Coupling of "cold" electron plasma wave via stationary ion inhomogeneity to the plasma bulk

TL;DR

This study investigates how stationary ion inhomogeneities couple with long-wavelength electron plasma waves using kinetic and fluid models, revealing mode coupling dynamics, the validity of Bessel function scaling, and effects of system size on phase mixing time.

Contribution

It introduces a detailed analysis of mode coupling between electron plasma waves and stationary ion inhomogeneity, including the scaling laws and finite size effects using both kinetic and fluid simulations.

Findings

Mode coupling dynamics between EPW and ion inhomogeneity are illustrated.

Bessel function scaling validity is confirmed in cold plasma approximation.

Finite system sizes significantly affect phase mixing time scaling.

Abstract

Using high resolution kinetic (VPPM-OMP 1.0) and fluid (BOUT++) solvers, evolution of long-wavelength electron plasma wave (EPW) in the presence of stationary periodic ion background non-uniformity is investigated. Mode coupling dynamics between long-wavelength EPW mode of scale k and ion inhomogeneity of scale $k_{0}$ is illustrated. Validity of well known Bessel function $J_{n}(x)$ scaling in the cold plasma approximation (i.e., when phase velocity $\omega /k >> v_{thermal}$) along-with the effect of ion inhomogeneity amplitude (A) on temporal evolution of energy density in the long-wavelength EPW mode is investigated. Effect of finite system sizes on the Bessel $J_{n}(x)$ scaling is examined and scaling law for $\tau_{FM}$ i.e the time required to attain first minimum of energy density of the corresponding perturbed mode (also called phase mixing time for $k \sim 0$ modes) versus ion inhomogeneity amplitude A obtained from both kinetic and fluid solutions for each of the cases studied, along-with some major differences in $\tau_{FM}$ scaling for small system sizes is also reported.