Group velocity of obliquely propagating Alfv\'en waves in a magnetized dusty plasma

TL;DR

This study analyzes how dust particles in a magnetized plasma influence the group velocity of Alfvén waves, revealing significant modifications in wave propagation directions due to dust parameters and radiation effects.

Contribution

It provides a kinetic theory-based numerical analysis of group velocities of oblique Alfvén waves in dusty plasmas, highlighting the impact of dust density, charge, and radiation on wave behavior.

Findings

Group velocity of compressional Alfvén waves is greatly affected by wave-vector direction.

Shear Alfvén waves propagate mainly along the magnetic field with minimal deviation.

High dust-to-ion density ratios can cause perpendicular group velocities to oppose phase velocities.

Abstract

In this work we investigate the characteristics of the group velocity of obliquely propagating Alfv\'en waves in a dusty plasma typical of a stellar wind. The dispersion relation is derived with the aid of the kinetic theory for a magnetized dusty plasma consisting of electrons and ions, with distribution of momenta described by a Maxwellian function. The dust particles are considered to be immobile and have all the same size; they are electrically charged by absorption of plasma particles via inelastic collisions and by photoionization. We numerically solve the dispersion relation and calculate the components of group velocity (along and transverse to the magnetic field) for the normal modes, namely the compressional and shear Alfv\'en waves (CAW and SAW). The results show that the direction of the group velocity of CAWs is greatly modified with the wave-vector direction. On the other hand, SAWs will present group velocity propagating practically along the magnetic field. The changes in dust parameters, such as number density and equilibrium electrical charge, may significantly change the waves' characteristics. It is seen that for sufficiently high dust to ion number density ratio, the SAWs may present perpendicular group velocity propagating in opposite direction to the perpendicular phase velocity, in a small interval of wavenumber values; we also notice that this interval may change, or even vanish, when the flux of radiation incident on the dust is altered, changing the equilibrium electrical charge of the grains.