High-power operation of a 170 GHz megawatt gyrotron

Recent gyrotron oscillator experiments have achieved record powers at 170 GHz. Single mode emission with a peak output power of 1.5 MW and an efficiency of 35% has been measured. The experiment is based on a resonant TE28,8,1 cylindrical cavity situated in a 6.7 T magnetic field. Microwaves are generated in the cavity by an 83 kV annular electron beam produced by a triode-type magnetron injection gun that is capable of currents up to 50 A. Megawatt power levels with efficiencies between 30%–36% have been measured over a wide range of operating parameters for the TE28,8,1 mode. Similar results were also achieved in the neighboring TE27,8,1 mode at 166.6 GHz, and the TE29,8,1 mode at 173.5 GHz. The high output power is the result of a carefully designed electron gun with low perpendicular velocity spread (6%–10%) and a novel cavity with an output iris that is less prone to mode competition. These results are in good agreement with nonlinear multimode simulations.

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