A computational model for exploring particle acceleration during reconnection in macro-scale systems

TL;DR

This paper introduces a new computational model for simulating particle acceleration during magnetic reconnection in large-scale systems, emphasizing energy conservation and key plasma instabilities.

Contribution

The model simplifies kinetic scales by excluding parallel electric fields, integrating macro-particles with MHD, and accurately capturing firehose instability effects.

Findings

Model conserves total energy of particles and fluid

Successfully simulates Alfven wave propagation with pressure anisotropy

Reproduces firehose instability dynamics accurately

Abstract

A new computational model is presented suitable for exploring the self-consistent production of energetic electrons during magnetic reconnection in macroscale systems. The equations are based on the recent discovery that parallel electric fields are ineffective drivers of energetic particles during reconnection so that the kinetic scales which control the development of such fields can be ordered out of the equations. The resulting equations consist of a magnetohydrodynamic (MHD) backbone with the energetic component represented by macro-particles described by the guiding center equations. Crucially, the energetic component feeds back on the MHD equations so that the total energy of the MHD fluid and the energetic particles is conserved. The equations correctly describe the firehose instability, whose dynamics plays a key role in throttling reconnection and in controlling the spectra of energetic particles. The results of early tests of the model, including the propagation of Alfven waves in a system with pressure anisotropy and the growth of firehose modes, establish that the basic algorithm is stable and produces reliable physics results in preparation for further benchmarking with particle-in-cell models of reconnection.