Generation of a High Current Density and High Compression Ratio Beam for THz TWT

In the terahertz (THz) band, electron beam quality significantly influences beam-focused transmission and beam-wave interaction, and the compressive electric field distribution determines it. This article introduces a stepped-conical (SC) electron gun optimized to improve beam laminarity. Compared with the traditional single-stage (SS) gun, the SC gun reduces velocity dispersion by 36.9%, resulting in a 55.3% reduction in population velocity standard deviation ( $\sigma $ ). Under a 0.67-T uniform magnetic (UM) field focusing, both beams achieve transmissions over 99% within a 40- $\mu $ m-radius, 80-mm-length beam tunnel. Verified through CST particle-in-cell (PIC) simulations, the hot transmission of the SC gun-based beam could maintain an over 99% transmission ratio, while the SS gun decreased to 95.6%. Under the 1-mW input signal, the SS gun-based beam amplifies the signal by 40 dB in the slow wave structure (SWS) circuit, yielding an output power of 400 mW. In contrast, the SC gun-based beam achieves a gain of 48 dB and an output power of 900 mW, representing a 112.8% improvement. The high-quality electron beam generated by the SC electron gun not only enhances the transmission efficiency of ultrafine electron beams but also significantly improves the gain and power output of the THz traveling-wave tubes (TWTs).