Physics – Atomic Physics
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...292..341t&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 292, no. 1, p. 341-349
Physics
Atomic Physics
22
Accretion Disks, Cataclysmic Variables, Chaos, Computational Astrophysics, Dynamo Theory, Magnetic Fields, Mathematical Models, Quenching (Atomic Physics), Stellar Models, Buoyancy, Diagrams, Magnetohydrodynamics, Nonlinearity, Plasmas (Physics), Spatial Dependencies
Scientific paper
We study nonlinear accretion disk dynamos, and demonstrate that different types of magnetic field configurations will arise depending on the dynamo number. Dynamo action is parametrised by the alpha-effect, whose strength is determined by a dimensionless number Calpha. Using alpha-quenching as the only nonlinearity, we find for Calpha greater than 0 that a steady quadrupolar field is first excited. However this solution disappears before any other field configuration is excited. Thus there is a gap without any magnetic field. At higher dynamo numbers oscillatory dipolar and quadrupolar fields emerge, and later the quadrupolar solution bifurcates to a chaotically varying mixed parity solution. Finally, at extremely high dynamo numbers the chaotic field transforms into a steady mixed parity solution, which is dominated by an even parity component. For Calpha less than 0 we first find an oscillatory dipolar field, which bifurcates to a doubly periodic mixed parity field, and later also to a chaotically varying field. Using magnetic buoyancy as the nonlinearity the gap no longer occurs. Nevertheless for the entire interval investigated, we only find a steady quadrupolar field for Calpha greater than 0, and an oscillatory quadrupolar or dipolar field for Calpha less than 0.
Brandenburg Axel
Torkelsson Ulf
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