Study of High-Tc Superconducting Bulk Moving With Different Speeds in Applied Magnetic Fields

The force-speed relationship of a bulk YBCO moving above a permanent magnetic guideway was studied. The experiments show that the levitation forces at the lowest position F_max increase with the increment of descending speed and tend to approach a certain levitation force F_S.max. Calculations based on a simplified superconducting ring and flux flow model show that the force variations can be ascribed to the resistive electric field produced by flux motion. Further calculation reveals that, by increasing the descending speed, the thermo-dissipation inside the superconducting ring immediately after the descending process exponentially declines, approaching zero while the speed approaches infinity, and F_max reaches F_S.max. Therefore, the thermo-dissipation inside the bulk YBCO can be defined as a parameter for evaluating levitation force losses. Those results might be useful in pragmatic design of high-Tc superconducting levitation devices and magnetization of type-II superconductors.