Turbulent resistivity evaluation in MRI generated turbulence

TL;DR

This paper investigates the efficiency of MRI-driven turbulence in transporting large-scale magnetic fields in accretion disks, combining analytical and numerical methods to estimate turbulent resistivity and its anisotropic nature.

Contribution

It introduces a linear MRI analysis with inhomogeneous magnetic fields and provides numerical estimates of turbulent resistivity, highlighting its magnitude and anisotropy.

Findings

Turbulent resistivity is comparable to turbulent viscosity, but slightly lower.

The turbulent resistivity tensor is highly anisotropic, with radial diffusion three times greater than vertical.

MRI-driven turbulence can effectively transport magnetic fields, supporting jet formation from turbulent disks.

Abstract

(abriged) MRI turbulence is a leading mechanism for the generation of an efficient turbulent transport of angular momentum in an accretion disk through a turbulent viscosity effect. It is believed that the same process could also transport large-scale magnetic fields in disks, reshaping the magnetic structures in these objects. This process, known as turbulent resistivity, has been suggested and used in several accretion-ejection models and simulations to produce jets. Still, the efficiency of MRI-driven turbulence to transport large-scale magnetic fields is largely unknown. We investigate this problem both analytically and numerically. We introduce a linear calculation of the MRI in the presence of a spatially inhomogeneous mean magnetic field. We show that, in this configuration, MRI modes lead to an efficient magnetic field transport, on the order of the angular momentum transport. We next use fully non linear simulations of MRI turbulence to compute the turbulent resistivity in several magnetic configurations. We find that the turbulent resistivity is on the order of the turbulent viscosity in all our simulations, although somewhat lower. The turbulent resistivity tensor is found to be highly anisotropic with a diffusion coefficient 3 times greater in the radial direction than in the vertical direction. These results support the possibility of driving jets from turbulent disks; the resulting jets may not be steady.