A filamentation instability for streaming cosmic-rays

TL;DR

This paper demonstrates that cosmic rays create filamentary magnetic structures upstream of supernova remnant shocks, leading to a large-scale instability that enhances magnetic field amplification and cosmic ray acceleration.

Contribution

It introduces a novel filamentation instability driven by cosmic rays, linking small-scale magnetic amplification to larger scales through self-generated structures.

Findings

Cosmic rays form filamentary structures due to self-generated magnetic fields.

The filamentation leads to a long wavelength instability.

Large-scale magnetic fields facilitate cosmic ray scattering and escape.

Abstract

We demonstrate that cosmic rays form filamentary structures in the precursors of supernova remnant shocks due to their self-generated magnetic fields. The cosmic-ray filamentation results in the growth of a long wavelength instability, and naturally couples the rapid non-linear amplification on small scales to larger length scales. Hybrid magnetohydrodynamics--particle simulations are performed to confirm the effect. The resulting large scale magnetic field may facilitate the scattering of high energy cosmic rays as required to accelerate protons beyond the knee in the cosmic-ray spectrum at supernova remnant shocks. Filamentation far upstream of the shock may also assist in the escape of cosmic rays from the accelerator.