Increasing Helicity to Achieve a Dynamo State in a Spherical Couette Sodium Experiment

Dynamo theory describes the generation of magnetic fields in the highly turbulent flows of conducting fluids, for example, in stars and planetary cores. Spherical Couette flows, which are shear-driven flows between two concentric and independently rotating shells, are one of the experimental models used to achieve dynamo action in the laboratory. We aim to achieve a dynamo state in our three-meter spherical Couette model that currently reaches Reynolds numbers up to 10⁸ with amplifications of the magnetic field between 10-30% but without a self-sustaining dynamo state. Numerical studies [K. Finke and A. Tilgner. Phys. Rev. E, 86:016310, Jul 2012] suggest adding roughness to the inner core, which we attempt by adding baffles on the inner sphere. Our proposed set up reduces the threshold for dynamo action by increasing the poloidal flows with respect to the zonal flows and hence increasing helicity. In this work, we present measurements of the velocity profiles and torque measurements in a 40-cm spherical Couette water apparatus for different baffle designs of the inner sphere. These results are fundamental for future modifications in the three-meter model such as shape and height of the baffles, and power of the motors. We gratefully acknowledge support from NSF EAR-1417148.