The Karlsruhe dynamo experiment

The Karlsruhe Dynamo experiment is aimed at showing that a liquid sodium flow in an array of columnar helical vortices, confined in a cylindrical container, can generate a magnetic field by self-excitation. The flow structures in the liquid core of the Earth are topologically comparable to those being realized within the Karlsruhe test module. In three test series it has been demonstrated that magnetic self-excitation occurs and a permanent magnetic saturation field develops which oscillates about a well defined mean value for fixed flow rates. Dynamo action is observed as an imperfect bifurcation from a seed magnetic field of the environment. Two quasi-dipolar magnetic fields of opposite direction have been realized. A transition between these two states can be enforced through an imposition of a sufficiently strong external magnetic perturbation on the initially existent dynamo field. These perturbations were induced with the aid of two Helmholtz coils. A time series analysis of the magnetic field fluctuations shows several characteristic dynamic features which are in agreement with theoretical predictions of models available in the literature. (orig.)