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radio-frequency

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PM12 Cavity Mode Related Wire Breaking of the SPS Wire Scanners And Loss Measurements of Wire Materials diagnostics, instrumentation, wire scanner 119
 
  • F. Caspers, B. Dehning, E. Jensen, J. Koopman, J.F. Malo, F. Roncarolo
    CERN, Geneva, Switzerland
  During 2002 SPS running with the high intensity LHC type beam the breaking of several of the carbon wires in the wire scanners has been observed. This damage occurred with the scanners in their parking position. The observation of large changes in the wire resistivity and thermionic electron emission indicated clearly a strong RF beam induced heating and its bunch length dependence. A subsequent analysis in the laboratory, simulating the beam by a RF-powered wire, showed two main problems. The housing of the wire scanner acts as a cavity with a mode spectrum starting around 350 MHz and high impedance values around 700 MHz. The carbon wire used appears to be an excellent RF absorber and thus dissipates a significant part of the beam-induced power. The classical cavity mode technique is used to determine the complex permittivity and permeability of different samples. As a resonator, a rectangular TE01N type device is used. Different materials such as silicon carbide (SiC), carbon and quartz fibres as well as other samples were measured, since no data for these materials was available. In particular SiC properties are of interest, since SiC bulk material is often used as a microwave absorber. As a result, the carbon wire will be replaced by a SiC wire, which shows much less RF losses. Placing ferrite tiles on the inner wall of the wire scanner housing considerably reduces the impedance of the cavity modes. The reduction of the Q values of these modes is confirmed by laboratory measurements.  
 
PT07 Cavity Beam Position Monitor For The TESLA Energy Spectrometer diagnostics, electro-magnetic fields, linear-collider, monitoring, TESLA 184
 
  • A. Liapine
    TU-Berlin, Technische Universität, Berlin, Germany
  In order to measure the beam position with a precision of better than 1μm in the TESLA energy spectrometer a cavity beam position monitor is proposed. The waveguide coupling is used to achieve a good common mode rejection and therefore a better precision. The paper gives a short overview of the monitor functionality and describes resolution measurements which were made on the cavity prototype.  
 
PT09 Cavity-Type BPMs For The TESLA Test Facility Free Electron Laser diagnostics, instrumentation, free-electron-laser, undulator, TTF 190
 
  • H. Waldmann, H.J. Schreiber
    DESY-Zeuthen, Deutsches Elektronen-Synchrotron, Zeuthen, Germany
  For measurements of the beam position at the undulator section of the TESLA Test Facility (TTF) at DESY cavity-type beam position monitors were developed, installed and brought into operation. Besides of some theoretical aspects results of in-beam measurements at the TTF are presented and pros and cons of this monitor concept are discussed.