Oblique propagation and nonlinear wave particle processes

Abstract

The wave-particle interaction plays a fundamental role in plasma physics; it is an energy momentum exchange mechanism between particles and waves. The most fundamental examples treated in the literature address the interaction of a single wave propagating along a background magnetic field with a single ion or electron. In the present paper we propose to investigate this specific problem, but this time we take into account the fact that the electromagnetic wave propagates obliquely with respect to the background field. The obliqueness manifests itself in the appearance of a parallel component in the electric field which in turn impacts the dynamics of the charged particle it interacts with and provides a mechanism of acceleration. This parallel component of the electric field can trap or untrap particles. The parallel propagation case is recovered automatically by setting the angle of propagation with respect to the background magnetic field to zero. A simple, yet complex, dynamical system is derived and limiting cases are treated analytically while numerical integration is used to investigate the general cases. We find that physical trapping occurs for a class of initial conditions and that phase space trapping (pitch angle versus gyrophase for example) remains in some cases a signature of the dynamical system. Copyright 2006 by the American Geophysical Union.