Quantifying energetics and dissipation in magnetohydrodynamic turbulence

TL;DR

This study uses MHD simulations to analyze energy transfer and dissipation mechanisms in turbulence, revealing magnetic tension's role in energy injection and the impact of explicit dissipation on dissipation scales.

Contribution

It introduces spectral energy transfer analysis to quantify energy exchange in MHD turbulence and examines the effects of explicit dissipation on dissipation scales.

Findings

Magnetic tension mediates energy injection into magnetic fields.

Turbulent magnetic energy cascades to smaller scales and exchanges with kinetic energy.

Explicit dissipation shifts the dissipation scale to larger scales.

Abstract

We perform a suite of two- and three-dimensional magnetohydrodynamic (MHD) simulations with the Athena code of the non-driven Kelvin-Helmholtz instability in the subsonic, weak magnetic field limit. Focusing the analysis on the non-linear turbulent regime, we quantify energy transfer on a scale-by-scale basis and identify the physical mechanisms responsible for energy exchange by developing the diagnostic known as spectral energy transfer function analysis. At late times when the fluid is in a state of MHD turbulence, magnetic tension mediates the dominant mode of energy injection into the magnetic reservoir, whereby turbulent fluid motions twist and stretch the magnetic field lines. This generated magnetic energy turbulently cascades to smaller scales, while being exchanged backwards and forwards with the kinetic energy reservoir, until finally being dissipated. Incorporating explicit dissipation pushes the dissipation scale to larger scales than if the dissipation were entirely numerical. For scales larger than the dissipation scale, we show that the physics of energy transfer in decaying MHD turbulence is robust to numerical effects.