Study of RF-asymmetry in photo-injector

In this paper, the RF-asymmetry existing in the full cell of the BNL/SLAC/UCLA 1.6 cell type photo-injector has been investigated. The fields of the multi-pole modes have been analyzed respectively, and lastly, a simple and reliable technique is presented to eliminate the dipole mode with the RF-asymmetry induced by dipole mode. In the process of simulation, the time domain module of CST Microwave Studio is mainly used as the tool to calculate the electro-magnetic fields. The FFT technique is employed to conduct frequency domain analysis for the fields. The results of FFT are utilized to estimate emittance growth induced by higher multi-pole modes, according to the framework of Panofsky–Wenzal theorem. Based on the above analysis, efforts have been made to eliminate dipole fields by modifying the length of vacuum port on the opposite side of RF-coupling port.