A high gain single stage gyrotron traveling-wave amplifier

A high gain gyrotron traveling-wave amplifier. experiment has been performed in which net linear gains exceeding 50 dB have been observed. The experiment, which operates at 35 GHz in the TE01circular-electric mode, uses a resistive wall waveguide for stabilization against both reflective instability due to feedback by reflections at the input and output couplers and absolute instability due to feedback by coupling to the backward traveling wave by the electron beam. A 70 kV annular electron beam with a perpendicular velocity to parallel velocity ratio of approximately 1.5 was used, with beam currents up to 3 amps. The experiment supports calculations in showing that bandwidth improvement occurs as an additional benefit of the lossy wall. Also, the gain reduction due to the lossy wall is about one third the cold tube loss implying that stability can be achieved without serious sacrifice of gain.