Charge exchange in fluid description of partially ionized plasmas

TL;DR

This paper develops a fluid model for partially ionized plasmas considering charge exchange effects, revealing new wave propagation behaviors and predicting a 90-degree displacement rotation of Alfven waves across different solar atmospheric layers.

Contribution

A new momentum equation for weakly ionized plasmas incorporating charge exchange effects, enabling accurate modeling of wave propagation in partially ionized environments.

Findings

Low-frequency magnetic waves can propagate without particle magnetization.

The displacement plane of Alfven waves rotates by 90 degrees across solar atmospheric layers.

Accurate cross sections allow precise altitude determination for wave behavior changes.

Abstract

The effects of charge exchange on waves propagating in weakly ionized plasmas are discussed. It is shown that for low-frequency processes, ions and neutrals should be treated as a single fluid with some effective charge on all of them. We have derived a new momentum equation which should be used in such an environment. As a result, the low-frequency magnetic waves can propagate even if particles are not magnetized, which is entirely due to the charge exchange and the fact that it is not possible to separate particles into two different populations as charged and neutral species. So there can be no friction force between ions and neutrals in the usual sense. The mean force per particle is proportional to the ionization ratio $n_i/(n_i+ n_n)$. Regarding the application of the theory to the Alfven wave propagation in the lower solar atmosphere, the results predict that the plane of displacement of the fluid must change by 90 degrees when an Alfven wave propagates from the area where particles are un-magnetized (photosphere) to the area where they are magnetized (chromosphere). Because of the most accurate cross sections which we have here, it is possible to very accurately determine altitudes at which such rotation of the Alfven wave takes place.