Vlasov Simulations of Electron-Ion Collision Effects on Damping of Electron Plasma Waves

TL;DR

This study uses Vlasov simulations to analyze how electron-ion collisions influence the damping of electron plasma waves, revealing that the collision-induced damping is about half of what fluid theory predicts, with implications for plasma wave dynamics.

Contribution

It provides the first detailed comparison between Vlasov simulations and linear kinetic theory on collision effects on EPWs, highlighting a significant discrepancy with fluid theory predictions.

Findings

Electron-ion collisions contribute about half the damping rate predicted by fluid theory.

Vlasov simulations show good agreement with linear kinetic theory for damping rates.

The grid-based Vlasov approach accurately measures wave damping without numerical noise.

Abstract

Collisional effects can play an essential role in the dynamics of plasma waves by setting a minimum damping rate and by interfering with wave-particle resonances. Kinetic simulations of the effects of electron-ion pitch angle scattering on Electron Plasma Waves (EPWs) are presented here. In particular, the effects of such collisions on the frequency and damping of small-amplitude EPWs for a range of collision rates and wave phase velocities are computed and compared with theory. Both the Vlasov simulations and linear kinetic theory find the direct contribution of electron-ion collisions to wave damping is about a factor of two smaller than is obtained from linearized fluid theory. To our knowledge, this simple result has not been published before. Simulations have been carried out using a grid-based (Vlasov) approach, based on a high-order conservative finite difference method for discretizing the Fokker-Planck equation describing the evolution of the electron distribution function. Details of the implementation of the collision operator within this framework are presented. Such a grid-based approach, which is not subject to numerical noise, is of particular interest for the accurate measurements of the wave damping rates.