The weakly nonlinear magnetorotational instability in a local geometry

Abstract

The magnetorotational instability (MRI) is a fundamental process of accretion disk physics, but its saturation mechanism remains poorly understood despite considerable theoretical and computational effort. We present a multiple scales analysis of the non-ideal MRI in the weakly nonlinear regime -- that is, when the most unstable MRI mode has a growth rate asymptotically approaching zero from above. Here, we develop our theory in a local, Cartesian channel. Our results confirm the finding by Umurhan et al. (2007) that the perturbation amplitude follows a Ginzburg-Landau equation. We further find that the Ginzburg-Landau equation will arise for the local MRI system with shear-periodic boundary conditions when the effects of ambipolar diffusion are considered. A detailed force balance for the saturated azimuthal velocity and vertical magnetic field demonstrates that even when diffusive effects are important, the bulk flow saturates via the combined processes of reducing the background shear and rearranging and strengthening the background vertical magnetic field. We directly simulate the Ginzburg-Landau amplitude evolution for our system and demonstrate the pattern formation our model predicts on long length and time scales. We compare the weakly nonlinear theory results to a direct numerical simulation of the MRI in a thin-gap Taylor Couette flow.

17 pages, 10 figures, accepted to ApJ

References in corpus (9)

• Impact of dimensionless numbers on the efficiency of MRI-induced turbulent transport
• Hall-effect Controlled Gas Dynamics in Protoplanetary Disks: II. Full 3D Simulations toward the Outer Disk
• The Role of the Magnetorotational Instability in Massive Stars
• On the viability of the shearing box approximation for numerical studies of MHD turbulence in accretion disks
• Termination of the magnetorotational instability via parasitic instabilities in core-collapse supernovae
• A weakly nonlinear analysis of the magnetorotational instability in a model channel flow
• On the nonlinear saturation of the magnetorotational instability near threshold in a thin-gap Taylor-Couette setup
• Local and global aspects of the linear MRI in accretion disks
• The weakly nonlinear magnetorotational instability in a global, cylindrical Taylor-Couette flow

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