Saturation Mechanism in a Model of the Karlsruhe Dynamo

Abstract

The dynamo experiment in Karlsruhe (Busse et al., 1998) has been successful in generating a self sustained magnetic field (Stieglitz and Müller, 2000). The focus of theoretical investigations now shifts from the study of the conditions for the onset of dynamo action to the mechanisms responsible for saturation. One might suspect that due to the guiding mechanical structures present in this experiment, saturation simply happens in that the magnetic field grows until the Lorentz force reduces the volumetric flow rate to its critical value, without any significant change to the shape of the velocity field. Any pressure applied by the pumps in addition to the critical pressure would be balanced by the Lorentz force according to this scenario. Experimental observations show however that volumetric flow rates continue to increase as a function of the applied pressure even when a steady dynamo field is present, which indicates that the velocity profile inside individual spin generators changes in response to the magnetic field.