UC Davis 94 GHz Gyrotron Traveling-wave Amplifier Development

During the past year, record performance has been obtained at W-Band from the University of California, Davis TE01 proof-of-principle gyro-TWT: 75 kW output, 45 dB gain, 22.5 % efficiency, and 3.7 % saturated bandwidth (BW) at 93.5 GHz. We report the design and fabrication of a new follow-on ultra high gain (71 dB) gyro-TWT (thereby permitting the direct use of a MMIC driver) producing 110 kW output at 5 % BW (with design rules consistent with 10% duty) with the focus on advanced millimeter wave radars. The existing gun and solenoid will be used, but the entire circuit and collector will be replaced by the new design. The work is proceeding in two stages. First, we will maintain the saturated gain at the current level (45 dB) and fabricate an interaction circuit intended for operation at full design parameters (e.g. 110 kW, 5% BW, stable) with the rf brought straight out of the tube in the TE01 mode. There will be an uptaper from the interaction waveguide to an output waveguide of larger radius, which will also serve as the collector. Following these initial experiments, we will proceed to the ultra high gain case where the gain level would permit use of a solid state driver.