Magnetised turbulent plasmas as high-energy particle accelerators

TL;DR

This paper models particle acceleration in magnetised turbulent plasmas, showing that relativistic turbulence acts as an extreme accelerator through stochastic interactions with magnetic field structures, with implications for particle spectra.

Contribution

It introduces a theoretical framework linking kinetic simulation results to a generalized Fermi acceleration mechanism in relativistic turbulence.

Findings

Acceleration is dominated by magnetic field bends and velocity compression regions.

Acceleration rate distribution follows a broken power law.

Relativistic turbulence can produce very high-energy particles.

Abstract

This proceedings paper reports on the theoretical modelling of particle acceleration in magnetised turbulent plasmas. It briefly reviews some recent findings obtained from fully kinetic numerical simulations of large-amplitude, semi to fully relativistic turbulence. The paper then argues that these findings can be understood within the framework of a ``generalised Fermi'' picture of stochastic acceleration, which it summarises. The dominant contributions to acceleration appear to arise from particle interactions with sharp, dynamic bends of the magnetic field lines and regions of velocity compression. Interestingly, the acceleration rate is spatially inhomogeneous and its probability distribution follows a broken power law extending up to large values. This makes relativistic, large-amplitude turbulence an extreme particle accelerator. Some implications for particle transport and the shape of the particle energy spectrum in the presence of radiative losses and over long timescales are also discussed.