Calculation of the external quality factor of the high power input coupler for the BEPCII superconducting cavity

It is very important to predict the coupling between the cavity and the high power input source in the coupler design. In this paper, a time domain method is used to calculate the external quality factor Q(ext) for the BEPC II superconducting cavity. A comparison between simulation results and experimental results is presented. The results of simulation and measurement of Q(ext) have a good agreement within an error of 10%. The geometry parameters related with Q(ext) are also studied.