Drag torque of high T c superconductor magnet bearings with multi-piece ring magnets or superconductors

Abstract

In order for a superconductor magnet levitation bearing to rotate freely, the magnetic field from the magnet must be axisymmetric about the axis of rotation. In contrast, the shape of the superconductor need not be axisymmetric. This allows us to make a large ring of high temperature superconductor out of smaller pieces in the fabrication of superconductor magnet bearings. The problem then arises as to whether the substitution of a single large piece of superconductor by smaller pieces might contribute to additional power loss. We have investigated this by studying the drag torque experienced by multi-piece ring magnets as they turn above multipiece rings of superconductors, and comparing with results from single pieces of similar sizes. We have coordinated the variation of the drag torque during a turn with the relative orientation of the magnet and superconductor pieces. We use the mean value of the drag torque over several turns as a measure of power loss.