Design of a Three-stage Depressed Collector for 220 GHz Travelling Wave Tubes

In this paper, a three-stage depressed collector is designed to improve the overall efficiency of a 220 GHz sheet beam travelling wave tube (SB-TWT). The collection efficiency and back-streaming current are two key indicators for a depressed collector. By analyzing the position and energy distribution of the spent electron beam observed at the end of the high-frequency system, the collector shape and electrode voltage are designed by using Computer Simulation Technology (CST). The optimized voltages applied to the three electrodes are −26779 V, −27937 V, and −29950 V, respectively. To simulate the performance of the collector in a more realistic situation, the Furman model is used as the secondary electron emission model in the design. CST Simulation results show that the collection efficiency is 96.1% and 95.2%, and the back-streaming rate is 0.008% and 0.02% for the case without and with considering secondary electrons, respectively.