On Self-Sustained Dynamo Cycles in Accretion Discs

Abstract

(abridged) MHD turbulence is known to exist in shearing boxes with either zero or nonzero net magnetic flux. However, the way turbulence survives in the zero-net-flux case is not explained by linear theory and appears as a purely numerical result. Aims: We look for a nonlinear mechanism able to explain the persistence of MHD turbulence in shearing boxes with zero net magnetic flux, and potentially leading to large-scale dynamo action. Method: Spectral nonlinear simulations of the magnetorotational instability are shown to exhibit a large-scale axisymmetric magnetic field, maintained for a few orbits. The generation process of this field is investigated using the results of the simulations and an inhomogeneous linear approach. Results: The mechanism by which turbulence is sustained in zero-net-flux shearing boxes is shown to be related to the existence of a large-scale azimuthal field, surviving for several orbits. In particular, it is shown that MHD turbulence in shearing boxes can be seen as a dynamo process coupled to a magnetorotational-type instability.

11 pages, 11 figures, Accepted in A&A

References in corpus (11)

• MHD simulations of the magnetorotational instability in a shearing box with zero net flux. II. The effect of transport coefficients
• Impact of dimensionless numbers on the efficiency of MRI-induced turbulent transport
• MHD simulations of the magnetorotational instability in a shearing box with zero net flux. I. The issue of convergence
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• Generation of Magnetic Field by Combined Action of Turbulence and Shear
• On the Magnetic Prandtl Number Behavior of Accretion Disks
• A self-sustaining nonlinear dynamo process in Keplerian shear flows
• On the viability of the shearing box approximation for numerical studies of MHD turbulence in accretion disks
• The fundamental difference between shear alpha viscosity and turbulent magnetorotational stresses
• Exact shering box solutions of MHD flows with resistivity, viscosity and cooling
• Toward Coupling Flow Driven and Magnetically Driven Dynamos

Cited by in corpus (5)

• Semi-global simulations of the magneto-rotational instability in core collapse supernovae
• High accretion rates in magnetised Keplerian discs mediated by a Parker instability driven dynamo
• Numerical experiments on dynamo action in sheared and rotating turbulence
• Axisymmetric Magnetorotational Instability in Viscous Accretion Disks
• Localized magnetorotational instability and its role in the accretion disc dynamo