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Turbulent Dynamos with Shear and Fractional Helicity
Stockholm University, Faculty of Science, Department of Astronomy.
2009 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 699, 1059-1066 p.Article in journal (Refereed) Published
Abstract [en]

Dynamo action owing to helically forced turbulence and large-scale shear is studied using direct numerical simulations. The resulting magnetic field displays propagating wave-like behavior. This behavior can be modeled in terms of an αΩ dynamo. In most cases super-equipartition fields are generated. By varying the fraction of helicity of the turbulence the regeneration of poloidal fields via the helicity effect (corresponding to the α-effect) is regulated. The saturation level of the magnetic field in the numerical models is consistent with a linear dependence on the ratio of the fractional helicities of the small and large-scale fields, as predicted by a simple nonlinear mean-field model. As the magnetic Reynolds number (Re M ) based on the wavenumber of the energy-carrying eddies is increased from 1 to 180, the cycle frequency of the large-scale field is found to decrease by a factor of about 6 in cases where the turbulence is fully helical. This is interpreted in terms of the turbulent magnetic diffusivity, which is found to be only weakly dependent on the Re M .

Place, publisher, year, edition, pages
2009. Vol. 699, 1059-1066 p.
Keyword [en]
MHD, turbulence
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:su:diva-32534DOI: 10.1088/0004-637X/699/2/1059OAI: oai:DiVA.org:su-32534DiVA: diva2:282395
Available from: 2009-12-20 Created: 2009-12-12 Last updated: 2017-12-12Bibliographically approved

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