Damping of Alfv\'{e}n waves in MHD turbulence and implications for cosmic ray streaming instability and galactic winds

TL;DR

This paper investigates how Alfvénic turbulence dampens Alfvén waves, affecting cosmic ray propagation and galactic winds, by comparing different damping mechanisms and their astrophysical implications.

Contribution

It provides a detailed comparison of turbulent damping of streaming instability versus plane wave damping and contrasts these with ion-neutral damping.

Findings

Turbulent damping significantly affects cosmic ray streaming.

Ion-neutral damping dominates at low ionization fractions.

Numerical tests support the theoretical analysis.

Abstract

Alfv\'{e}nic component of MHD turbulence damps Alfv\'{e}nic waves. The consequences of this effect are important for many processes, from cosmic ray (CR) propagation to launching outflows and winds in galaxies and other magnetized systems. We discuss the differences in the damping of the streaming instability by turbulence and the damping of a plane parallel wave. The former takes place in the system of reference aligned with the local direction of magnetic field along which CRs stream. The latter is in the reference frame of the mean magnetic field and traditionally considered in plasma studies. We also compare the turbulent damping of streaming instability with ion-neutral collisional damping, which becomes the dominant damping effect at a sufficiently low ionization fraction. Numerical testing and astrophysical implications are also discussed.