Low friction in mixed-mu superconducting bearings

Abstract

Individual magnetic steel rotors were levitated by combining the attractive force between permanent magnets and the steel with the repulsive force between high-temperature superconductors and the steel. The free spindown of several rotors was observed, and the effective coefficient of friction for the bearing was calculated as a function of geometry. Low-speed coefficients of <10−8 were observed, and the velocity dependence of MnZn ferrite rotors suggest that coefficients of <10−6 are attainable at bearing rim velocities of 100 m/s.