Recent experimental results on a whispering-gallery-mode gyrotron

The development of gyrotron oscillators capable of generating output powers of 1 MW CW at a frequency of 140 GHz is described. The tubes use a simple, tapered interaction cavity in combination with a hollow electron beam to generate output power in the TE/sub 15.2/ whispering-gallery mode. The first experimental tube was designed to achieve pulse powers of 1 MW and 400 kW CW. In recent tests on this gyrotron, short-pulse power levels of 655 kW, 750 kW, and 820 kW have been obtained at beam voltages of 80 kV, 90 kV, and 95 kV, respectively. During operation at peak power levels at 350-400 kW, the duty factor has been raised to 10% (30 p.p.s., 3.33-ms pulse duration). Pulse durations of 10 ms have also been achieved in the same range of output power. Power losses in various parts of the tube have been measured and are in agreement with theoretical predictions. >