A new low-frequency backward mode in inhomogeneous plasmas

TL;DR

This paper investigates a novel low-frequency backward mode in inhomogeneous plasmas caused by the coupling of electromagnetic and electrostatic waves due to density gradients, revealing new wave behaviors in electron-ion and pair plasmas.

Contribution

It introduces a new low-frequency backward wave mode resulting from electromagnetic-electrostatic coupling in inhomogeneous plasmas, expanding understanding of plasma wave dynamics.

Findings

Discovery of a new low-frequency backward mode.

Modification of ion acoustic waves due to coupling.

Analysis of wave behavior in electron-ion and pair plasmas.

Abstract

When an electromagnetic transverse wave propagates through an inhomogeneous plasma so that its electric field has a component in the direction of the background density gradient, there appears a disbalance of charge in every plasma layer, caused by the density gradient. Due to this some additional longitudinal electric field component appears in the direction of the wave vector. This longitudinal field may couple with the usual electrostatic longitudinal perturbations like the ion acoustic, electron Langmuir, and ion plasma waves. As a result, these standard electrostatic waves are modified and in addition to this a completely new low-frequency mode appears. Some basic features of the coupling and modification of the ion acoustic wave, and properties of the new mode are discussed here, in ordinary electron-ion and in pair plasmas.