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Title:
Magnetic Quenching of α and Diffusivity Tensors in Helical Turbulence
Authors:
Brandenburg, Axel; Rädler, Karl-Heinz; Rheinhardt, Matthias; Subramanian, Kandaswamy
Affiliation:
AA(NORDITA, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden.), AB(Astrophysical Institute Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany), AC(Astrophysical Institute Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany), AD(Inter University Centre for Astronomy and Astrophysics, Post Bag 4, Pune University Campus, Ganeshkhind, Pune 411 007, India.)
Publication:
The Astrophysical Journal, Volume 687, Issue 1, pp. L49-L52. (ApJL Homepage)
Publication Date:
11/2008
Origin:
UCP
Astronomy Keywords:
Magnetohydrodynamics: MHD, Turbulence
DOI:
10.1086/593146
Bibliographic Code:
2008ApJ...687L..49B

Abstract

The effect of a dynamo-generated mean magnetic field of Beltrami type on the mean electromotive force is studied. In the absence of the mean magnetic field the turbulence is assumed to be homogeneous and isotropic, but it becomes inhomogeneous and anisotropic with this field. Using the test-field method the dependence of the α and turbulent diffusivity tensors on the magnetic Reynolds number ReM is determined for magnetic fields that have reached approximate equipartition with the velocity field. The tensor components are characterized by a pseudoscalar α and a scalar turbulent magnetic diffusivity ηt. Increasing ReM from 2 to 600 reduces ηt by a factor ~5, suggesting that the quenching of ηt is, in contrast to the two-dimensional case, only weakly dependent on ReM. Over the same range of ReM, however, α is reduced by a factor ~14, which can be explained by a corresponding increase of a magnetic contribution to the α-effect with opposite sign. Within this framework, the corresponding kinetic contribution to the α-effect turns out to be independent of ReM for 2<=ReM<=600. The level of fluctuations of α and ηt is only 10% and 20% of the respective kinematic reference values.
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