# Test particle energization and the anisotropic effects of dynamical MHD turbulence

## TL;DR

This study investigates how dynamical MHD turbulence influences test particle energization, revealing that particle trapping in moving current sheets reduces acceleration, with anisotropy further affecting energization by altering structure sizes.

## Contribution

It provides a comparative analysis of particle acceleration in static versus dynamical MHD fields and explores the impact of anisotropy on energization mechanisms.

## Key findings

- Dynamical fields reduce particle acceleration due to trapping in moving current sheets.
- Anisotropy caused by strong magnetic fields increases structure size and decreases energization.
- Particles become magnetized in large coherent structures, limiting acceleration.

## Abstract

In this paper we analyze the effect of dynamical three-dimensional MHD turbulence on test particle acceleration, and compare how this evolving system affects particle energization by current sheets interaction, against frozen-in-time fields. To do this we analize the ensamble particle acceleration for static electromagnetic fields extracted from direct numerical simulations of the MHD equations, and compare with the dynamical fields. We show that a reduction in particle acceleration in the dynamical model results from the particle trapping in the field lines, which forces the particles to remain in a moving current sheet that suppress the longer exposure at the strong electric field gradients located between structures, which is an efficient particle acceleration mechanism. In addition, we analize the effect of anisotropy caused by the mean magnetic field. It is well known that for sufficiently strong external fields, the system suffers a transition towards a two-dimensional flow. This causes an increment in the size of the coherent structures, resulting in a magnetized state of the particles and the reduction of the particle energization.