Interpretation of complex patterns observed in the electron-cyclotron instability of a mirror confined plasma produced by an ECR discharge

A specific nonlinear regime of electron-cyclotron instability is discussed aimed at explaining the complex temporal patterns of stimulated electromagnetic radiation from a mirror trap with a non-equilibrium plasma typical of an ECR discharge. This regime is characterized by self-modulation of a plasma cyclotron maser due to coherent interference of two counter-propagating unstable waves with degenerate frequencies resulting in the spatial modulation of the amplification coefficient. The proposed simple theoretical model allows one to reproduce the multi-scale time behavior of quasiperiodic pulses of electromagnetic radiation and related precipitation of energetic electrons detected in a laboratory setup based on a magnetic mirror trap with a plasma sustained by mm-wave gyrotron radiation.