Simulation studies of nonlinear magnetosonic waves in a two-ion-species plasma

Abstract

Magnetosonic waves propagating perpendicular to a magnetic field in a plasma containing two ion species is studied. In a two-ion-species plasma there are two kinds of magnetosonic waves; low- and high-frequency modes. First, linear dispersion relations and Korteweg–de Vries (KdV) equations for these modes are briefly described. The KdV equation for the low-frequency mode is valid when the amplitudes ε are quite small, while that for the high-frequency mode is valid when (me/mi)1/2≪ε≪1, where me/mi is a measure of electron-to-ion mass ratios. Then, a one-dimensional, electromagnetic simulation code based on a three-fluid model is used to study evolution of a large-amplitude low-frequency mode and a small-amplitude high-frequency mode, which the KdV theory cannot deal with. It is found that, from a profile of a large-amplitude solitary wave of the low-frequency mode, short-wavelength solitary waves of the high-frequency mode can be generated. A small-amplitude solitary wave of the high-frequency mode produces long-wavelength perturbations behind the pulse. It leads to the gradual damping of the original pulse.