Preliminary measurement of a novel 140 GHz gyro-TWT amplifier

Summary form only given. We have designed and are currently building a novel gyro-TWT amplifier to operate at 100 kW and a frequency of 95 GHz. However, due to equipment availability in our laboratory, the amplifier will actually be operated at a frequency of 140 GHz. The electron beam will be provided by an existing MIG electron gun which has been previously used in gyrotron oscillator research at 100 kW power level at 140 GHz. The gun operates at 65 kV and up to 8A with a velocity ratio of 1.5. The novel wave circuit consists of two facing mirrors with confocal profiles in the transverse direction and flat profiles in the longitudinal direction. The mode is Gaussian-like in the transverse direction. This design effectively reduces the mode competition problem in conventional amplifiers from two dimensional to one dimensional. Another advantage of this circuit is the relatively large cavity size, which improves power capacity. Calculations indicate that the linear gain is about 2.7 dB/cm with an efficiency exceeding 20%. An experiment using an oscillator configuration has also been designed. Preliminary experimental results including cold tests will be presented at the conference.