High Average Current Electron Guns for High-Power FELs

High average power FELs require high average current electron injectors capable of generating high quality, short duration electron bunches with a repetition rate equal to the frequency of the rf linac. In this paper we propose, analyze and simulate an rf-gated, gridded thermionic electron gun for use in high average power FELs. Thermionic cathodes can provide the necessary high current, have long life times and require modest vacuums. In the proposed configuration the rf-gated grid is modulated at the fundamental and 3 harmonic of the linac frequency. The addition of the 3 harmonic on the grid results in shorter electron bunches. In this configuration, every rf bucket of the linac accelerating field contains an electron bunch. PIC simulations indicate that this approach can provide the necessary charge per bunch, bunch duration, longitudinal and transverse emittance, and repetition rate for high average power FELs operating in the IR regime. 1. Icarus Research, Inc 2. National Research Council Postdoctoral Fellow