Issue |
A&A
Volume 388, Number 2, June III 2002
|
|
---|---|---|
Page(s) | 688 - 691 | |
Section | Astronomical instrumentation | |
DOI | https://doi.org/10.1051/0004-6361:20020510 | |
Published online | 31 May 2002 |
Magnetic instability in a sheared azimuthal flow
Department of Mathematics, University of Newcastle, Newcastle upon Tyne, NE2 7RU, UK
Corresponding author: C. F. Barenghi, c.f.barenghi@newcastle.ac.uk
Received:
8
January
2002
Accepted:
3
April
2002
We study the magneto-rotational instability of an incompressible
flow which rotates with angular velocity where
r is the radius and a and b are constants.
We find that an applied magnetic field destabilises the flow, in
agreement with the results of [CITE].
We extend the investigation in the region of parameter space which
is Rayleigh stable.
We also study the instability at values of magnetic Prandtl number
which are much larger and smaller than Rüdiger & Zhang.
Large magnetic Prandtl numbers are motivated by
their possible relevance in the central region of galaxies
(Kulsrud & Anderson 1992). In this regime we find that increasing the
magnetic Prandtl number greatly enhances the instability; the stability
boundary drops below the Rayleigh line and tends toward the solid body
rotation line. Very small magnetic Prandtl numbers are motivated by the
current MHD dynamo experiments performed using liquid sodium and gallium.
Our finding in this regime confirms Rüdiger & Zhang's conjecture
that the linear magneto-rotational instability and the nonlinear
hydrodynamical instability (Richard & Zahn 1999) take place at Reynolds
numbers of the same order of magnitude.
Key words: accretion discs / instabilities / magnetohydrodynamics / turbulence
© ESO, 2002
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