Modeling Magnetic Field Amplification in Nonlinear Diffusive Shock Acceleration

TL;DR

This paper presents a numerical model of collisionless shocks that self-consistently couples magnetic field amplification with particle acceleration, helping to explain strong magnetic fields observed in supernova remnants.

Contribution

It introduces a Monte Carlo simulation framework that integrates analytic plasma instability models with nonlinear shock acceleration, providing new insights into magnetic turbulence and particle energization.

Findings

Magnetic field amplification can significantly increase maximum particle energies.

The model predicts efficient particle acceleration in strong shocks.

Turbulence spectra can be used to estimate nonthermal emission.

Abstract

This research was motivated by the recent observations indicating very strong magnetic fields at some supernova remnant shocks, which suggests in-situ generation of magnetic turbulence. The dissertation presents a numerical model of collisionless shocks with strong amplification of stochastic magnetic fields, self-consistently coupled to efficient shock acceleration of charged particles. Based on a Monte Carlo simulation of particle transport and acceleration in nonlinear shocks, the model describes magnetic field amplification using the state-of-the-art analytic models of instabilities in magnetized plasmas in the presence of non-thermal particle streaming. The results help one understand the complex nonlinear connections between the thermal plasma, the accelerated particles and the stochastic magnetic fields in strong collisionless shocks. Also, predictions regarding the efficiency of particle acceleration and magnetic field amplification, the impact of magnetic field amplification on the maximum energy of accelerated particles, and the compression and heating of the thermal plasma by the shocks are presented. Particle distribution functions and turbulence spectra derived with this model can be used to calculate the emission of observable nonthermal radiation.