli: White cell. This enables us to reach a limit detection Proceedings of the Combustion Institute 31, pp of about 1 ppm. An example of a parametric study is 3319 (2007)

P2-14 Breakdown regimes in temperature-dependent mixtures of Ar and Hg

A. Sobota1,2∗ , R.A.J.M. van den Bos2 , F. Manders3

1Laboratoire de physique des plasmas, Ecole Polytechnique, Palaiseau, France 2Elementary processes in gas discharges, Technische Universiteit Eindhoven, Eindhoven, The Netherlands 3Philips Innovative Applications, Turnhout, Belgium ∗Contact e-mail: [email protected]

Atmospheric pressure discharges can exhibit dif- was 100 kHz and the amplitude varied between 0.5 ferent regimes [1]. The two extremes are the and 7 kV. Townsend and the streamer breakdown [2], and the The cool-down phase was used for the exper- transition point between them depends on a variety iments, as in the time window of about 500 sec- of variables, such as voltage driving frequency, gas onds the gas temperature drops from 1400 K to room composition, pressure and temperature. The effects temperature. During this time the gas composition of these factors are examined in several fields of changes from 10 bar of Hg and 0.05% admixture of research, such as plasma-assisted combustion, sup- Ar at 1400 K to 150 mbar of Ar and 0.01% admix- pressing surface discharges in printed circuit boards ture of Hg. Hg starts condensing at about 75 s after or high voltage insulation. High frequency discharges the start of the experiment, at 750 K. The tempera- can take the glow form and are as such investigated in ture of the gas during the cool-down phase was deter- surface processing. All of the above mentioned fac- mined independently by using pyrometry. The chem- tors are examined in the lighting industry, as the hot- ical composition of the gas phase was calculated as a re-ignition problem remains a challenge to this day. function of temperature from the amounts of species When a plasma-based lamp has to be started a large dosed at room temperature. amount of energy needs to be put into the gas to turn it The reduced electric field was calculated from into a plasma. If a lamp has been preheated, the con- the measured breakdown voltage, temperature and ditions are far less favorable for breakdown, as the gaseous species density as a function of time. The gas density is far higher due to the evaporation of Hg E/N at breakdown as a function of temperature and and electron-scavenging species such as iodine and gas composition was found to have a particular shape iodides are present in the gas mixture. with a peak at 600 K, when Hg makes up for 66% of This study examines properties of electrical the gaseous mixture and Ar 34%. To explain this be- breakdown in temperature dependent gaseous mix- havior we considered the effects of temperature, gas tures of Ar and Hg and determines the influence of density and gas mixture on the discharge. The peak the gas mixture, of the temperature and the transition was found to be an effect of gas mixture, while the from the streamer to the Townsend regime as the gas gas temperature had a limited effect on the breakdown temperature drops. properties. The experiments were done on a setup made The analysis has shown that at this frequency both for hot re-ignition research in the lighting industry. streamer and diffuse breakdown regimes can take Lamps were used as experimental vessels; this is an place, depending on the gas composition and pres- approach with several advantages. First, they allow sure. Streamer discharges are present at high pres- experiments in high temperatures, which is difficult to sures and high Hg content, while at room temperature achieve in an ordinary vacuum vessel. Second, they in Ar the breakdown has a diffuse nature. In between can be filled with well-defined mixture of gaseous those two cases, the radius of the discharges during or solid compounds accurately determining the gas breakdown was found to change in a monotonic man- composition, which is a significant safety risk when ner, covering one order of magnitude from the size using a common vacuum vessel and compounds that typical for streamer discharges to a diffuse discharge pose a health or safety risk. Finally, one can exper- comparable to the size of the reactor. iment on more than one lamp and get a statistically significant result independent of small changes in the References geometry. [1] D. Z. Pai, D. A. Lacoste, and C. O. Laux, J. The driving voltage used in the experiments had a Appl. Phys. 107, 093303 (2010) sinusoidal shape with linearly rising amplitude, as the goal was to detect the minimum breakdown voltage [2] Y. P. Raizer, Gas Discharge Physics, Springer- for various sets of parameters. The frequency used Verlag, Berlin (1991)

P2-15 Pump-probe-experiments at a microplasmajet using supercontinuum radiation for broadband-absorption spectroscopy

S. Spiekermeier1, B. Niermann1, L. Budonoglu2, K. Gurel¨ 2, F. O. Ilday2, M. Boke¨ 1 , and J. Winter1

1Institut fur¨ Experimentalphysik II, Ruhr-Universitat¨ Bochum, Bochum, Germany 2Ultrafast Optics and Lasers Group, Bilkent University, Ankara, Turkey E-mail: [email protected]

1. Laser assisted plasma breakdown and phase re- chronisation is very good. The laser frequency can solved broadband absorption spectroscopy also be used as trigger-signal for the RF-generator The voltage for plasma ignition and collapse are that drives the plasmajet. Because the RF-generator not overlapping. This can be used to ignite a with is synchronized with the laser pulses, the laser is able the help of short intense laser pulses while the volt- to set the ignition point with a precision of less than age is between the collapse and ignition thresholds. one nanosecond in an RF-cycle. By delaying the su- Measuring metastable densities during ignition can percontinuum beam, the point of measurement can be be done by laser assisted pump-probe experiments us- shifted and hence the first nanoseconds of ignition can ing a high power laser beam and simultaneously gen- be observed. erated supercontinuum radiation for broadband ab- 2. Laser induced transition from α- to γ-mode sorption spectroscopy. These experiments may yield Another way to use high power laser radiation space resolved and highly time resolved information is laser assisted transition from α- to γ-mode. The about the ignition process. γ-mode of microplasmajets shows high densities and For the generation of these laser beams a fiber- thus it is more reactive than the α-mode. However based femtosecond laser is used, that was build by it is not stable and can easily turn into a thermal arc. the group of Prof. Omer¨ Ilday at Bilkent University, The transition from α-mode to γ-mode is also not Ankara. The laser provides to different beam outputs very well understood. By pointing the high power that are generated by the same oscillator. One of them output of the laser at the electrodes of the microplas- is a high power output that generates a laser with a majet, the plasma can be driven from α- to γ-mode average power of 1,1 W. The second output generates while measuring the metastable density at the same a supercontinuum spectrum ranging from 800 nm to time with BBAS. 1400 nm at a lower power of 8,3 mW. A more detailed description is given in reference [1]. Acknowledgements This work is supported by DFG within the frame- By pointing the beam of the high power output at work of the Reasearch Group FOR1123 / A2 the microplasmajets electrodes, electrons at the elec- trodes surface are released and the breakdown of the plasma is initiated (”pump”). At the same time the References supercontinuum beam is used for broadband absorp- [1] B. Niermann, I. L. Budunoglu, K. Gurel,¨ M. tion spectroscopy (”probe”). Since both beams are Boke,¨ F. O.¨ Ilday and J. Winter: J. Phys. D: generated by the same oscillator their temporal syn- Appl. Phys. 45 (2012) 245202

P2-16 Characterization of a low pressure RF plasma jet generated in Ar/H 2/C 2H2 admixture utilized for carbon nanowalls synthesis

S.D. Stoica 1*, B. Mitu 1, S. Vizireanu 1, M. Bazavan 2, G. Dinescu 1,2

1National Institute for Lasers, Plasma and Radiation Physics, Magurele, Bucharest, 077125, Romania 2Faculty of Physics, Magurele, Bucharest, 077125, Romania *Contact e-mail: [email protected]

1. General conditions. The rotational and vibrational We have previously reported [1] on the temperatures obtained upon simulation of C2 radical successful synthesis of various carbon were in the range 700 – 900 K, and respectively nanostructures, such as carbon nanotubes, 2000 – 3500 K. nanofibers and carbon nanowalls layers by using a From Langmuir probe measurements we have low pressure plasma jet generated in radiofrequency obtained values in range of 3.5 – 4.4 x10 17 m-3 for in argon and injected with acetylene in presence of the electron density, 1 - 4 eV for the electron hydrogen. By studying the growth conditions of temperature and 30 – 55 V for the plasma potential, carbon nanowalls in relation to the experimental respectively. The electron energy distributions parameters we observed which plasma related present two maxima corresponding to slow and fast parameters have a strong influence on their structure electronic populations, respectively. The positions of and morphology. Thus, we have noticed that the maxima on the energy scale depend on the used Ar/H 2/C 2H2 gas ratio, substrate position with respect experimental parameters. to the injection point and deposition pressure are the The main categories of ions obtained from MS most important plasma parameters that control the measurements can be grouped in three types: + + material characteristics [2, 3]. hydrogen related (H , H 3 ), argon related (excess + + + In this contribution we present results concerning signal) and carbon related (C Hx, C 2Hx , C 3Hx , + the characteristics of the plasma jet under the C4Hx , etc.). The most important feature in the mass conditions favorable for carbon nanowalls synthesis. spectra is the presence of hydrocarbon clusters + Specifically, the emission of the excited species was CnHx (x=1, 2, 3) with ascending number of carbon monitored by optical emission spectroscopy. The atoms, up to n = 8. These ions present various electron temperature, density, energy distribution abundances according to their energies, with the and plasma potential have resulted from the particularity that the carbonic clusters with high Langmuir probe investigations. Other species, as mass disappear at high energies. neutrals and ions, were studied by mass Neutral species recorded with mass spectrometer spectrometry. are: H, H 2, H 3, Ar, Ar 2, C 2H2, and a small signal associated to the impurities: H 2O, N2, O 2. For mass 26 (acetylene) a drop in signal intensity upon the discharge initiation, due to its dissociation in plasma, corroborated to a moderate gain of intensity of smaller carbon related masses was observed.

Acknowledgments This work has been partially funded by the Romanian Ministry, Research and Innovation under the contract C1 - 05/2010.

References [1] S. Vizireanu, L. Nistor, M. Haupt, V. Katzenmaier, C. Oehr, G. Dinescu, Plasma Fig.1: Configuration of PECVD set-up for plasma Process. Polym., 5, 3, pp. 263 (2008) characterization [2] S. Vizireanu, S.D. Stoica, C. Luculescu, L.C. 2. Results and discussions Nistor, B. Mitu, G. Dinescu, Plasma Sources From OES investigations we could observe the Sci. Technol., 19 , pp. 034016 (2010) [3] S. Vizireanu, B. Mitu, C.R. Luculescu, L.C. presence in optical emission spectra of C 2, CH carbonic radicals and H and Ar atoms, with Nistor, G. Dinescu, Surf. Coat. Tech., 211 , pp. intensities depending on the experimental 2–8 (2012)

P2-17 Pre-breakdown emission of triggered streamer micro-discharge developing in surface coplanar DBD geometry in argon at atmospheric pressure

1 2 2 2 1 1 M. Šimek *, P.F. Ambrico , S. De Benedictis , G. Dilecce , V. Prukner , V. Babický

1Institute of Plasma Physics v.v.i., Czech Academy of Sciences, Prague, Czech Republic 2Instituto di Metodologie Inorganiche e dei Plasmi- CNR, Sezione di Bari, Bari, Italy *Contact e-mail: [email protected]

1. General current in the near-infrared spectral range by Spatio-temporal evolution of AC HV driven accumulating up to 5103 samples per one spectrum. single-surface DBD micro-discharges in argon were studied by ICCD microscopy [1]. The recorded 3. Results and conclusions images revealed presence of the pre-breakdown Spectrally-resolved emission was registered and (Townsend) phase several tens of ns before the onset analysed with time-resolution defined by the of a fully developed streamer occurs. Due to minimum ICCD gate of 2 ns and for a given delay stochastic nature of the onset of the micro-discharge, fixed with respect to the rising edge of the positive high temporal resolution (2ns gating) spectroscopic high-voltage pulse. Thanks to the low jitter of the studies, requiring a good statistic, could not be onset of triggered micro-discharge with respect to performed at that time. the HV pulse, we succeeded to isolate and analyse In this work, emission spectra (700-850 nm) of a very weak emission produced during the pre- single-surface coplanar dielectric barrier (CSDBD) breakdown phase as well as subsequent (and much micro-discharge were acquired with high time stronger emission) during streamer micro-discharge resolution. In order to study the evolution of an evolution. During initial pre-discharge phase, individual streamer developing on the surface of the emission by argon occurs after electron impact dielectric barrier, we triggered the onset of the excitation process Ar(3s23p6) + e → Ar* + e’. micro-discharge by using positive high-voltage Spectra acquired at medium spectral resolution pulses of ~150 ns duration and of ~3 kV amplitude show lines originating from ArI(3p54p → 3p54s) superimposed with amplitude-modulated AC high multiplet transitions. Observed peaks were used to voltage waveforms. evaluate relative populations of the ArI(3p54p) state energy levels. During ~5 ns long pre-breakdown 2. Experimental setup phase, quite efficient population of 2p’1, 2p’4, 2p5 The single micro-discharge CSDBD reactor and 2p9 terms (in Paschen notation) is observed. consists of a MACOR® glass-ceramic disk with two During ~10 ns streamer evolution period relative embedded metallic electrodes placed in a Plexiglas populations of the 2p’1 and 2p5 terms become chamber. The chamber is equipped with quartz significantly under-populated evoking questions windows for optical diagnostics, gas feed about possible role of Ar 4s metastable states in the input/output ports and a high voltage interface [1-2]. excitation kinetics of the Ar 4p states in nano- The triggered CSDBD was powered by a power second timescales [3]. supply superimposing an AC HV waveform with a positive HV pulse. Superposition of the two (AC Acknowledgements and pulsed) HV waveforms at a selected phase of This work was financed by the Czech Science the AC waveform was realised by means of a Foundation (GAČR contract no. P205/12/1709). passive LC filter. Stays of P.F. Ambrico, G. Dilecce and S. De A fast Andor DH740i-18U-03 iStar ICCD Benedictis at IPP Prague were supported by AVCR- camera was used to register time and spectrally CNR cooperative agreement 2010-2012. resolved emission through the iHR-320 spectrometer. A Tektronix oscilloscope (DPO4034) References was used to record the discharge characteristics (the [1] M.Šimek, P.F.Ambrico and V.Prukner: Plasma HV, current and R2949 photomultiplier waveforms) Sources Sci. Technol. 19, 025010 (2011) and to control the timing of the intensifier of the [2] M.Šimek, V.Prukner and J.Schmidt: Plasma iStar camera through the ICCD gate monitor. Sources Sci. Technol. 19, 025009 (2011) Emission spectra of the micro-discharge were [3] X.M.Zhu, J.L.Walsh, W.C.Chen and Y.K.Pu: recorded synchronously with micro-discharge J.Phys. D: Appl. Phys. 45, 295201 (2012)

P2-18 Diagnostics of the glide arc under varying gravity conditions

Jirˇ´ı Sperkaˇ 1∗ , Pavel Soucekˇ 1 , Jack J.W.A. Van Loon2,3, Alan Dowson2, Jutta Krause2, Gerrit Kroesen4,V´ıt Kudrle1

1 Masaryk University Brno, Czech Republic 2 European Space Agency, ESTEC, TEC-MMG, Noordwijk, The Netherlands 3 Dutch Experiment Support Center, ACTA-VU-University and University of Amsterdam, The Netherlands 4 Technische Universiteit Eindhoven, The Netherlands ∗Contact e-mail: [email protected]

Introduction charage channel, obtained by the video motion analy- The behaviour of electric discharges in altered sis of high speed video recording, was correlated with gravity has, besides the aspect of fundamental re- the discharge voltage waveforms. search, also important practical consequences, such The difference in density of the heated gas in the as safety precautions in manned space flight, ion discharge column and the cold surrounding atmo- thrusters design or simulation of planetary atmo- sphere produced buoyancy which exerted a force on spheric chemistry. Some types of laboratory plasmas the plasma column. Increasing the centrifugal accel- have already been investigated in both hypergravity eration made the glide arc movement faster. Also the and microgravity conditions. One of the first to be appearance of the discharge channel became progres- investigated was the arc discharge in free fall [1]. Re- sively more turbulent. The observed motion of the cently, the flow phenomena in metal-halide arc dis- glide arc was compared to an analytical model. charge lamps have been intensively investigated un- der varying gravity conditions [2, 3]. Single-walled Acknowledgement carbon nanotubes were produced by arc discharge A special thank goes to European Space Agency Ed- method in hypergravity [4] and also microgravity [5]. ucation office for the Spin Your Thesis! 2012 pro- The gravity effect on the low pressure discharges gramme. can be observed in the case of dusty plasma, where gravity strongly influences heavy dust particles and Coulomb crystals can be formed in microgravity. References Herein, we report how the buoyancy influences [1] M. Steenbeck. Z. tech. Physik, 18:593, 1937. the dynamics of the glide arc discharge channel. The behaviour of the glide arc plasma has been inves- [2] W.W. Stoffels, A.J. Flikweert, T. Nimalasuriya, tigated under varying gravity (1 g–18 g) using the J. Van der Mullen, G.M.W. Kroesen, and Large Diameter Centrifuge (LDC) situated in Life M. Haverlag: Pure and applied chemistry, and Physical Sciences Instrumentation and Life Sup- 78(6):12391252, 2006. port Laboratory at ESTEC, the Netherlands [6]. Suit- [3] A.J. Flikweert, T. Nimalasuriya, G.M.W. Kroe- able device GRAVARC (acronym for GRAVity ARC) sen, M. Haverlag, and W.W. Stoffels: Micro- has been designed and constructed for this experi- gravity Science and Technology, 21(4):319326, ment. The whole experimental setup was situated 2009. inside closed centrifuge gondola and was remotely controlled. The discharge was operated in helium [4] T. Mieno, M. Takeguchi: Journal of applied and helium/methane gas mixture and gas continu- physics 99, 104301104301, 2006. ously flowed through the discharge chamber. The dis- charge voltage and current waveforms together with [5] J. Alford, G. Mason, D. Feikema: Review of the videosignal from a fast camera (480 fps) have scientific instruments 77, 074101074101, 2006. been recorded during the experiment. The optical emission spectra were also captured using a standard [6] J.J.W.A. van Loon, J. Krause, H. Cunha, J. grating spectroscope which was situated in the cen- Goncalves, H. Almeida, and P. Schiller. Proc. tre of the centrifuge. We performed several exper- Of the Life in Space for Life on Earth Sympo- iments in different gas flow rates always in depen- sium (Angers, France 22-27 June 2008), ESA dence on gravity. The gliding frequency of the dis- SP-663, 2008.

P2-19 Investigations of a long and stable filamentary plasma jet generated at atmospheric pressure

M. Teodorescu 1, E. R. Ionita 1, M. Bazavan 2, G. Dinescu 1,2

1 National Institute for Laser, Plasma and Radiation Physics, PO Box Mg36, Magurele- Bucharest, 077125,Romania 2 University of Bucharest, Faculty of Physics, Magurele- Bucharest, 077125 Romania [email protected]

1. Introduction species present in the discharge were Ar and OH Non-thermal plasma jets operating at molecular radical. atmospheric pressure in ambient atmosphere are From the comparison of the OH simulated required for applications in dentistry, medicine, spectra with the experimental ones [1], the rotational electronics. Their dimensions are an important factor temperature was calculated, with a mean value of for these fields, since long and thin plasma jets are 460 K. Also the electron density (on the order of required. 10 15 cm -3), and electron temperature (around 1eV) Plasma sources based on Dielectric Barrier were extracted from intensity ratios between various Discharges can achieve both goals of being cold yet Ar “blue” and “red” lines [2]. having length in the order of centimeters. In this contribution we present a study of a 2.3. Electrical study long and thin atmospheric pressure filamentary To correlate both imagistic and spectral plasma jet generated in argon at flows up to 2000 measurements and to further characterize this sccm, using a radiofrequency (13.56 MHz) power filamentary jet, electrical measurements were employed. By assuming an electric model for the plasma source, the capacitance, resistance and active power of the discharge were calculated. 10% of the total forwarded power was found to be used as active power in the discharge.

3. Conclusion Fig. 1: The filamentary plasma jet operated in Ar in Several plasma characterization measurements ambient atmosphere have been performed on a long atmospheric filamentary jet. Their correlation allowed a better supply (40 – 100 W forwarded power). The understanding of the phenomena involved in jet filament, of ~ 0.6 mm diameter, is ignited inside a generation and stability. It has been shown that the glass tube of 4 mm inner diameter, and exits in the plasma is relatively cold with predominant emission ambient atmosphere up to 60 mm (Figure 1). originating from molecular OH bands and atomic Ar lines, and that the use of an electrical model can help 2. Results and discussions in determinate some important parameters such as 2.1. Imagistic study active power. To evaluate the discharge stability, an operating domain imaging study was conducted as a function Acknowledgement : This work was partially of gas flow and radiofrequency power. founded by the Romanian Ministry of Education and The study reflected the domains for which the Research under the Contract PN 09390401/2009. stability is achieved, regarding both the position and length of the filamentary jet, while the peculiarities References: of the jet in the unstable regime or at the interface [1] T. Yuji , T. Urayama , S. Fujii, N. Mungkung , with different materials are also presented. H. Akatsuka, Surface & Coatings Technology, 202 (22-23), 5289–5292, (2008) 2.2. Spectral study [2] Z. Machala, M. Janda, K. Hensel, I. Jedlovský, Another study concerned the spectral signatures L. Leštinská, V. Foltin, V. Martišovitš, M. present in the jet. It was conducted along the length Morvová, Journal of Molecular Spectroscopy, of the jet with good spatial resolution. The dominant 243 (2), 194-201, (2007)

P2-20 Examination of time-varying electron properties in the plasma plume of a Hall thruster.

S. Mazouffre 1†, K. Dannenmayer 1, A. Pétin 1, P. Kudrna 2, M. Tich ỳ2

1ICARE-CNRS, 1c, av. de la recherche scientifique, 45071, Orléans, France. 2 Charles University, Faculty of Mathematics and Physics, Prague, Czech Republic. † [email protected]

1. Background and goal The three quantities oscillate as a function of time. A Hall thruster (HT) is one type of electric Vp(t) and Te(t) are correlated. They exhibit a engine currently in use onboard geosynchronous complex waveform with HF structures. Ne(t) is satellites and scientific space probes. In a HT, the harmonic with small amplitude changes. electric field at the origin of ion acceleration is 3. Time-dependent EEDF generated in a low-pressure magnetized discharge in The EEDF(t) was computed from the time- crossed E and B field configuration [1]. As no grid dependent I-V characteristics in order to extract assembly is employed for beam generation, such a additional information. As can be seen in Fig. 1, the thruster is not current limited and a relatively large EEDF amplitude changes during one breathing thrust, in comparison with gridded ion engines, is oscillation but the distribution stays Maxwellian in first order approximation. achieved, which makes this technology of great interest for orbit transfer maneuvers, end-of-life deorbiting and deep-space exploration missions. One important issue in the field of electric propulsion is the interaction between the host spacecraft and the plasma plume. Up to now, a large amount of studies has been performed on ion flow properties. Recently we carried out time-averaged measurements of the electron properties (ne, Te and

Vp) in several HTs plume by means of Langmuir probe. The goal was to provide accurate data for validation of plasma plume numerical simulations. Nevertheless, as the discharge of a HT is highly non stationary, it appeared necessary to turn to time- resolved data acquisition. In this contribution we Fig. 1: EEDF(t) measured in the far-field plume of a present electrostatic probe measurements of the 1.5 kW class Hall thruster (250 V, 3 mg/s Xe, 13.8 kHz) time-varying electron parameters and EEDF at a microsecond time-scale in HT plasma. 3. High-speed electrostatic probe system The current challenge is to perform similar 2. Time-varying electron parameters measurements near the exhaust of a Hall thruster, a Measurements have been carried out in the region of large energy flux density wherein probe plasma plume of two HTs of different sizes and lifetime is very short. Thus, a compact high-speed reciprocating probe system has recently been power levels during one period of the high- developed [3]. Details about the design and first amplitude breathing oscillation of the discharge measurements will also be given in this contribution. (typically 10-30 kHz) [2]. A cylindrical Langmuir probe was used for measuring ne, Te and Vp [2]. The References current is recorded as a function of time for a fixed [1] K. Dannenmayer, S. Mazouffre, J. Propulsion. potential. The time-dependent I-V characteristic Power 27 , 236 (2011). [2] K. Dannenmayer et al, Plasma Sources Sci. curve is reconstructed from bias voltage series. Vp Technol. 21 055020 (2012). was also acquired with an current-heated emissive [3] K. Dannenmayer, S. Mazouffre, Rev. Sci. probe of which the bandwidth is 60 kHz [2]. Instrum. 83 123503 (2012).

P2-21 Thomson scattering at the high flux linear plasma generator Magnum-PSI for the determination of electron and ion properties

H.J. van der Meiden1, M.A. van den Berg1, S. Brons1, T.W. Morgan1, N.N. Naumenko2, M.J. van de Pol1, J. Scholten1, P.H.M. Smeets1, S.N. Tugarinov3, and G. De Temmerman1

1FOM Institute DIFFER, Dutch Institute for Fundamental Energy Research, Association EURATOM-FOM, Trilateral Euregio Cluster, P.O. Box 1207, 3430 BE Nieuwegein, The Netherlands 2IPh NASB, Minsk, Belarus 3SRC TRINITI, Troitsk, Moscow reg. Russian Federation *Contact e-mail: [email protected]

1. Introduction The system utilises 50 spatial channels of ~2 mm The linear plasma generator Magnum-PSI length, along a laser chord of 95 mm. By summing a [1] has been built to reproduce the plasma-wall total of 30 laser pulses (0.6 J, 10 Hz), an conditions expected in the ITER divertor. Particle observational error of 3% in ne and 6% in Te (at ne = fluxes, of up to 1025 m-2s-1, corresponding to power 9.4×1018 m-3) can be obtained. The minimum 2 17 fluxes of up to 40 MW/m continuously and 2 measurable density and temperature are ne < 1×10 2 −3 GW/m pulsed, can be generated. This contributes to m and Te < 0.07 eV, respectively. Using the our understanding of the underlying erosion (and Rayleigh peak superimposed on the TS spectrum, deuterium retention) mechanisms of plasma facing the neutral density of an argon plasma can be 20 −3 materials. To determine the power flux to plasma measured: accuracy 25% at n0 = 1×10 m . facing components, measurements of electron The CTS system is based on a Nd:YAG density (ne) and temperature (Te) and ion tempera- laser operating at 1064 nm and an extreme high ture (Ti) as well as that of the axial velocity (vplasma) resolution spectrometer equipped with an InGaAs of the plasma are necessary. An advanced Thomson SWIR camera. Ti and vplasma can be determined with scattering system (TS) [2] is used at Magnum-PSI an accuracy better than 15%. Forward CTS is for measuring ne and Te profiles across the plasma applied for enhancing the size of the observable radius. For measuring Ti and vplasma of the plasma a scattering wave 2/ k with k  4 sin  / 2 0 and collective TS system (CTS) is being built. As will be  the laser wavelength (see Fig. 2). shown in this report, the small Debye length of the 0 Magnum-PSI plasma enables application of this method using commercially available techniques.

2. Thomson scattering diagnostics The TS system for Magnum-PSI is based on a Nd:YAG laser operating at the second harmonic and a detection branch featuring a high etendue (f/3) transmission grating spectrometer (see Fig. 1).

Fig. 2: CTS observation system for Magnum-PSI: forward scattering angle between 17 and 30

In this report measurements of a magnetized hydrogen/deuterium plasma beam will be presented along with accurate Thomson-Rayleigh scattering measurements of a low-temperature argon plasma expansion. Finally, the feasibility and development of the CTS system will be presented in this report.

References [1] J. Rapp et al, Fusion Eng. Des. 85, 1455 (2010) Fig. 1: Magnum-PSI and TS laser beam line [2] H.J. van der Meiden et al, Rev. Sci. Instrum. 83, 123505 (2012)

P2-22 Excitation kinetics and NO production in a cold RF atmospheric pressure plasma jet

A.F.H. van Gessel , K.M.J. Alards and P.J. Bruggeman*

1Eindhoven University of Technology, The Netherlands *Contact e-mail: [email protected]

1. Introduction A time modulated RF atmospheric pressure plasma jet (APPJ), operated in ambient air with a flow of argon and a few percent of air, N 2 or O 2, was characterized by measuring the gas temperature with Rayleigh scattering, the absolute NO density with laser induced fluorescence, and the emission of NO A and N 2 C with time resolved optical emission spectroscopy. The jet is excited by a 13.6 MHz RF voltage which is time modulated at 20 kHz with a duty cycle of 20%. The gas temperature, NO density and the emis- sion measurements have been performed both time and spatially resolved [1]. The APPJ has the ad- vantage that the plasma dissipated power can be ac- Fig. 1: Time resolved NO and gas temperature during the curately measured [2]. time modulated plasma on and off phase.

2. Results It was found that the gas temperature depends on the power, rather than the gas mixture. The NO den- sity increases with increasing plasma power, and was found to have a maximum in the investigated range around 1.5 ·10 21 m-3 at an air admixture of 2%. The N 2 C emission is modulated by the 13.6 MHz RF frequency, while the NO A emission front increases with much slower velocity during the 20 kHz duty cycle. This gives an insight into the excita- tion mechanisms in the plasma. It shows that N 2 C is produced by electron excitation of the ground state N2 X while the NO A is produced by N 2 A metastable Fig. 2: Spatially resolved NO density in an RF jet with the induced excitation of NO X, similarly as observed in nozzle at axial position 0, with 2% added air and 3.5 W low pressure RF plasmas [3]. plasma dissipated power. While the emission is highly time modulated, it is shown that the NO X density and the gas tempera- ture are in good approximation constant (see figure References 1). [1] A.F.H. van Gessel, B. Hrycak, M. Jasi ński, J. Through the addition of either N 2 or O 2 to the Mizeraczyk, J.J.A.M. van der Mullen and P.J. plasma it was experimentally confirmed that the Bruggeman, J. Phys. D: Appl. Phys. 46, 095201 production of atomic N radicals are of key im- (2013) portance for the NO production in this APPJ. It is [2] S. Hofmann, A.F.H. van Gessel, T. Verreycken shown (as in figure 2) that the NO is mainly pro- and P.J. Bruggeman, Plasma Sources Sci. duced in the core of the discharge and it is rapidly Technol. 21 , 065010 (2011) decreasing with increasing distance from the nozzle [3] S.D. Benedictis, G. Dilecce, and M. Simek, J. due to oxidation into species such as NO , N O , Phys. D: Appl. Phys. 30, 2887-2894 (1997) 2 2 5 HNO 2 and HNO 3 as found previously in air chemis- [4] R. Dorai and M.J. Kushner, J. Phys. D: Appl. try models [4]. Phys. 36 666-685 (2003)

P2-23 Optical cavity based infrared spectroscopy of plasma using QCLs

J. H. van Helden∗ , U. Macherius , N. Lang , J. Ropcke¨

Leibniz-Institute for Plasma Science & Technology, Felix-Hausdorff-Str. 2, 17489 Greifswald, Germany ∗Contact e-mail: [email protected]

1. Introduction Molecular plasmas are increasingly being used, 2. Optical cavities not only for basic research, but also, due to their In CEA techniques, light is trapped in a high favourable properties, for materials processing tech- finesse optical cavity consisting of two highly re- nology. However, a number of processes and proper- flective mirrors (R > 99.9 %) and containing the ties are far from being fully understood for this type sample under investigation. The light then under- of plasma. To understand the gas phase and surface goes repeated reflections such that the effective op- reaction kinetics, the absolute concentration of the tical pathlength is of the order a few kilometers in a radicals and neutral molecules and their temperature table-top setup whilst the sampling volume remains in the plasma need to be known. Over the last two relatively small. It has been demonstrated that setups decades chemical sensing using mid-infrared (MIR) of this type using diode lasers in the near-infrared laser absorption spectroscopy in the molecular fin- have the ability to achieve very low detection limits gerprint region from 3 to 20 µm has been established [4]. However, the combination of cw QCLs with high as a powerful in situ diagnostic tool for molecular finesse cavities to achieve the desired sensitivities plasmas; this enables access to strong fundamental is not straightforward due to the different properties vibrational bands of a large number of compounds of these lasers to the diode lasers employed in the allowing sensitive and selective spectroscopic mea- NIR. As a result, the achievement of the desired path- surements of these compounds. The innovation and lengths in a table-top configuration has proven to be subsequent development of quantum cascade lasers a challenging undertaking as the enhancement is cur- (QCLs) has transformed the way MIR radiation is rently orders of magnitudes less than in the NIR [5]. generated, and has allowed relatively simple access We are currently exploring the combination of QCLs to a wide spectral region. QCLs, whether pulsed or with optical cavities by employing cavity-enhanced continuous wave, offer high output power, room tem- absorption spectroscopy (CEAS) to reach the desired perature operation, single-mode character, narrow- detection limits down to ppt levels. bandwidth and wide tunability, making them ideal tools for high-resolution spectroscopy with a wide Work supported by the DFG within the frame- variety of applications. In recent years, the appli- work of Project no. RO 2202/6-1 and by the BMBF cation of quantum cascade lasers to spectroscopy project VIP-USD, FKZ: 16V0122. for trace gas sensing and plasma characterisation in the MIR region has increased rapidly [1, 2, 3]. References Nowadays, high-power (up to 100 mW) cw single- [1] R.F. Curl, F. Capasso, C. Gmachl, A.A. mode operation is routinely achievable at room tem- Kosterev, B. McManus, R. Lewicki, M. perature using distributed feedback quantum cas- Pusharsky, G. Wysocki, F.K. Tittel: Chem. cade lasers (DFB-QCLs) tunable over a couple of Phys. Lett. 487 pp 1 (2010) cm−1 and the recent commercial availability of ex- ternal cavity QCLs (EC-QCLs) has led to increas- [2] G. Hancock, G. Ritchie, J. van Helden, R. ingly wide (mode-hop free) tuning ranges (∼ 200 Walker, D. Weidmann, Opt. Eng. 49 pp cm−1) enabling multi-component detection includ- 111121(2010) ing molecules with broader absorption structures. [3]J.R opcke,¨ P.B. Davies, N. lang, A. Rousseau, S. As a result, QCLs are progressively taking over the Welzel: J. Phys. D. Appl. Phys. 45, pp 423001 MIR laser market and will continue to do so as their (2012) reliability, output power, wall plug efficiency, and tunability continue to improve, and their emission [4] G. Berden, R. Engeln: Cavity Ring-Down Spec- wavelengths decrease toward the 3 µm region where troscopy Techniques and Applications, Wiley, many molecules have strong C-H, N-H, and O-H Chichester (2009) stretching vibrations. In this contribution, we will demonstrate that the requirements to detect low den- [5] S. Welzel, G. Lombardi, P.B. Davies, R. Engeln, sities of relevant species in plasma can be achieved D.C. Schram, J. Ropcke:¨ J. Appl. Phys. 104 pp by combining QCLs with cavity enhanced absorption 093115 (2008) (CEA) techniques based on optical cavities. P2-24

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P2-25 Detection of Hydrogen Atoms by Two Photons Absorption Laser Induced Fluorescence in a High Power Density H2/CH 4 Microwave Plasma

M. Wartel*, C. Rond, N. Derkaoui, C.Y Duluard, A. Gicquel

LSPM-CNRS, Laboratoire des Sciences des Procédés et des Matériaux, Université Paris 13, Sorbonne Paris Cité, 99 avenue Jean-Baptiste Clément, 93430 Villetaneuse, France *Contact e-mail: [email protected]

1. Introduction hydrogen atoms densities have been carried out into Microwave Plasma Assisted Chemical Vapour the plasma. Results, showed in Fig 1, highlight a Deposition (MPACVD) is widely used for the strong increase in H density into the plasma bulk production of diamond films, for which hydrogen with power density and confirm previous results atoms and methyl radicals have been shown to obtained by OES. constitute the key species for growing crystal 7x10 17 ] -3 diamond [1]. The growth of very high purity and 17 600 W 6x10 cm

[ 800 W quality diamond at elevated deposition rate relies on 1000 W 5x10 17 high production of H atoms and CH 3 radicals in a 1250 W 17 1500 W 4x10 very clean system at very high power density. That 2000 W is the reason why understanding the physical and 3x10 17 2500 W 3000 W chemical processes involved in diamond deposition 2x10 17 and how the experimental conditions impact the 1x10 17

growth mechanisms at high pressure / high power (> Hydrogen atom density Black : OES measurements 0 100 hPa, > 2 kW) requires in particular the Blue : TALIF measurements determination of H plasma density. Following 0 50 100 150 200 250 300 350 400 450 Pressure (hPa) Optical Emission Spectroscopy (OES) used previously [2], Two-Photons Absorption Induced Fig. 1: H density vs pressure and microwave power. Fluorescence (TALIF) technique has been implemented to study a H 2/CH 4 CVD plasma under Furthermore, excitation spectra of hydrogen atoms high pressures and high microwave power densities. have been recorded and H temperatures have been Indeed, this laser technique is a powerful and determined by Doppler broadening. Results, spatially resolved tool for chemical characterization presented in Fig 2, show an increase in gas of plasma [3]. temperature in the plasma bulk with power density. 4000

2. Experimental results 3500 The microwave (MW) diamond deposition reactor is a water-cooled stainless steel nearly 3000 resonant cavity operating at high pressure (25- 400 2500 hPa) and high power density (600-4000 W). The discharge, produced by a 2.45 GHz MW generator, 2000 600 W 2000 W sparks off the activation of the feed gas (0- temperatureGas (K) 1500 3000 W 10%CH 4/H 2) which leads to the formation of a close 4000 W to hemispheric plasma on the 5 cm diameter 1000 50 100 150 200 250 300 350 400 substrate holder supporting a crystal diamond Pressure (hPa) substrate. A TALIF set up has been implemented in order to detect hydrogen atoms for high power Fig. 2: H temperature vs pressure and microwave power. density conditions. After excitation of the n=3 level by two photons at 205.1nm, fluorescence emission References of H α at 656.3nm have been recorded. A calibration [1] D. G. Goodwin, J. Appl. Phys. 74 (1993) 6888- method allows estimating the H density in the 6894 plasma from a measurement of the TALIF signal [2] A. Gicquel, Chem. Phys. 398 (2012) 239-247 generated from krypton at a well-known pressure, [3] M. G. H. Boogaarts, Rev. Sci. Instrum. 73 (2002) using a known Kr to H detection sensitivity ratio. By 73-86 this way, spatially resolved measurements of

P2-26 Time-resolved quantum cascade laser based in-situ diagnostics applied to dielectric barrier discharges

S. Welzel 1*, F. Brehmer 1,2 , M.C.M. van de Sanden 1,3 , R. Engeln 1

1Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands 2AFS GmbH, Von-Holzapfel-Straße 10, 86497 Horgau, Germany 3Dutch Inst. for Fundamental Energy Research (DIFFER), P.O. Box 1207, 3430 BE Nieuwegein, The Netherlands *Contact e-mail: [email protected]

1. Introduction The detection of stable and transient species along with gas temperature measurements remains a challenge for the majority of molecular (complex) plasmas used for e.g. gas conversion or plasma- assisted deposition processes. Considering particularly plasmas at atmospheric pressure with inherently small discharge volumes, (optical) access to the active plasma is often hampered. On the other hand, time-resolved in-situ measurements are a Fig. 1: Experimental arrangement used for in- and ex- situ detection of CO dissociation products in DBDs. valuable tool (i) to establish temperatures of heavy 2 particles, (ii) to identify excitation mechanisms in 3. Results & Discussion the plasma, (iii) to discriminate gas phase and The time-resolved quantification of CO in surface reactions as they occur on significantly (filamentary) DBDs revealed the same densities as different time scales, and (iv) to unravel particularly established in earlier ex-situ measurements. By temperature-dependent reaction mechanisms. contrast to electronically excited states a variation of Modern mid-infrared (MIR) laser sources, known as ground state densities with the discharge current was quantum cascade lasers (QCLs), provide a means for not observed. In case the discharges were operated highly time-resolved absorption spectroscopy in the in pulsed mode, relatively slow changes in the CO molecular "fingerprint" region (3 - 20 µm). The absorbance values were detected (fig. 2). The CO time-resolution can be thereby as good as a few formation and depletion rates are strongly dependent hundred nanoseconds, if pulsed QCLs are applied, on the residence time, i.e. under atmospheric and are thus perfectly suited for transient discharges. pressure conditions CO densities are only weakly

modulated. The trends displayed in fig. 2 may 2. Experimental suggest a non-negligible contribution of surface QCLs, mainly operated in pulsed mode at room- reactions, i.e. reaction mechanisms significantly temperature, were applied to different mid- different from electronic impact excitation and frequency (kHz) dielectric barrier discharges ionisation or vibrationally stimulated dissociation. (DBDs) at atmospheric pressure, more precisely to high-current (glow-like) and conventional 1000 mbar, 148 sccm filamentary DBDs, respectively. Special beam 1000 mbar, 518 sccm shaping optics were used to facilitate in-situ 0.06 500 mbar, 518 sccm On Off 200 mbar, 518 sccm ] measurements and to reduce the MIR beam diameter -1 to typical gap widths of ~ 1 mm. Different synchronisation schemes were used to achieve 0.04

phase-resolved measurements during individual AC cycles as well as to monitor molecular concentrations during pulsed discharge operation. 0.02

Apart from examples given for high-current air- Absorbance[cm like plasmas that were developed for the deposition 0.00 of silica-like layers on polymer substrates, the 0 100 200 300 400 500 activation of CO 2 in a parallel-plate flow-tube Time [ms] reactor (fig.1) will be discussed. Links to e x-situ Fig. 2: Temporal evolution of CO absorbance measured studies of the effluent and to the temporal evolution at 2212.63 cm -1 in pulsed DBDs. of the optical emission are provided.

P2-27 Scaling parameter determined in high-current dielectric barrier discharges used for plasma-enhanced CVD of SiO 2 thin films

S. Welzel 1* , S.A. Starostin 2, H. de Vries 2, M.C.M. van de Sanden 1,3 , R. Engeln 1

1Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands 2FUJIFILM Manufacturing Europe B.V., P.O. Box 90156, 5000 LJ Tilburg, The Netherlands 3Dutch Inst. for Fundamental Energy Research (DIFFER), P.O. Box 1207, 3430 BE Nieuwegein, The Netherlands *Contact e-mail: [email protected]

1. Introduction Gas samples were fed to a multi-pass absorption Large-area plasma-enhanced (PE) processing of cell at reduced pressure (~50 mbar) to increase the polymeric substrates in diffusive dielectric barrier selectivity for different absorption features (Tab. 1). discharges (DBDs) have been shown to yield high- The DBD was sinusodially driven (185 kHz) and quality SiO 2-like barrier layers. This has been operated in pulsed mode for power adjustment obtained through chemical vapour deposition (CVD) purposes using duty cycles between 10 - 75 %. at atmospheric pressure (AP) using organo-silicon precursors (HMDSO or TEOS) and industrially 3. Results & Discussion relevant air-like gas mixtures (N 2/O 2/Ar). An Main stable products were quantified under essential requirement to establish a diffusive mode is various discharge conditions such as different power an electronic stabilisation circuit with which high densities (e.g. Fig. 1) and precursor admixtures (type discharge currents of a few A can be obtained. A of precursor, mixing ratio). model for the precursor consumption along the 1.5 active plasma zone was developed earlier and 10 %

] 25 % TEOS corroborated by thin film diagnostic techniques. -1 50 % Complementary gas phase studies using infrared 1.0 absorption spectroscopy were carried out to assess the model prediction and are reported here. 0.5 O 3 (C H OH) Additionally, the deposition process in the (at least x y spatially) transient discharges is tested against Absorbance[cm 0.0 typical scaling parameters for technical plasmas, HCOOH such as the mean energy, to obtain a more general 950 1000 1050 1100 1150 1200 -1 description of the plasma-chemical processes Wavenumber [cm ] regardless of the precursor used. Fig. 2: Gas phase spectra of products formed in N2/O 2/Ar plasmas containing TEOS as precursor 2. Experimental (database value of absorption cross section offset for The experimental AP PE-CVD setup used was an comparison and clarity) at different duty cycles (power). industrial roll-to-roll configuration, which makes the A typical H-N-O chemistry with traces of direct optical access to the gap (0.5 mm) even more hydrocarbons is observed under full precursor challenging. Therefore, ex-situ Fourier-Transform consumption. Formic acid was found to be a good IR spectroscopy was applied to identify and quantify marker molecule for strong etching of the polymeric gas phase species extracted from the effluent of the substrate or - as soon as layer growth starts and discharge under flowing conditions. protects the polymer - incomplete precursor

Molecule Spectral range LOD dissociation. A clear transition in the downstream [cm -1] [ppm] gas phase (i.e. the species concentrations) can be observed as a function of injected power and hence CO 2030 - 2230 10 the level of precursor consumption. Additionally, the CO 2260 - 2270 100 2 CO density in the gas phase is closely linked with H2CO 2 1750 - 1810 10 NO 1845 - 1925 20 the growth rate of the SiO 2 films. More importantly,

N2O 2185 - 2255 5 all trends observed can be described by a scaling

NO 2 1590 - 1612 5 parameter that is further normalised to a 'reactor O3 1045 - 1050 30 constant' and allows to define a parameter range for

Tab. 1: Limits of detection (LOD) of main stable species good quality films. that were identified and quantified in the effluent.

P2-28