Theory and experiment of ultrahigh-gain gyrotron traveling wave amplifier

Physics and technology issues of importance to the high-gain gyrotron trave ling wave amplifier (gyro-TWT) are investigated in theory and experiment. T he gyro-TWT is known to be highly susceptible to spurious oscillations, esp ecially in high gain operations. In the current study, oscillations of vari ous origins are classified and characterized with detailed theoretical mode ling. They are shown to be intricately connected to the interplay between t he absolute/convective instabilities, circuit losses, and reflective feedba ck. Knowledge of these processes leads to the concept of an ultra high gain scheme which employs distributed wall losses for the suppression of spurio us oscillations. A proof-of-principle Ka-band gyro-TWT experiment stable at zero drive has produced 93 kW saturated peak power at 26.5% efficiency and 70 dB gain, with a 3 dB saturated output power bandwidth of 3 GHz, The sat urated gain is more than 30 dB beyond that previously achieved.