Effects of external reflections on gyrotron backward wave oscillators

The gyrotron backward-wave oscillator is sensitive to external reflections because it employs a nonresonant interaction structure. These reflections may result in serious output power variations and frequency pulling. A numerical model is developed for the investigation of the reflection effects. It treats beam-wave interactions in the presence of external reflections. As a new feature of the formalism, external reflections are self-consistently determined by the structures, rather than artificially set as a constant value as in previous models. The model has been employed to examine the effects of long-line reflection on the tunable bandwidth and start-oscillation conditions of the gyro-BWO. Results will be presented in the paper.