The saturation of the Bell instability and its implications for cosmic ray acceleration and transport

TL;DR

This paper develops a covariant theory for the saturation of the Bell instability, which is essential for understanding magnetic field amplification and cosmic ray acceleration in various astrophysical environments.

Contribution

It introduces a new covariant theoretical framework for the Bell instability saturation, supported by kinetic simulations applicable to diverse cosmic ray distributions.

Findings

The theory accurately predicts the saturation level of the Bell instability.

Simulations confirm the theory's applicability across different astrophysical scenarios.

Implications for cosmic ray acceleration and transport are discussed.

Abstract

The non-resonant (Bell) streaming instability driven by energetic particles is crucial for producing amplified magnetic fields that are key to the acceleration of cosmic rays (CRs) in supernova remnants, around Galactic and extra-galactic CR sources, and for the CR transport. We present a covariant theory for the saturation of the Bell instability, substantiated by self-consistent kinetic simulations, that can be applied to arbitrary CR distributions and discuss its implications in several heliospheric and astrophysical contexts.