Damping of Alfven waves in solar partially ionized plasmas: effect of neutral helium in multi-fluid approach

TL;DR

This study investigates how neutral helium influences the damping of Alfven waves in partially ionized solar plasmas using a multi-fluid MHD model, revealing that neutral helium significantly enhances wave damping under certain conditions.

Contribution

It introduces a three-fluid MHD approach to analyze the impact of neutral helium on Alfven wave damping in solar plasmas, an aspect previously largely unexplored.

Findings

Neutral helium significantly increases Alfven wave damping at specific temperatures.

Damping peaks near the ion-neutral collision frequency.

Ion-neutral helium collisions are important in chromospheric and prominence regions.

Abstract

Chromospheric and prominence plasmas contain neutral atoms, which may change the plasma dynamics through collision with ions. Most of the atoms are neutral hydrogen, but a significant amount of neutral helium may also be present in the plasma with a particular temperature. Damping of MHD waves due to ion collision with neutral hydrogen is well studied, but the effects of neutral helium are largely unknown. We aim to study the effect of neutral helium in the damping of Alfven waves in solar partially ionized plasmas. We consider three-fluid magnetohydrodynamic (MHD) approximation, where one component is electron-proton-singly ionized helium and other two components are the neutral hydrogen and neutral helium atoms. We derive the dispersion relation of linear Alfven waves in isothermal and homogeneous plasma. Then we solve the dispersion relation and derive the damping rates of Alfven waves for different plasma parameters. The presence of neutral helium significantly enhances the damping of Alfven waves compared to the damping due to neutral hydrogen at certain values of plasma temperature (10000-40000 K) and ionization. Damping rates have a peak near the ion-neutral collision frequency, but decrease for the higher part of wave spectrum. Collision of ions with neutral helium atoms can be of importance for the damping of Alfven waves in chromospheric spicules and in prominence-corona transition regions.