Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

1 Publication
On the axissymmetric dominance of the magnetic field in the VKS dynamo experiment.
Giesecke, A.; Stefani, F.; Gerbeth, G.;
In order to understand the results of recent dynamo experiments, the behavior of kinematic dynamos in cylindrical geometries is analyzed. Simulations are performed applying a hybrid finite volume/boundary element method that allows a stringent treatment of insulating boundary conditions.

A suitable prescribed velocity field, either analytic or -- more realistic -- from measurement data of water experiments, leads to dynamo action if a critical value for the magnetic Reynolds number is exceeded.

In case of an axisymmetric velocity field the simulations always result in a non-axisymmetric eigenfield which is dominated by the azimuthal m=1-mode. However, in contradiction to this expected result, the experimental realisation exhibits an axissymmetric field configuration.

Until today, no satisfactory explanations for the dominating m=0-mode are established. A recently presented approach is based on an alpha-effect caused by helical fluid motions between the impeller blades that drive the flow. However, it turned out, that the necessary
amplitude which is required for m=0 dominated solutions is well above realistic values that might be realized in the experiment.

Further potential explanations involve non-axissymmetric contributions either caused by a drifting large scale vortex structure as observed in water experiments or introduced through the azimuthal varying high permeability region from the ferrous impeller blades, which should ideally give rise to a strong axisymmetric azimuthal field component within the impeller region.
Keywords: Dynamo
  • Lecture (Conference)
    11th MHD days, 01.-03.12.2008, Ilmenau, Germany

Publ.-Id: 11958 - Permalink