Magnetorotational Instability in Liqid Metal Couette Flow
Abstract
The Magnetorotational Instability (MRI) is a fundamental process in magnetized accretion disks. We expect to observe this instability at an early phase of a liquid sodium αω dynamo experiment at New Mexico Tech. The turbulence generated by the instability in a rotating metal annulus (Couette flow) may alter the dynamo effect. We have performed a local stability analysis, studying the effects of the flow shear, magnetic field strength, magnetic Reynolds number, and turbulent Prandtl number (Noguchi et al. 2001, ApJ, submitted). We also consider the minimum turbulence induced by the formation of an Ekman layer against the rigidly rotating end walls of the cylindrical vessel. We have delineated the stability conditions for the liquid sodium experiment as well as the liquid gallium experiment at Princeton. Liquid sodium is MRI unstable with weak magnetic fields (<100 Gauss) because of strong shear in the flow, and so high wave number unstable modes are excited. These unstable modes are predicted to be sustained within high turbulence, up to a turbulent Prandtl number P_M=ν_t/η ~ 6, where νt is an effective turbulent viscosity and η is a magnetic diffusivity.
- Publication:
-
APS April Meeting Abstracts
- Pub Date:
- April 2002
- Bibcode:
- 2002APS..APRB17079N