Dynamo action in heterogenous domains

From the technically point of view the realisation of dynamo action in the laboratory is a demanding task because it requires magnetic Reynolds numbers of the order of 10...100. In order to reach such values in experiments, materials with high relative magnetic permeabilities have been utilized (Lowes & Wilkinson, von Karman Sodium dynamo).

The modification of the induction process by material properties is examined by means of simulations of the kinematic induction equation in hetrogenous domains where disk like assemblies with high conductivity and/or high permeability are introduced in a cylindrical volume filled with liquid sodium.

Both material properties not only lead to a decrease of the effective magnetic Reynolds number but also result in a quite distinct geometric structure of the final eigenmode. Furthermore, high permeability material even if localized in a small volume like the soft iron impellers in the VKS dynamo, essentially determines the field generation process and is reponsible for the selection of the dominating azimuthal dynamo mode.