Nonlinear energy transfers in accretion discs MRI turbulence. I-Net vertical field case

TL;DR

This paper investigates how molecular dissipation influences MRI-driven turbulence in accretion disks, revealing non local spectral energy transfers and proposing their role in the turbulence-dissipation correlation.

Contribution

It provides a spectral analysis linking molecular dissipation to MRI turbulence, emphasizing non local energy interactions and challenging existing linear theories.

Findings

Energy exchanges are mainly direct from large to small scales.

Non linear interactions are non local in spectral space.

A correlation between turbulence and dissipation may vanish with scale separation.

Abstract

The magnetorotational instability (MRI) is believed to be responsible for most of the angular momentum transport in accretion discs. However, molecular dissipation processes may drastically change the efficiency of MRI turbulence in realistic astrophysical situations. The physical origin of this dependency is still poorly understood as linear and quasi linear theories fail to explain it. In this paper, we look for the link between molecular dissipation processes and MRI transport of angular momentum in non stratified shearing box simulations including a mean vertical field. We show that magnetic helicity is unimportant in the model we consider. We perform a spectral analysis on the simulations tracking energy exchanges in spectral space when turbulence is fully developed. We find that the energy exchanges are essentially direct (from large to small scale) whereas some non linear interactions appear to be non local in spectral space. We speculate that these non local interactions are responsible for the correlation between turbulent transport and molecular dissipation. We argue that this correlation should then disappear when a significant scale separation is achieved and we discuss several methods by which one can test this hypothesis.