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

Abstract

Abstract. 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. IntroductionRecently, energy saving has become a critical feature of mechanical systems because of an increase in energy consumption by the growing world population. Superconducting magnetic levitation technologies are deemed to be a promising approach for energy conservation [1-3]. Magnetic levitation above a bulk superconductor is caused by the penetration and pinning of the flux lines in the superconductor. The absence of physical contact between the rotor and stator in superconducting bearings effectively eliminates a major source of friction. Moreover, no active control is required for positioning the levitated magnets. The performance of applications using a superconducting levitating system depends on the stability of the levitation force. An application (e.g., superconducting bearings for energy storage flywheels) having high levitation stability can operate with high-speed rotation and store more energy. The possibility of experiencing failure will also decrease. Therefore, to achieve performance elevation in superconducting mechanical systems, improving levitation stability by increasing the magnetic stiffness of superconducting levitation is important. We propose a hybrid stator comprising a superconductor and a ring-shaped permanent magnet for high-performance bulk superconducting applications [4]. Upon addition of a ring-shaped magnet under the superconducting stator, the attractive force between the floating magnet and stator becomes greater at large distances as compared with short distances. Hence, vertical magnetic stiffness is enhanced and levitation stability