Rotation loss reduction of superconducting magnetic bearings by stacking and rearranging the shape of the bulks

Energy storage by a flywheel system has recently been developed as a promising application of high temperature superconducting bulks. Rotation loss reduction is necessary for an efficient operation of the superconducting magnetic bearings (SMB), which is the most essential component of the system. Typical radial type SMB consists of a superconductor stator and a permanent magnet rotor that is sustained by a magnetic force deduced from high flux pinning of the bulk superconductors. If the stator is a simply segmented circular array of Y-Ba-Cu-O bulks, inhomogeneity of the trapped magnetic field is unavoidable, which induces eddy currents in the metallic component in the rotor. Such a rotation loss is one of the major problems for a practical use of SMB. We will present the relationship between the inhomogeneous magnetic field and the rotation loss of SMB and give a general principle for reduction of rotation loss in SMB