Microwave Heating and Cyclotron Instability of Hot Electron Plasmas

摘要

A relativistic theory of electron heating to high energies by narrow-band microwaves directed into a spatially limited region of plasma is formulated. A novel feature of the analysis is its prediction regarding the motion of electrons along field lines. Specifically, the phase space of trapped electrons is found to be divided into two parts. In one, as an electron gains energy its turning point moves towards the region of weaker magnetic field; in the other, energy gain results in the turning point moving towards the region of strong magnetic field, with possible detrapping. For field amplitudes well above the threshold for intrinsic stochasticity in the coherent microwaves, a Fokker-Planck equation for the particle distribution is derived, and the steady-state solution for energetic particles reduced to quadrature. Electron cyclotron instabilities, brought about by the energetic population, induce diffusion of electrons and tend to deform the microwave-generated distribution. The distribution function under the joint action of heating and instability is derived. Superadiabaticity of particle motion is discussed. The dispersion relation for the cyclotron waves provides a relationship between the energy density in the microwaves and that in the saturated state of the cyclotron fluctuations. (ERA citation 12:015171)