High permeability material and dynamo action

A prescribed flow of liquid sodium provides an energy source for self-generation of a magnetic field. The influences of non-uniform material properties on the dynamo process are examined by means of kinematic simulations of the electromagnetic induction equation.

High permeability material even if localized in a small volume like the flow driving impellers in the French VKS dynamo experiment, essentially determines the field generation process (decrease of the effective critical magnetic Reynolds number and enforcement of internal boundary conditions on material interfaces). Permeability caused facilitation of dynamo action might be important as well for the helical flow in cooling circuits of fast breeders. Preliminary simulations for a model flow in and around soft-iron sub-assemblies (that comprise the nuclear fuel pins) show a reduction of the critical magnetic Reynolds number for the onset of dynamo action by a factor of 2.