Nonlinear Analysis of Low-Frequency Oscillations in Gyrotrons

Low-frequency oscillations (LFOs) had been observed in many gyrotron experiments. These oscillations are believed to be caused by electrons trapped in the region between the electron gun and the cavity. A 1-D numerical simulation method is developed to analyze the self-consistent accumulation and bunching caused by the space-charge field of these trapped electrons. Velocity spread and loss mechanisms for the trapped electrons are taken into account. The threshold conditions for excitation, the spatial character, and the nonlinear evolution of the LFOs are analyzed and interpreted. The numerical simulation results agree with some experimental data.