Depressed collector experiments on a quasioptical gyrotron

A simple, single-stage depressed collector has been tested on the quasioptical gyrotron (QOG) experiment at the Naval Research Laboratory (NRL). This is the first application of a depressed collector to a high-power gyrotron, and was relatively easily accomplished due to the natural separation of the electron beam and the output radiation in the QOG. Collector efficiencies as high as 50% and overall efficiencies up to 16% were observed. The output power reached 431 kW with an overall efficiency of 13% and a collector efficiency of 41%. The collector efficiency was limited in this experiment due to interception of approximately 15% of the electron beam on an undepressed section of the beam guide, a problem readily correctable with a small change in the beam guide dimensions. If this part of the electron beam was collected at the collector potential, the overall and collector efficiencies would increase to 16% and 55%, respectively. The maximum collector efficiency would increase to 58% (at high output power) and the best overall efficiency would increase to 20% (at lower output power).