• V. Akcelik, K. Ko, L. Lee, Z. Li, C.-K. Ng, L. Xiao
  SLAC, Menlo Park, California

Funding: Work supported by DOE contract DE-AC02-76SF00515.
The shape deviation of a SRF cavity from the design shape may result in significant impact on cavity performance and wakefields that could lead to unexpected effects in beam dynamics. Yet, most of these deviations are unknown in the final cavity installation because of the complicated process of assembly and tuning. It is desirable to be able to uncover such distortions using measurable rf quantities. With these data, the cavity performance can be analyzed and realistic tolerance criteria may be implemented in the cavity design and manufacture for quality assurance. To perform such analyses, SLAC has developed advanced Shape Determination Tools, under the SciDAC support for high performance computing, that recover the real cavity shape by solving an inverse problem. These tools have been successfully applied to analyze shape distortions to many SRF cavities, and identified the cause of unexpected cavity behaviors. The capabilities and applications of these tools will be presented.

• J.K. Sekutowicz, G. Ciovati, P. Kneisel
  JLAB, Newport News, Virginia
• L. Xiao
  SLAC, Menlo Park, California

Funding: This manuscript has been authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Higher Order Modes generated by a particle beam passing through a superconducting accelerating cavity have to be damped to avoid beam instabilities. A coaxial coupler located in the beam pipes of the cavities provides for better propagation of HOMs and strong damping in appropriate HOM dampers. The whole damping device can be designed as a detachable system. If appropriately dimensioned, the rf currents can be minimized at the flange position. Additionally, the coaxial system also provides efficient coupling of fundamental mode rf power into the superconducting cavity. Compared to presently available solutions for HOM damping, this scheme provides for several advantages: stronger HOM damping, flangeable solution, exchangeability of the HOM damping device on a cavity, less complexity of the superconducting cavity, possible cost advantages. This contribution will describe the results of room temperature measurement and discuss modeling, which resulted in an optimized layout of a cavity-coupler system.

• G. Burt, P.K. Ambattu, R.G. Carter, A.C. Dexter, M.I. Tahir
  Cockcroft Institute, Lancaster University, Lancaster
• C. Adolphsen, Z. Li, A. Seryi, L. Xiao
  SLAC, Menlo Park, California
• C.D. Beard, D.M. Dykes, P. Goudket, A. Kalinin, L. Ma, P.A. McIntosh
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
• L. Bellantoni, B. Chase, M. Church, T.N. Khabiboulline
  Fermilab, Batavia
• R.M. Jones
  UMAN, Manchester
• A. Latina, D. Schulte
  CERN, Geneva

Crab cavities have been proposed for a wide number of accelerators and interest in crab cavities has recently increased after the successful operation of a pair of crab cavities in KEK-B. In particular crab cavities are required for both the ILC and CLIC linear colliders for bunch alignment. Consideration of bunch structure and size constraints favours a 3.9 GHz superconducting, multi-cell cavity as the ILC solution, whilst bunch structure and beam-loading considerations suggest an X-band copper travelling wave structure for CLIC. These two cavity solutions are very different in design but share complex design issues. Phase stabilisation, beam loading, wakefields and mode damping are special issues for these crab cavities. Requirements and potential design solutions will be discussed for both colliders.