• P.K. Ambattu, G. Burt, R.G. Carter, A.C. Dexter
  Cockcroft Institute, Lancaster University, Lancaster
• V.A. Dolgashev
  SLAC, Menlo Park, California
• R.M. Jones, V.F. Khan
  UMAN, Manchester

Funding: The work is supported by STFC

A crab cavity is required in the CLIC to allow effective head-on collision of bunches at the IP. A high operating frequency (X-band) for the crab cavity is preferred as the deflection voltage required and the RF phase tolerance are inversely proportional to the operating frequency. However, the strong inter-bunch wakefields deteriorate the quality of the colliding bunches. The short bunch spacing of the CLIC scheme and the crab cavity's high sensitivity to dipole kicks demands very high damping of the inter-bunch wakes. A crab cavity requires special attention to the damper design as its wakefield spectrum is entirely different from that of an accelerating cavity. In addition to the higher-order modes, the orthogonally polarised dipole mode (same order mode) and the fundamental monopole mode (lower order mode) also need to be damped, however their resonant frequencies make damping these modes complicated. The same order mode suppression requires the use of an azimuthally asymmetric damper. This paper investigates the nature of the wakefields in the CLIC crab cavity and the possibility of using choke-mode damping and various types of waveguide damping to suppress them effectively.

• P. Goudket, S.C. Appleton, R. Bate, C.D. Beard, B.D. Fell, J.-L. Fernandez-Hernando, P.A. McIntosh, S.M. Pattalwar
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
• P.K. Ambattu, G. Burt, A.C. Dexter, B.D.S. Hall, M.I. Tahir
  Cockcroft Institute, Lancaster University, Lancaster

The ILC crab cavities require very tight phase control in order to operate within the ILC parameters. In order to verify that the phase control system met the design tolerances, two single-cell niobium 3.9GHz superconducting dipole-mode cavities were tested in a liquid helium cryostat. The preparation of the cavities, design of the testing apparatus and performance of the phase control system are described in this paper.