Cap core design for high levitation force in a 3D superconducting actuator with HTS bulk

We have been developing a 3D superconducting actuator with HTS (high temperature superconducting) bulk and two-dimensionally arranged multiple electromagnets. The application of HTS bulk enables stable levitation and suspension due to its strong pinning force. The performance of the actuator is determined mainly by the spatial distribution of the generated magnetic field of the electromagnets. For the sake of improving the levitation force, we proposed to attach a sliced iron sheet (we called this cap core) on the top surface of the core in each electromagnet. The proposed cap core was expected to lead to an intensive concentration and abrupt gradient increase of the perpendicular component in the magnetic field through the HTS bulk of the electromagnets. We experimentally confirmed and measured the effect of the cap core. For the optimized design of the cap core, we calculated the spatial distribution of the magnetic field on the surface of the electromagnet using 3D FEM analysis for several cap cores and estimated the levitation force of the HTS bulk using the calculated result.