Electrostatic solitary waves in an electron-positron pair plasma with suprathermal electrons

A Danehkar

doi:10.1063/1.5000873

Abstract

The nonlinear propagation of electrostatic solitary waves is studied in a collisionless electron-positron pair plasma consisting of adiabatic cool electrons, mobile cool positrons (or electron holes), hot suprathermal electrons described by a κ distribution, and stationary ions. The linear dispersion relation derived for electrostatic waves demonstrates a weak dependence of the phase speed on physical conditions of positrons in appropriate ranges of parameters. The Sagdeev's pseudopotential approach is used to obtain the existence of electrostatic solitary wave structures, focusing on how their characteristics depend on the physical conditions of positrons and suprathermal electrons. Both negative and positive polarity electrostatic solitary waves are found to exist in different ranges of Mach numbers. As the positrons constitute a small fraction of the total number density, they slightly affect the existence domains. However, the positrons can significantly change the wave potential at a fixed soliton speed. The results indicate that the positive potential can largely be grown by increasing the electron suprathermality (lower κ) at a fixed true Mach number. It is found that a fraction of positrons maintain the generation of positive polarity electrostatic solitary waves in the presence of suprathermal electrons in pair plasmas.

Highlights

Electron-positron (e-p) pair plasmas are present in many astrophysical environments such as the solar wind [1,2,3,4,5,6], the Earth’s magnetosphere [7, 8], pulsars [9, 10], and microquasars [11]
It is important to study the occurrence of electrostatic solitary wave structures in e-p pair plasmas with suprathermal electrons, which may lead to theexistence of positive and negative polarity electrostatic waves similar to what observed in the Earth’s magnetosphere [34, 35], as well as a possible explanation for coherent pulsar radio emissions [45]
We aim to explore the effect of mobile cool positrons on electrostatic solitary waves in an e-p pair plasma with suprathermal electrons

Summary

INTRODUCTION

Electron-positron (e-p) pair plasmas are present in many astrophysical environments such as the solar wind [1,2,3,4,5,6], the Earth’s magnetosphere [7, 8], pulsars [9, 10], and microquasars [11]. It was proposed that coherent pulsar radio emissions could be due to nonlinear electrostatic solitary oscillations generated by effective electron-positron streams on the polar caps in rotating magnetized neutron stars [45]. It is important to study the occurrence of electrostatic solitary wave structures in e-p pair plasmas with suprathermal electrons, which may lead to the (co-)existence of positive and negative polarity electrostatic waves similar to what observed in the Earth’s magnetosphere [34, 35], as well as a possible explanation for coherent pulsar radio emissions [45]. Our results are summarized in the concluding section VI

THEORETICAL MODEL

LINEAR DISPERSION RELATION

NONLINEAR ANALYSIS

NONLINEAR WAVE STRUCTURES

CONCLUSIONS