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May, J.

Paper Title Page
THOAC03 Measurement of the Beam's Trajectory Using the Higher Order Modes it Generates in a Superconducting Accelerating Cavity 2642
  • S. Molloy, J. C. Frisch, J. May, D. J. McCormick, M. C. Ross, T. J. Smith
    SLAC, Menlo Park, California
  • N. Baboi, O. Hensler, R. Paparella, L. M. Petrosyan
    DESY, Hamburg
  • N. E. Eddy, L. Piccoli, R. Rechenmacher, M. Wendt
    Fermilab, Batavia, Illinois
  • O. Napoly, C. Simon
    CEA, Gif-sur-Yvette
  Funding: US DOE Contract #DE-AC02-76SF00515

It is well known that an electron beam excites Higher Order Modes (HOMs) as it passes through an accelerating cavity~[panofsky68]. The properties of the excited signal depend not only on the cavity geometry, but on the charge and trajectory of the beam. It is, therefore, possible to use these signals as a monitor of the beam's position. Electronics were installed on all forty cavities present in the FLASH~[flashref] linac in DESY. These electronics filter out a mode known to have a strong dependence on the beam's position, and mix this down to a frequency suitable for digitisation. An analysis technique based on Singular Value Decomposition (SVD) was developed to calculate the beam's trajectory from the output of the electronics. The entire system has been integrated into the FLASH control system.

slides icon Slides  
THPMS049 Investigations of the Wideband Spectrum of Higher Order Modes Measured on TESLA-style Cavities at the FLASH Linac 3100
  • S. Molloy, C. Adolphsen, K. L.F. Bane, J. C. Frisch, Z. Li, J. May, D. J. McCormick, T. J. Smith
    SLAC, Menlo Park, California
  • N. Baboi
    DESY, Hamburg
  • N. E. Eddy, L. Piccoli, R. Rechenmacher
    Fermilab, Batavia, Illinois
  • R. M. Jones
    UMAN, Manchester
  Funding: US DOE Contract #DE-AC02-76SF00515

Higher Order Modes (HOMs) excited by the passage of the beam through an accelerating cavity depend on the properties of both the cavity and the beam. It is possible, therefore, to draw conclusions on the inner geometry of the cavities based on observations of the properties of the HOM spectrum. A data acquisition system based on two 20 GS/s, 6 GHz scopes has been set up at the FLASH facility, DESY, in order to measure a significant fraction of the HOM spectrum predicted to be generated by the TESLA cavities used for the acceleration of its beam. The HOMs from a particular cavity at FLASH were measured under a range of known beam conditions. The dipole modes have been identified in the data. 3D simulations of different manufacturing errors have been made, and it has been shown that these simulations can predict the measured modes.

FRPMS049 Resolution of a High Performance Cavity Beam Position Monitor System 4090
  • S. Walston, C. C. Chung, P. Fitsos, J. Gronberg
    LLNL, Livermore, California
  • S. T. Boogert
    Royal Holloway, University of London, Surrey
  • J. C. Frisch, S. Hinton, J. May, D. J. McCormick, S. Smith, T. J. Smith, G. R. White
    SLAC, Menlo Park, California
  • H. Hayano, Y. Honda, N. Terunuma, J. Urakawa
    KEK, Ibaraki
  • Yu. G. Kolomensky, T. Orimoto
    UCB, Berkeley, California
  • P. Loscutoff
    LBNL, Berkeley, California
  • A. Lyapin, S. Malton, D. J. Miller
    UCL, London
  • R. Meller
    Cornell University, Department of Physics, Ithaca, New York
  • M. C. Ross
    Fermilab, Batavia, Illinois
  • M. Slater, M. Thomson, D. R. Ward
    University of Cambridge, Cambridge
  • V. Vogel
    DESY, Hamburg
  International Linear Collider (ILC) interaction region beam sizes and component position stability requirements will be as small as a few nanometers. It is important to the ILC design effort to demonstrate that these tolerances can be achieved – ideally using beam-based stability measurements. It has been estimated that RF cavity beam position monitors (BPMs) could provide position measurement resolutions of less than one nanometer and could form the basis of the desired beam-based stability measurement. We have developed a high resolution RF cavity BPM system. A triplet of these BPMs has been installed in the extraction line of the KEK Accelerator Test Facility (ATF) for testing with its ultra-low emittance beam. A metrology system for the three BPMs was recently installed. This system employed optical encoders to measure each BPM's position and orientation relative to a zero-coefficient of thermal expansion carbon fiber frame and has demonstrated that the three BPMs behave as a rigid-body to less than 5 nm. To date, we have demonstrated a BPM resolution of less than 20 nm over a dynamic range of ± 20 microns.