Initial operation of a 1 MW, 140 GHz gyrotron

A 140 GHz gyrotron capable of powers in excess of 1 MW has recently been operated at MIT. This device is expected to achieve a total efficiency of 38% with an 80 kV, 35 A electron beam. Although operated with 3µsec pulses, the gyrotron can be scaled to cw operation. In the first set of experiments, a single cavity designed for the TEm,2,1modes was investigated. Stable operation was achieved in the TE5,2,1at 140.8 GHz. Output powers up to 645 kW were generated in this mode, with peak efficiencies of 24% Single mode emission was indicated by our frequency mixer system. In addition, other TEm,2,1modes ranging from the TE12,2,1at 119.2 GHz to the TE16,2,1at 147.9 GHz were strongly excited. Harmonic emission was detected at 219.4 GHz when operating at 4.56 T. A comparison of these results with self-consistent theory will be presented. Future experiments include an investigation of coaxial and multiple cavity configurations with reduced mode competition.