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higher-order-mode

 
Paper Title Other Keywords Page
MOP36 Preliminary Study on HOM-Based Beam Alignment in the TESLA Test Facility polarization, dipole, alignment, gun 117
 
  • N. Baboi, G. Kreps, M. Wendt
    DESY, Hamburg
  • G. Devanz, R. Paparella
    CEA/DAPNIA-SACM, Gif-sur-Yvette Cedex
  • O. Napoly
    CEA/DSM/DAPNIA, Gif-sur-Yvette
  The interaction of the beam with the higher order modes (HOM) in the TESLA cavities has been studied in the past at the TESLA Test Facility (TTF) in order to determine whether the modes with the highest loss factor are sufficiently damped. The same modes can be used actively for beam alignment. At TTF the beam alignment based on the HOM signals is planned to be studied in the first cryo-module, containing 8 accelerating cavities. One of several modes with higher loss factor will be used. Its polarization has to be determined. The options to use single bunches or bunch trains will be analyzed. The results will be discussed in this paper.  
 
MOP66 Calculation of RF Properties of the Third Harmonic Cavity dipole, scattering, coupling, quadrupole 171
 
  • K. Rothemund, D. Hecht, U. van Rienen
    Rostock University, Faculty of Engineering, Rostock
  Recently a third harmonic structure has been proposed for the injector of the TTF-FEL to avoid nonlinear distortions in the longitudinal phase space. This structure, consists of four nine cell TESLA-like cavities. For the use of this structure in combination with the TTF-FEL it might be interesting to investigate higher order modes (HOM) in the structure and their effect on the beam dynamics. The complexity of the structure, four nine cell cavities assembled with four input couplers and eight HOM-couplers, results in an extremely high numerical effort for full 3D modelling. Therefor Coupled S-Parameter Calculation (CSC) [1] has been applied. This method is based on the scattering parameter description of the rf components found with field solving codes or analytically for components of special symmetry. This paper presents the results of the calculation of rf properties (e.g. scattering parameters, Q-values) of the complete four times nine cell structure equipped with all input- and HOM-couplers.

[1] H.-W. Glock, K. Rothemund, U. van Rienen, CSC - A Procedure for Coupled S-Parameter Calculations, IEEE Trans. Magnetics, vol. 38, pp. 1173 - 1176, March 2002

 
 
MOP84 First Cryogenic Tests with JLab's new Upgrade Cavities* damping, coupling, impedance, pick-up 216
 
  • P. Kneisel, G. Ciovati, G. Myneni, G. Wu
    Jefferson Lab, Newport News, Virginia
  • J. Halbritter
    FZ Karlsruhe, Karlsruhe
  • J. Sekutowicz
    DESY, Hamburg
  For the upgrade of CEBAF to 12 GeV two types of 7-cell cavities have been developed: the High Gradient type (HG) has been optimized with respect to the ratio of Epeak/Eacc and for the Low Loss (LL) type the shunt impedance has been maximized. Each cavity type features four DESY type coaxial HOM couplers and a waveguide input coupler. Design goals for these cavities have been set to Eacc = 20 MV/m with a Q-value at 2.05 K of Q0 = 8·109. A niobium prototype of each cavity has been fabricated at JLab and in a first test the HG cavity has been evaluated at cryogenic temperatures after appropriate buffered chemical polishing. Data for Q(E) were taken at several temperatures after R(T) was measured during initial pump down. In addition the pressure sensitivity as well as the Lorentz force detuning were evaluated. The damping of approximately 20 High Order Modes was measured to verify the room temperature data. Measurements on the LL prototype are in progress. We present in this contribution a summary of measured results of tests we performed on the new proposed shapes of the upgrade cavities.  
 
WE102 State of the Art SRF Cavity Performance damping, linac, electron, coupling 518
 
  • L. Lilje
    DESY, Hamburg
  The paper will review superconducting RF cavity performance for β=1 cavities used in both linear and circular accelerators. These superconducting cavities are used in two kinds of applications: High current storage rings and efficient high duty cycle linacs. In recent years the performance of those cavities has been improving steadily. High accelerating gradients have been achieved using advanced surface preparation techniques like electropolishing and surface cleaning methods like high pressure water rinsing. High intensity beams can be handled with advanced higher-order-mode damping schemes.  
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