EDP Sciences
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Volume 395, Number 1, November III 2002
Page(s) 339 - 343
Section Physical and chemical processes
DOI http://dx.doi.org/10.1051/0004-6361:20021284

A&A 395, 339-343 (2002)
DOI: 10.1051/0004-6361:20021284

Nonaxisymmetric patterns in the linear theory of MHD Taylor-Couette instability

D. A. Shalybkov1, 2, G. Rüdiger1 and M. Schultz1

1  Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
2  A.F. Ioffe Institute of Physics and Technology, 194021 St. Petersburg, Russia

(Received 1 July 2002 / Accepted 29 July 2002 )

The linear stability of MHD Taylor-Couette flow of infinite vertical extension is considered for various magnetic Prandtl numbers Pm. The calculations are performed for a wide gap container with $\hat\eta=0.5$ with an axial uniform magnetic field excluding counterrotating cylinders. For both hydrodynamically stable and unstable flows the magnetorotational instability produces characteristic minima of the Reynolds number for certain (low) magnetic field amplitudes. For Pm  $\la$ 1 there is a characteristic magnetic field amplitude beyond which the instability sets in in form of nonaxisymmetric spirals with the azimuthal number m=1. Obviously, the magnetic field is able to excite nonaxisymmetric configurations despite the tendency of differential rotation to favor axisymmetric magnetic fields, which is known from the dynamo theory. If Pm is too big or too small, however, the axisymmetric mode with m=0 appears to be the most unstable one possessing the lowest Reynolds numbers - as it is also true for hydrodynamic Taylor-Couette flow or for very weak fields. That the most unstable mode for modest Pm proves to be nonaxisymmetric must be considered as a strong indication for the possibility of dynamo processes in connection with the magnetorotational instability.

Key words: magnetohydrodynamics -- accretion, accretion disks -- turbulence

Offprint request: G. Rüdiger, gruediger@aip.de

© ESO 2002