• S.V. Kuzikov, M.E. Plotkin
  IAP/RAS, Nizhny Novgorod

A new two-beam accelerating structure based on periodic chain of rectangular shape multi-mode cavities was suggested recently*. The structure is aimed to increase threshold breakdown surface field and thus to provide a high gradient. This threshold increase is to be brought about by designing cavities of the structure to operate simultaneously in several harmonically-related TMn,n,0 modes, thereby reducing the effective exposure time of the cavity surface to the peak fields. The more number of the operating modes is the more reduction of the exposure time. Unfortunately, a big amount of modes leads to limitation for cavity length and practical limitation of filling factor. In order to avoid this, it is suggested to operate with several TMn,n,l modes with non-zero longitudinal indices. These modes are able to provide the long interaction of a moving bunch with RF fields along the cavity. Such regime requires for the longitudinal index l to be strictly proportional the mode frequency. A cylindrical shape cavity design is also considered.

*S.V. Kuzikov, S.Yu. Kazakov, M.E. Plotkin, J.L. Hirshfield, High-Gradient Multi-Mode Two-Beam Accelerating Structure, Proc. of EPAC’08 Conf., Genoa, June 23-27, 2008, WEPP133.

• S.V. Kuzikov, A.A. Vikharev
  IAP/RAS, Nizhny Novgorod
• J.L. Hirshfield
  Yale University, Physics Department, New Haven, CT
• S. Kazakov
  Omega-P, Inc., New Haven, Connecticut

Funding: Sponsored in part by US Department of Energy, Office of High Energy Physics.

A multi-mode cavity design for a two-beam accelerator aimed to achieve an accelerating gradient exceeding 150 MeV/m is reported. The cavity has a square cross section which allows excitation in several equidistantly-spaced eigen modes by a bunched drive beam in such a way that the RF fields reach peak values only during time intervals that can be much shorter than for excitation of a single mode, thus exposing the cavity surfaces to strong fields for shorter times. This feature is expected to raise the breakdown and pulse heating thresholds. In order to measure an increase in breakdown threshold surface electric field due to this reduction of exposure time during each RF period, a high-power experiment is planned. Preliminary calculations show that such a study in which comparison of breakdown threshold would be made of a conventional single-mode cavity with a multi-mode cavity can in principle be carried out using the drive beam of the CTF-3 test stand at CERN.