Modeling the Saturation of the Bell Instability Using Hybrid Simulations

TL;DR

This paper investigates the saturation mechanism of the Bell instability, a key process in cosmic ray acceleration near supernova remnants, using hybrid simulations to predict magnetic field amplitudes.

Contribution

It provides the first systematic study of the saturation of the non-resonant streaming instability with hybrid simulations, linking plasma and cosmic ray parameters to magnetic field saturation.

Findings

Identifies how plasma and CR parameters influence magnetic field saturation.

Provides insights into CR acceleration and diffusion processes.

Offers a predictive framework for magnetic field amplitudes in astrophysical shocks.

Abstract

The nonresonant cosmic ray instability, predicted by Bell (2004), is thought to play an important role in the acceleration and confinement of cosmic rays (CRs) close to supernova remnants. Despite its importance, the exact mechanism responsible for the saturation of the instability has not been determined, and there is no first-principle prediction for the amplitude of the saturated magnetic field. Using a survey of self-consistent kinetic hybrid simulations (with kinetic ions and fluid electrons), we study the saturation of the non-resonant streaming instability as a function of the parameters of both the thermal background plasma and the CR population. The strength of the saturated magnetic field has important implications for both CR acceleration in supernova remnants and CR diffusion in the Galaxy.