Analysis of levitation stability of a superconducting ball with two charging methods

A superconducting bearing fabricated by low temperature superconductors is introduced in which the ball, field-shaping rings all work in the Meissner state. The levitation stability of the ball is related to the values of lower and upper charging currents and the charging method of coils. The distribution of magnetic field and magnetic force are calculated with finite element method during the vibration of the ball. According to the Newton's laws of motion, the vibration characteristics, including the bearing stiffness, tolerable disturbing energy, and vibration amplitude, are analyzed at different charging currents when the coils are charged by constant current source method and closed-loop coil method respectively. The values of charging currents are calculated at which the tolerable disturbing energy reaches the maximum value. The calculated results show that the maximum tolerable disturbing energy with closed-loop coil method is larger than that with constant current source method. Moreover the corresponding vibration amplitude with closed-loop coil method is smaller. With this charging method, the total magnetic flux of the coils is invariable during the vibration of the ball, but their charging currents vary with the displacement.