Design of a chopper system in a compact THz-FEL facility

An independently tunable cell gun of Huazhong University of Science and Technology Free Electron Laser Terahertz facility has an imperfect performance in longitudinal bunching. The long beam tail not only wastes microwave power and leads to the deterioration of beam quality, but also be a serious threat to the security and stability of the facility. A chopper system based on rectangular deflector is designed to solve these problems. This paper analyzes the principle of chopper system to eliminate tail particles. The beam dynamics simulation was carried out by particle tracking software Parmela, the particles whose phase is after 48° are cut off, and the correctness of the theoretical results was verified. Last but not least, the cavity is manufactured and the measurement of bead perturbation is investigated. The deflecting field distribution on the central axis of the cavity obtained by bead perturbation is compared with the CST simulation result.