The numerical analysis of higher-order modes for superconducting rf cavity at SRRC

The beam current in the storage ring at Taiwan Light Source (TLS) is limited by the longitudinal coupled-bunch instabilities and the available rf power. Two Doris cavities are currently used for particle acceleration in the storage ring at TLS. The higher-order modes (HOMs) from Doris cavities are the major source of longitudinal impedance in the storage ring at TLS. In order to increase the electron beam current in the storage ring, a superconducting (SC) rf cavity developed by Cornell University will be installed to replace those two Doris cavities. The property of HOMs of SC rf cavity is obtained from numerical simulations by using a three-dimensional parallel code GdfidL. The preliminary results show that the storage ring at TLS will not suffer from the longitudinal coupled-bunch instabilities for a beam current not exceeding 450 mA.