Experimental study of megawatt gyrotrons

Results will be presented from recent megawatt gyrotron experiments operating between 100 and 300 GHz. Powers up to 1.3 MW have been obtained in a high-Q tapered cavity at 148 GHz, and with a two-section cavity at 140 GHz. In both cases efficiencies of 40% were achieved. We have also measured the beam velocity spread using a retarding potential diagnostic. The measured perpendicular velocity spread was typically between ±10% and ±15% for velocity ratios between 1.5 and 2.0. The spread was larger at higher beam currents. Good agreement was also obtained between two separate measurements of the velocity ratio. A new experiment at 110 GHz has been assembled and is now operational. This device produces power in the TE _22,6,1 mode, and has an internal mode converter to convert the RF power into a Gaussian output beam. Initial experiments have produce powers up 0.4 MW at 110.2 GHz