Reduction of levitation decay in high Tc superconducting magnetic bearings

Relaxations of levitation properties in high T(c) superconducting (HTSC) magnetic bearings are known to reveal different behaviors on the ascending and descending branches of their force-displacement curves, i.e. the relaxations on the ascending branch seem to be reduced more than those on the descending one. In this paper, the effect has been theoretically illustrated in a superconducting half-space based on the Bean model and interpreted by the hysteretic behaviors of shielding current. Numerical simulations on the relaxation of levitation forces have been carried out, taking the hysteresis effect of shielding current into account. The relaxations of levitated heights (displacements) have also been evaluated numerically and simulated results were compared with measured data. The effect improves the levitation characteristics both in calculations and experiments. Furthermore, the practical applications of the above mentioned effect (referred to a Hysteresis Hardening Effect) are also discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.