Modeling the Transport of Nonthermal Particles in Flares Using Fokker-Planck Kinetic Theory

TL;DR

This paper introduces a comprehensive numerical approach using the Fokker-Planck equation to model high-energy particle transport in solar flares, accounting for various physical forces and interactions, and provides a publicly available code for the community.

Contribution

The paper presents a new numerical method and code for modeling particle transport in flares, incorporating multiple physical effects and applicable to particles of any charge and mass.

Findings

Successfully models particle transport with realistic physics

Predicts bremsstrahlung emission for observational comparison

Demonstrates effectiveness through test cases

Abstract

We describe a new approach for modeling the transport of high energy particles accelerated during flares from the acceleration region in the solar corona until their eventual thermalization in the flare footpoint. Our technique numerically solves the Fokker-Planck equation and includes forces corresponding to Coulomb collisions in a flux loop with nonuniform ionization, synchrotron emission reaction, magnetic mirroring and a return current electric field. Our solution to the Fokker-Planck equation includes second-order pitch angle and momentum diffusion. It is applicable to particles of arbitrary mass and charge. By tracking the collisions, we predict the bremsstrahlung produced as these particles interact with the ambient stellar atmosphere. This can be compared directly with observations and used to constrain the accelerated particle energy distribution. We have named our numerical code FP and have distributed it for general use. We demonstrate its effectiveness in several test cases.