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Periodic magnetorotational dynamo action as a prototype of nonlinear magnetic-field generation in shear flows

Herault, Johann and Rincon, Francois and Cossu, Carlo and Lesur, Geoffroy and Ogilvie, Gordon I. and Longaretti, Pierre-Yves Periodic magnetorotational dynamo action as a prototype of nonlinear magnetic-field generation in shear flows. (2011) Physical Review E, vol. 84 (n° 3). pp. 036321(1)-036321(9). ISSN 1539-3755

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Official URL: http://link.aps.org/doi/10.1103/PhysRevE.84.036321

Abstract

The nature of dynamo action in shear flows prone to magnetohydrodynamc instabilities is investigated using the magnetorotational dynamo in Keplerian shear flow as a prototype problem. Using direct numerical simulations and Newton’s method, we compute an exact time-periodic magnetorotational dynamo solution to three-dimensional dissipative incompressible magnetohydrodynamic equations with rotation and shear. We discuss the physical mechanism behind the cycle and show that it results from a combination of linear and nonlinear interactions between a large-scale axisymmetric toroidal magnetic field and nonaxisymmetric perturbations amplified by the magnetorotational instability. We demonstrate that this large-scale dynamo mechanism is overall intrinsically nonlinear and not reducible to the standard mean-field dynamo formalism. Our results therefore provide clear evidence for a generic nonlinear generation mechanism of time-dependent coherent large-scale magnetic fields in shear flows and call for new theoretical dynamo models. These findings may offer important clues to understanding the transitional and statistical properties of subcritical magnetorotational turbulence.

Item Type:Article
Additional Information:Thanks to APS editor. The original PDF is available at http://pre.aps.org/
Audience (journal):International peer-reviewed journal
Uncontrolled Keywords:
Institution:French research institutions > Centre National de la Recherche Scientifique - CNRS
Université de Toulouse > Institut National Polytechnique de Toulouse - INPT
Other partners > Université de Paris Diderot - Paris 7 (FRANCE)
Other partners > University of Cambridge (UNITED KINGDOM)
Other partners > Université Pierre et Marie Curie, Paris 6 - UPMC (FRANCE)
Université de Toulouse > Université Paul Sabatier-Toulouse III - UPS
Other partners > Ecole Normale Supérieure de Paris - ENS Paris (FRANCE)
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Deposited By:Carlo COSSU

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