Acceleration and heating of heavy ions by circularly polarized Alfvén waves

Abstract

We study the dispersion relation of left‐hand‐polarized Alfvén waves in multicomponent plasmas. If initially the plasma components are not drifting relative to each other, the Alfvén waves propagate until they meet the gyrofrequency of the species with the largest M l = m l / z l m p value ( m l is the ion mass, z l is the degree of ionization, and m p is the proton mass). As a result of resonance absorption, these ions are heated and accelerated by quasi‐linear resonant interaction. When these ions reach a given velocity, the dispersion relation of the Alfvén waves changes drastically. The Alfvén branch of the dispersion relations no longer goes to the gyrofrequency of the ion species with the largest M l value, but it goes to the gyrofrequency of the species with the second largest M l value. In this way, more and more channels open up. We apply these results to high‐speed solar wind streams, and we argue that Alfvén waves generated in coronal holes or in nearby regions can heat and accelerate heavy ions.