SUPPRESSION OF HOMs IN A MULTICELL SUPERCONDUCTING CAVITY FOR CORNELL’S ERL*

Minimization of power of higher order modes (HOMs) in a multicell cavity was done using derivatives of the parameter defining losses with respect to geometric parameters of the cavity cells. For the Cornell Energy Recovery Linac most dangerous are dipole modes causing beam break-up (BBU). As a start point of optimization the shape with minimal losses at the fundamental mode was taken. Further changing the shape for better propagation of HOMs was done with degradation of the fundamental mode loss parameter ) ( Q GR within 1 % while decrease of the BBU parameter was nearly 3 orders of magnitude. The BBU threshold current tends to be inversely proportional to this parameter.