Turbulent energy dissipation and intermittency in ambipolar diffusion magnetohydrodynamics

TL;DR

This study investigates how ambipolar diffusion influences energy dissipation and intermittency in magnetohydrodynamic turbulence within the interstellar medium, revealing that AD causes energy to dissipate at larger scales and concentrates dissipation in thin, intermittent sheets.

Contribution

It provides the first detailed spectral simulation analysis of ambipolar diffusion effects on turbulence, highlighting its role in energy dissipation scale and intermittency properties.

Findings

AD heating peaks within the inertial range due to magnetic-current alignment

Energy dissipation occurs mainly in thin, sheet-like structures

Dissipation exhibits intermittency with a lognormal distribution and power-law tail

Abstract

The dissipation of kinetic and magnetic energy in the interstellar medium (ISM) can proceed through viscous, Ohmic or ambipolar diffusion (AD). It occurs at very small scales compared to the scales at which energy is presumed to be injected. This localized heating may impact the ISM evolution but also its chemistry, thus providing observable features. Here, we perform 3D spectral simulations of decaying magnetohydrodynamic turbulence including the effects of AD. We find that the AD heating power spectrum peaks at scales in the inertial range, due to a strong alignment of the magnetic and current vectors in the dissipative range. AD affects much greater scales than the AD scale predicted by dimensional analysis. We find that energy dissipation is highly concentrated on thin sheets. Its probability density function follows a lognormal law with a power-law tail which hints at intermittency, a property which we quantify by use of structure function exponents. Finally, we extract structures of high dissipation, defined as connected sets of points where the total dissipation is most intense and we measure the scaling exponents of their geometric and dynamical characteristics: the inclusion of AD favours small sizes in the dissipative range.