Recent Developments of the Liquid Metal Taylor Couette Experiment PROMISE

In the beginning of the 20th century Taylor-Couette (TC) experiments were carried out with transparent liquids like water or air, which are electrical no-conducting. With the first experiments of Donnelly [1] in the sixties, a more general approach with liquid metal experiments started to investigate the interaction between magnetic fields and the TC flows of electrically conducting fluids. Two challenges of opaque liquid metal experiments are the measurement technique to investigate the flow structure inside the liquid and the precision and strength of the magnetic field.
We like to report recent results carried out with a quasi coaxial return path, which was introduced to the PROMIS experiment in the last years. Instead of the former frame coil an axial-symmetric return path closes the electrical circuit, which improves the field symmetry inside the experiment and minimizes the stray field outside the setup. Since this arrangement consists of an electrical parallel connection of the return conductors and the parallel connection of the hydraulic cooling circuit, it must be checked whether stability problems can occur in the current distribution in the return conductors. It turned out that the current return design can be controlled by simple and cheap proportional heater valves [2].

[1] R. J. Donnelly and M. Ozima, Phys. Rev. Lett., 4(10), 497--498, 1960
[2] M. Seilmayer and N. Krauter, IEEE Sensors Journal, 18(3), 1256--1264, 201