Study of momentum diffusion with the effect of adiabatic focusing

TL;DR

This paper investigates how adiabatic focusing influences momentum diffusion of energetic charged particles, revealing a new second order acceleration mechanism and the impact of magnetic field focusing on particle transport.

Contribution

It introduces a modifying term for momentum diffusion due to magnetic focusing and identifies a new second order acceleration mechanism in particle transport.

Findings

The focusing effect modifies momentum diffusion based on the sign of the focusing length.

A new second order acceleration mechanism is identified.

The modifying term depends on Fokker-Planck coefficients and focusing characteristic length.

Abstract

Momentum diffusion of the energetic charged particles is an important mechanism of the transport process in astrophysics, physics of the fusion devices, and laboratory plasmas. In addition to the uniform field momentum diffusion, we obtain the modifying term due to the focusing effect of the large-scale magnetic field. After evaluating the modifying term, we find that it is determined by the sign of the focusing characteristic length and the Fokker-Planck coefficients $D_{\mu\mu}$, $D_{\mu p}$, $D_{p\mu}$, and $D_{pp}$. It is shown that we get a new second order acceleration mechanism in this work.