High efficiency operation of a 140 GHz pulsed gyrotron

Abstract

The operating characteristics of a 140 GHz pulsed gyrotron are reported. Total efficiencies of 36% and output powers of 175 kW have been obtained in single-mode operation. Measurements of power and efficiency have been made for a variety of modes between 120 and 160 GHz, and these results are in good agreement with predictions based on non-linear theory. The best results have been obtained with isolated asymmetric modes, such as the TE_{4, 2, 1} (127·3 GHz), TE_{2, 3, 1},(136·7 GHz) and TE_{3, 3, 1}(155·6 GHz). Although mode competition was found to prevent the TE_{0, 3, 1}, mode (139·5 GHz) from reaching the optimum operating conditions, an output power of 138 kW and total efficiency of 29% were achieved with this mode. A variety of new and highly accurate diagnostic techniques that have been developed to measure the power, frequency and mode content of the output radiation are reviewed. In addition, the operating characteristics of both laminar and non-laminar magnetron injection guns are compared. The high powers and efficiencies obtained in this experiment are promising for the extension of gyrotron output powers to the megawatt range.