PROPOSAL PROJECT

DEREP

“Characterization and DEvelopment of a stable and REproducible scheme for -driven Proton sources”

Principal Investigator: Dr. Luca Volpe Scientific coordinator: Prof. Dario Giove

ISTITUTO NAZIONALE DI FISICA NUCLEARE

Concorso per il Finanziamento di n. 1 progetto per giovani ricercatrici/ricercatori nell’ambito delle Linee di ricerca della Commissione Scientifica Nazionale 5

Abstract In this project we propose to study possible stable configurations for producing laser-driven proton beams with a maximum energy around 40-50 MeV by using well established national and international laser facilities of reasonable complexity, cost and size and also to design a “micro” transport line for collimation and energy selection of the proton beam . This could represent the first scheme for a future prototype of laser-driven proton beam system for medical applications. The Europen project ELIMED seems to be the natural framework in which the proposal can be developed DEREP

1. Project objectives

Interest in laser driven proton acceleration continues to be strong since 2000, with a potentially wide range of applications among which the most important are that related to medical applications. The importance of laser and target advancements for source optimization has been made clear by many laser- interaction experiments done in laboratories around the world. The development of suitable instrumentation and beam lines that can exploit the unique features of laser- accelerated proton emission is critical and timely. Since 2000 tremendous fundamental research and development have been performed on laser-driven proton and ion sources, even if a lot of long-term effort is still required for the implementation of laser-driven medical accelerators: i) the proton acceleration mechanisms and the target conditions should be optimized in order to obtain the beam energy, spectrum and divergence which match well the desired application requirements ii) the design of a “micro scaled” proton beam transport line is an important issue to makes these type of sources usable for medical application. In this context the goal of this project is to study possible stable configurations for producing laser-driven proton beams with a maximum energy around 40-50 MeV by using “conventional laser systems” and also to design a “micro” transport line. This could represent the first scheme for a future prototype of laser -driven proton beam system for medical applications. As will be explained in the following this project can be thought as part of an European project ELIMED (Extreme Light Infrastructure Medicine) which was proposed by the National Institute of Nuclear Physics [It] (INFN) within the framework of the European project ELI (Extreme Light Infrastructure) which aim is to build a new generation of large research facilities selected by the European Strategy Forum for Research Infrastructures (ESFRI). The aim of the ELIMED project is to perform proof-of-principle experiments (in 1-10 Hz regime) which might demonstrate the validity of new approaches, based on laser-driven proton sources, for potential future applications in the field of hadron-therapy. It also involves contributes from many worldwide institutions that expressed a strong interest in this new pioneering field. The hope of this new community is to give in the next years, a new vital impulse to the tumor radiation treatments with ion beams. Stable laser-driven proton (ions) source is demanded principally for medical application but also for many other applications among which the most relevant are: i) proton imaging of matter by using mono energetic beam obtained by chromatic selection of the proton sources; ii) proton imaging (proton radiography) of imploding plasma and proton mapping of elctric and magnetic fields (proton deflectometry) in the context of the inertial confinement approach to nuclear fusion. Moreover the broad energy spectrum of laser-driven proton beam permit to follows plasma implosion in time (proton time of flight); iii) warm and hot dense matter generation. Indeed thanks to the Bragg peak property of protons is possible to warm up the matter from inside; iv) nuclear and particle physics: the interaction of laser-driven high-energy ions with secondary targets can initiate nuclear reactions of various types can be used as a tool to diagnose the beam properties. This also presents the opportunity of carrying out nuclear physics experiments in laser laboratories rather than in accelerator or reactor facilities, and to apply the products of the reaction processes in several areas. To reach the goal of the project we focus on three main items: 1) Proton source development 2) Beam Transport Design 3) Beam Instrumentation development. The source development activities will be focused on the study of the processes involved in the design, construction and alignment of specific targets. These activities will take as “reference” laser facilities able to deliver beams with energies of at least 5-10 J, contrast of the order of 109-1010, pulse duration of the order of 100 fs, focal spot of the order of 20 micron (FWHM), intensity of the order of 10 19 at least. with these characteristics may be considered of reasonable complexity, cost and size. Experimental results obtained by Ogura and collaborators in 2012 and reported in ref [Ogura2012] can be used as “reference case” . By using 40 fs laser pulse duration, 1021 W /cm2 and irradiating targets of 800 nm thickness, they reported proton energies up to 40 MeV, the highest value reported so far for pulse energies below 10 J. Within this framework, once the main laser parameters are fixed, the performance of the laser-generated proton beams can be studied as follows :

1) Controlling target properties. → Reducing target density down to the critical density to enhance laser absorption (foams) → Reducing target thickness (thin targets )

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→ reducing target area (mass limited targets) → modifying target surface geometry (cone shaped targets) → using multilayer targets (foam+solid or with tracers to reveal Ka emission) 2) Controlling chamber set-up → Laser diagnostic tools → Target Positioning 3) Controlling transport of the laser-genereted proton beam: → designing “micro-scaled” transport device for laser-driven proton beam based on quadrupole magnets for treatment of the incoming proton beam and for selection minimization of other secondary particle (electrons and photons) production.

Developing this project will includes experimental and theoretical work. The theoretical work will be dedicated to numerical simulations connected to laser-matter interaction as well as electron generation and transport for target design, design of a “micro-scaled” transport device (magnetic quadrupole or solenoid) for ion beam transport and for chromatic energy selection. The experimental work will be the main part of the project. In particular the definition of an experimental campaign will be the first step of the project and all the other activities will be connect to that. Several physical regimes are involved in this type of processes which require using different physical models and approaches at the same time. This makes collaboration between different laboratories and different institutions very profitable. Therefore “collaboration” with other institutions and laboratories represent one of the key point of the project. Within the framework of this project, two different scientific areas are naturally involved: the physic of High energy lasers and the physics of accelerators. It is a matter of fact that connecting two different areas of science will lead, naturally to new advancements and open new scientific opportunities. One example of that is the recent installation of the new femto-second Laser system called FLAME (Frascati Laser for Acceleration and Multidisciplinary Experiments) [FLAME] at the National Laboratories of Frascati beside the per-existence Free Electron Laser. As anticipated before the natural context of the outlined project is the European ELIMED project by INFN [It], therefore, within national context, the main collaboration will be with the INFN Section of Milano (Carlo De Martini and Dario Giove) and with the INFN section of Bologna (Giorgio Turchetti) as well as with the National laboratory of Frascati in which the laser FLAME is located. Indeed Laser Flame is one of the laser facilities considered for possible experiment in this project. Milano and Bologna sections have a long collaboration in many national and international projects as for example ELIMED. For target preparation the project will also profit from collaboration with Prof. P. Piseri at the molecular beams laboratory of CIMaINa and Physics Department of the Università degli Studi di Milano, that will provide expertise on the synthesis of nanostructured material layers via supersonic cluster beam deposition (SCBD) [MIlani2001]. This technique allows the deposition of porous material from carbon, metal or oxide nano-particles. The PI and the group of Prof. Piseri collaborated in 2012 for an experiment in Accademy of Science in Bejing China which aim was to study carbon target thickness and density optimization for relativistic electron transport in matter. On the other hand the international collaboration will be started with the theoretical and experimental group of the research center CELIA at the University of Bordeaux for numerical simulations and experimental support, with the group of prof. I. Hofmann of the GSI laboratory In Darmstad and finally with the RAL target area group for target fabrications.

2. State of research with respect of the proposed project

Laser-driven proton beams are a well established topic since many years and many experiments have been done to reach maximum proton energy. The aim of this project is mostly related to the optimization of proton sources with energy range which have been just demonstrated in recent experiments. Therefore a connection with the current status of the research is compulsory. In this section the state of the art of laser-driven proton beam generation is presented together with applications.

2.1 Laser-driven proton beam state of the art Recently, ultra-intense laser-driven ion acceleration has turned out to be an extremely interesting phenomenon,

Page 3 of 19 DEREP capable to produce ion beams which could potentially be suitable for applications as hadron therapy or dense matter diagnostics High intensity laser matter interaction experiments provided ions up to energies of few MeVs already before the 2000s but the low brilliance and broad divergence features of such particles were not attractive for specific applications. It was only in the 2000 that laser driven ion acceleration has gained considerable attention, thanks to the results achieved by three independent experiments on laser-generated electron. In these experiments [Clark2000; Maksimchuk2000; Snavely2000 ] the authors, independently, reported the observation of an intense emission of multi-MeV protons from solid targets, either metallic or plastic, of several microns thickness irradiated by high-intensity laser pulses. The basic setup of one of these [Snavely2000] experiments is shown in Fig. 1.1 (left) . The laser intensity, number of protons, and maximum ion energy observed for was 3 x1020 W/cm2 , 2x1013 and 58 MeV. Fig. 1.1 (right) shows the observed proton spectrum. The protons were detected at the rear side of the target, opposite to the laser irradiated surface and were emitted, as a rather collimated and laminar beam, along the target normal direction. The emission of protons from metallic targets whose chemical composition does not include hydrogen may sound surprising, but it was already clear from previous experiments that protons originated from impurities, i.e., thin layers of water or hydrocarbons which are ordinarily present on solid surfaces under standard experimental conditions.

Fig. 2.1: (left) view of a typical experiment on proton emission from laser-irradiated solid targets. (right) Proton energy spectrum from the rear side of a 100 m solid target irradiated by a 423 J, 0.5 ps pulse at normal incidence, corresponding to an intensity of 3 1020 Wcm2. The integrated energy of protons indicates a conversion efficiency of ’ 10% for protons above 10 MeV. From [13]

These findings generated an enormous interest both in fundamental research and in the possible applications. In an applicative perspective, the most relevant and peculiar feature of multi-MeV ions is the profile of energy deposition in dense matter. Different from electrons and x rays, protons and light ions deliver most of their energy at the end of their path, at the so-called Bragg peak. This property makes protons and ions very suitable for highly localized energy deposition. The applications that were proposed immediately after the discovery of multi-MeV proton acceleration included ion beam cancer therapy, proton radiography, laser triggering and control of nuclear reactions, production of warm dense matter, ‘‘fast ignition’’ of inertial confinement fusion targets (see section 2.2 ). Experimental results in ref [Snavely2000] shows also evidence that protons were accelerated at the rear side. To support the interpretation the so-called target normal sheath acceleration (TNSA) model was introduced by Wilks et al. [Wilks2001] . Briefly, TNSA is driven by the space-charge field generated at the rear surface of the target by highly energetic electrons accelerated at the front surface, crossing the target bulk, and attempting to escape in vacuum from the rear side. Beyond simple modelling a rich and complex dynamics of laser-plasma interaction and ion acceleration, involving collective and self-organization effects, is apparent. Unfolding such dynamics requires the use of self-consistent electromagnetic (EM), kinetic simulations. To this aim, the particle-in-cell (PIC) method is by far the most commonly used approach. Large-scale, multidimensional PIC simulations running on parallel supercomputers are an effective support for the design and interpretation of laser-plasma acceleration experiments. A major requirement for several of the foreseen applications is an increase of the energy per nucleon up to hundreds of MeV and beyond. After the first years of research, the combined vigorous development in both laser technology and advanced target manufacturing allowed the investigation of TNSA exploring a continuously increasing range of laser and target parameters. In most cases the two sets of parameters are intimately related. For example, the use of ‘‘extreme’’ geometrical target properties, such as thicknesses in the submicrometric range, requires the availability

Page 4 of 19 DEREP of extraordinarily clean, prepulse-free pulses to avoid early target evaporation and deformation. Such pulses can be obtained with recently developed techniques, such as plasma mirrors [Dromey2004; Fuchs2006a; Thaury2007], optical parametric amplification [Shah2009] or crossed polarized wave (XPW) generation [Jullien2005; Zaouter2011] Mackinnon [Mackinnon2002] studied the dependence of ion acceleration on the target thickness, with the aim of addressing the role played by the electron temporal dynamics and its effect on the formation of the accelerating sheath electric field. The experimental results showed an increase in the peak proton energy from 6.5 to 24 MeV when the thickness of the Al foil target was decreased from 100 to 3 mm. These data clearly indicate that an increase in the target thickness implies a lower mean density of the hot electrons at the surface and a consequent lowering of the peak proton energy.

FIG. 2.2. Maximum detectable proton energy as a function of target thickness for high-contrast (HC) and low-contrast (LC) conditions. Data are shown for both backward (BWD) and forward (FWD) directed ions, respectively, showing the symmetrical behavior of TNSA for HC and ultrathin targets. The LC results show the existence of an ‘‘optimal’’ thickness determined by the laser prepulse causing early target disruption, similar to [Kaluza2004]. The laser pulse had 65 fs duration, [0.5-1.0] 1019 W/cm2 intensity, 45 incidence, and P polarization. From [Ceccotti2007].

T

The influence of the laser prepulse due to amplified spontaneous emission (ASE) on the acceleration of protons in thin-foil experiments has been investigated in detail by Kaluza et al. [Kaluza2004]. In this experiment Al foils of different thickness (from 0.75 to 86 mm) were used in the presence of an ASE prepulse whose duration could be controllably varied. The results indicated an optimal value for the target thickness, strongly depending on the prepulse duration, at which the TNSA process leads to the highest proton energies. For thinner targets, a prepulse- induced plasma formation at the rear side effectively suppressed TNSA. Related experimental work, where a wide range of laser parameters and different target materials have been considered, can be found in the literature [Spencer2003; Fuchs2006]. Effective suppression of the laser prepulse level, that is, the adoption of ultra-high laser contrast, can significantly alter the physical picture, since ultra-thin targets, down to the nm level, can maintain their integrity until the interaction with the main pulse. With these conditions a more effective acceleration process can be expected because the refluxing and concentration of hot electrons in a smaller volume may lead to the establishment of a stronger electric field and, consequently, to higher ion energies. These ideas have been successfully tested by Neely et al. [Neely2006] at the Lundt laboratory using Al target with thickness’s as low as 20 nm in combination with 33 fs pulses with ASE intensity contrast reaching 1010. A significant increase of both maximum proton energy and laser-to-proton energy conversion efficiency was found at an optimum thickness of 100 nm. Similar results have been obtained by Antici et al. [Antici2007] and Ceccotti [Ceccotti2007]. As a further interesting feature of this latter experiment, a symmetrical TNSA on both front and rear sides has been demonstrated, as shown in Fig. 1.2, when a sufficiently high ( > 1010) laser contrast is used. This result confirms the universality of the TNSA process, which may also occur at the front side (accelerating ions in the backward direction) if the density profile is sharp enough. Recently, using a laser pulse with similar contrast, 40 fs duration, 1021 W/cm2 and irradiating targets of 800 nm thickness, Ogura et al. [Ogura2012] reported proton energies up to 40 MeV, the highest value reported so far for pulse energies below 10 J. Another possible strategy to exploit the effectiveness in the formation of the accelerating field in mass-limited targets is to reduce the lateral dimensions. Numerical investigations [Psikal2008] have shown that a reduced surface leads to higher densities of hot electrons at the rear side of the target and, thus, to higher accelerating electric fields. Buffechoux et al. [Buffechoux2010] experimentally confirmed these findings showing that in targets having limited transverse extent, down to tens of mm, the laser-generated hot electrons moving with a component of the velocity along the lateral direction can be reflected from the target edges during time scales of the same order of the acceleration of the most energetic ions. This transverse refluxing can result in a hotter, denser, and more homogeneous electron sheath at the target-vacuum interface. A significant increase in the maximum proton energy

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(up to threefold), as well as increased laser-to-ion conversion efficiency, can be obtained with these conditions, as shown in Fig.2.3.

Fig.2.3 Experimentally observed (a) cutoff proton energies and (b) conversion efficiency (for >1:5 MeV protons) for 2 m thick Au targets as a function of surface area, evidencing the effect of electron refluxing. The laser pulse had 400 fs duration,2 1019 W/cm2 intensity, 45 incidence, and P polarization. From [Buffechoux2010]

Similar results obtained with different laser and target parameters, have been found by Tresca [Tresca2011], who also measured an increase in the maximum energy of protons accelerated from the edges of the target with decreasing target area. Several other attempts have been made to increase the energy density of the hot electrons in the sheath and, consequently, the maximum proton energy. Following from the indications in ref. [Kaluza2004], McKenna et al. [McKenna2008] investigated whether there exists an optimum density profile at the front of the target which maximizes the laser absorption. The proton cutoff energy was increased by 25% with respect to a sharp interface case at ‘‘intermediate’’ plasma scale length (tens of mm). Under such conditions, the higher conversion efficiency into fast electrons was attributed to self-focusing of the driver pulse. Other studies of controlled prepulse effects on ion acceleration have been reported by Flacco et al. [Flacco2008] and Batani et al. [Batani2010]. Recently, an energy cutoff increase up to 67.5 MeV, 35% higher than for comparator flat foil shots, was demonstrated by Gaillard in ref. [Gaillard2011] using specially devised targets, namely, flattop hollow microcones [Flippo2008], which are a modification of conical targets used in fast ignition experiments . The laser pulse is focused inside the target and starts interacting with the walls of the cone that it grazes while focusing down toward the flattop section. The reported result, obtained with 80 J of laser energy on the Trident laser at Los Alamos National Laboratory (LANL), is attributed to an efficient mechanism of electron acceleration taking place on the inner cone walls, named ‘‘direct laser-light-pressure acceleration.’’ The resulting increase in the number of high energy electrons results in the increase of the maximum proton energy. The use of targets with various structures has also been investigated with the particular aim to increase the ion energy already at relatively low laser intensities (below 1018 W/cm2), using, e.g., double layer targets [Badziak2001] and more recently nanowire-covered targets [Zigler2011] for which surprisingly high energies up to 5.5–7.5 MeV for a 5x1017 W/cm2, 40 fs laser pulse were reported. Finally Fig.2.2.4 summarize the staet of the art in terms of maximum proton energy compared with scaling laws coming from theoretical investigation and/or PIC simulations [Macchi2012].

Fig.2.4 Experimental scaling of proton energy cutoff with laser power and pulse duration. Squares are data from experiments performed with the DRACO laser at FZD (Dresden), showing a linear scaling with power in the short-pulse (30 fs) regime. Other points are data from other laboratories; see [Zeil2010] for references and details. The fitting lines correspond to the static model by [Schreiber2006] with different colors (labels) corresponding to different values of the pulse duration t1 as given in the legend. From [Zeil2010].

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Various approaches have been proposed in order to manipulate the spectrum of TNSA protons and ions, in most cases with the intent of obtaining narrow-band peaks, in other cases with the aim to enhance proton numbers throughout the whole spectrum or in some spectral bands as required by specific applications. Proton spectrum can be modified at the source or acting on the proton beam after the initial acceleration. Here the second methods is discussed. The first attempts to build and test a transport system for laser-driven proton beam can be found in ref [Ter- Avetisayan2008, Schollmeier2008, Nishiuchi2009]. In these papers the authors shows that the spatial and spectral characteristics of the laser-produced ion beam can be manipulated with a simple quadrupole-magnet system. From the accelerated ion burst with a broad kinetic energy spectrum, selectively the particles with certain energy are collimated or focused. By tuning the magnetic field strength and the geometry of the magnetic lens system, a particle beam with a necessary energy can be formed. Also, this collimated and quasi-monoenergetic ion beam can be transported over long distances without significant loses. This simple and unique method can be used independent on the source characteristics and also at any repetition rate. Other attempt has been done by using solenoid field as reprted in [Harres2010]. In fig. 2.2.1 a simple sketch of the experimental set up used in [Schollmeier2008] is shown

Fig.2.2.1 Scheme of the experimental setup. A high-intensity laser pulse irradiates a Cu foil. Protons from the rear side propagate into a RCF stack with a 5 mm axial aperture for the detection of the initial beam. The transmitted protons enter two PMQ devices that transport and focus the beam. Another RCF stack in the focal plane records the intensity distribution of the protons.

The success of the experiment reported here compete with the very high losses of protons. Indeed the necessary small aperture in the quadrupole (5 mm to generate necessary B field to deflect 14 MeV protons) lead to a very small proton transport efficiency i.e more than 90 % of the protons are lost. To avoid such strong particle losses caused by the focusing devices other authors [Harres2010] established an alternative to control the transport of laser-accelerated protons that uses a pulsed high field solenoid to collimate the beam directly behind the target foil. This solenoid runs at a magnetic field strength of 8.6 T and has an open aperture of 44 mm in diameter to catch nearly the full beam at a proton energy of 2.5 MeV. The coil of the solenoid consists of a brass helix originally designed as a Faraday rotator. The design was modified to fit the requirements of the new application as a focusing device, especially to enable the operation under high mechanical stress.

2.3 Applications

2.2.1 Biomedical applications Hadron therapy is the radiotherapy technique that uses protons, neutrons, or carbon ions to irradiate cancer tumors. The use of ion beams in cancer radiotherapy exploits the advantageous energy deposition properties of ions as compared to more commonly used x rays (see Fig. 2.2.1.1 ): the range for a proton or ion is fixed by its energy, which avoids irradiation of healthy tissues at the rear side of the tumor, while the well-localized Bragg peak leads to a substantial increase of the irradiation dose in the vicinity of the stopping point. The proton energy window of therapeutical interest ranges between 50 and 250 MeV, depending on the location of the tumor. The typical dose of a treatment session is in the 1–5 gray range, and typical currents are 10 nA for protons and 1.2 nA for singly charged carbon ions. Ion beam therapy has proven to be effective and advantageous in a number of tumors and several clinical facilities, employing mainly protons from synchrotron, cyclotron, or linac accelerators are operational and routinely treating a significant number of patients. While protons are the most widespread form of ion treatment, facilities using carbon ions also exist, as their higher biological effectiveness makes them suitable to treating radioresistant and hypoxic tumors [Schardt, 2007]. The use of laser-based accelerators was proposed as an alternative to rf accelerators in proton and ion therapy systems [Bulanov2002a ; Bulanov2002b ; Fourkal2003; Malka2004] with potential advantages in terms of compactness and costs. Proposed options range from using laser-driven protons as high quality injectors in a rf

Page 7 of 19 DEREP accelerator [Antici2011] to all-optical systems, in which ion beam acceleration takes place in the treatment room itself and ion beam transport and delivery issues are thus minimized [Bulanov2002a]. It is recognized that there are significant challenges ahead before laser-driven ion beams meet therapeutic specifications, in terms of maximum energy, energy spectrum, repetition rate, and general reliability, to the levels required by the medical and therapeutic standards, as reviewed by [Linz2007] , where specific issues are mentioned and a comparison with existing accelerator technologies is made.

Fig.2.2.1.1 Example of the profile of energy deposition of protons and C ions in water, compared to those of electrons, x and rays, and neutrons. Protons and C ion profiles are characterized by the Bragg peak at the end of the path. The quantity plotted is the relative dose, i.e., the energy absorbed per unit mass. From [Amaldi2005].

Several projects are currently active worldwide to explore the potential of laser-driven proton and ion sources for biomedical applications; see, e.g., [Bolton2010, Borghesi2011] , and [Enghardt2011] . Several authors have started to design possible delivery systems, including target chamber and shielding [Ma2006] , particle energy selection, and beam collimation systems to enable operation with the broadband and diverging laser-driven beams [Fourkal2003 ; Nishiuchi2010b ; Hofmann2011]. While currently a relative energy spread DE/E~10-2 is required for optimal dose delivery over the tumour region, many have also modeled approaches in which the native broad spectrum of laser-accelerated ions is used to directly obtain the spread out Bragg peak distributions which are normally used to cover the tumor region [Fourkal2007 ; Luo2008] and more in general advanced methods exploiting the properties of laser-accelerated beams [Schell2010].

2.2.2 proton imaging of imploding plasma (proton radiography) and proton mapping of electric and magnetic fields (proton deflectometry) The unique properties of protons from high-intensity laser matter interactions, particularly in terms of spatial quality and temporal duration, have opened up a totally new area of application of proton probing or radiography. TNSA protons from a laser-irradiated foil can be described as emitted from a virtual, point like source located in front of the target . A point-projection imaging scheme is therefore automatically achieved with magnification M depending on the geometry. Backlighting with laser-driven protons has intrinsically high spatial resolution, which, for negligible scattering in the investigated sample, is determined by the size of the virtual proton source and the width of the point spread function of the detector (mainly due to scattering near the end of the proton range), offering the possibility of resolving details with spatial dimensions of a few mm. Multilayer detector arrangements employing RCFs or CR39 layers offer the possibility of energy resolved measurements despite the broad spectrum. Energy dispersion provides the technique with an intrinsic multiframe capability. In fact, since the sample to be probed is situated at a finite distance from the source, protons with different energies reach it at different times. As the detector performs spectral selection, each RCF layer contains, in a first approximation, information pertaining to a particular time, so that a movie of the interaction made up of discrete frames can be taken in a single shot. Depending on the experimental conditions, 2D proton deflection map frames spanning up to 100 ps can be obtained. The ultimate limit of the temporal resolution is given by the duration of the proton burst at the source, which is of the order of the laser pulse duration. Several radiographic applications of laser-produced protons have been reported to date and radiographs of objects for various size and thickness (down to a few mm ) have been obtained. The most successful applications to date of proton probing are related to the detection of electric and magnetic fields in plasmas [Borghesi2002,MacKinnon2004, Batani2009]. Jointly with a parallel technique using monoenergetic protons from fusion reactions driven from laser-driven compressions [Li2006], proton probing with laser-accelerated protons has provided in this way novel and unique information on a broad range of plasma phenomena. The high temporal resolution is here fundamental in allowing the detection of highly transient fields

Page 8 of 19 DEREP following short-pulse interaction. The proton probing technique has provided uniquely detailed information on many nonlinear phenomena in high-intensity laser-plasma interaction. Application to ns laser-produced plasmas of ICF interest has also allowed one to investigate laser filamentation in underdense plasmas [Lancia2011,Sarri2011], plasma expansion inside hohlraums [Sarri2010], and self-generation of magnetic fields [Sarri2011]. As an example of the use of a time-resolved proton diagnostic, Fig. 2.2.1.1 reports data from an experiment where the protons are used to probe the rear of a foil following ultraintense irradiation of the front of the foil [Romagnani2005] .

Fig.2.2.1.1Proton probing of the expanding sheath at the rear surface of a laser-irradiated target. (a) Setup for the experiment. A proton beam is used as a transverse probe of the sheath. (b)–(g) Temporal series of images produced by the deflection of probe protons in the fields, in a time-of-flight arrangement. The probing times are relative to the peak of the interaction. (h) A deflectometry image where a mesh is placed between the probe and the sheath plasma for a quantitative measure of proton deflections. From [34].

The probe proton pattern is modified by the fields appearing at the target rear as a consequence of the interaction, and the technique effectively allows spatially and temporally resolved mapping of the electrostatic fields associated with TNSA acceleration from the foil Figure 2.2.1.1(a) shows the setup for both imaging and deflectometry measurements. Figures 2.2.1.1(b) – 2.2.1.1(g) correspond to proton images at different times taken in a single shot, resolving the expansion of the plasma sheath and highlighting the multiframe capability of this diagnostic. On the other hand density diagnosis via proton radiography has potential application in ICF. PR using laser-generated protons, and Radio Chromic Films (RCF) as detectors, has already been used in two experiments at the system at RAL to probe the implosion of a spherical [MacKinnon2006] and cylindrical [Perez2009] shell. Experimental results of the 2008 experiment were analysed considering the whole time evolution of the target implosion and comparing them with a time dependent Monte Carlo (MC) simulations in which the plasma nature of the medium has been taken into account. A complete report of the results can be found in ref [Volpe2011a,Volpe2011b]. The last two above mentioned experiments have shown that proton radiography of high dense matter. These phenomena are connected also to the variation of parameters (density, temperature and ionization degree) during the target implosion so the multiple scattering effects are dominant in the high density regions of the target compared to the plasma corona. Detailed Monte Carlo simulation have been performed to study the dependence of proton radiography resolution from beam energy and from plasma parameters [Volpe2011b]. As example in Fig. 2.2.1.2 is shown the beam energy requirements to overcome a certain areal density based on the assumption to preserve collinearity of the proton beam. As was shown in the same reference this condition can be relaxed depending on the spatial distribution of the proton beam and of the imploding plasma density.

Fig. 2.2.2.2 Mean scattering angle q vs plasma areal density for different beam energy. The dark disk represent (left top) the plasma condition of the experiment reported in [37,38] and (bottom right) typical expected conditions at Omega facility.

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2.2.3 Warm dense matter generation Laser-driven ions have found application in a number of experiments aimed to heat up solid-density matter via isochoric heating, and create so-called warm dense matter (WDM) states, i.e., matter at 1–10 times solid density and temperatures up to 100 eV [Koenig 2005] of broad relevance to material, geophysical, and planetary studies [Ichimaru1982, Lee2003]. The high-energy flux and short temporal duration of laser-generated proton beams are crucial parameters for this class of applications. WDM states can be achieved by several other means, e.g., x-ray heating [Tallents2009] and shock compression [Kritcher2008]. However, when studying fundamental properties of WDM, such as the equation of state (EOS) or opacity, it is desirable to generate large volumes of uniformly heated material; ion beams, which can heat the material in depth, are in principle better suited to this purpose than the methods described above. Heating of solid-density material with ions can be achieved with accelerator-based or electrical-pulsed ion sources; see, e.g., [Bailey1990, Hoffmann2000 and Tahir2006] . However, the relatively long durations of ion pulses from these sources (1–10 ns) imply that the materials undergo significant hydrodynamic expansion already during the heating period. On the contrary, laser-generated proton beams, emitted in ps bursts, provide a means of very rapid heating, on a time scale shorter than the hydrodynamic time scale. By minimizing the distance betweenthe ion source and the sample to be heated, it is possible to limit the heating time to tens of ps. The target then stays at near-solid density before significant expansion occurs, and the WDM properties can be investigated within this temporal window. The first demonstration of laser-generated proton heating was obtained by Patel et al. [Patel2003] . In this experiment a 10 J pulse from the 100 fs JanUSP laser at LLNL was focused onto an Al foil producing a 100–200 mJ proton beam used to heat a second Al foil. Target heating was monitored via time resolved rear surface emission. A focused proton beam, produced from a spherically shaped target, was seen to heat a small target region to a temperature (of 23 eV ). With a similar ion focusing arrangement on a higher energy laser system, Gekko at ILE Osaka, Snavely et al. [Snavely2007] demonstrated secondary target heating up to 80 eV by imaging both visible and extreme-ultraviolet Planckian emission from the target’s rear surface. In all the experiments mentioned above the isochoric heating by the protons is volumetric, but not uniform [Brambrink2007]. Uniform heating requires some degree of proton energy selection, and choosing the sample thickness so that the Bragg peak of the selected protons does not fall within the sample, as suggested, for example, by Schollmeier et al. [Schollmeier2008].

2.2.4 Proton Fast ignition approach for Inertial Confinement Fusion The traditional route to ICF [Atzeni2004] relies on the driven implosion of a pellet of thermonuclear fuel (a DT mixture). Ignition occurs in a central ‘‘hot spot’’ following pulse compression. This approach requires an extremely high symmetry and is prone to hydrodynamics instabilities, making ICF a historically difficult goal. In the fast ignition (FI) concept [Key 2007] ignition is driven by an external trigger, creating the hot spot in a time much shorter than the typical fuel disassembly time. Hence, ignition is separated from pulse compression. The FI approach might relax symmetry and stability requirements, reduce the energy need for ignition, and allow fuel burn in a isochoric regime with high fusion . In the original FI proposal by [Tabak1994] , the ignitor beam consisted of multi-MeV electrons accelerated by a petawatt laser pulse. Observation of efficient generation of multi-MeV proton beams in petawatt experiments soon stimulated the proposal of the use of such protons as the ignitor beam [Roth2001] . The most promising features of proton beam ignition as claimed were the highly localized energy deposition profile (see Fig. 3 ), the low emittance of the beam, and its focusability, for instance, by parabolically shaping the rear side of the proton-producing target as suggested by numerical simulations [Wilks2001]. Detailed calculations in ref [Atzeni2002] and [Temporal2002] addressed, in particular, the effects of the quasithermal energy distribution typical of TNSA protons, and of the related temporal dispersion. The latter could be beneficial for energy deposition since the proton stopping range increases with plasma temperature. Hence, heating due to the more energetic protons favors energy deposition by the less energetic ones which arrive later in the dense fuel region. Integration of the foil inside the cone of conical ICF targets already designed for electron FI was then proposed in order to reduce d and thus Eig . This raised the issue of shielding the foil from preheating caused, e.g., by external radiation, which may jeopardize efficient TNSA a preliminary analysis was mentioned by [Geissel2005] . Fig.2.2.4.1 sketches the target and foil assembly and summarizes suitable parameters for proton FI with cone targets. [Temporal2006, Temporal2008] investigated a similar scheme but used two proton beams with suitably shaped radial profiles, obtaining a 40% reduction of the ignition energy.

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Fig.2.2.4.1 Concept of proton-driven fast ignition in the TNSAbased, cone guided scheme. Typical parameters required for the ion beam and optimization issues are also indicated. From [Key, 2007].

2.3 project objectives Vs state of the art Proton energy of 40-50 MeV has been obtained by using today's technology [Ogura2010] , at the same time new target configurations have been tested in order to increase maximum energy [Flippo2008]. Many application require proton energies above 50 MeV as for example adro-theraphy. The way to reach the maximum energy seems to be not so far then we need to start the implementation of these application even if the required energy is not still available. Proton therapy could be tested by using proton energy of 40-50 MeV for distances of the order of 1.5 cm. A possibility will be to start to treat superficial tumor or tumors of small animals. The huge literature in this field report essentially activities focused to reach absolute maximum proton energy. In this project the goal is to search the optimum of all the other involved parameters, mainly focusing on target manipulation, for a given proton energy and for a given “reference” lases system. The study on the pre-pulse effect on laser target coupling, explained before suggest to use femto-second laser systems in such a way to be able to use very thin targets. Another important information come from the experience with mass limited targets which increase the ions accelerating electric field thank to the increasing of electron refluxing and the reduction of the interaction surface (or volume). The fast development of the target manufacturing ability have opened new possibility to modified (at a moderated cost) the target surface (cone targets) and the target composition (foams). The outlined project include the collaboration with one of most active laboratory in this field; the Rutherford Appleton laboratory (see cooperation RAL) for target design and construction, and with the group of Prof. P. Piseri at the molecular beams laboratory of CIMaINa and Physics Department of the Università degli Studi di Milano which is expert on the synthesis of nanostructured material layer. Moreover simulations

Working with a laser-driven proton source of 40-50 MeV open new scientific possibilities for proton radiography. “micro-scaled” Quadrupole as been proved successfully to be one of the promising tolls to complete proton source [schollmeier2008, Ter-avetisyan2008, Nishiuchi2009, Harres2010] and for doing monochromatic selection of the beam. Time-resolved proton radiography can also be done by using the total proton spectrum. This technique is useful in the context of Inertial Confinement Fusion to image the imploding target. Working with 40-50 MeV protons will permit to increase the resolution of this technique and to avoid problems of mixing of the signal in the RCF detector. The possibility to test proton radiography at 40-50 MeV is not one of the goal of the project, in addition to test proton radiography of plasma require facilities which joint together short and long pulses and the access to such facility cannot be guaranteed “a priori “. The same possibilities as for proton radiography will be opened for the Warm dense matter generation, in addition the chromatic selection is important to know exactly the proton Bragg in order to maximize the isochoring heating of the sample. Indeed knowing the position of the Bragg imply the possibility to choose the best target thickness.

3 Research approach and method, work schedule and Project implementation As was outlined in the first section the project activities will be focused on three possible items: • Proton source development • Beam Transport Design • Beam Instrumentation development. These activities will be carried out as much as possible in parallel even if a minimum time organization is needed. Indeed, since the access to the laser facilities need the presentation of detailed proposals the first part of the project will be mainly devoted to the preparation of these proposal and the related activities such us the target design, diagnostics preparation (some diagnostic tools are present in the laboratory while particular diagnostics must be

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provided by the users) and experimental set-up. Only when this phases will be done there will be the possibility to buy targets and prepare (or where is necessary to buy) diagnostic tools which are needed fro the planned experiments. The head quarter of the project will be located at the INFN section of Milan. In particular the INFN section of Milan will provide experimental support with the INFN infrastructures for the beam diagnostic and instrumentation development. The INFN sections of Bologna and Lecce will provide support respectively for numerical simulations and target development. In addition, both the INFN sections of Milano and Bologna will take care the design for the transport line based on using quadrupole magnets or solenoids. The activities related to the target development will be shared by different group participating to the project.

The time line of the project is defined as follows: (1th-3th month) state of the art and decision of the strategies that must be activated to develop the project mission and to reach the final goals. In this phase the road map of the project for the national and international collaboration will be planned. (1th-6th month) application for experiments, in dedicated laboratories and where is possible using LASERLAB EUROPE access to test the first results of the other phases, will be done in collaboration with partners from Italy INFN, France CELIA_1, UK RAL, and Germany GSI. The Laser FLAME system in the National Laboratory of Frascati will be also considered for experiments (1th-6th month) Target fabrication and diagnostic development will be important lines of research carried out in collaboration with both partners, from UK RAL (target fabrication), and from Italy UNIMI (nano- structure) and INFN section of Milano (solid state detectors) (6th-21th month) experimental campaign to test different type of target (composition, thickness geometry) at different laser facilities in Italy (FLAME) and in Europe (RAL, LULI, GSI etc..) in this experiments could participate master students, and PhD students from national and international institutions. (1th-24th month) In parallel numerical simulations will be started in collaboration with I) University of Bologna (target composition and design to increase laser absorption by using PIC code ALADYN code (ALADYN)), ii) CELIA laboratory (CELIA) ( target composition and design to increase laser absorption by using the PIC code CALDER) ii) INFN section of Milano, the Principal investigator and partner for Germany (design of a transport line for the laser-generated proton beam by using Monte Carlo Codes MXNPX, FLUKA) (20th-24th month) Analysis of the experimental results compared with prediction will be done the last 3 mounts in collaboration with all the partners of the project. In this phases numerical simulations will be used to describe and reproduce experimental data.

Laboratories The final goal of the project is to give a clear and stable set of parameters for having a laser-driven proton source within the todays technology possibilities. To do this “conventional ” laser system have been selected ; these are: (LNF) National Laboratory of Frascati, Roma Italy www.lnf.infn.it/ (RAL) Rutherford Appleton Laboratory Didcot UK www.stfc.ac.uk/76.aspx (GSI) Helmholtz Centre for Heavy Ion Research, Darmstad, Germany www.gsi.de/en.htm (LULI) Laboratoire pour l'Utilisation des Lasers Intenses . Ecole Polytecnique Paris, France www.luli.polytechnique.fr (IOP) Institute of Physics, Chinese Academy of Sciences, Beijing, China english.iop.cas.cn (MBI) Max Born Institute Berlin, Germany www.mbi-berlin.de

Tab.1 report the main characteristic of the laser system in the above mentioned laboratory

Lab Coun Laser Type Dt l(nm) E(J) P(W) I(W/cm2) Laserlab try system energy power intensity acces LNF It FLAME Ti:sa 20 fs 800 <6 J 300 TW ~1019-20 no RAL UK VULCAN Nd:glass >0.5 ps 103 < 500 J 1 PW ~1020-21 yes RAL UK ASTRA Ti:sa >30 fs 800 <15 J 0.5 PW ~1021-22 yes

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LULI Fr LULI2000 Nd:glass >1 ps 103 <150 J 100 TW ~1018-19 yes GSI Ge PHELIX Nd:glass >0.5 ps 103 <250 J 0.5 PW ~1021 yes MBI Ge ATLAS Ti:sa >50 fs 800 < 1.5 J 40 TW ~1019 yes IOP China Ti:sa >50 fs 800 <10 J 0.2 PW ~1019-20 no MPI Ge PHELIX Ti:sa >50 fs 800 <1 J 20 TW ~1018-19 yes LOA Fr LOA Ti:sa >25 fs 800 <3 J 100 TW ~1019-20 yes Jena Ge HIJ Ti:sa >25 fs 800 <1.5 J 45 TW ~1019-20 yes

Target development With the use of flat-top cone targets, Flippo et al (Flippo2008) demonstrated a maximum proton energy of at least 30 MeV (limited by the detector stack thickness; simulations indicate the possibility of 40–45MeV protons) at an intensity of 1019 Wcm-2 with 20 J, 600 fs laser pulses. This proton energy is significantly higher than those produced with a standard flat 10 μm Au foil (19 MeV under similar conditions). The proton acceleration enhancement is attributed to the guiding and microfocusing of the laser pulse, larger absorption on the cone walls and preformed underdense plasma filling the inner volume, and better conditions of hot electron transport to the flat-top surface.

Fig.3.1 a Schematic of the flat-top cone targets developed by NanoLabz, Reno, NV under contract with the University of Nevada, Reno. b An actual target imaged in a microscope with ranges of top and neck dimensions actually shot.

Experiments with higher intensity (80 J, 600 fs, 1.5 × 1020 W cm−2 , 106 contrast) showed that a high contrast is mandatory to avoid laser pulse absorption in the preplasma far from the cone top, which reduces the proton energy and number significantly Gaillard et al (Gaillard 2010). Cone target will be used in the experimental campaign of this project and with respect to this RAL laboratory, which is one of the partners of the project, will provide us in a reasonable time and cost conical targets similar to that used in ref [Flippo2008] (see fig.3.1 and fig.3.2).

Fig.3.2 (left) picture of cone targets provided by RAL laboratory (to be coated). (right) an example of nano-structured metallic target “smoked target ” provided by RAL

A number of studies have been devoted to ion acceleration in near-critical plasmas with electron density close to the cutoff value (ne~nc), in order to allow a more efficient generation of hot electrons to drive TNSA. Another possible strategy to reduce the electron density is to use special target materials such as foams, which may be manufactured in order to have an average value of the electron density slightly larger, or even lower than nc (the average is meant over a length larger than the typical submicrometric scale of inhomogeneity). Foams have been so far produced with di fferent materials, like carbon, silicon carbide, silica, aluminum and aluminum, and by di efferent techniques. Fig.3.2 shows fully threedimensional (3D) and two-dimensional (2D) simulations from the group of prof. G. Turchetti at University of Bologna, with oblique incidence run using the PIC code ALaDyn [ALADYN], in order to investigate the dynamics of the laser interaction with the slightly overcritical density plasma and the role of the foam electrons in the rise of the longitudinal electric field which accelerates the protons.

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Fig.3.2 3D simulations results of proton maximum energy evolution with respect to time: comparison of 3D (solid) and 2D (dashed) cases without foam (red, lower lines) and with (blue, upper lines) nf =2ncr , lf =2 m, ns =40ncr , a =10.

Transport beam line Target normal sheath acceleration regime provides an exponential energy spectrum with a significant divergence. The low count number at the cutoff energy seriously limits at present its possible use. One realistic scenario for the near future is offered by hybrid schemes. The use of transport lines for collimation and energy selection has been considered in many work as was shown in section 2 (see for example [Harres2010]). In this project we would focus on a design based on “standard” accelerator focusing elements as PMQ (permanent quadrupole magnets) and solenoids. The most significant advantage of a solenoid magnet compared with quadrupole magnets is the collection efficiency of almost 100%. At the same time a suitable RT solenoid calls for a high power pulsed power supply, synchronized with the laser trigger. This element is a very challenge one from the point of the technological issues involved. Recently part of the people involved in this project have published a paper presenting a scheme based on a high field pulsed solenoid and collimators which allows one to select a beam suitable for injection at 30 MeV into a compact linac in order to double its energy while preserving a significant intensity. The results are based on a fully 3D simulation starting from laser acceleration. Fig.3.3 shows experimental set up characterized by numerical simulations.

Fig.3.3 (top) Schematic drawing of the transport line: DA =DB =10 mm, D1 =510 mm, L=300 mm, first iris radius =0:5 mm, second iris radius =0.5 mm, second iris minimum thickness =5 mm. (bottom left): Plot of the transverse emittances ex, ey in mm-mrad as a function of in cm for an energy selection of the beam 29

Beam Instrumentation development. A common background for the source development and beam transport activities is represented by the need to develop a number of beam instrumentation devices. The specific features of laser induced proton beams, and the consideration of the high background of other particles and radiation emitted in the process, call for specifically designed devices. This part of the project will be developed mainly by the INFN section of Milano that will focus on the following elements: • fast Faraday cups, matched to detect these short pulses and to measure the whole current in a pulse • destructive diagnostics based on pixels, solid state CMOS detectors and scintillating fibers, to measure

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transverse characteristics • non intercepting diagnostics based on AC thoroids and beam profile monitors, to measure longitudinal characteristics and pulse current.

Each one of these devices requires a specific electronic card to handle the signals as close as possible to the device itself. The purpose of the card is to adapt the signals coming from the beam instrumentation to standard high quality electronic data acquisition and analysis systems. We will study, design, build and characterize the Faraday cup and a large (25 mm x 50 mm) pixel detector. We will start the development of first stage prototypes for BPM and AC thoroids. At the same time we will continue the use and development of new techniques based on standard radiochromic, CR39 and MCP based detectors.

Laser diagnostic tools and Target Positioning To qualify the behavior of the targets so far discussed we need to have a deep knowledge of the main parameters of the laser beam and to be able to define and reproduce the exact positioning of the target with respect to the laser focus. In a laser system it is common to observe fluctuations in the functional parameters. A precise control of shot to shot behavior is even more important in experiments where a single measurement cannot be repeated a number of times sufficiently high to authorize a statistical treatment. Nevertheless a strong correlation between the different parameters (energy, direction of the beam, contrast, etc.) is observed; this enables us to limit our observation of the laser status to some key parameters and be able to set a rejection criterion out of them. The energy of the laser shots may be obtained from the knowledge of the energy before compression and then calculate the efficiency and the losses percentages in the compression processes. The focusing of the laser may be measured imaging the focal spot. The focused beam is intercepted by a removable mirror and sent through a microscope objective to a linearized camera. The quality of the spot is defined by measuring its transverse size and the ratio of energy contained in its 1/e2 contour. The Rayleigh range of a from lasers as the ones we are interested range from 20-300 μm. This sets the scale of precision that is needed to align the target. Moreover, a precise absolute reference is important to ensure repeatability and meaningful comparison among different shots. The technique we would like to investigate is the collection of a part of the light that, from an Helium-Neon laser collinear to the main IR beam, is diffused by the rough target surface. A small lens images the helium-neon spot to a camera: the lens is aligned to provide a very big magnification (≈ ×20), that is enough to map a range of 400 μm of movement in target focus to the entire chip of a CCD camera. A small aperture lens may work better, for its small level of detail produces a cleaner spot, which eases the reference. We estimate that the error on target positioning may be smaller than 15μm.

Solid State Detectors In addition to the more traditional passive radio-chromic films, active solid state detectors have been studied and tested. The main advantage of the latter is the real-time capability: you can have the measurement result immediately after the shot, using the same detector at high repetition rate. These detectors are thought for imaging beam transverse size being a 2D array with proper spatial resolution. Different materials and structures have been considered and partly characterised: silicon photodiodes (PD), monolithic silicon telescope (MST) and SiC diodes (SiC). Commercial silicon photodiodes (Hamamatsu) are relatively cheap and available in linear array, monolithic silicon telescopes (STm) offer two fully depleted diodes for optimum particle discrimination and large energy range, SiC diodes are radiation hard. Preliminary ests have been performed on the two silicon structures at INFN-LNS and INFN-LNL with 30 MeV proton beam for the first (PD) and 1-5 MeV proton beam and 60 MeV/u carbon beam for the second (MST). Results show that charge collection is optimal in the fully depleted structure (MST), being the other affected by long tails and partial collection. The main specifications for these detectors may be so summarized: - Maximum energy of the order of 50/60 MeV). - Energy range of two decades (1-100 MeV for protons) for exploring the high and medium energies, - Identification and selection of the particles with different Z/A ratio, - Single particle detection capability in order to have good energy resolution even at low fluence, - Dynamic range of three decades, - Response to singe shot capability in order to sustain real-time operation mode, - Repetition rate equal at least to the laser repetition rate (10 Hz).

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Fast electron beam Diagnostics The knowledge of the physics of fast electrons transport in matter is crucial for development of laser-generated proton sources. Indeed these type of source should called properly “laser-electron-generated” because the involved physical processes are multiple and consecutive: firstly high intensity and short laser interact with thin foils generating a relativistic population of electrons, secondary electrons start to propagate inside the target until they reach the rear side, finally the ion acceleration occur due to the quasi static electric field generated by the electrons sheet. The diagnostics used to reveal energy spectrum and divergence of the electron beam are based on revealing K a radiation resulting from the interaction between relativistic electrons and target electrons; such radiation is detected usually by using a spherically bent Bragg crystal [Koch2003] coupled to a X-ray CCD. The spherical crystal combines the reflecting properties, typical of a Bragg crystal, to the focusing properties of a spherical mirror. Fast electron transport is one of the main topics in which the Pi and the experimental group of CELIA have been involved in the last years, many experiments have been done in the intermediate scale facility all over the word with international collaboration. This type of diagnostics will be provided by experimental group of CELIA. In particular Spherically bent crystals for revealing copper or titanium fluorescence. Ka radiation can be collected by using the Image Plate or by using a CCD camera which permit repetition rates. A Ka based spectrometer will be also useful to measure the temperature of fast electrons. numerical simulations The physical process involved in laser-driven proton acceleration and transport are essentially

1) laser matter interaction and electron beam generation 2) electron beam transport inside target 3) proton beam acceleration and transport

This three process involve different physical scale lengths and cannot be described with the same physical model and so cannot be simulated by using the same numerical scheme. The first and the second part of the processes can be “in principle” described by using PIC simulations but the extreme cost in time computation suggest to separate the two processes (generation and transport). Study laser matter interaction is necessary to understand how the transmission of laser energy into fast electron depend on target parameters. This can be done by using the so Called PIC (particle in cell ) codes. In the PIC code the Laser is described by Maxwell equations valuated in a grid and the electron beam is described by Vlasov equation. Since collisional effects are not included the description of fast electron transport in matter will be performed by using kinetic codes based on the integration of the full fokker Plank equation and/or by using Monte Carlo codes. PIC simulations for target optimization will be provided both by INFN_BO (ALADYN)(for that concerning thin, ultra thin foils and foams) and by CELIA_2 (CALDER) (for that concerning conical targets). Monte Carlo simulations (MCNPX, FLUKA ) as well as kinetic simulations (M1) will be provided by the PI in collaboration with CELIA team and INFN_MI. The transport of the proton beam just after the rear target surface can be described both analytically and by using Monte Carlo simulation (FLUKA). The ability to perform a start-to-end simulation of the whole process is explained in detail in a recent published paper [Sinigardi2013] that has been written by many of the authors involved in the project. Reference for numerical codes → ALDYN (Acceleration by LAser and DYNamics of chared particles) is a fully self-consistent, relativistic, parallelized PIC code to investigate the interaction of a laser pulse with a plasma and/or an externally injected beam. The code is based on compact high order finite differences schemes ensuring higher spectral accuracy compared to standard Yee schemes. (see C. Benedetti, A. Sgattoni, G. Turchetti, and P. Londrillo) IEEE transactions on plasma science, vol. 36, no. 4, august 2008) → PICLS PICLS is a 1D/2D/3D relativistic Particle-In-Cell (PIC) code, a numerical scheme that is widely used to study systems with a large number of particles interacting with electromagnetic fields.The ultra-short laser accelerated electrons have an energy spread of a hundred percent from non-relativistic to ultra relativistic energies. Collisions in the target are an important issue to determine the characteristics of hot electron transport. A fully relativistic

Page 16 of 19 DEREP binary-collision model that is based on Takizuka and Abe model is included. (see Y. Sentoku, A. Kemp, Numerical methods for particle simulations at extreme densities and temperatures: weighted particles, relativistic collisions and reduced currents, J. Comput. Phys. 227, no 14, 6846-6861,2008)

→ MCNPX (Monte Carlo N-Particle eXtended) MCNPX is a general-purpose Monte Carlo radiation transport code for modeling the interaction of radiation with everything. It extends the capabilities of MCNP4C3 to nearly all particles, nearly all energies, and to nearly all applications without an additional computational time penalty. MCNPX is fully three-dimensional and time dependent. It utilizes the latest nuclear cross section libraries and uses physics models for particle types and energies where tabular data are not available. (see www.mcnpx.lanl.gov)

→ FLUKA (FLUktuierende KAskade) FLUKA is a fully integrated particle physics MonteCarlo simulation package. It has many applications in high energy experimental physics and engineering, shielding, detector and telescope design, cosmic ray studies, dosimetry, medical physics and radio-biology. The FLUKA CG has been designed to track correctly also charged particles (even in the presence of magnetic or electric fields). Various visualisation and debugging tools are also available. (see www.fluka.org)

→ M1 M1 is a fast electron transport modules. This modules is based on a reduce kinetic model and can account for electric and magnetic quasi-static fields in the scale of tens of picoseconds (see [3] Ph. Nicolai, et al, Phys. Rev. E. 84, 016402 2011) 4. Cooperation partners (Each of the partners have written one letter to support the project. All these letters are stored together with the publications in the file 10_best_publication_and_letter_of_support.pdf ) The project “Characterization and Development of a Stable and Reproducible scheme for laser-driven Proton Sources” will be acted in close collaboration with the INFN section of Milano which is the natural partner because the research lines are compatible with the project. However, due to the huge variety of competence needed to reach the goal of the proiect many other collaborations are compulsory. In the following the list of all the institutions (external partners) that have shown their interested and their competence for the project: → INFN_MI [It] National Institute of Nuclear Physics Section of Milan contact person: Dario Giove action: Scientific coordinator and experimental support activities: The INFN section of Milano is involved in many national (LILIA) and international (ELIMED) research projects connected to proton beam generation. The expertize of the group is maily experimental and is focused on the development of beam instrumentation for protons and ions detection as well as for the successive transport and chromatic selection. → INFN_BO [It] National Institute of Nuclear Physics Section of Bologna() contact person: Prof. G. Turchetti action: theoretical support activities: The INFN section of Bologna is also involved in many national (LILIA) and international (ELIMED) research projects connected to laser-driven electron beam generation and proton beam generation by TNSA mechanism. The expertize of the group is mainly theoretical and is focused on the development of a Particle In Cell code (ALADYN) for describing laser matter interaction at target densities clos to critic density. → (RAL) [UK] Rutherford Appleton Laboratory www.stfc.ac.uk/76.aspx contact person: Dr. Christopher Spindloe action: nanostructure deposition activities: The Rutherford Appleton Laboratory (RAL) is one of the national scientific research laboratories in the UK operated by the Science and Technology Facilities Council (STFC). It has a staff of approximately 1,200 people who support the work of over 10,000 scientists and engineers, chiefly from the university research community. Christopher Spindloe is in charge at target area development of RAL and he is a recognized expert in the field of target fabrication an manipulation. → (Unimi) [It] University of Milano www.fisica.unimi.it/ecm/home contact person: Prof. Paolo Piseri action: nanostructure deposition

Page 17 of 19 DEREP activities: The group of Prof. P. Piseri at the molecular beams laboratory of CIMaINa and Physics Department of the Università degli Studi di Milano,is expert on the synthesis of nanostructured material layers via supersonic cluster beam deposition (SCBD) [Milani2001]. This technique allows the deposition of porous material from carbon, metal or oxide nano-particles. The properties of the deposits are controlled by the properties of the precursor particles and their velocity distribution at low kinetic energy impact upon the surface of the growing film. Nanoparticle beams are formed after aerodynamic acceleration in a supersonic expansion and inertial separation effects are used for particle filtering and beam focusing [Piseri2004]. → (GSI) [Ge] Helmholtz Centre for Heavy Ion Research www.gsi.de/en.htm contact person: Prof. Ingo Hofmann: action :Experimental and theretical support activities : head of the High-Current Beam Physic group at GSI and Proessor of Physics at Johann Wolfgang Goethe – Universität, Frankfurt. Expertize in both theoretical and experimental developments in the area of high-power laser systems, especially in the interplay with accelerator facilities and ion sources, as well as in the corresponding optical techniques and components. → (CELIA_1) [Fr] J. Santos (experimental support) www.celia.u-bordeaux1.fr contact person: Dr. J. Joao Santos action: experimental support diagnostic for fats electrons activities: J. Santos is in charge at CELIA of coordinating the experimental research related to relativistic laser matter interactions, fast electron energy transport and development of proton beam sources by laser as a diagnostic of high energy density plasmas. He is co-author of more than 75 peer-reviewed scientific papers in these fields. → (CELIA_2) [Fr] (theoretical support) www.celia.u-bordeaux1.fr contact person: E. D'humierre action: experimental support diagnostic for fats electrons activities: is in charge at CELIA in the theoretical group he is expert in the physics of laser plasma interaction and on using PIC simulations for target optimization in the context of laser-driven proton sources .

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