The Dynamical Generation of Current Sheets in Astrophysical Plasma Turbulence

TL;DR

This paper demonstrates through gyrokinetic simulations that strong nonlinear interactions between counterpropagating Alfvén waves naturally generate current sheets in plasma turbulence, which are key to understanding energy dissipation in astrophysical plasmas.

Contribution

It provides a conceptual and simulation-based explanation that current sheets form via constructive interference during Alfvén wave collisions, highlighting a fundamental dissipation mechanism.

Findings

Current sheets arise from nonlinear Alfvén wave interactions.

Constructive interference explains current sheet formation.

Landau damping likely dominates energy dissipation.

Abstract

Turbulence profoundly affects particle transport and plasma heating in many astrophysical plasma environments, from galaxy clusters to the solar corona and solar wind to Earth's magnetosphere. Both fluid and kinetic simulations of plasma turbulence ubiquitously generate coherent structures, in the form of current sheets, at small scales, and the locations of these current sheets appear to be associated with enhanced rates of dissipation of the turbulent energy. Therefore, illuminating the origin and nature of these current sheets is critical to identifying the dominant physical mechanisms of dissipation, a primary aim at the forefront of plasma turbulence research. Here we present evidence from nonlinear gyrokinetic simulations that strong nonlinear interactions between counterpropagating Alfven waves, or strong Alfven wave collisions, are a natural mechanism for the generation of current sheets in plasma turbulence. Furthermore, we conceptually explain this current sheet development in terms of the nonlinear dynamics of Alfven wave collisions, showing that these current sheets arise through constructive interference among the initial Alfven waves and nonlinearly generated modes. The properties of current sheets generated by a strong Alfven wave collisions are compared to published observations of current sheets in the Earth's magnetosheath and the solar wind, and the nature of these current sheets leads to the expectation that Landau damping of the constituent Alfven waves plays a dominant role in the damping of turbulently generated current sheets.