On the two-dimensional state in driven magnetohydrodynamic turbulence

TL;DR

This study uses high-resolution simulations to explore how a strong external magnetic field influences the development and energy distribution of the two-dimensional state in driven 3D magnetohydrodynamic turbulence, revealing significant 2D contributions and spectral behaviors.

Contribution

It demonstrates that the 2D state becomes prominent quickly under strong magnetic fields and affects the energy spectra, providing new insights into turbulence dynamics with external magnetic influences.

Findings

2D state becomes significant within a few turnover times when magnetic field is strong

Large-scale driving causes a spectral break in 3D modes, which disappears after stopping the drive

Energy at large scales is dominated by the 2D state in strong magnetic fields

Abstract

The dynamics of the two-dimensional (2D) state in driven tridimensional (3D) incompressible magnetohydrodynamic turbulence is investigated through high-resolution direct numerical simulations and in the presence of an external magnetic field at various intensities. For such a flow the 2D state (or slow mode) and the 3D modes correspond respectively to spectral fluctuations in the plan $k_\parallel=0$ and in the area $k_\parallel>0$. It is shown that if initially the 2D state is set to zero it becomes non negligible in few turnover times particularly when the external magnetic field is strong. The maintenance of a large scale driving leads to a break for the energy spectra of 3D modes; when the driving is stopped the previous break is removed and a decay phase emerges with alfv\'enic fluctuations. For a strong external magnetic field the energy at large perpendicular scales lies mainly in the 2D state and in all situations a pinning effect is observed at small scales.