Dissipative effects on the sustainment of a magnetorotational dynamo in Keplerian shear flow

Abstract

The magnetorotational (MRI) dynamo has long been considered one of the possible drivers of turbulent angular momentum transport in astrophysical accretion disks. However, various numerical results suggest that this dynamo may be difficult to excite in the astrophysically relevant regime of magnetic Prandtl number (Pm) significantly smaller than unity, for reasons currently not well understood. The aim of this article is to present the first results of an ongoing numerical investigation of the role of both linear and nonlinear dissipative effects in this problem. Combining a parametric exploration and an energy analysis of incompressible nonlinear MRI dynamo cycles representative of the transitional dynamics in large aspect ratio shearing boxes, we find that turbulent magnetic diffusion makes the excitation and sustainment of this dynamo at moderate magnetic Reynolds number (Rm) increasingly difficult for decreasing Pm. This results in an increase in the critical Rm of the dynamo for increasing kinematic Reynolds number (Re), in agreement with earlier numerical results. Given its very generic nature, we argue that turbulent magnetic diffusion could be an important determinant of MRI dynamo excitation in disks, and may also limit the efficiency of angular momentum transport by MRI turbulence in low Pm regimes.

7 pages, 6 figures

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• Impact of dimensionless numbers on the efficiency of MRI-induced turbulent transport
• On the Magnetic Prandtl Number Behavior of Accretion Disks
• A self-sustaining nonlinear dynamo process in Keplerian shear flows
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• Magnetorotational instability driven dynamos at low magnetic Prandtl numbers
• Subcritical dynamos in shear flows
• Dissipative effects on the sustainment of a magnetorotational dynamo in Keplerian shear flow

Cited by in corpus (9)

• Angular momentum transport and large eddy simulations in magnetorotational turbulence: the small Pm limit
• Magnetorotational instability and dynamo action in gravitoturbulent astrophysical discs
• Dissipative effects on the sustainment of a magnetorotational dynamo in Keplerian shear flow
• Magnetorotational dynamo chimeras. The missing link to turbulent accretion disk dynamo models?
• Small-scale dynamos on the solar surface: dependence on magnetic Prandtl number
• Nonlinear transverse cascade and sustenance of MRI-turbulence in Keplerian disks with an azimuthal magnetic field
• Magnetohydrodynamics of protoplanetary discs
• Sustained Turbulence in Differentially Rotating Magnetized Fluids at Low Magnetic Prandtl Number
• Magnetorotationally driven wind cycles in local disc models