Relativistic Particle Transport and Acceleration in Structured Plasma Turbulence

TL;DR

This paper investigates how relativistic particles gain energy in 3D plasma turbulence, revealing stochastic acceleration mechanisms and the role of large-scale structures in exponential energization, with implications for astrophysical phenomena.

Contribution

It demonstrates that turbulent plasma induces stochastic acceleration of relativistic particles and identifies conditions for exponential energization within large-scale structures.

Findings

Particles are accelerated via a second-order Fermi process.

Large-scale structures trap particles, leading to exponential acceleration.

Results are relevant for understanding astrophysical plasma turbulence.

Abstract

We discuss the phenomenon of energization of relativistic charged particles in three-dimensional (3D) incompressible MHD turbulence and the diffusive properties of the motion of the same particles. We show that the random electric field induced by turbulent plasma motion leads test particles moving in a simulated box to be accelerated in a stochastic way, a second-order Fermi process. A small fraction of these particles happen to be trapped in large-scale structures, most likely formed due to the interaction of islands in the turbulence. Such particles get accelerated exponentially, provided their pitch angle satisfies some conditions. We discuss at length the characterization of the accelerating structure and the physical processes responsible for rapid acceleration. We also comment on the applicability of the results to realistic astrophysical turbulence.