HR: 16:20h
AN: NG44A-02 INVITED    [Abstracts]
TI: Magneto Rotation Instability and the Problem of Magneto Dynamo
AU: * Velikhov, E P
EM: velikhov@mac.com
AF: velikhov, pechotnaja 24, moscow, 123610, Russian Federation
AB: A new approach to the geophysical Earth's problem is considered, where the main role of geophysical time variation of magnetic force of Earth is due to magneto rotation instability rather than the theory of magneto dynamo. Besides the attention is drawn to magneto rotation instability (MRI) as a source of evolution of Earth's magnetic force. First studied theoretically by E.P. Velikhov in ideal condtions, then experimentally and numerically, MRI is never observed at real laboratory conditions. Most part of experiments is dedicated to the instability Raileigh-Taylor that is very close to MRI: viz., non compressible liquid metal is between rotating coaxial cylinders; permanent magnetic field along the axis is produced by currents beside cylinders. A great challenge is that motion of liquid metal is very far from ideal for MRI proof. So Reinolds Number appears to be large, meantime magnetic Reinolds Number is of order of unity or even less. A ratio = , since viscosity, . At study MRI which often called Standard MRI (SMRI) one more condition is to be satisfied: time of motion of perturbation between cylinders is to be less then the time of magnetic force diffusion. Hence one has two inequalities: - Lundquist Number, -Alfven velocity. It follows that and magnetic forces are to be several KGs. Besides, a difficulty appears due to height of cylinders and boundary conditions on the butts of cylinders. It brings about additional motion, for instance due to Eckman force in usual hydrodynamics and counter currents in unit on checking of SMRN. The way out is either search of modification SMRN (like Goodman), or checking of thresholds MRN (like Taylor) with very large aspect relation, to forget butts cylinder conditions. To escape the difficulty tackled with Eckman force Goodman at Princeton University create rotating butts of cylinders to get closer to configuration Taylor but with larger aspect ratio. For Taylor aspect ratio was of the order of 100, for Goodman and cooperators of the order of one ( rotating butts took place). It was shown that unit at Princeton demonstrates the absence of transfer of substance across magnetic force and is a proof that Reileigh-Taylor instability in any configuration does not transfer a substance across magnetic force. At RRC"Kurchatov Institute" is published results when rotation of liquid sodium is created in chamber with motionless walls due to interaction radial current with axis magnetic force. Unit has following parameters, magnetic force ~250 Gs,the butts appeared to be insulator, radial current . An advantage is that rotating force is volume. The velocities near were achieved, however large radial current brings about toroidal magnetic force, that interacting with radial current creates flow of substance like Eckman for in hydrodynamics. However in this case it is simpler since radial potential one can distribute introducing electrodes as rings on the butts of cylinder.
DE: 0500 COMPUTATIONAL GEOPHYSICS (3200, 3252, 7833)
DE: 4255 Numerical modeling (0545, 0560)
SC: Nonlinear Geophysics [NG]
MN: 2007 Fall Meeting