Parallel and perpendicular diffusion coefficients of energetic charged particles with adiabatic focusing

TL;DR

This paper develops a new correction to the parallel diffusion coefficient of energetic charged particles considering adiabatic focusing, and also derives the perpendicular diffusion coefficient in non-uniform magnetic fields.

Contribution

It introduces a novel correction term to the parallel diffusion coefficient using an improved perturbation method and explores the effects of adiabatic focusing on both parallel and perpendicular diffusion.

Findings

New correction term T' with opposite sign to T for parallel diffusion.

Derived the perpendicular diffusion coefficient considering adiabatic focusing.

Showed the impact of adiabatic focusing on particle diffusion in non-uniform magnetic fields.

Abstract

It is very important to understand stochastic diffusion of energetic charged particles in non-uniform background magnetic field in plasmas of astrophysics and fusion devices. Using different methods considering along-field adiabatic focusing effect, various authors derived parallel diffusion coefficient $\kappa_\parallel$ and its correction $T$ to $\kappa_{\parallel 0}$, where $\kappa_{\parallel 0}$ is the parallel diffusion coefficient without adiabatic focusing effect. In this paper, using the improved perturbation method developed by He \& Schlickeiser and iteration process, we obtain a new correction $T'$ to $\kappa_{\parallel 0}$. Furthermore, by employing the isotropic pitch-angle scattering model $D_{\mu\mu}=D(1-\mu^2)$, we find that $T'$ has the different sign as that of $T$. In this paper the spatial perpendicular diffusion coefficient $\kappa_\bot$ with the adiabatic focusing effect is also obtained.