Sweet Spots for Dynamo Action in a 1000 Rm Spherical Couette Experiment.

The search for a spherical Couette magnetic dynamo in the laboratory continues. The dynamo action is the process through which a magnetic field is amplified and sustained by electrically conductive flows. Galaxies, stars and planets, all exhibit magnetic field amplification by their conductive constituents. For the Earth in particular, the magnetic field is generated due to flows of conductive material in its outer core. At the University of Maryland our Three-meter diameter spherical Couette experiment uses liquid sodium between concentric spheres to mimic some of the dynamics of these flows, giving insight into these natural phenomena. We are now progressing from the previous amplified magnetic fields toward a possible dynamo state based on roughing the inner sphere boundary by adding baffles. While the modifications take place we focus our attention on previous unpublished experimental runs with a smooth inner sphere that achieved substantial amplification of the magnetic field but without dynamo generation. We present magnetic field amplification as a function of the different experimental parameters including Reynolds and Rossby numbers, and applied magnetic field. Thanks to recent studies in a hydrodynamic scale model, we can bring a better insight into these results and propose locations in the parameter space of the experiment as possible candidates for a dynamo generation given the forthcoming modifications that are currently taking place. If time allows, and these modifications are implemented by the time you are reading this abstract, we will additionally present new results on magnetic field amplification in a rough spherical Couette flow experiment. We gratefully acknowledge the support of NSF Grant EAR-IF 1909055.