Superpower E-Beam Sources and Performance Estimates for Compact THz FELs

High peak and average power free-electron lasers (FELs) in the terahertz (THz) region require small-diameter, low-emittance, and high-voltage electron beams. This article presents two 1.5–2-MV, 100–200-A, thermionic cathode electron source approaches for compact megawatt range peak power, multikilowatt average power, high repetition rate, THz FELs. The preferred beam generation system includes grading electrodes and is quite compact compared to the other standard diode gun approaches. Both provide highly compressed beams at the waist having low values of normalized rms emittance. In particular, the new injector approach with grading electrodes, operating at a body voltage of 1.5–2 MV and 100 A, has a normalized rms emittance of roughly $10~\mu $ m at the beam waist. Power supply switching considerations are considered in this article as well as considerations for very high-voltage multistage depressed collectors for device efficiency enhancement. Based on these designs, we provide performance estimates for FELs operating in the THz spectral region.