A 0.5 MW quasi-optical gyrotron experiment

The quasi-optical gyrotron is under development at the Naval Research Laboratory as a source for fusion plasma heating. Early experiments with a 24 A, 75 kV electron gun produced output powers up to 150 kW and efficiencies up to 12%. Single-mode operation was observed at powers up to 125 kW despite the resonator being highly overmoded. One drawback of this experiment was the use of a resonator with relatively low output coupling (necessitated by the low electron beam power) resulting in a resonator with comparable output and ohmic loses. The ohmic losses can be reduced to a small fraction of the total resonator losses through the combined use of a higher-power electron beam and a resonator with larger output coupling. Such an experiment has been assembled and began producing data in June 1989. The high-power electron gun has been run at voltages up to 106 kV and currents up 54 A, which produced 515 kW of power at approximately 120 GHz. The output efficiency peak of 15.4% occurred at an electron gun voltage of 88 kV and current of 16 A, corresponding to 220 kW of output power