Practical Thermal and Structural Simulations for Performance Improvement of Electron Gun in TWTs

Low-perveance electron guns are highly desired in high-efficiency space TWTs mainly due to the low operating beam current. In a low-perveance electron gun, the distance between the cathode and beam-forming electrode (BFE) plays a critical role in achieving laminar electron beam flow with the required specifications. It is an extremely sensitive parameter that gets affected by minor variations in the dimensions occurring due to thermal expansion. Hence, thermal and structural simulations are carried out to back-calculate the distance at which the cathode must be placed from the BFE during fabrication under cold conditions. In this article, the authors have presented the development of two electron guns–one developed based on the ideal simulation results and for the other one, the practical brazing conditions were considered in the simulations. Both the guns were integrated with TWTs, and their performances were evaluated under the same operating voltages and magnetic focusing conditions. It has been observed that the electron gun fabricated based on practical simulation conditions performed well with a low helix interception current. In contrast, the other gun had poor performance with a high helix interception current. Hence, it experimentally validates the fact that simulation considering the practical brazing scenario has resulted in precise back-computation of the cathode-BFE distance and hence better beam transmission characteristics of the tube.