This paper mainly designs a high-power FEL injector system, which has a low-emittance electron gun using a gridded thermionic cathode. The distance between the anode and the RF cavity exit is designed to be as short as possible in the manufacturing level. In the process of optimizing the electron gun, simulation by CST STUDIO SUITE is mainly conducted on the effects of the shape, hole spacing, wire size, and thickness of the grid on the electron beam’s emittance, particle passing rate and so on. Therefore, the optimal parameters of the electron gun, especially the structure of the grid and the grid bias voltage, are obtained, generating a uniformly distributed current with current intensity of 0.5 A, the pulse length of 1 ns, and a normalized root mean square emittance of 1.6 mm∙mrad. In order to reduce the increase in emittance caused by the space charge effect in the low energy region, a -50 kV electron gun is connected to a 476 MHz sub-harmonic buncher through a drift section with the solenoid. The optimization in Parmela resulted in excellent longitudinal phase space, beam spot size, and emittance of the electron beam at the injector exit.

injector,electron gun,sub-harmonic buncher,CST STUDIO SUITE,Parmela