CW operation of a 140 GHz gyrotron†

Abstract

The results of tests on a Varian 140 GHz CW gyrotron are presented. In initial pulse tests on the tube, an output power of 100 kW was achieved at 28% efficiency in the desired TEU⁰ ₀₃₁ cavity mode. Under CW operating conditions, the tube achieved an output power level of 75 kW at 31% efficiency. This is the highest CW power level ever obtained at a frequency above 100 GHz in a microwave tube. During CW tests, measurements of the ohmic losses in the interaction circuit were made and the temperature of the output window was monitored. These measurements, as well as those of the output power and efficiency, are presented and compared with theoretical predictions. Future experimental 140 GHz tubes will employ alternate electron gun and interaction cavity designs. The benefits of these design changes are discussed in the context of achieving higher output power levels and efficiencies.