Design of an asymmetric multi-stage depressed collector for terahertz traveling wave tubes

The multi-stage depressed collector (MDC) plays an important role in the terahertz traveling wave tube (TWT) for recovering spent electron beam, which has significant impact on its working total efficiency. For the purpose of improving the efficiency of the whole tube, the designscheme method of a depressed collector with non-axisymmetric structure in terahertz TWT is proposed. The axisymmetric depressed collector for terahertz TWT is designed by analyzing the energy characteristics of spent electron beam after beam-wave interaction, and then on-axisymmetric structure is used for optimization. The results of three-dimensional particle simulation (PIC) show that for the TWT with the three-stage axisymmetric MDC, the optimal recovery efficiency is 79.30%, electron reflux rate is 3.12%, and the working efficiency is 4.47% when considering the secondary electron emission. For the TWT with the three-stage non-axisymmetric MDC, the recovery efficiency increases to 89.50%, the particle reflux rate decreases to 0.53%, and the whole tube working efficiency reaches 8.38%. The working efficiency of the whole tube can be increased effectively by taking the asymmetric structure.