Electron acceleration in the magnetosphere

The mechanisms of auroral electron acceleration are studied by two particle simulation models. The first model is a two-dimensional hybrid-kinetic description used to study the self consistent electron kinetics of Alfven waves on the electron inertial scale. The ions are assumed to follow a fluid description and the parallel electron motion is treated kinetically using particle-in-cell techniques. In this model the electron plasma mode is eliminated and only the physics of the Alfven waves is retained. For a cold plasma, it is found that oblique Alfven waves break due to finite electron inertia. The consequence of wave breaking is the formation of an electron beam which can be unstable to the beam-plasma instability. The electrons supporting the parallel current thermalize into a non-Maxwellian distribution with an energetic tail up to several keV, assuming a reasonable magnetospheric Alfven speed. In hot plasma simulations, electron trapping is the principal mechanism of electron acceleration. It is proposed that wave breaking or electron trapping of oblique Alfven waves at 1 {dollar}Rsb{lcub}E{rcub}{dollar} can result in electron acceleration and may explain some observed auroral phenomena. The second model is a two-dimensional high frequency magnetized electron plasma particle code, which is used to investigate the parametric coupling of electromagnetic modes to the upper-hybrid and electrostatic whistler modes. A large amplitude X-mode generated by auroral kilometric radiation is shown to excite the electrostatic whistler wave and Z-mode by a parametric instability. The parallel electric field of the electrostatic whistler wave can cause the wave to break and pitch angle scatter electrons into the loss cone. This may account for the electron precipitation of diffuse aurora.