Improvements in depressed collector performance by modifications to electrode geometry vis-a-vis trajectories of backscattered electrons

Backscattering of electrons in depressed collectors has a significant effect on the collector efficiency and other performance parameters. We have studied these phenomena using our code BSCAT. It allows for tracking of multiple generations of backscatter by a representative set of trajectories without going to an excessively large number of them. By examining the trajectories and the impact angles of incoming rays, it is possible to modify the geometry of the electrodes, such that the effects of backscatter are minimized. In particular, we have studied the effects of using an undulating surface of the collector, and analyzed its effects taking into account the effect on angles of incidence of impacting rays. Using as a test vehicle a two-stage depressed collector for a 1.5-MW 110-GHz gyrotron, we have thus been able to increase the estimated collector efficiency from 62% to 65%. We present these results along with data on other performance parameters such as the heat-dissipation profile. We discuss the potential for application of the approach to other devices operating at different frequencies and power levels.