Particle Transport in intense small scale magnetic turbulence with a mean field

TL;DR

This paper investigates how a mean magnetic field influences particle transport in small-scale turbulence, revealing that transverse diffusion saturates at high energies, contrary to previous models, with theoretical derivation and simulation support.

Contribution

It provides an exact theoretical derivation of diffusion coefficients considering a mean field, showing significant deviations from classical models in particle transport.

Findings

Transverse diffusion reaches a finite limit at high particle energies.

Mean field significantly alters particle diffusion behavior.

Theoretical results are validated by Monte Carlo simulations.

Abstract

Various astrophysical studies have motivated the investigation of the transport of high energy particles in magnetic turbulence, either in the source or en route to the observation sites. For strong turbulence and large rigidity, the pitch-angle scattering rate is governed by a simple law involving a mean free path that increases proportionally to the square of the particle energy. In this paper, we show that perpendicular diffusion deviates from this behavior in the presence of a mean field. We propose an exact theoretical derivation of the diffusion coefficients and show that a mean field significantly changes the transverse diffusion even in the presence of a stronger turbulent field. In particular, the transverse diffusion coefficient is shown to reach a finite value at large rigidity instead of increasing proportionally to the square of the particle energy. Our theoretical derivation is corroborated by a dedicated Monte Carlo simulation. We briefly discuss several possible applications in astrophysics.