Diffusive shock acceleration and magnetic field amplification

TL;DR

This paper reviews theories of magnetic field amplification driven by cosmic ray streaming instabilities, crucial for explaining high-energy particle acceleration at shocks.

Contribution

It synthesizes recent developments over the past decade on how cosmic ray streaming induces magnetic field amplification in shock environments.

Findings

Cosmic ray streaming induces instabilities that amplify magnetic fields.

Magnetic field amplification is essential for efficient diffusive shock acceleration.

Recent theoretical advances clarify the mechanisms of magnetic field growth.

Abstract

Diffusive shock acceleration is the theory of particle acceleration through multiple shock crossings. In order for this process to proceed at a rate that can be reconciled with observations of high-energy electrons in the vicinity of the shock, and for cosmic rays protons to be accelerated to energies up to observed galactic values, significant magnetic field amplification is required. In this review we will discuss various theories on how magnetic field amplification can proceed in the presence of a cosmic ray population. On both short and long scales, cosmic ray streaming can induce instabilities that act to amplify the magnetic field. Developments in this area that have occurred over the past decade are the main focus of this paper.