14–18 Feb 2011
Wenner Gren Center
Europe/Stockholm timezone

Helicity generation and α-effect in MHD Taylor-Couette flows

14 Feb 2011, 16:00
30m
Wenner-Gren Center, floor 7, Hörsalen (Wenner Gren Center)

Wenner-Gren Center, floor 7, Hörsalen

Wenner Gren Center

Sveavägen 164 SE-113 46 Stockholm Sweden

Speaker

Markus Gellert

Description

Helical magnetic background fields with adjustable pitch angle are imposed on a conducting fluid in a differentially rotating cylindrical container. The small-scale kinetic and current helicities are calculated for various field geometries, and shown to have the opposite sign as the helicity of the large-scale field. These helicities and also the corresponding $\alpha$-effect scale with the current helicity of the background field. The $\alpha$-tensor is highly anisotropic as the components $\alpha_{\phi\phi}$ and $\alpha_{zz}$ have opposite signs. The amplitudes of the azimuthal $\alpha$-effect computed with the cylindrical 3D MHD code are so small that the operation of an $\alpha\Omega$ dynamo on the basis of the current-driven, kink-type instabilities of toroidal fields is highly questionable. In any case the low value of the $\alpha$-effect would lead to very long growth times of a dynamo in the radiation zone of the Sun and early-type stars of the order of mega-years.

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