Excitation of large-amplitude Alfvén waves in a nonrelativistic electron–positron plasma with a temperature anisotropy T⊥>T∥

Abstract

Excitation of large-amplitude Alfvén waves in an anisotropic electron–positron plasma is investigated with a two-and-one-half-dimensional (212-D), electromagnetic particle code. If the plasma distribution is a bi-Maxwellian with T⊥/T∥>1, where the subscript symbols denote directions perpendicular and parallel to the ambient magnetic field, Alfvén waves with arbitrary polarization are generated. Simulations show that the amplitude of the waves increases both with increasing temperature anisotropy and parallel plasma β∥. The stabilization of individual wave modes occurs sequentially, from higher values of wave number down to lower ones, in the evolution of the temperature anisotropy instability. Wave–particle scattering by the enhanced waves maintains the initially bi-Maxwellian character throughout the simulation, even as it reduces T⊥ and increases T∥. After saturation of wave magnetic energy a large residual temperature anisotropy still remains and persists through the end of the simulation.