Turbulent dynamo action in a shear flow |
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Authors: | V. Urpin |
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Affiliation: | Department of Mathematics, University of Newcastle, Newcastle upon Tyne NE1 7RU; A. F. Ioffe Institute of Physics and Technology, 194021 St. Petersburg, Russia |
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Abstract: | We consider the mean electromotive force and a dynamo-generated magnetic field, taking into account the stretching of turbulent magnetic field lines by a shear flow. Calculations are performed by making use of the second-order correlation approximation. In the presence of shear, the mirror symmetry of turbulence can be broken; thus turbulent motions become suitable for the generation of a large-scale magnetic field. Regardless of the shear law, turbulence can lead to a rapid amplification of the mean magnetic field. The growth rate of the mean magnetic field depends on the length-scale: it is faster for the fields with smaller length-scale. The mechanism considered is qualitatively different from the alpha dynamo, and can generate only a magnetic field that is inhomogeneous in the direction of flow. In contrast to the alpha dynamo, this mechanism also allows the generation of two-dimensional fields. The suggested mechanism may play an important role in the generation of magnetic fields in accretion discs, galaxies and jets. |
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Keywords: | accretion, accretion discs hydrodynamics magnetic fields turbulence stars: magnetic fields ISM: magnetic fields |
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