140-GHz gyrotron with multimegawatt output power

The operational features of a 140-GHz, transverse electric TE/sub 22,6/ mode gyrotron oscillator with an advanced quasi-optical mode converter, a Brewster window, and a single-stage depressed collector at 140 GHz with an output power of 2.1 MW and an efficiency of 34% without depressed collector and 53% with depressed collector are presented. The high output power level is possible due to an almost reflectionless termination of the radio frequency (RF) beam line outside the tube. The operation of the TE/sub 22,6/ mode gyrotron is described in detail, and the significant features for achieving the high-output power are pointed out.