Dynamics of Alfv\'en waves in partially ionized astrophysical plasmas

TL;DR

This paper presents a self-consistent 2D fluid model for Alfvén wave dynamics in partially ionized plasmas, revealing wave damping and energy transfer due to collisions with neutral atoms.

Contribution

It introduces a novel coupled fluid model that simultaneously describes plasma and neutral interactions, including non-adiabatic energy exchanges, in astrophysical plasmas.

Findings

Alfvén wave speed is reduced due to neutral collisions.

Energy transfer occurs between plasma and neutral fluids.

Wave damping is primarily caused by direct collisions.

Abstract

We develop a two dimensional, self-consistent, compressible fluid model to study evolution of Alfvenic modes in partially ionized astrophysical and space plasmas. The partially ionized plasma consists mainly of electrons, ions and significant neutral atoms. The nonlinear interactions amongst these species take place predominantly through direct collision or charge exchange processes. Our model uniquely describe the interaction processes between two distinctly evolving fluids. In our model, the electrons and ions are described by a single fluid compressible magnetohydrodynamic (MHD) model and are coupled self-consistently to the neutral fluid via compressible hydrodynamic equations. Both plasma and neutral fluids are treated with different energy equations that adequately enable us to monitor non adiabatic and thermal energy exchange processes between these two distinct fluids. Based on our self-consistent model, we find that the propagation speed of Alfvenic modes in space and astrophysical plasma is slowed down because these waves are damped predominantly due to direct collisions with the neutral atoms. Consequently, energy transfer takes place between plasma and neutral fluids. We describe the mode coupling processes that lead to the energy transfer between the plasma and neutral and corresponding spectral features.