The Weakly Nonlinear Magnetorotational Instability in a Local Geometry

Journal Article · Sat May 20 00:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA6FF1· OSTI ID:22663602

Clark, S. E. ^[1]

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1. Department of Astronomy, Columbia University, New York, NY 10027 (United States)

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. 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 scales of length- and timescales. We compare the weakly nonlinear theory results to a direct numerical simulation of the MRI in a thin-gap Taylor Couette flow.

• OSTI ID: 22663602
• Journal Information: Astrophysical Journal, Vol. 841, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ACCRETION DISKS
AMBIPOLAR DIFFUSION
BOUNDARY CONDITIONS
COMPARATIVE EVALUATIONS
COMPUTERIZED SIMULATION
COUETTE FLOW
DISTURBANCES
GINZBURG-LANDAU THEORY
INSTABILITY
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
NMR IMAGING
NONLINEAR PROBLEMS
PERIODICITY
PERTURBATION THEORY
PLASMA
SATURATION
SHEAR