Levitation stability of superconducting stators with addition of a ring-shaped magnet

High magnetic rigidity is required to optimize superconducting levitation. In this study, we propose a hybrid stator comprising a superconductor and a ring-shaped permanent magnet for improving levitation stability. We measured the oscillation characteristics of a magnet levitating above several hybrid stators with ring-shaped magnets of different thicknesses. The magnetic force between the hybrid stator and the levitating magnet was determined via semi-static displacement. By adding a ring-shaped magnet to the stator, we found that vertical attractive magnetic force and stiffness of the hybrid stator increased compared with that of a simple superconducting stator. The magnetic force showed hysteresis against the displacement of the levitating magnet. We observed that hysteresis energy loss increased with a thicker ring-shaped magnet. The oscillation frequency of the levitating magnet above the hybrid stator was higher than that of the simple superconducting stator. Faster decay due to hysteresis energy loss and small amplitude resulting from enhanced magnetic stiffness were also observed. An improvement in the stability of the levitating magnet was thus realized by the hybrid stator.