Beams Department

Issue 11 NEWSLETTER September 2014

Inside This Issue Editorial p. 1  Editorial – Ronny Billen Dear Readers, p. 2  Simulating beam cleaning in the LHC Luckily, the weather was awful over the summer – Roderik Bruce, BE-ABP-HSS period, so that we all could remain focussed on the p. 3  The CERN Resonant WISP Search gradual start-up of the injector complex. This trick – – Michael Betz, BE-BI-QP played by the god of rain – worked out very well: beams are being served for to the PS p. 5  The LHC sees the light at the end of the East Area, nTOF, users of Isolde and also of the AD tunnel – Matteo Solfaroli Camillocci, & now. When were knocking on the door of the Mirko Pojer, BE-OP-LHC SPS last weekend, they were rapidly taken to top energy including for LHC-type beams. Via Linac3 p. 6  New Magnetic Alloy Based RF Cavities and LEIR, the PS receives currently a new ion for Synchrotrons – Mauro Paoluzzi, BE-RF-IS species (Argon), which is accelerated and extracted.

p. 9  Safety column As expected after such a long shutdown, it has been Prevention against oxygen deficiency a very rough ride to get to this point with many hazard (ODH) in the LHC problems that had to be overcome (and some that – Safety Unit are still being discovered). Thanks to all of you who

p. 10  Responsibility changes & spare neither time nor effort to put all hands on deck Newsletter contacts and turn drawbacks into triumphs!

For the LHC, all consolidation work is now finished and the eight sectors follow their individual schedule

of cool-down and hardware tests.

This September 2014 issue of the BE newsletter Next issue cannot escape from the excitement around CERN’s The next issue will be published beginning of 60th anniversary. You have seen the announcements December 2014. Contributions for that issue for several cultural events, exhibitions, retrospective should be received mid of November. lectures, visionary talks and an official celebration

on September 29th. They all look very interesting, so Suggestions for contributions are always do not hesitate to participate if you have the most welcome: simply contact your Correspondent (see last page). opportunity!

Happy Anniversary to those reaching their 60th …

Ronny Billen Editor, BE Newsletter

The Newsletter does not necessarily reflect the views of the Beams Department The contributions solely reflect the views of their author(s) Simulating beam cleaning cleaning of the LHC collimation system. It is used to track protons through the more than 5000 in the LHC magnets of the LHC over hundreds of turns and it uses a built-in Monte Carlo code to simulate the The LHC is designed to store proton beams of -matter interaction in collimators. The unprecedented energy. During the first very output is the proton loss distribution around the successful running period (Run I) in 2010–2013, LHC. An example is shown in Fig. 3 together with the LHC stored routinely protons at 3.5–4 TeV a measurement from Run I. There is a very good with a total energy per beam of up to 146 MJ, and qualitative agreement between the two, and the even higher stored energies are foreseen in the simulation predicts all potentially limiting cold loss future. This puts extraordinary demands on the locations. However, significant quantitative control of beam losses. An uncontrolled loss of deviations are observed in some locations. One even a tiny fraction of a few 10−9 of the full beam dominant reason for the discrepancy is that the (order of 106 protons) could cause a simulation shows the number of locally lost superconducting magnet to undergo a transition protons, while the beam loss monitors, used for the into a normal-conducting state, called a quench, or measurement, register secondary in the worst case cause material damage. Quenches produced in the showers caused by the primary must be avoided, since the recovery is a lengthy losses. This makes a direct comparison hard. process that reduces the available time for collecting physics data.

LHC collimation To protect against losses, a multistage collimation system is installed to safely intercept any protons that are likely to be lost elsewhere. It consists of primary, secondary, and tertiary collimators, as well as active absorbers and special protection devices for injection and dump. In total, more than 100 collimators are installed. An example of a collimator is shown in Fig. 1.

Figure 2: Beam loss distributions around the LHC

Figure 1: A secondary collimator jaw made of as measured (top) and from a SixTrack simulation carbon fiber composite (left) and two parallel jaws (bottom) for the 3.5 TeV LHC configuration of installed in a collimator tank seen from the top 2011. The results are normalized to the highest (right), where the beam should pass in the center loss and the colours indicate losses on cold and between the jaws. warm elements as well as on collimators.

SixTrack simulations FLUKA simulations To guarantee adequate protection from the To do a better quantitative comparison, the full collimators, a detailed theoretical understanding is electromagnetic and hadronic showers between the needed. Therefore, detailed simulations have been initial proton loss and the detectors are simulated developed. First, SixTrack is used to simulate the using FLUKA, starting from the output loss

2 Beams Department Newsletter Issue 11 distribution from SixTrack. FLUKA is a particle The CERN Resonant WISP physics Monte Carlo code for the transport and interaction of particles in matter. As the Search implementation of the geometry and the simulation itself are time-consuming, this second step is The CERN ResOnant Weakly interacting sub-eV carried out only for some selected important loss particle Search (CROWS) is a small-scale table- locations. One example is the cold region just top experiment, which was designed and operated downstream of the betatron collimation insertion, from 2010 to 2013 at CERN in the framework of which is the most critical loss position of the LHC. my PhD thesis. Its goal was to search for A comparison with measurements for these losses Like Particles and Hidden Sector . is shown in Fig. 4. Exploiting microwave techniques, CROWS is to date the most sensitive laboratory based hidden sector experiment in its energy range.

Weakly Interacting Sub-eV Particles" (WISPs) are hypothesized to solve some of the outstanding issues with the of and are a prime candidate for . Popular WISPs are the axion [1] and the hidden sector photon.

Figure 3: Comparison of measured losses at the While there is a strong theoretical motivation for most critical loss location of the LHC with their existence, these particles are extremely hard different simulation methods. to detect experimentally. Similar to , they are basically invisible to us and can penetrate large Conclusions amounts of matter without interacting in any way. The combined simulation produces typically a However, an experimental search is not completely quantitative agreement within a factor 2, which is hopeless – theory predicts a very weak coupling more than satisfactory when considering the high between the hidden particles and photons, which is complexity of the simulation chain, the many what CROWS tries to exploit. unknown imperfections, and the fact that the loss levels span 7 orders of magnitude. Unfortunately, a huge number of WISPs (>> 1012) Apart from demonstrating that a complex physical are required before a single photon can be process, such as multi-turn beam losses in the observed. Furthermore, the WISP mass is only LHC, can be accurately simulated, the good very vaguely predicted by the theoretical models, agreement with measurements gives confidence opening up a huge parameter space from 10-12 eV that the tools can be used to reliably estimate the to 103 eV [1]. This needs to be searched by collimation performance in future LHC experiments utilizing different technologies, with a configurations. photon of 10-6 eV corresponding to microwaves, 1 eV to optical light and 10 eV to x-rays. Further reading This work summarizes a recent paper: [R. Bruce et The CROWS experiment is based on the "Light al., Phys. Rev. ST Accel. Beams 17, 081004 Shining through the Wall" (LSW) principle [2], (2014)], where more details can be found. which basically means that we search for photons that traverse a solid wall, which can only happen if they convert to a WISP. The experiment is therefore split into two parts: an emitting RF cavity to produce WISPs, and a detecting RF cavity, where the WISPs can reconvert back into ordinary Roderik Bruce, microwave photons. This leads to a weak for the LHC collimation team and excitation of the detecting cavity and a microwave FLUKA team signal, which can be coupled out, amplified and fed into a sensitive microwave detector. Theory requires the experiment to sit in a magnetic field to

3 Beams Department Newsletter Issue 11 detect axion like particles, while no magnetic field large number of frequency bins. Each bin contains is necessary for detecting hidden sector photons. only a small fraction of the overall noise signal, while the wanted signal resides within a single bin, concentrating its power there. A typical run lasts 30 h, resulting in ~10 µHz wide frequency bins and an average noise floor of -224 dBm (or 4×10-26 W of power at that specific frequency).

Several measurement campaigns to search for both hidden sector photons and axion like particles were carried out. The latter required the experimental set-up to be placed in a strong magnet, which was Figure 1: The "microwave reconversion" principle made possible by collaborating with the Brain & of the CROWS experiment. (a) = Axion Like Behaviour Laboratory of Geneva University, Particle (γ) = photon providing access to a 3 T superconducting MRI magnet. While no axion like particles were The biggest engineering challenge was the detected, a similar sensitivity to the most sensitive electromagnetic shielding between the emitting experiments [1] that work in the optical regime has and detecting cavities. More than 300 dB of been achieved. screening attenuation (a factor of one thousand million million) is required to avoid fake signals For hidden sector photons, an improvement in leaking from the emitting cavity to the detecting sensitivity by almost one order of magnitude cavity. This problem has been solved by using compared to previous experiments has been several custom-made shielding enclosures and a achieved. Hence the existence of the hidden system for signal transmission over optical fibres. particle has been excluded in a hitherto unexplored Furthermore, the front-end components needed to mass range [3]. be compatible with strong magnetic fields and the high-Q cavities had to be stabilized in temperature for the > 30 h long measurement runs.

Figure 3: The most sensitive measurement run [4] of the CROWS experiment excluded the existence of HSPs in the black area. Other experiments are Figure 2: Part of the CROWS setup to search for shown for comparison. The x-axis represents the HSPs. Both cavities and the shielding enclosure unknown HSP mass, the Y-axis the HSP coupling are visible. strength to photons (χ). A more sensitive experiment can search for HSPs with a lower χ. The signal detection makes use of the fact that the WISP signal will appear at the same frequency as The CROWS experiment was not only a proof of the emitting cavity drive signal. Hence extremely concept constructed with a relatively small amount narrowband filtering is possible. This is carried out of time and manpower, but also produced by recording the signal from the detecting cavity competitive results compared to existing over several hours and then processing it by a experiments. This pioneering work will be of value specialized Discrete Fourier Transform routine, for the design and implementation of future which can operate on > 1011 points (hundreds of microwave based WISP search experiments at both GB worth of data). The resulting spectrum has a CERN and elsewhere.

4 Beams Department Newsletter Issue 11 References: These tests typically consist of the verification of [1] K. Baker et al., “The quest for and other new all interlocks and connections, some individual light particles", Annalen der Physik 525.6 (2013) system checks and a heat run performed with all power converters in the same service area powered [2] J. Jäckel and A. Ringwald, „A cavity experiment to simultaneously for several hours. During this last search for hidden sector photons", Physics Letters B 659.3 (2008) phase the temperature of the different part of the circuits and the resistance of the cable connections [3] M. Betz et al., “First results of the CERN Resonant are recorded by means of thermography, as shown Weakly Interacting sub-eV Particle Search (CROWS)", in Figure 1. At present, the SCT campaign has Phys. Rev. D 88 (2013) been carried out on the whole machine, with the exception of the cables powering the resistive circuits at point 7.

Michael Betz BE-BI-QP

The LHC sees the light at the

end of the tunnel Figure 1: Thermography of cables during the SCT

After more than one and a half years of long The CSCM is a newly designed test technique, shutdown (LS1) the sleeping giant is finally about which is performed at a temperature of around 20 to wake up again. But before entering Run II phase Kelvin on the main dipole circuits. It is done to with a new energy record, an extensive set of check the continuity of the entire bus-bar of a hardware tests has to be carried out to ensure sector (6 km long), the protecting diodes and the correct and reliable functionality of the different connections between them. The diodes bypass the systems. Among them, the qualification of the magnets in case of a quench in order to protect superconducting circuits, that consists of three them. phases: • The Short Circuit Tests (SCT) At 20 Kelvin the magnets are not yet • The Copper Stabilizer Continuity superconducting and have a larger resistance than Measurements (CSCM) that of the bypass diodes. Thus, when injecting a • The superconducting circuit powering tests small current of a few hundred Amperes at a high voltage of 200-300 V in the circuit, the diodes The SCT campaign is performed in order to short-out and bypass the magnets. In this case the validate the warm part of the superconducting current circulates only through the bus-bar and the circuits and spot potential problems early enough diodes. In less than ten seconds the power to implement necessary corrections. For these tests, converters ramp the current to a defined value and the resistive cables are short-circuited just before reduce it from there exponentially. This test is the connection to the superconducting part. The repeated six times with a gradually increased current then flows from the power converter current, to finally reach the nominal current of 11 through the cables and (if present) into the Energy kA, the equivalent of 6.5 TeV beam energy. This Extraction (EE) system. The SCT campaign allows power function is shown in Figure 2 for the dipole verification tests of the cooling system for the circuit test of sector 6-7. A special configuration of different circuits, the current sharing into the EE the quench protection system is used to protect the system, the quality of the cable connections and circuit in this unusual condition. the global ventilation in the area where the power converters are located.

5 Beams Department Newsletter Issue 11 There are two possible outcomes during this test. New Magnetic Alloy Based RF Either too much energy is deposited in a splice (causing a thermal runaway), rendering it a faulty Cavities for Synchrotrons connection; or no significant voltage drop (thus temperature increase) is detected, which validates At high energy the accelerating cavities used in the splice for this energy level. synchrotrons can be narrow band, practically fixed frequency devices, whereas at lower energies they must cope with the velocity increase of the beam and follow the increasing revolution frequency. The need to cover a wide frequency range can also come from the operation with different harmonic numbers, the need of multi-harmonic accelerating fields or other technical reasons. As an example the PSB RF systems cover the range of 0.6 MHz - 1.8 MHz and 1.2 - 3.6 MHz but in MedAustron the range spans over a decade (0.35 MHz - 3.5 MHz) and even more in LEIR (0.36 MHz - 5.0 MHz).

Most of the existing systems in this frequency

Figure 2: Final test cycle of CSCM validation in range handle the problem using ferrite loaded sector 6-7 cavities. The ferrite loading artificially increases the cavity equivalent electrical length by a factor The last part of the superconducting circuit proportional to its permeability which can be qualification is the so-called powering tests. This controlled using a bias field. The result is a tunable phase is performed at nominal cryogenic device whose resonance can be adjusted as conditions used for beam operation, i.e. 1.9 K for required. most of the circuits. The eight sectors are progressively cooled-down. One sector is already In recent years modern Magnetic Alloys (MA) that at nominal conditions and two more are on their can replace the ferrites became available. A way. Once cold, almost 1600 circuits will be tailored development for their use in accelerators has been carried out by Hitachi Metals on its powered at gradually increasing current levels up ® to their nominal currents. Similar to tests done in Finemet MA now widely employed in the J- 2009, a total of more than 10.000 test steps have to PARC Main Ring (MR) and Rapid Cycling be executed and analyzed by the different system Synchrotron (RCS) in Japan. This material exhibits experts in less than 4 months. interesting properties such as saturation fields substantially higher than those in ferrites (factor 5 Moreover, the increase of beam energy to 6.5 TeV or more) and wideband frequency response. The introduces additional complication. The magnets first potentially allows achieving higher need to be trained, in order to reach the necessary accelerating gradients; the latter avoids the need magnetic fields. This is done by repeatedly pushing for a tuning system and allows multi-harmonic the current up until they quench. Based on operation. experience acquired in 2008, it is known to be a long process of slight increases in the magnetic field and will take about a week per sector. POWER RF AMP RF CAVITY

Another big challenge that Operation is ready to take up!

Mirko Pojer Matteo Solfaroli Camillocci,

BE-OP-LHC

Figure 1: LEIR RF system

6 Beams Department Newsletter Issue 11 Considering the pioneering work done in Japan, a represents 60% of the maximum present intensity very profitable collaboration was established with (Fig. 4). But tests also highlighted design KEK in Tsukuba, Japan. This led to the first use at weaknesses CERN of a MA loaded cavity for the LEIR RF system (Fig.1). Despite the use of new material, the system was a traditional arrangement using a single gap cavity and vacuum tubes for the amplifier final stage. The achievable accelerating gradient allowed building a compact cavity, the power requirements however, imposed a big amplifier.

For the renovation and upgrade study within the LIU-PSB project for the PSB RF systems the maximum size allowed for each cavity due to the four superimposed rings must be taken into account. This can be achieved adopting a more a modular configuration based on small cells composed of a gap with a single MA core on each Figure 4: Main parameters with 4.6E12 protons. side. The arrangement (Fig. 2) chosen is particularly well fit to be driven by solid-state in the cavity and the amplifier, the need of an power amplifiers that, if placed close to the cavity, effective compensation of wake fields and a can also solution to the radiation effects on the solid-state devices used in the power stage. The radiation Gap issue was addressed with a test campaign in the J-

GAP PARC main ring.

BEAM As expected the test showed that the most sensitive FINEMET parameter change in the RF MOSFETS is the threshold voltage (VTH) shift. Lifetime differences RF in were also highlighted (Fig. 5 left). Based on these Figure 2: Basic cell configuration. results a radiation compensation circuit was devises and tested at the Fraunhofer Institut in implement a fast RF feedback for compensating Germany. It allows reducing drastically the VTH the beam loading effects. A 5-cell prototype effects (Fig. 5 right) up to doses in the order of system has been built for the PSB (Fig. 3) with the 2 kGy which represent many years of operation in aim of replacing in the future the C02 and C04 RF the PSB. systems with a common wideband solution. V , A VRF151G 18

16 Un-compensated drain current

14

12 Compensated bias voltage 10

8 Compensated drain current devices #1, 2 and 3 6

4

2 Dose [Gy] 0 0 500 1000 1500 2000

Figure 5: Lifetime and VTH change vs integrated dose for tested RF Mosfets(left) and effect of the radiation compensation circuit (right). Figure 3: PSB 5-cell open cavity (left) and solid- state amplifier (right). In parallel with the radiation test, a single-gap cavity was installed in the J-PARC MR for testing The prototype, completed by dedicated low level the wake field compensation using the Feed electronics, was installed and tested during 2012. Forward Low Level electronics designed at Used in parallel with the existing RF system it JPARC. allowed accelerating 4.6e12 protons which

7 Beams Department Newsletter Issue 11 The test gave excellent results (Fig. 6) for beam beam induced voltage up to ~10 MHz is required intensity up to 1.4e13 ppb corresponding to peak to reduce the adverse effects of beam loading. beam currents ranging from 10 A to 20 A Each cell is driven by two power stages instead of depending on the bunching factor during the cycle. one as in the PSB. Dedicated steel shielding is used This is an important indication that the amplifiers to reduce the ionizing radiation to the power can cope with high beam current. All these amplifiers. The solid-state devices lifetime is activities converged in the completion of the PSB expected to be well above 10 years. Beam tests prototype system and the production of a second with the installed prototype are foreseen for the series of upgraded amplifiers. The complete accelerator run in 2014 - 2015. system now installed in the PSB has 10 gaps, provides 7 kV RF voltage and is expected to be able to independently accelerate the beam.

Figure 7: The 6-cell prototype PS Longitudinal Damper.

Figure 6: Wake fields compensation by FF. Future candidates using the flexible building (Acceleration is at h=9) blocks include at CERN the RF systems required for ELENA (anti-proton decelerator) and the Tests are foreseen in 2014-2015. The flexibility of planned TSR ring, an extension to the future HIE- this kind of design comes from the wideband, basic Isolde facility being projected currently. building block. When working on the PSB prototype, the MedAustron RF system also had to be designed and it seemed natural to go towards a similar solution. In this case two 6-cell systems were designed and fabricated. Due to the low beam intensity, no wake field compensation is required. This gave the additional flexibility of moving the RF power stages out of the ring into the equipment Mauro Paoluzzi, BE-RF-IS room.

For the new PS Longitudinal damper prototype developed within the LIU-PS project the same kind of system has been adopted. 6-cells are required to deliver the total voltage of 5 kV over the frequency band from 0.5 MHz - 5 MHz. Cancellation of the

8 Beams Department Newsletter Issue 11 Se protéger contre le risque de Prevention against manque d’oxygène (ODH) oxygen deficiency hazard (ODH) dans le LHC in the LHC

Pourquoi? Why? L’Hélium est présent en grande quantité dans le LHC sous Large quantities of Helium are present in the LHC at différentes formes (liquide ou gazeux), à des pressions various states (liquid or gas), at different pressures (from 1 différentes (de 1 à 17 bars) et à des températures qui varient to 17 bars) and with a wide range of temperatures (from entre 293K à 1.9K. 293K down to 1.9K) Le détecteur ODH mesure le taux d’oxygène ambiant à The ODH meter measures the ambient oxygen level at your l’endroit même où vous vous trouvez dans le LHC. location in the LHC. Le détecteur ODH est une aide par exemple lors d’une The ODH meter is an helpful tool; for example in case of évacuation liée à une alarme ODH car il vous permet de an evacuation due to an ODH alarm because it enables you vérifier dans quel environnement vous êtes et le cas to check if the environment is safe and therefore can échéant, d'éviter de céder à la panique. prevent panicking. Où doit-on porter un détecteur ODH ? Where must I wear an ODH meter? Depuis septembre 2014, le port d’un détecteur ODH est : From September 2014, wearing personal ODH meters is: • Obligatoire dans les arcs lorsque la machine LHC • mandatory in the arcs when the LHC machine is est froide. (< 80 K). cold (< 80 K). • Pas obligatoire dans les sections droites (Long • not needed in Long Straight Sections (LSS) and Straight Sections ou LSS) et dans les « Inner Inner Triplets areas (IT) where work is subjected Triplets areas » (ou IT) où des procédures spéciales to special procedure. s’appliquent. Is an ODH meter personal? Est-ce qu’un détecteur ODH est un équipement An ODH meter is not personal. They are for borrowing as personnel ? needed. But each person shall wear one when going in the C’est un équipement de protection qui n’est pas nominatif. LHC. Il est partagé au sein d’une équipe. Chaque personne qui 40 ODH detectors are allocated as follows in the BE descend dans les zones concernées du LHC doit porter un Department: détecteur ODH. • 3 for ASR, including HDO, stored in their secretariat, 40 détecteurs ODH sont disponibles dans le Dépt BE : • 4 for RF, stored at LHC-4, • 3 chez ASR et HDO stockés au secrétariat, • 5 for CO stored in their secretariat, • 4 chez RF, stockés au LHC-4, • 10 for BI stored in their secretariat, • 5 chez CO stockés au secrétariat, • None for ABP. • 10 chez BI stockés au secrétariat, • Aucun chez ABP. And finally 18 for OP and the rest of the BE Department if needed, stored in the CCC. Enfin, 18 chez OP stockés au CCC et également disponibles pour tout le département BE si besoin. How to use an ODH meter? Comment utiliser un détecteur ODH ? ODH meters are delivered with a user manual. An on-line course on sir..ch will Les détecteurs ODH sont soon be available. More livrés avec un guide complete and technical d’utilisateur. Un cours en ligne details can be found in the sur sir.cern.ch sera bientôt document Helium spill disponible. Pour plus de détails risks in the LHC, EDMS techniques, consultez le 1410252 document Helium spill risks in the LHC, EDMS 1410252. BE-Safety Unit, Send a message BE-Safety Unit, Envoyer un message

9 Beams Department Newsletter Issue 11

Responsibility Changes As from 1.10.2014

End of appointment as Deputy

Department Head on 30.09.2014: BE Deputy Department Head: Roland Garoby who will take new functions as Oliver Brüning Technical Director at the European

Spallation Source in Lund.

BI Deputy Group Leader ABP Group Leader: as from 01.06.2014: Gianluigi Arduini Thibaut Lefevre, BE-BI-QP

End of appointment as RF Deputy ABP Deputy Group Leader: Group Leader on 30.06.2014: Richard Scrivens Maurizio Vretenar who joined DG-DI

RF Deputy Group Leader ABP-HSL Section Leader: as from 01.07.2014: Alessandra Lombardi Andy Butterworth, BE-RF-CS

Newsletter Contacts

ABP Correspondent ASR Correspondent Elena Benedetto Annie Di Luca

BI Correspondent CO Correspondent Barbara Holzer Mick Draper

OP Correspondent RF Correspondent Christoph Kittel Wolfgang Höfle

Copy Editor Editor-In-Chief Laurence Van Cauter-Tanner Ronny Billen

10 Beams Department Newsletter Issue 11