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Negative magnetic eddy diffusivities from the test-field method and multiscale stability theory
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Department of Astronomy, Stockholm University, AlbaNova University Center, Stockholm, Sweden.ORCID iD: 0000-0002-7304-021X
2015 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 811, no 2, 135Article in journal (Refereed) Published
Abstract [en]

The generation of a large-scale magnetic field in the kinematic regime in the absence of an alpha-effect is investigated by following two different approaches: the test-field method and the multiscale stability theory relying on the homogenization technique. Our computations of the magnetic eddy diffusivity tensor of the parity-invariant flow IV of G. O. Roberts and the modified Taylor-Green flow confirm the findings of previous studies. and also explain some of their apparent contradictions. The two flows have large symmetry groups; this is used to considerably simplify the eddy diffusivity tensor. Finally, a new analytic result is presented: upon expressing the eddy diffusivity tensor in terms of solutions to auxiliary problems for the adjoint operator, we derive relations between the magnetic eddy diffusivity tensors that arise for mutually reverse small-scale flows v(x) and - v(x).

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2015. Vol. 811, no 2, 135
Keyword [en]
dynamo, magnetic fields, magnetohydrodynamics (MHD), turbulence
National Category
Other Physics Topics Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:kth:diva-177420DOI: 10.1088/0004-637X/811/2/135ISI: 000363513800063ScopusID: 2-s2.0-84945582810OAI: diva2:873594

QC 20151124

Available from: 2015-11-24 Created: 2015-11-20 Last updated: 2015-11-24Bibliographically approved

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Brandenburg, Axel
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