Discussions about measurement results of levitation force and its time relaxation between GdBCO bulk superconductors and superconducting magnet with a high magnetic field gradient

High temperature bulk superconductors have significant potential for various engineering applications such as a flywheel energy storage system. This system is expected to decrease the energy loss by using bulk superconductors for the bearing. Recently, the authors have developed a new superconducting magnet to realize the large levitation force. The magnet has two coils on the same axis and each coil's current flows to the opposite direction. In this system, the axial component of magnetic field is canceled each other but the radial component of magnetic field is expected to be enhanced. In this paper, the authors measured the levitation force and its time relaxation at different bulk positions in both cases of one and two bulks by using this new magnet. From the results, it was made clear that the levitation force of two bulks was twice as large as that of one bulk and its time relaxation was decreased. In addition, Hall sensors were attached on the sample surface to measure the surface magnetic field distribution. The behavior of the magnetic field was discussed.