Progress on Three Meter Spherical Couette Experiment and Implementation of TEM method

The three-meter experiment located at the University of Maryland is a liquid sodium spherical Couette apparatus designed to better understand the conditions that bring about Earth's dynamo. The dynamo theory describes how rotating, convecting, and electrically conducting fluid interactions in Earth's outer core can generate and maintain a magnetic field. After adding baffles to the inner sphere based on the advice of Finke and Tilgner [Phys. Rev. E 86.1, 016310 (2012)] , we see greatly enhanced torques and induced magnetic fields. Impulsive starts to the rotation of the inner sphere with no externally applied magnetic field generate exponentially growing magnetic fields over one order of magnitude, with a time constant of 2.1 seconds. We are working toward building a geophysical instrument that employs transient electromagnetics, a technique that should allow us to estimate the angular velocity profile of the fluid, previously unmeasured in this apparatus. This new instrument consists of a dipolar primary coil and a quadrupolar secondary coil. By applying Faraday's and Lenz's laws we are able to compare the field generated from the primary with the fields measured in the secondary. This allows us to track the eddy currents and magnetic fields being dragged by azimuthal motions in the fluid. We describe design specifications on coil parameters, as well as experimental choices in applying the system to estimate the azimuthal velocity profile.