Damping of Alfven waves by Turbulence and its Consequences: from Cosmic-Rays Streaming to Launching Winds

TL;DR

This paper analyzes how turbulence dampens Alfven waves in magnetized plasmas, affecting cosmic-ray streaming and wind launching, with analytical damping rates across different turbulence regimes and astrophysical implications.

Contribution

It provides analytical expressions for Alfven wave damping rates in various turbulence regimes and explores their astrophysical consequences, including cosmic-ray propagation and wind launching.

Findings

Weak turbulence affects a broad range of cosmic-ray energies in subAlfvenic regimes.

Strong Alfvenic turbulence limits the energy range impacted by damping.

Turbulent damping influences cosmic-ray isotropy in the Milky Way.

Abstract

This paper considers turbulent damping of Alfven waves in magnetized plasmas. We identify two cases of damping, one related to damping of cosmic rays streaming instability, the other related to damping of Alfven waves emitted by a macroscopic wave source, e.g. stellar atmosphere. The physical difference between the two cases is that in the former case the generated waves are emitted in respect to the local direction of magnetic field, in the latter in respect to the mean field. The scaling of damping is different in the two cases. We the regimes of turbulence ranging from subAlfvenic to superAlfvenic we obtain analytical expressions for the damping rates and define the ranges of applicability of these expressions. Describing the damping of the streaming instability, we find that for subAlfvenic turbulence the range of cosmic ray energies influenced by weak turbulence is unproportionally large compared to the range of scales that the weak turbulence is present. On the contrary, the range of cosmic ray energies affected by strong Alfvenic turbulence is rather limited. A number of astrophysical applications of the process ranging from launching of stellar and galactic winds to propagation of cosmic rays in galaxies and clusters of galaxies is considered. In particular, we discuss how to reconcile the process of turbulent damping with the observed isotropy of the Milky Way cosmic rays.