RF characters study of the 1.3 GHz 4-cell TESLA cavity for the CAEP THz-FEL facility

A superconducting accelerator module is developed for the CAEP THz-FEL facility, which contains two 1.3GHz 4-cell TESLA-type cavities. This paper presents the microwave properties study of the 4-cell cavity. The microwave parameters of the cavity were simulated, such as frequencies, R/Q values, and HOM passbands etc. The most harmful mode types have been identified according to simulation results. And the frequency and field flatness of the fundamental mode were adjusted to satisfy the operation requirement. The Qe of the pickup port and the HOM coupler ports were measured by microwave measurement at room temperature. The measurement techniques and results are revealed in this paper.