Design of uniform permanent magnet electronic optical system for 220 GHz sheet electron beam traveling wave tube

The sheet electron beam (SEB), for which is the low current density and large current, is highly attractive in the region of millimeter wave and terahertz vacuum electronic devices (VEDs). A uniform permanent magnet (UPM) electronic optical system (EOS) driven by a SEB for 220 GHz traveling wave tube (TWT) is designed in present work, in which the voltage and current for SEB is 17 kV and 0.3 A, respectively. For obtaining the stable high transmission rate EOS, the characteristics of SEB in UPM EOS are studied, including the emittance, orbital angle, and beam trajectories, which are discussed through the CST simulation. The results show that the emittances in the x-direction are varied from 0.003 to 0.016 mm rad and in y-direction are various from 1 × 10^-4 to 3 × 10^-4 mm rad, respectively, keeping below than 2.5 × 10^-4 mm rad during transmission, which guarantees the stability of SEB in y-direction. For the design of complete EOS, the normal rectangular collector is used, in which the SEB is uniformed scattering.