Author: Caspers, F.
Paper Title Page
MOPPC009 Multipactor for E-cloud Diagnostics 139
  • P. Costa Pinto, F. Caspers, P. Edwards, M. Holz, M. Taborelli
    CERN, Geneva, Switzerland
  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 though 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 field. Preliminary result 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.  
WEPPD072 Frequency Fine-tuning of a Spin-flip Cavity for Antihydrogen Atoms 2690
  • S. Federmann, F. Caspers, E. Mahner
    CERN, Geneva, Switzerland
  • B. Juhasz, E. Widmann
    SMI, Vienna, Austria
  As part of the ASACUSA collaboration physics program a spin-flip cavity for measurements of the ground-state hyperfine transition frequency of anti-hydrogen atoms is needed. The purpose of the cavity is to excite anti-hydrogen atoms depending on their polarisation by a microwave field operating at 1.42 GHz. The delicacy of designing such a cavity lies in achieving and maintaining the required properties of this field over a large aperture of 10cm and for a long period of time (required amplitude stability is 1% within 12h). The present paper presents the frequency fine tuning techniques to obtain the desired centre frequency of 1.42 GHz with a Q value below 500 as well as the tuning circuit used for the frequency sweep over the desired bandwidth of 6 MHz.  
WEPPR010 Comparison between Electron Cloud Build-Up Measurements and Simulations at the CERN PS 2955
  • G. Iadarola
    Naples University Federico II, Science and Technology Pole, Napoli, Italy
  • F. Caspers, S.S. Gilardoni, G. Iadarola, E. Mahner, G. Rumolo, C. Yin Vallgren
    CERN, Geneva, Switzerland
  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. A dedicated EC experiment, equipped with two button pick-ups, a pressure gauge, a clearing electrode, and a small dipole magnet, is available in one of the 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.  
WEPPR070 Beam Coupling Impedance Simulations of the LHC TCTP Collimators 3090
  • H.A. Day, R.M. Jones
    UMAN, Manchester, United Kingdom
  • F. Caspers, A. Dallocchio, L. Gentini, A. Grudiev, E. Métral, B. Salvant
    CERN, Geneva, Switzerland
  As part of an upgrade to the LHC collimation system, 8 TCTP and 1 TCSG collimators are proposed to replace existing collimators in the collimation system. In an effort to review all equipment placed in the accelerator complex for potential side effects due to collective effects and beam-equipment interactions, beam coupling impedance simulations are carried out in both the time-domain and frequency-domain of the full TCTP design. Particular attention is paid to trapped modes that may induce beam instabilities and beam-induced heating due to cavity modes of the device.  
WEPPR071 Evaluation of the Beam Coupling Impedance of New Beam Screen Designs for the LHC Injection Kicker Magnets 3093
  • H.A. Day, R.M. Jones
    UMAN, Manchester, United Kingdom
  • M.J. Barnes, F. Caspers, H.A. Day, E. Métral, B. Salvant
    CERN, Geneva, Switzerland
  During the 2011 run of the LHC there was a measured temperature increase in the LHC Injection Kicker Magnets (LHC-MKI) during operation with 50ns bunch spacing. This was suspected to be 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 and HL-LHC parameters.  
THPPC020 Accurate Measurement of Ferrite Garnets to be used for Fast-tuned Ferrite Loaded Cavities in the Range of 20-40 MHz 3317
  • C. Vollinger, F. Caspers
    CERN, Geneva, Switzerland
  For the implementation of ferrite-tuned cavities with perpendicular biased ferrites in the frequency range of 20 to 40 MHz, different types of ferrite garnets were evaluated in terms of their electromagnetic properties. We describe a precision measurement method applicable to small-sized ferrite samples of 1-square-inch surface and 2 mm thickness in the given frequency range. During measurement, these samples are exposed to varying magnetic bias fields of different orientations. Two different techniques for the determination of the real and the imaginary part of the permeability are required to achieve sufficiently accurate results. We present a detailed description of these methods as well as results obtained.  
THPPC021 A Microwave Paraphoton and Axion Detection Experiment with 300 dB Electromagnetic Shielding at 3 GHz 3320
  • M. Betz, F. Caspers
    CERN, Geneva, Switzerland
  Funding: Work supported by the Wolfgang-Gentner-Programme of the Bundesministerium für Bildung und Forschung (BMBF).
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 push beyond the 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 show the results to date.
THPPC023 RF Loads for Energy Recovery 3326
  • S. Federmann, M. Betz, F. Caspers
    CERN, Geneva, Switzerland
  Different conceptional designs for RF high power loads are presented. One concept implies the use of solid state rectifier modules for direct RF to DC conversion with efficiencies beyond 80%. In addition, robust metallic low-Q resonant structures, capable of operating at high temperatures (>150 ̊C) are discussed. Another design deals with a very high temperature (up to 800 ̊C) air cooled load using a ceramic foam block inside a metal enclosure. This porous ceramic block is the actual microwave absorber and is not brazed to the metallic enclosure.