Effects of dust particles charged by inelastic collisions and by photoionization on Alfv\'en waves in a stellar wind

TL;DR

This study investigates how dust particle charging mechanisms, including inelastic collisions and photoionization, influence Alfvén wave propagation and damping in stellar wind plasmas, revealing mode coupling and charge-dependent damping effects.

Contribution

It introduces a kinetic model analyzing the impact of photoionization and inelastic collisions on Alfvén waves in dusty stellar winds, highlighting mode coupling and charge-related damping variations.

Findings

Alfvén mode decouples into whistler and ion cyclotron modes with negatively charged dust.

Mode coupling occurs for certain wavenumbers when dust is neutral or positively charged.

Photoionization reduces the maximum wavenumber for wave propagation.

Abstract

Using a kinetic description of a homogeneous magnetized dusty plasma with Maxwellian distribution of electrons and protons and dust particles charged by inelastic collisions and by photoionization, we analyse the dispersion relation considering the case where waves and radiation propagate exactly parallel to the ambient magnetic field. The investigation emphasizes the changes that the photoionization process brings to the propagation and damping of the waves in a stellar wind environment, since Alfv\'en waves are believed to play a significant role in the heating and acceleration processes that take place in the wind. The results show that, in the presence of dust with negative equilibrium electrical charge, the Alfv\'en mode decouples into the whistler and ion cyclotron modes for all values of wavenumber, but when dust particles acquire neutral or positive values of electrical charge, these modes may couple for certain values of wavenumber. It is also seen that the whistler and ion cyclotron modes present null group velocity in a interval of small wavenumber, and that the maximum value of wavenumber for which the waves are non-propagating is reduced in the presence of the photoionization process. For very small values of wavenumber, the damping rates of the modes could change significantly from very small to very high values if the sign of the dust electrical charge is changed.