Search

The Large Hadron Collider (LHC) is one of the largest scientific instruments ever built. Since opening up anew energy frontier for exploration in 2010, it has gathered a global user community of about 9000 scientists working in fundamental particle physics and the physics of hadronic matter at extreme temperature and density. To sustain and extend its discovery potential, the LHC will need a major upgrade in the 2020s. This will increase its instantaneous luminosity (rate of collisions) by a factor of five beyond the original design valueand the integrated luminosity (totalnumber of collisions) by a factor ten. The LHC is already a highly complexand exquisitely optimised machine so this upgrade must be carefully conceived and will require new infrastructures(underground and on surface)and over a decade to implement. The new configuration, known as High Luminosity LHC (HL-LHC), relies on a number of key innovations that push accelerator technology beyond its present limits. Among these are cutting-edge 11–12Tesla superconducting magnets, compact superconducting cavities for beam rotation with ultra-precise phase control, new technology and physical processes for beam collimation and 100 metre-long high-power superconducting links with negligible energy dissipation, all of which required several years of dedicated R&D; effort on a global international level. The present document describes the technologies and components that will be used to realise the projectand is intended to serve as the basis for the detailed engineering design of the HL-LHC.

Pugnat, P. "Preliminary Study for a New Axion Dark-Matter Haloscope" in 12th "Patras" Workshop on Axions, WIMPs and WISPs, PATRAS 2016 / Kim, Younglm, Lindner, Axel, Semertzidis, Yannis K. (eds.), Verlag Deutsches Elektronen-Synchrotron : 2017 ; PATRAS 2016 : 12th "Patras" Workshop on Axions, WIMPs and WISPs, 2016-06-20 - 2016-06-24, Jeju Island 12th Patras Workshop on Axions, WIMPs and WISPs, AXION-WIMP 2016, Jeju Island, South Korea, 20 Jun 2016 - 24 Jun 2016; Hamburg : Verlag Deutsches Elektronen-Synchrotron, DESY-PROC, 129-132 (2017). doi:10.3204/DESY-PROC-2009-03/Pugnat_Pierre, A new haloscope for Axion dark-matter search is under study using in a first step the large bore superconducting magnet in construction at the LNCMI in Grenoble, which will produce 9~T in 812~mm diameter and 1400~mm height. Microwave cavities of high quality factor $Q\sim10^5-10^6$ will be developed at CAPP/IBS in Daejeon. Low-noise microwave amplification of the signal will be ensured by DC superconducting quantum interference devices (SQUID) or/and Josephson parametric amplifiers (JPA) cooled-down to 20~mK by a $^3$He/$^4$He dilution refrigerator. This new haloscope will be designed to probe QCD dark-matter Axions in the mass range of 1-100~$\mu$eV with unprecedented sensitivity., Published by Verlag Deutsches Elektronen-Synchrotron, Hamburg

The TOTEM experiment has been designed to measure the total proton-proton cross section and to study the elastic and diffractive scattering at the LHC energy. The measurement requires detecting protons at distances as small as 1 mm from the beam center: TOTEM uses Roman Pots, movable beam pipe insertions, hosting silicon detectors. In the first period of LHC operation no relevant problems were detected with Roman Pots retracted or inserted during special runs. However, when operating the LHC with high intensity beams, impedance induced heating has been observed during the Roman Pots insertion. In order to be compatible with the higher LHC beam current foreseen after the LS1, a new version of the Roman Pot has been proposed and optimized with respect to the beam coupling impedance. In this work we present the bench impedance measurements carried out on the new Roman Pot prototype. Single and double wire measurements, as well as probe measurements, were performed in order to detect possible harmful resonant modes. The laboratory setup has been as well simulated with the help of CST Particle Studio in order to benchmark the measurement results. Measurements and simulations are in close agreement confirming the equipment compatibility with the LHC requirements for safe operation.

Secondary electron emission processes under electron bombardment are central to many effects at surfaces and interfaces, and to many in vacuum high power RF electronic devices where multipactor can be very intense [1,2]. Ferrite materials are usually used in microwave components used in space telecommunication systems, as circulators, phase-shifters, switches, and isolators. The physics of the multipactor phenomenon existing in microwave devices based on ferrite materials is an important issue and it is urgent to be researched [3]. One difficulty in the analysis of the multipactor effect in RF components containing ferrite lies on the fact that this material is an anysotropic magnetic medium controlled by an applied permanent magnetic field, which is used to magnetize the ferrite material. SEY and other properties (structure, magnetic behaviour,...) of soft-magnetic materials were studied in this work. MnZn soft ferrites magnets are suitable in the situation of frequency < 3MHz, low loss and high μi. Compared with MnZn soft ferrite, NiZn soft ferrite are used at higher frequencies

This article describes a study performed on one of the CERN-SPS vertical rotational wire scanners in order to investigate the breakage of the wire, which occurred on several occasions during operation in 2012. The thermionic emission current of the wire was measured to evaluate temperature changes, and was observed to rise significantly as the wire approached the ultimate LHC beam in the SPS, indicating the possibility of strong coupling between the beam’s electromagnetic field and the wire. Different laboratory measurements, complemented by CST Microwave Studio simulations, have therefore been performed to try and understand the RF modes responsible for this heating. These results are presented here, along with the subsequent modifications adopted on all of the operational SPS wire scanners.

A radioactive source is proposed as a calibration device to verify the sensitivity of a microwave dark matter search experiment. The interaction of e.g., electrons travelling in an arbitrary direction and velocity through an electromagnetically “empty” microwave cavity can be calculated numerically. We give an estimation of the energy deposited by a charged particle into a particular mode. Numerical examples are given for beta emitters and two particular cases: interaction with a field free cavity and interaction with a cavity which already contains an electromagnetic field. Each particle delivers a certain amount of energy related to the modal R/Q value of the cavity. The transferred energy is a function of the particles trajectory and its velocity. It results in a resonant response of the cavity, which can be observed using a sensitive microwave receiver, provided that the deposited energy is significantly above the single photon threshold.

The feasibility of cleanly separating the main 10.128MHz bunches from the 101.28MHz satellite bunches with a travelling-wave type chopper at HIE-ISOLDE was investigated using a simple model comprising a chain of synchronised capacitors pulsed at high-voltage. Even with a relatively large transverse aperture of 30mm it appears feasible to remove the satellite bunches spaced at 75mm without significantly perturbing the main bunch. We estimate that for a chopping voltage of 1.2 kV a string of 20 capacitors is required to impart the required deflection of 4 mrad to beams with A=q = 4:5 and the mechanical length of the system can be kept under 0.5 m. The deflection imparted on the main pulse is . 1% of that received by the discarded satellite bunches and the transverse emittance growth of the beam is small if the rise/fall times are kept below 5 ns. The HIE-ISOLDE specification is similar to the specification of the meander strip-line chopper developed at CERN for Linac4 and the application of this technology at HIE-ISOLDE could be of interest.

For the characterization of components, systems and signals in the radiofrequency (RF) and microwave ranges, several dedicated instruments are in use. In this article the fundamentals of the RF signal techniques are discussed. The key element in these front ends is the Schottky diode which can be used either as a RF mixer or as a single sampler. The spectrum analyser has become an absolutely indispensable tool for RF signal analysis. Here the front end is the RF mixer as the RF section of modern spectrum analyses has a ra ther complex architecture. The reasons for this complexity and certain working principles as well as limitations are discussed. In addition, an overview of the development of scalar and vector signal analysers is given. For the determination of the noise temperature of a one-port and the noise figure of a two-port, basic concepts and relations are shown as well as a brief discussion of commonly used noise-measurement techniques. In a further part of this article the operating principles of network analysers are shown. A distinction can be made between scalar and vector network analysers and their methods of measuring the transmission or reflection coefficients are explained. As digital signal processing has become cheap and easily available over the last 30 years, these instruments have become extremely versatile and powerful. Fourier transformation permits time-domain measurements and allows the removal of undesired parts of the signal trace in the time domain by gating. Network analysers require sophisticated calibration procedures, which are now indispensable for many measurement applications. Non-linear network analysis completes tests of most characteristic amplifier features. The Smith chart is a very valuable and important tool that facilitates interpretation of S-parameter measurements. The last part of this article gives a brief overview of how to use the chart. Its definition as well as an introduction on how to navigate inside the chart are illustrated. Useful examples show the broad possibilities for use of the chart in a variety of applications. This article is a compilation of previous CAS proceedings where information being in the scope of the intermediate-level RF course was extracted.

During the development of ferrite-loaded accelerating cavities, the electromagnetic properties of the dispersive ferrite material need to be known. We describe a coaxial short-circuit measurement technique to measure the complex permeability of toroidal-shaped samples (127mm outer and 70mm inner diameter) that are exposed to an external magnetic bias field. The external magnetic bias field is applied perpendicular to the RF magnetic field. With this method it is possible to characterize the frequency dependence of the permeability for a frequency range of 1- 100MHz. The dependence of the permeability on the external magnetic bias is presented for the ferrite G-510 from Trans-Tech Inc. and the material characterization is shown in the same frequency range. The measurement results are verified by simulations of the measurement set-up.

For the special requirements related to particle accelerators, knowledge of the different material parameters of dielectrics and other materials are needed in order to carry out simulations during the design process of accelerator components. This includes also properties of magnetically biased ferrites of which usually little information is available about material characteristics, especially in magnetic bias fields. Several methods of measurement are discussed and compared of which some require delicate sample preparation whereas others can work with unmodified material shapes that makes those methods also suited for acceptance checks on incoming materials delivered by industry. Applications include characterization of different materials, as absorbers in which dielectric losses play an increasing role, as well as low frequency measurements on ferrites that are used for tunable cavities. We present results obtained from both broadband and resonant measurements on different materials determined in the same sample holder. Where possible, the results were confirmed with alternative methods.

To mitigate electron cloud in particle accelerators a carbon coating with low SEY (Secondary Electron Yield) has been developed. In the case of the SPS (Super Proton Synchrotron), which belongs to the LHC injector chain, testing of the performance of coated beam pipes directly in the accelerator must cope with the schedule of the regular machine operation. For this reason an alternative tool based on RF induced multipacting in a coaxial configuration has been designed for ex-situ characterization of the main bending dipoles of the SPS. In this contribution we report the results obtained before and after coating for two 6.4 meter dipoles with different cross sections of the vacuum chambers. The multipacting is monitored by measuring the pressure rise and the RF reflected power. After coating, the power threshold to induce multipacting is strongly reduced indicating a lower propensity for electron cloud. The impact of the RF coupling on the sensitivity of the technique is discussed.

The two LHC injection kicker systems produce an integrated field strength of 1.3 T·m with a flattop duration variable up to 7860 ns, and rise and fall times of less than 900 ns and 3000 ns, respectively. A beam screen is placed in the aperture of each magnet, which consists of a ceramic tube with conductors in the inner wall. The conductors provide a path for the beam image current and screen the ferrite yoke against wakefields. Recent LHC operation, with high intensity beam stable for many hours, resulted in significant heating of both the ferrite yoke and beam impedance reduction ferrites. For one kicker magnet the ferrite yoke approached its Curie temperature. As a result of a long thermal time-constant the ferrite yoke can require several hours to cool sufficiently to allow re-injection of beam, thus limiting the running efficiency of the LHC. Thermal measurement data has been analysed, a thermal model developed and emissivity measurements carried out. Various measures to improve the ferrite cooling have been simulated, including an improved emissivity of the vacuum tank and active cooling on the outside of the tank.

High secondary electron yield of metallic surfaces used in accelerator and also in space applications is of general concern. In addition to several well-known coating preparation techniques and microscopic or macroscopic mechanical roughness (grooves) which may significantly increase microwave losses the concept of magnetic surface roughness has been proposed recently to lower the effective secondary electron yield (SEY). In this concept a smooth and very good conducting surface with low microwave losses is maintained, but underneath this surface a large number of tiny permanent magnets are located to build a rough magnetic equipotential structure. In this paper we present and discuss measurement of the SEY and the improvement in terms of SEY for different parameter ranges.

In this work we describe the latest results for the measurements of the hyperfine structure of antiprotonic $^3$He. Two out of four measurable super-super-hyperfine {SSHF} transition lines of the $(n,L)=(36,34)$ state of antiprotonic $^3$He were observed. The measured frequencies of the individual transitions are $11.12548(08)$ GHz and $11.15793(13)$ GHz, with an increased precision of about 43% and 25% respectively compared to our first measurements with antiprotonic $^3$He [S. Friedreich {\it et al.}, Phys. Lett. B 700 (2011) 1--6]. They are less than $0.5$~MHz higher with respect to the most recent theoretical values, still within their estimated errors. Although the experimental uncertainty for the difference of $0.03245(15)$~GHz between these frequencies is large as compared to that of theory, its measured value also agrees with theoretical calculations. The rates for collisions between antiprotonic helium and helium atoms have been assessed through comparison with simulations, resulting in an elastic collision rate of $\gamma_e = 3.41 \pm 0.62$~MHz and an inelastic collision rate of $\gamma_i = 0.51 \pm 0.07$~MHz.

A novel type of 2.76 m long slotted, or perforated, strip-line pick-up, or kicker electrode structure, for CSRe stochastic cooling of non-relativistic particle beams with β~ 0.7 is presented. It is installed inside a bending vacuum chamber with the output signal taken from the downstream end. This slotted structure features a sufficiently broad bandwidth, good beam coupling impedance, low losses and a comparatively easy mechanical construction and installation into the CSRe dipole chamber. In this paper the electrode structure and pickup tank, as well as the beam test results will be presented.

CERN, the European Organization for Nuclear Research, is actively engaged in identifying technologies developed for its accelerator complex that could be profitably used by partner research organizations or commercial companies in applications with potentially high socio-economic impact beyond pure fundamental physics research. \nIn the first part of the paper, an overview of CERN current strategy in the field of Technology Transfer and Intellectual Property Management will be presented, with details on the most effective models, implementation tools and processes developed to achieve satisfactory dissemination and valorisation of the knowledge generated within the Organization. \nIn the second part, CERN currently available technology portfolio will be described with focus on cases originated from the Accelerator and Technology Sector. A selection of promising on-going projects embracing a variety of technology fields and application areas will be detailed to showcase technical challenges and possible benefits of initiatives driven by (but not limited to) the needs of CERN scientific programme.

As the ELENA project is now well underway, focus is turned to the Antiproton Decelerator (AD) itself. Most of the machine’s key components are in operation since more than 25 years and a substantial consolidation program is now being launched in view of continued operation beyond 2025. \nOver the course of the next few years a progressive consolidation of the AD Target area, the AD ring and all associated systems will take place. Several investigations have recently been performed in the target area with the objective of establishing the radiation environment and the sensitivity of the antiproton production to potential misalignment of the production elements. Identification of reliability and serviceability issues of the AD ring components and associated systems has been done and will continue during the 2013 shut-down. Planned and on-going consolidation activities are also discussed with emphasis on stochastic and electron beam cooling, instrumentation, RF systems, vacuum, magnets, power converters and beam transfer equipment.

A common problem in all kinds of cavity-like structures in particle accelerators is the occurrence of RF-resonances. Typically, ferrite plates attached to the walls of such structures as diagnostic devices, kickers or collimators, are used to dampen those undesired modes. However, the heat transfer rate from these plates to the walls is rather limited. Brazing ferrite plates to the walls is not possible in most cases due to the different thermal expansion coefficients. To overcome those limitations, atmospheric plasma spraying techniques have been investigated. Ferrite layers with a thickness from 50 μm to about 300 μm can be deposited on metallic surfaces like stainless steel exhibiting good thermal contact and still reasonable absorption properties. In this paper the technological aspects of plasma deposition are discussed and results of specifically developed RF loss measurement procedures for such thin magnetically lossy layers on metal are presented.

During the 2011 LHC run it was found that beam-induced heating causes many issues for accelerator components. Particularly some of the double-bellow modules, called VMTSA modules, were found to have deformed RF fingers and a broken spring, which had ensured good contact between them and a central insert. Impedance studies have been performed for different types of nonconformities. It was found that even a small gap between the fingers and a central insert could be fatal for the VMTSA operation. Results of this study were an input for the further thermal analysis.

Conventional ferrite-tuned cavities operate either with bias fields that are orthogonal or parallel to the magnetic RF-field. For a cavity that tunes rapidly over an overall frequency range around 100-400 MHz with high Q, we use ferrite garnets exposed to an innovative new biasing method consisting of a superposition of perpendicular and parallel magnetic fields. This method leads to a significant enlargement of the high-Q cavity tuning range by defining an operation point close to the magnetic saturation and thus improving ferrite material behaviour. A further advantage of this technique is the fast tuning speed resulting from the fact that tuning is carried out either with pure parallel biasing, or together with a very small change of operating point from perpendicular bias. In this paper, several scaled test models of ferrite-filled resonators are shown; measurements on the set-ups are compared and discussed.

Some of the efforts of CERN to optimize its energy usage are presented. Work is proceeding in several areas: campus and infrastructure, accelerators and beam lines, as well as R&D for future accelerators. The existing building stock is being renovated and new buildings apply an integrated energy concept. The energy efficiency of the accelerators and beam lines can be further enhanced by powering more equipment dynamically only during the time it is really needed. For designing new accelerators novel approaches are being investigated to re-use energy which in today’s installations gets dumped thermally.

The CERN LHC is equipped with two Synchrotron Radiation Monitor (BSRT) systems used to characterise transverse and longitudinal beam distributions. Since the end of the 2011 LHC run the light extraction system, based on a retractable mirror, has suffered deformation and mechanical failure that is correlated to the increase in beam intensity. Temperature probes have associated these observations to a strong heating of the mirror support with a dependence on the longitudinal bunch length and shape, indicating the origin as electromagnetic coupling between the beam and the structure. This paper combines all this information with the aim of characterising and improving the system in view of its upgrade during the current LHC shutdown. Beam-based observations are presented along with electromagnetic and thermomechanical simulations and complemented by laboratory measurements, including the study of the RF properties of different mirror bulk and coating materials.

It is important to collect all the relevant information to qualify the present status of the electron cloud in the SPS before the Long Shutdown (LS1). Therefore several electron cloud studies have taken place in the SPS during the 2012 run. At the beginning of the running period, five days were fully dedicated to electron cloud activities and scrubbing studies. After that, a few more MD sessions were devoted to following up on the studies started in the scrubbing week. These results, in combination with detailed simulation studies, will provide the basis for defining strategies of electron cloud mitigation as required for the production of future high intensity and high brightness beams within the LHC Injectors Upgrade (LIU) project.

The CERN Extra Low ENergy Antiproton (ELENA) Ring is a new synchrotron that will be commissioned in 2016 to further decelerate the antiprotons coming from CERN’s Antiproton Decelerator (AD). Required longitudinal diagnostics include the intensity measurement for bunched and debunched beam and the measurement of Dp/p to assess the electron cooling performance. A novel method for the calculation of these parameters is proposed for ELENA, where signals from the twenty electrostatic Pick-Ups (PU) used for orbit measurements will be combined to improve the signal-to-noise ratio. This requires that the signals be digitally down-converted, rotated and summed so that the many electrostatic PUs will function as a single, distributed PU from the processing system viewpoint. This method includes some challenges and will not be used as the baseline longitudinal diagnostics for the initial ELENA operation. This paper gives an overview of the hardware and digital signal processing involved, as well as of the challenges that will have to be faced.

The CERN Antiproton Decelerator (AD) has now completed its 12th year of supplying low-energy antiproton beams for the successful physics program. Most of the machine’s key components are in operation since more than 25 years and prompted by the approval of the ELENA project, a substantial consolidation program is now being launched to ensure continued reliable operation. Over the course of the next few years a progressive renovation of the AD-Target area and the AD-ring with all the associated systems will take place. Status and performance of the AD are presented along with an overview of planned and ongoing consolidation activities with emphasis on stochastic and electron beam cooling.

Electron cloud accumulation in particle accelerators can be mitigated by coating the vacuum beam pipe with thin films of low secondary electron yield (SEY) material. The SEY of small coated samples are usually measured in the laboratory. To further test the properties of different coating materials, RF-induced multipacting in a coaxial waveguide configuration can be performed. The technique is applied to two main bending dipoles of the SPS, where the RF power is fed through a tungsten wire stretched along the vacuum chamber (6.4 m). A dipole with a bare stainless steel chamber shows a clear power threshold initiating an abrupt rise in reflected power and pressure. The effect is enhanced at RF frequencies corresponding to electron cyclotron resonances for given magnetic fields. Preliminary results show that the dipole with a carbon coated vacuum chamber does not exhibit any pressure rise or reflected RF power up to the maximum available input power. In the case of a large scale coating production this technique will be a valuable resource for quality control. In parallel, electron cloud measurements via the microwave transmission method have been performed during the annual scrubbing run in the SPS. Clear electron cloud signals have been observed while operating with high intensity beams, confirming that this measurement technique provides a valuable tool for in-situ diagnostic. This paper is divided into two parts, where the first part deals with the multipacting test stand on stand-alone dipoles and the second part deals with the TE wave diagnostics in the CERN SPS.

Lakic, B. "IAXO-the Future Axion Helioscope" in Proceedings, 9th Patras Workshop on Axions, WIMPs and WISPs (AXION-WIMP 2013) / Oberlack, Uwe, Sissol, Pierre (eds.), 2013 ; AXION-WIMP 2013 : 9th Patras Workshop on Axions, WIMPs and WISPs , 2013-06-23 - 2013-06-28, Mainz 9th Patras Workshop on Axions, WIMPs and WISPs, AXION-WIMP 2013, Mainz, Germany, 24 Jun 2013 - 28 Jun 2013; Hamburg : Verlag Deutsches Elektronen-Synchrotron, DESY-PROC 115-118 (2013). doi:10.3204/DESY-PROC-2013-04/lakic_biljana_IAXO, International Axion Observatory (IAXO) is a new generation axion helioscope aiming to search for axions and axion-like particles with a sensitivity to the axion-photon coupling that is 1 to 1.5 orders of magnitude beyond the one achieved by currently the most sensitive axion helioscope, CAST. IAXO relies on large improvements in magnetic field volume, X-ray focusing optics and detector backgrounds with respect to CAST. Additional IAXO searches would include electron-coupled axions, relic axions, and other more generic axion-like particles., Published by Verlag Deutsches Elektronen-Synchrotron, Hamburg

Betz, M. "Status report of the CERN microwave axion experiment" in Proceedings, 9th Patras Workshop on Axions, WIMPs and WISPs (AXION-WIMP 2013) / Oberlack, Uwe, Sissol, Pierre (eds.), 2013 ; AXION-WIMP 2013 : 9th Patras Workshop on Axions, WIMPs and WISPs , 2013-06-23 - 2013-06-28, Mainz 9th Patras Workshop on Axions, WIMPs and WISPs, AXION-WIMP 2013, Mainz, Germany, 24 Jun 2013 - 28 Jun 2013; Hamburg : Verlag Deutsches Elektronen-Synchrotron, DESY-PROC 51-54 (2013). doi:10.3204/DESY-PROC-2013-04/betz_michael, the existence of " axion like particles " through their weak coupling to photons. We have adapted such an experiment to the microwave regime and constructed the table top apparatus. This work presents an overview of the experimental setup and then focuses on our latest measurement run and its results. By operating the apparatus within a superconducting MRI magnet, competitive exclusion limits for axion like particles to the first generation optical light shining through the wall experiments have been achieved., Published by Verlag Deutsches Elektronen-Synchrotron, Hamburg

CERN’s Extra Low ENergy Antiproton (ELENA) ring is a new synchrotron that will be commissioned in 2016 to further decelerate the antiprotons coming from CERN’s Antiproton Decelerator (AD). Essential longitudinal diagnostics required for commissioning and operation include the intensity measurement for bunched and debunched beams and the measurement of 􀀧p/p for debunched beams to assess the electron cooling performance. The beam phase information is also needed by the Low-Level RF (LLRF) system. The baseline system for providing the required beam parameters and signals is based upon two ultra-low-noise AC beam transformers and associated digital signal processing. The AC beam transformers cover different frequency regions and are an adaptation to the ELENA layout of those used in the AD. Two AC beam transformers will also be installed in the extraction lines to provide beam intensity measurements. The digital signal processing will be carried out with the leadingedge hardware family used for ELENA’s LLRF system. The paper provides an overview of the AC beam transformer and associated digital signal processing.

Measurements of the beam stability in the SPS in 1982 - 1983 have shown a transversal instability for high intensity beams [1]. The fact that this related technical note is published nearly 30 years later, is related to the revival of interest in the frame of SPS impedance evaluation for LS1. Until now there was just a barely known paper folder available which could be consulted on request. The instability mentioned above was identified from beam measurements as raised by a deflecting mode at approximately 940 MHz in the 200 MHz travelling wave cavities of the SPS. Estimates showed that an attenuation of this particular mode by 20 dB would be desirable. In order to achieve this attenuation some vacuum ports on top of the cavities were available. For the damping devices three requirements had to be met: - sufficient damping at about 940 MHz - no serious change of cavity input VSWR at 200 MHz - no water cooling requirement for this higher order mode coupler.

The highest priority for the RF group in 2011 was to contribute to a successful physics run of the LHC. This comprises operation of the superconducting 400 MHz accelerating system (ACS) and the transverse damper (ADT) of the LHC itself, but also all the individual links of the injector chain upstream of the LHC – Linac2, the PSB, the PS and the SPS – don’t forget that it is RF in all these accelerators that truly accelerates! A large variety of RF systems had to operate reliably, often near their limit. New tricks had to be found and implemented to go beyond limits; not to forget the equally demanding operation with Pb ions using in addition Linac3 and LEIR. But also other physics users required the full attention of the RF group: CNGS required in 2011 beams with very short, intense bunches, AD required reliable deceleration and cooling of anti-protons, Isolde the post-acceleration of radioactive isotopes in Rex, just to name a few. In addition to the supply of beams for physics, the RF group has a number of projects and studies to look after: CLIC studies the feasibility of a normal-conducting linear collider and probes feasibility of extreme high-gradient X-band acceleration as well as a number of novel concepts, SPL is a superconducting linear proton or H˗ accelerator with large average beam power, HIE-Isolde is extending the reach of Isolde to even higher energy for radioactive isotopes with superconducting (SC) quarter-wave resonators. For HL-LHC, the LHC luminosity upgrade project, the RF group looks at novel, compact crab cavities required to bring colliding bunches well on top when using a crossing angle, Linac4 is the on-going project for a 160 MeV H˗ injector to eventually replace Linac2 and LIU, the LHC Injector Upgrade project, focuses on targeted upgrades of the other identified RF bottle-necks of the injectors, in particular in the PSB and the SPS. Many of the CERN accelerators are very old – older than the people operating them; to keep them running reliably requires substantial maintenance and consolidation work, which has to be taken very seriously. Taking good care of these old machines and teaching them new tricks, adapting them to a changing environment and concepts nicely fits between operation and maintenance on one side, upgrades and new projects on the other.

Electron cloud in particle accelerators can be mitigated by coating the vacuum beam pipe with thin films of low secondary electron yield (SEY). SEY of small samples can be measured in the laboratory. Verifying the performance of long pipes is more complex, since it requires their insertion in the accelerator and the subsequent measurement of the beam induced pressure rise. RF induced multipacting in a coaxial waveguide configuration is proposed as a test before insertion in the machine. The technique is applied to two main bending dipoles of the SPS, where the RF power is fed through a tungsten wire stretched along the vacuum chamber (6.4 m). A dipole with a bare stainless steel chamber shows a clear power threshold initiating an abrupt rise in reflected power and pressure. The effect is enhanced at RF frequencies corresponding to cyclotron resonances for given magnetic fields. Preliminary results show that the dipole with a carbon coated vacuum chamber does not exhibit any pressure rise or reflected RF power up to the maximum available input power. In the event of a large scale coating production this technique will be a valuable resource for quality control.

During the 2011 run of the LHC there was a significant measured temperature increase in the LHC Injection Kicker Magnets (MKI) during operation with 50ns bunch spacing. This was due to increased beam-induced heating of the magnet due to beam impedance. Due to concerns about future heating with the increased total intensity to nominal and ultimate luminosities a review of the impedance reduction techniques within the magnet was required. A number of new beam screen designs are proposed and their impedance evaluated. Heating estimates are also given with a particular attention paid to future intensity upgrades to ultimate parameters. During the 2011 run of the LHC there was a significant measured temperature increase in the LHC Injection Kicker Magnets (MKI) during operation with 50ns bunch spacing. This was due to increased beam-induced heating of the magnet due to beam impedance. Due to concerns about future heating with the increased total intensity to nominal and ultimate luminosities a review of the impedance reduction techniques within the magnet was required. A number of new beam screen designs are proposed and their impedance evaluated. Heating estimates are also given with a particular attention paid to future intensity upgrades to ultimate parameters.

For the microwave equivalent of "light shining through the wall" (LSW) experiments, a sensitive microwave detector and very high electromagnetic shielding is required. The screening attenuation between the axion generating cavity and the nearby detection cavity should be greater than 300 dB, in order to improve over presently existing exclusion limits. To achieve these goals in practice, a "box in a box" concept was utilized for shielding the detection cavity, while a vector signal analyzer was used as a microwave receiver with a very narrow resolution bandwidth in the order of a few micro-Hz. This contribution will present the experimental layout and the results to date., Presented at 3rd International Particle Accelerator Conference 2012, New Orleans, LA, USA, 20 - 25 May 2012

The build up of an Electron Cloud (EC) has been observed at the CERN Proton Synchrotron (PS) during the last stages of the LHC high intensity beam preparation, especially after the bunch shortening before extraction. Two dedicated EC experiments, both equipped with two button pick-ups, a pressure gauge, a clearing electrode and a small dipole magnet, are available in two straight sections of the machine. A measurement campaign has been carried out, in order to scan the EC build-up of LHC-type beams with different bunch spacing, bunch intensity and bunch length. Such information, combined with the results from build up simulations, is of relevance for the characterization in terms of Secondary Emission Yield (SEY) of the chamber inner surface. The interest is twofold: this will enable us to predict the EC build up distribution in the PS for higher intensity beams in the frame of the upgrade program, and it will provide validation of the EC simulation models and codes.