Author: Bergstrom, J.C.
Paper Title Page
WEP119 Coherent Radiation in Whispering Gallery Modes 1710
 
  • R.L. Warnock
    SLAC, Menlo Park, California, USA
  • J.C. Bergstrom
    CLS, Saskatoon, Saskatchewan, Canada
 
  Funding: Work at SLAC: U.S. Department of Energy Contract No. DE-AC03-76SF00515 Work at CLS: NSERC, NRC, Province of Saskatchewan, U. of Saskatchewan.
Theory predicts that CSR in storage rings should appear in whispering gallery modes *, which are resonances of the entire vacuum chamber and are characterized by their high frequencies and concentration of the field near the outer wall of the chamber. The theory assumes that the chamber is a smooth circular torus. We observe that a power spectrum from the NSLS-VUV ring **, which has a vacuum chamber in bends like that of the model, shows a series of sharp peaks with frequencies close to those of the theory. Sharp peaks are also seen in highly resolved spectra at the Canadian Light Source***, and those are invariant in position under large changes in the machine setup (energy, fill pattern, bunch length, CSR bursting or steady, optical beam line, etc.). Invariance of the spectrum suggests that it is due to resonances like whispering gallery modes, but they must be strongly perturbed from the circular case because of large outer wall excursions at the two IR ports.
* R. L. Warnock and P. Morton, Part. Accel. 25, 113 (1990).
** G. L. Carr et al., Proc. PAC 2001, Chicago.
*** T. May et al., IEEE 33rd Intl. Conf. IR Millimeter and THz Waves, 2008.