Novel Energy Relaxation Properties of Strongly Magnetized Plasmas*

A model is developed to describe energy relaxation processes in strongly magnetized plasmas, characterized by having at least one species for which the cyclotron frequency greatly exceeds the plasma frequency. This is an unusual and challenging regime for kinetic theory because the gyro orbits of particles must be accounted for in the binary collision dynamics. We construct a simplified model for the particle trajectories in the strong magnetic field limit, based on characterizing collisions as either reflections or pass through based on their initial kinetic energies and the maximum potential energy along a 1D trajectory. The change of a generalized momentum perpendicular to the magnetic field is determined by numerically solving a single initial value problem for a 1D trajectory. All other properties are solved iteratively from this, including the change of energies parallel and perpendicular to the magnetic field, and the scattering of the gyrocenter coordinates. Results of the simplified trajectory models are used in a recently developed kinetic equation for strongly magnetized plasma to compute energy relaxation processes. Results are compared with full-orbit calculations and with molecular dynamics simulations. Novel energy transport properties are observed, including enhanced relaxation rates between electrons and ions, and extreme suppression of energy relaxation in one-component systems.