Effect of window reflection on gyrotron operation

A simple nonlinear theoretical model is developed to study the effects of small reflections from gyrotron output windows on gyrotron operation. The results obtained from this model show that when the product of the reflection coefficient and the delay time is small enough the gyrotron oscillates stably, and the output frequency will vary smoothly with changes in the cold cavity frequency. When the product is large, however, the output frequency jumps when the cold cavity frequency changes. Further, the reflection can, under certain conditions, cause the gyrotron to become unstable and the output frequency will have a spectrum that either consists of periodically spaced discrete lines, a dense set of narrow lines, or even a broadband spectrum. The width of this spectrum is inversely proportional to the delay time.