Nonstationary behavior of the gyrotron backward-wave oscillator

Nonstationary processes in the gyrotron backward-wave oscillator (gyro-BWO) are investigated numerically using a time-dependent self-consistent model which allows the authors to study multifrequency operation of the device. The results indicate that the behavior of the gyro-BWO is strongly influenced by higher order axial modes (HOMs) whose excitation results from an increase in gyro-BWO beam current or structure length. In both cases, the gyro-BWO behavior changes from stationary to nonstationary, however, in different ways. Furthermore, the influence of HOM's excitation on the gyro-BWO efficiency and its output signal spectrum is analyzed. Moreover, a comparative study of two regimes of operation-the gyro-BWO and the gyromonotron-is conducted and the obtained results are compared to experiments.