Energy spectrum, dissipation and spatial structures in reduced Hall magnetohydrodynamic

TL;DR

This paper investigates how the Hall effect influences energy transfer, dissipation, and structures in reduced magnetohydrodynamic turbulence, revealing shifts in dissipation scales and changes in current sheet morphology.

Contribution

It provides the first detailed numerical analysis of the Hall term's impact on energy cascade and dissipation structures in RHMHD turbulence.

Findings

Hall effect slows energy transfer to the Hall scale

Increased Hall effect widens and structures current sheets

Strong Hall effect reduces flow intermittency

Abstract

We analyze the effect of the Hall term in the magnetohydrodynamic turbulence under a strong externally supported magnetic field, seeing how this changes the energy cascade, the characteristic scales of the flow and the dynamics of global magnitudes, with particular interest in the dissipation. Numerical simulations of freely evolving three-dimensional reduced magnetohydrodynamics (RHMHD) are performed, for different values of the Hall parameter (the ratio of the ion skin depth to the macroscopic scale of the turbulence) controlling the impact of the Hall term. The Hall effect modifies the transfer of energy across scales, slowing down the transfer of energy from the large scales up to the Hall scale (ion skin depth) and carrying faster the energy from the Hall scale to smaller scales. The final outcome is an effective shift of the dissipation scale to larger scales but also a development of smaller scales. Current sheets (fundamental structures for energy dissipation) are affected in two ways by increasing the Hall effect, with a widening but at the same time generating an internal structure within them. In the case where the Hall term is sufficiently intense, the current sheet is fully delocalized. The effect appears to reduce impulsive effects in the flow, making it less intermittent.