Author: Caspers, F.
Paper Title Page
MOPRO062 Investigating Polarisation and Shape of Beam Microwave Signals at the ANKA Storage Ring 4090
 
  • J. Schwarzkopf, M. Brosi, C. Chang, E. Hertle, V. Judin, B. Kehrer, A.-S. Müller, A.-S. Müller, A.-S. Müller, M. Schuh, M. Schwarz, P. Schönfeldt, P. Schütze, J.L. Steinmann
    KIT, Karlsruhe, Germany
  • F. Caspers
    CERN, Geneva, Switzerland
 
  At the ANKA synchrotron radiation facility measurements in the microwave range (~10 to 12 GHz) employing a LNB (Low Noise Block), which is the receiving part of a Satellite-TV system, have been carried out. Experiments showed that the observed signal depends on the length of the electron bunches. Furthermore the temporal shape of the microwave signal depends on the detector's position along the accelerator. Due the LNB antenna's sensitivity to polarisation it was also possible to measure the polarisation along the several ns long signal, revealing polarised and non-polarised regions. This paper describes the experimental setup and summarises the observations of the systematic studies performed with the LNB system.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-MOPRO062  
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TUPME029 Identification of High-frequency Resonant Impedance in the CERN SPS 1416
 
  • E.N. Shaposhnikova, T. Argyropoulos, T. Bohl, J.V. Campelo, F. Caspers, J.F. Esteban Müller, A. Lasheen, B. Salvant, H. Timko
    CERN, Geneva, Switzerland
 
  The spectrum of long bunches injected into the ring with RF switched off has been used in the SPS in the past to probe the longitudinal coupling impedance. After a large campaign of shielding of 800 inter-magnet vacuum ports in 1999 - 2001, the microwave instability threshold was significantly increased and the high-frequency spectrum of the beam became practically flat, apart from a prominent peak at around 1.4 GHz. As corresponding high-frequency impedance could potentially lead to microwave instability of high intensity bunches observed now at high energies in the SPS, a search of the source of this impedance was launched. Using a combination of impedance simulations and measurements, vacuum flanges that are present in a large quantity in the machine have been identified as a main source of impedance at this frequency. Particle simulations based on the SPS impedance model, which includes this previously unknown impedance, are able to reproduce the characteristics of the bunch spectrum and amplitude growth rates and hence, confirm that the impedance of the vacuum flanges is responsible for the observed spectral peak.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME029  
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TUPRI030 Beam Coupling Impedance of the New Beam Screen of the LHC Injection Kicker Magnets 1627
 
  • H.A. Day, M.J. Barnes, F. Caspers, E. Métral, B. Salvant, J.A. Uythoven
    CERN, Geneva, Switzerland
 
  The LHC injection kicker magnets experienced significant beam induced heating of the ferrite yoke, with high intensity beam circulating for many hours, during operation of the LHC in 2011 and 2012. The causes of this beam coupling impedance were studied in depth and an improved beam screen implemented to reduce the impedance. Results of measurements and simulations of the new beam screen design are presented in this paper: these are used to predict power loss and temperature of the ferrite yoke for operation after long shutdown 1 and for proposed HL-LHC operational parameters.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI030  
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THPRI053 Ferrite Material Characterization in a Static Bias Field for the Design of a Tunable Cavity 3890
SUSPSNE088   use link to see paper's listing under its alternate paper code  
 
  • J. Eberhardt, F. Caspers, C. Vollinger
    CERN, Geneva, Switzerland
 
  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.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI053  
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THPRI054 Permittivity and Permeability Measurement Methods for Particle Accelerator Related Materials 3893
 
  • C. Vollinger, F. Caspers, E. Jensen
    CERN, Geneva, Switzerland
 
  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.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI054  
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