Design of a new DC-RF injector used in high average power FEL

Here we give the design proposal of a new DC-RF injector used in high average power FEL. The injector includes a Pierce gun and a 1 + 1/2 SC cavity. It will be able to provide high average beam current because it can work in CW mode. By changing the shape of the first 1/2 cell of SC cavity to enforce the focusing effect, we can decrease the distance between photocathode and SC cavity. Thus, the growth of emittance can be suppressed effectively. Through the simulation of particle dynamics with PARMELA, the shape of Pierce gun and the optimized synchronous phase of the SC cavity can be decided. The simulation results show that this kind of injector is feasible.