Slowing Down of Magnetic Relaxation in Superconducting Levitation System

Abstract

An effect of slowing down of lift force relaxation in a superconducting levitation system was studied. The relaxation dependences for the interaction force between a high-temperature superconductor and a permanent magnet, when a levitating object was fixed (force-in-time experiments), and for the levitation height in a real levitation system (height-in-time experiments) were measured. In force-in-time experiments, we observed that the force relaxation with the rate depended on the stiffness of the mechanical constraint, which was imposed on the object of levitation. However, the principle of levitation was violated in these experiments, since force measurements required a contact with the object to which the force was applied. Therefore, force-in-time measurements could not be as an experimental verification of the force relaxation in levitation. Height-in-time experiments clearly indicated that in the case of natural levitation, when a high-temperature superconductor (HTS) sample bore only on magnetic field, the height of levitation (and hence the lift force) did not change over a long period of time. When the levitating object was fixed for some time, the latent force relaxation took place and the levitation height decreased after the removal of the external linkage. It is assumed that the free oscillations of the sample cause small variations of magnetic field on the superconductor’s boundary; it suppresses flux creep.