Direct comparison of the energization of self-consistent charged particles vs test particles in a turbulent plasma

TL;DR

This study compares particle energization in turbulent plasmas using self-consistent models versus test particle approaches, revealing that test particles overestimate energization and do not capture localized suprathermal particle behavior.

Contribution

It provides a direct comparison between self-consistent and test particle models in turbulent plasma simulations, highlighting the limitations of the test particle approach.

Findings

Test particles show higher temperature than self-consistent particles.

Suprathermal particles in test models occupy entire domain, unlike localized regions in self-consistent models.

Test particles overestimate energization and miss finer phenomena.

Abstract

The test particle approach is a widely used method for studying the dynamics of charged particles in complex electromagnetic fields and has been successful in explaining particle energization in turbulent plasmas. However, this approach is fundamentally not self-consistent, as test particles do not generate their own electromagnetic fields and therefore do not interact with their surroundings realistically. In this work, we compare the energization of a population of test protons in a magnetofluid to that of a plasma composed of self-consistent particles. We use a compressible Hall magnetohydrodynamic (CHMHD) model for the test particle case and a hybrid particle-in-cell (HPIC) approach for the self-consistent case, conducting both 2D and 3D simulations. We calculate the rate of energization and conversion to thermal energy in both models, finding a higher temperature for the test particle case. Additionally, we examine the distribution of suprathermal particles and find that, in the test particle scenario, these particles eventually occupy the entire domain, while in the self-consistent case, suprathermal particles are confined to specific regions. We conclude that while test particles capture some qualitative features of their self-consistent counterparts, they miss finer phenomena and tend to overestimate energization.