The operation of a megawatt gyrotron in the submillimeter wave region

The operation of a high-power, tunable gyrotron oscillator at wavelengths extending into the submillimeter-wave regime is reported. Using a 14-T Bitter magnet, frequencies from 141 GHz (TE/sub 15,2,1/ mode) up to 328 GHz (TE/sub 27,6,1/ mode) have been measured. As in earlier experiments, it was possible to step tune through a sequence of TE/sub m,p1/ modes over this range. From 198 GHz to 328 GHz, these modes corresponded to p=4, 5, and 6. Even though the cavity is highly overmoded at 328 GHz, output powers remain quite high, with a peak output power of 430 kW at 80 kV and 35 A. This corresponds to an efficiency of 15%. This is the highest power generated by a gyrotron in the submillimeter region. Even better results were obtained in the TE/sub 22,5,1/ mode at 267 GHz. A peak power of 600 kW was produced when operating at 80 kV and 35 A, for an efficiency of 21%. A detailed study of the TE/sub 16,2,1/ mode at 148 GHz has been made, and the beam parallel velocity was measured with a capacitive probe.<
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