Kinetic effects of dust size distribution on Alfvén waves in magnetized space plasmas

Abstract

Dust populations in space plasmas are often described by a size distribution function, generally a power law distribution. In view of that, we include this feature in the kinetic description of a homogeneous magnetized dusty plasma with electrically charged immobile dust grains, in order to study its effects in the propagation and damping of Alfvén waves. The dispersion relation is numerically solved using parameters typically found in the dust-driven stellar winds of carbon-rich stars and in Earth’s auroral acceleration region, two space systems with unalike plasma parameters and in which Alfvén waves are known to play important roles in the plasma acceleration and heating processes. We show that the characteristics of the normal modes, namely the ion cyclotron and whistler modes, will change when one considers a power law distribution of dust sizes in the theory, as compared to a mono-sized dust population; and that these differences will depend on the exponent p of the power law, which alters the plasma charge imbalance between electrons and ions. We also notice that power law distribution functions will modify the waves’ damping rate values. In particular, we show that in a stellar wind environment the ion cyclotron mode at very small wavenumber decreases with the reduction of p, while for higher wavenumber the damping of this mode increases with the reduction of p. For the Earth’s magnetosphere, the results obtained show that the wave damping increases with the decrease of p for all wavenumbers, for the parameters considered in the analysis.