Alfven Waves in Partially Ionised Solar Steady-State Plasmas

TL;DR

This paper explores how steady plasma flows influence Alfvén wave propagation and damping in partially ionised solar plasmas, revealing flow-induced modifications and new wave modes through analytical and numerical methods.

Contribution

It introduces a two-fluid model with steady flows to analyze Alfvén waves in partially ionised plasmas, highlighting flow effects on wave behavior and mode conversion.

Findings

Steady flows cause Doppler shifts and propagation reversal of Alfvén waves.

Flow-dependent damping rates are identified, affecting wave energy dissipation.

A new mode associated with neutral flow and collisional coupling is discovered.

Abstract

Our study investigates the properties of Alfv\'en waves in partially ionised solar plasmas in the presence of steady, field-aligned, flows of charged and neutral particles. Our work aims to understand how such flows modify wave propagation and damping in environments where ion-neutral collisions are significant. We employ a two-fluid model that treats ions and neutrals as separate, colliding fluids and incorporates background steady flows for both species. Using a combination of analytical dispersion analysis and numerical solutions, we examine the impact of these flows on the behaviour of Alfv\'en waves. Our results show that steady flows lead to substantial modifications of wave properties, including Doppler shifts, propagation direction reversal, flow-dependent changes in damping rates, and the appearance of a new mode associated with neutral flow and collisional coupling. We also identify conditions under which flow-driven mode conversion can arise. Our results offer new insights into the interplay between plasma flows and particle collisions in the regions of the solar atmosphere where partial ionisation is relevant.