The transport of cosmic rays in self-excited magnetic turbulence

TL;DR

This paper uses high-resolution simulations to study how self-generated magnetic turbulence affects cosmic ray diffusion, showing it can reduce the diffusion coefficient near the Bohm limit, impacting cosmic ray acceleration.

Contribution

It provides the first explicit demonstration that self-excited turbulence can lower the cosmic ray diffusion coefficient to near the Bohm limit.

Findings

Diffusion rate close to Bohm limit for various energies.

Self-excited turbulence reduces cosmic ray diffusion.

Implications for cosmic ray acceleration in supernova remnants.

Abstract

The process of diffusive shock acceleration relies on the efficacy with which hydromagnetic waves can scatter charged particles in the precursor of a shock. The growth of self-generated waves is driven by both resonant and non-resonant processes. We perform high-resolution magnetohydrodynamic simulations of the non-resonant cosmic-ray driven instability, in which the unstable waves are excited beyond the linear regime. In a snapshot of the resultant field, particle transport simulations are carried out. The use of a static snapshot of the field is reasonable given that the Larmor period for particles is typically very short relative to the instability growth time. The diffusion rate is found to be close to, or below, the Bohm limit for a range of energies. This provides the first explicit demonstration that self-excited turbulence reduces the diffusion coefficient and has important implications for cosmic ray transport and acceleration in supernova remnants.