Nonstationary and chaotic behavior of the electron cyclotron maser

The gyrotrons based on the electron cyclotron maser instability generally have very complicated nonlinear behavior due to the intrinsic distributed interaction nature. We focus on the single-mode nonstationary behavior, called self-modulation, by proposing a model to analyze its route to chaos as the beam current rises. This model provides the basis for an in-depth understanding of some interesting nonlinear processes and their implications. The puzzling effect of the alternatingly appearing stationary and nonstationary zones is elucidated through the RF-field forming process and is found to be a common property of gyrotron oscillators. The evolution of nonlinear phenomena from bifurcation to chaos is clearly demonstrated for the gyromonotron, which agrees well with the experimental results. However, for the gyro-BWO nonlinear field, contraction reduces the feedback strength and thus significantly raises the nonstationary threshold. Reasons for superior stability of gyro-BWO to that of gyromonotron are discussed. A time-dependent self-consistent code is independently used to examine the real-time chaotic behavior of the oscillation.