Electron multipacting in TESLA cavities and input couplers

Electron multipacting is a serious problem in many rf components operating in vacuum. The knowledge of the possible multipacting resonances is valuable when planning new rf designs and when struggling against multipacting in already existing structures. In this paper a detailed numerical analysis of electron multipacting in the TeV Energy Super-conducting Linear Accelerator (TESLA) cavities and coaxial input couplers with ceramic windows is presented. TESLA is an international linear collider R&D effort based on superconducting components. The input coupler design for TESLA has been developed at both DESY and FNAL. In the couplers (both DESY and FNAL type) the discussion is confined to the cylindrically symmetric cold window sections. In the cavities the well-known (two-point) multipacting phenomenon is verified and the computed values agree with the measured ones. In the couplers the situation is more involved, since the rf operation conditions vary and a large number of simulations are required for a complete multipacting analysis. It is found that the cylindrical DESY window design is less sensitive to multipacting than the conical FNAL window design. With the present analysis method it is possible to optimize the rf operation conditions in the DESY design so that multipacting can be avoided.