Tuning a precession driven flow for optimized magnetic field generation in the DRESDYN dynamo experiment.

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Cosmic magnetic fields are ubiquitous phenomena that are observed on all scales, from planets and stars to galaxies and clusters of galaxies. The origin of these fields involves the formation of electrical currents by means of complex flows of conducting fluids or plasmas. Fluid flow induced magnetic fields via this dynamo effect have also been observed in experiments, which, however, require considerable technical efforts due to the significantly smaller scales available in the laboratory. The project DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) conducted at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) provides a new platform for a variety of liquid sodium experiments devoted to problems of geo- and astrophysical magnetohydrodynamics. The most ambitious experiment within this project is a precession driven dynamo experiment currently under construction which consists of a cylinder filled with liquid sodium that simultaneously rotates around two axes. The present proposal addresses numerical and experimental studies aimed at the discovery of parameter regimes that will allow dynamo action in the planned experiment and at optimizing the precession driven flow in order to improve the dynamo process. For this purpose, we pursue a particular approach to increase the forcing efficiency and to control the large scale flow pattern by considering radial baffles mounted onto the inner side of the lids of the cylindrical container. The interaction of solid baffles with an internal fluid flow presents a complex fluid mechanical problem that can only be addressed by following complemental numerical and experimental approaches. The corresponding simulations and model experiments will provide the basis for future experimental campaigns of the large scale liquid sodium dynamo experiment at HZDR.