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 valuabl e 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 Accelerato r (TESLA) cavities and coaxial input couplers with ceramic windows is prese nted. TESLA is an international linear collider R&D effort based on superco nducting components. The input coupler design for TESLA has been developed at both DESY and FNAL. In the couplers (both DESY and FNAL type) the discus sion is confined to the cylindrically symmetric cold window sections. In th e cavities the well-known (two-point) multipacting phenomenon is verified a nd the computed values agree with the measured ones. In the couplers the si tuation is more involved, since the rf operation conditions vary and a larg e number of simulations are required for a complete multipacting analysis. It is found that the cylindrical DESY window design is less sensitive to mu ltipacting than the conical FNAL window design. With the present analysis m ethod it is possible to optimize the rf operation conditions in the DESY de sign so that multipacting can be avoided.