Particle-In-Cell simulations of circularly polarised Alfven wave phase mixing: a new mechanism for electron acceleration in collisionless plasmas

摘要

Particle-In-Cell simulations of a circularly polarised Alfven wave interaction with one dimensional, across the uniform magnetic field, plasma density inhomogeneity (phase mixing) in collisionless plasmas were performed. In our preliminary work (Tsiklauri et al. 2004, astro-ph/0409537) we reported discovery of a new electron acceleration mechanism. In this mechanism, progressive distortion of Alfven wave front, due to the differences in local Alfven speed, generates oblique (nearly parallel to the magnetic field) electrostatic fields, which accelerate electrons through the Landau resonance. Here we report detailed study of this novel effect, including analysis of broadening of ion distribution function due to the presence of Alfven waves and the generation of compressive perturbations due to weak non-linearity and plasma density inhomogeneity. The amplitude decay law in the inhomogeneous regions, in the kinetic regime, is shown to be the same as in the MHD approximation described by Heyvaerts and Priest (1983).