First-principles Fermi acceleration in magnetized turbulence

TL;DR

This paper develops a first-principles model for particle acceleration in magnetized turbulence, linking energization rates to magnetic field line velocity gradients and validating it with numerical simulations.

Contribution

It introduces a novel theoretical framework connecting Fermi acceleration to turbulence intermittency and provides a transport equation validated by simulations.

Findings

Validation of the model with large-scale MHD turbulence simulations

Derivation of a transport equation for particle distribution

Connection of energization rates to magnetic field gradients

Abstract

This work provides a concrete implementation of E. Fermi's model of particle acceleration in magnetohydrodynamic (MHD) turbulence, connecting the rate of energization to the gradients of the velocity of magnetic field lines, which it characterizes within a multifractal picture of turbulence intermittency. It then derives a transport equation in momentum space for the distribution function. This description is shown to be substantiated by a large-scale numerical simulation of strong MHD turbulence. The present, general framework can be used to model particle acceleration in a variety of environments.