Ion Diffusion and Acceleration in Plasma Turbulence

TL;DR

This study uses 2D hybrid-PIC simulations to analyze ion diffusion and acceleration in turbulent plasmas, revealing the role of current sheets and resonance effects across various space and laboratory plasma conditions.

Contribution

It adapts the NLGC theory to 2D turbulence and investigates how coherent structures influence ion energization and diffusion.

Findings

Current sheets significantly enhance ion acceleration when ion Larmor radii match their size.

Resonance effects lead to magnetic moment violation and increased velocity-space diffusion.

The model applies to diverse plasma environments from solar to laboratory settings.

Abstract

Particle transport, acceleration and energisation are phenomena of major importance for both space and laboratory plasmas. Despite years of study, an accurate theoretical description of these effects is still lacking. Validating models with self-consistent, kinetic simulations represents today a new challenge for the description of weakly-collisional, turbulent plasmas. We perform two-dimensional (2D) hybrid-PIC simulations of steady-state turbulence to study the processes of diffusion and acceleration. The chosen plasma parameters allow to span different systems, going from the solar corona to the solar wind, from the Earth's magnetosheath to confinement devices. To describe the ion diffusion, we adapted the Nonlinear Guiding Center (NLGC) theory to the 2D case. Finally, we investigated the local influence of coherent structures on particle energisation and acceleration: current sheets play an important role if the ions Larmor radii are on the order of the current sheets size. This resonance-like process leads to the violation of the magnetic moment conservation, eventually enhancing the velocity-space diffusion.