Generation of axisymmetric modes in cylindrical kinematic mean-field dynamos of VKS type
Abstract
In an attempt to understand why the dominating magnetic field observed in the von-Kaacutermaacuten-sodium (VKS) dynamo experiment is axisymmetric, we investigate in the present article the ability of mean field models to generate axisymmetric eigenmodes in cylindrical geometries. An agr-effect is added to the induction equation and we identify reasonable and necessary properties of the agr distribution so that axisymmetric eigenmodes are generated. The parametric study is done with two different simulation codes. We find that simple distributions of agr-effect, either concentrated in the disk neighborhood or occupying the bulk of the flow, require unrealistically large values of the parameter agr to explain the VKS observations.