Time-dependent behavior of the gyrotron backward-wave oscillator

Summary form only given, as follows. Nonstationary oscillations of the gyrotron backward-wave oscillator (gyro-BWO) have been studied with time-dependent simulation and were found to be the major reason for the erratic frequency tuning. In a uniform waveguide, the nonstationary oscillations exhibit self-modulation behavior while displaying no evidence of axial mode competition. But in an interaction structure with tapered sections, high order axial modes could be serially excited before gyro-BWO reaches its stationary state or cause its nonstationary oscillations. These different types of nonstationary oscillations are comparatively studied and the marginal conditions for the stationary operation of gyro-BWO will be presented in the paper.