Numerical Simulation and Theoretical Analysis of Terahertz Sheet Beam TWTs Based on a Ridge-Loaded Folded Waveguide SWS

Abstract

Generation of terahertz (THz) radiation from an interaction between sheet electron beam with the electromagnetic wave in a smooth transition ridge-loaded folded waveguide (RFWG) structure is proposed in this article. It was found that in the structure the electric field density can be increased so that the average interaction impedance of the proposed circuit is higher than that of conventional sheet beam (SB) folded waveguide (FWG) circuit. According to the beam–wave simulation results, at a designed voltage of 13.1 kV and an electron beam current of 100 mA, a maximum output power of 91.13 W can be achieved, which corresponds to a power gain of 32.88 dB and an efficiency factor of 6.96%. Therefore, the smooth transition RFWG traveling wave tube (TWT) should be considered as a promising THz radiation source. Moreover, based on a recently published 3-D nonlinear theory for a SB FWG-TWT, a version of the 3-D large-signal frequency-domain nonlinear theory model representation for the proposed smooth-transition SB RFWG-TWT was developed. The code is orders of magnitude faster than, and nearly as accurate as, full 3-D particle-in cell (PIC) simulations.