Quasi-Current-Free Approximation in the Electrodynamics of a Hot Current-Carrying Collisionless Plasma

Abstract

To study slow electromagnetic processes of induction type in a hot collisionless nonmagnetized high-beta plasma near magnetic-reconnection regions, where the influence of eddy electric currents on magnetic-field configuration should be described self-consistently, we develop a kinetic description in the quasi-current-free (QCF) approximation, which includes the quasi-neutral approximation. The QCF approximation is valid for large-scale nonstationary processes if the scale of spatial inhomogeneity of the fields exceeds the scale of the diamagnetic current screening, the anomalous skin scale, and the polarization-screening scale. In this case, the diamagnetic currents are compensated by the conductivity currents. The equations of the QCF approximation for accelerated particles with narrow distribution functions are formulated as the MHD equations. To illustrate the method, we consider a one-dimensional problem on magnetic annihilation. The self-similar solution of this problem describes the relaxation of the current system typical for solar streamers and the tail of the Earth's magnetosphere.