Theoretical derivation of diffusion-tensor coefficients for the transport of charged particles in magnetic fields

TL;DR

This paper presents a theoretical derivation of diffusion-tensor coefficients for charged particle transport in magnetic fields, extending previous models to include mean magnetic fields and applicable to various astrophysical regimes.

Contribution

It extends the derivation of diffusion-tensor coefficients to include mean magnetic fields, enhancing modeling accuracy for astrophysical charged particle transport.

Findings

Derived diffusion-tensor coefficients for combined turbulence and mean fields.

Applicable to gyro-resonant and high-rigidity regimes.

Provides analytical expressions for astrophysical environments.

Abstract

The transport of charged particles in various astrophysical environments permeated by magnetic fields is described in terms of a diffusion process, which relies on diffusion-tensor parameters generally inferred from Monte-Carlo simulations. Based on a red-noise approximation to model the two-point correlation function of the magnetic field experienced by charged particles between two successive times, the diffusion-tensor coefficients were previously derived in the case of pure turbulence. In this contribution to ECRS2022, the derivation is extended to the case of a mean field on top of the turbulence. The results are applicable to a variety of astrophysical environments in regimes where the Larmor radius of the particles is resonant with the power spectrum of the turbulence wavelength (gyro-resonant regime), or where the Larmor radius is greater than the largest turbulence wavelength (high-rigidity regime).