Dissipative Ion-Acoustic Solitary Waves in Magnetized κ-Distributed Non-Maxwellian Plasmas

Sharmin Sultana,Ioannis Kourakis

doi:10.3390/physics4010007

Abstract

The propagation of dissipative electrostatic (ion-acoustic) solitary waves in a magnetized plasma with trapped electrons is considered via the Schamel formalism. The direction of propagation is assumed to be arbitrary, i.e., oblique with respect to the magnetic field, for generality. A non-Maxwellian (nonthermal) two-component plasma is considered, consisting of an inertial ion fluid, assumed to be cold for simplicity, and electrons. A (kappa) κ-type distribution is adopted for the electron population, in addition to particle trapping taken into account in phase space. A damped version of the Schamel-type equation is derived for the electrostatic potential, and its analytical solution, representing a damped solitary wave, is used to examine the nonlinear features of dissipative ion-acoustic solitary waves in the presence of trapped electrons. The influence of relevant plasma configuration parameters, namely the percentage of trapped electrons, the electron superthermality (spectral) index, and the direction of propagation on the solitary wave characteristics is investigated.

Highlights

The occurrence of highly energetic particles is a ubiquitous feature in space plasmas and in laboratory plasmas [1,2,3,4,5,6,7,8,9,10,11,12]
The velocity distribution in such plasmas may deviate from the usual thermal Maxwellian distribution, developing a long-tail for high-velocity arguments due to an excess in the fast part of the population; such a behavior is effectively modeled by a κ-type distribution function [1,4,12,13,14,15,16,17,18,19]
Particle “trapping”, i.e., the fact that a portion of, for example, the electron population remains confined in a finite region— generating vortices—in phase space, is an intrinsic characteristic of plasma dynamics, often overlooked in studies based on basic fluid theory

Summary

Introduction

The occurrence of highly energetic particles is a ubiquitous feature in space plasmas (e.g., in the ionosphere, the auroral zone, solar wind, and at the mesosphere, etc.) and in laboratory plasmas [1,2,3,4,5,6,7,8,9,10,11,12]. The combined effect of electron superthermality and phase-space trapping was first considered by Williams et al [40], who adopted the Schamel equation approach to model and characterize ion-acoustic solitary waves in an unmagnetized electron-ion plasma with κ-distributed electron populations subject to trapping. There is no rigorous and systematic study of the nonlinear propagation of the ion-acoustic waves in a magnetized collisional plasma in the presence of trapped κ-nonthermal electrons. The investigation at hand is an attempt to fill in this gap by presenting a rigorous and systematic study of the characteristics of ion-acoustic waves propagating in a magnetized κ-nonthermal plasma [41], taking into account the combined impact of electron trapping and of a suprathermal electron distribution, in account of the inherent plasma collisionality. The results obtained are summarized in the concluding Section 5

Basic Plasma-Fluid-Dynamic Formalism

Parametric Analysis

Conclusions