Experimental Investigations Of Influence Of Temperature Cycling And Lateral Moving Speed On Electromagnetic Forces In High-Temperature Superconductor Levitation Systems

Owing to its higher upper critical magnetic field, higher critical current density and transition temperature above the temperature of liquid nitrogen, high temperature superconductor (HTS) shows some very important features in applications. The diamagnetic and flux pinning characteristics make high temperature superconducting levitation system has excellent loading capacity and novel passive stable characteristic. Thus the high temperature superconducting levitation system become an important branch of applications of superconductivity. The electromagnetic force characteristic researches on the typical superconducting levitation style, a superconductor and a permanent magnet (PM) levitation system, have become the basis of the superconducting levitating system operation design, and a subject of considerable interest, which have been extensively investigated. This Ph. D. dissertation presents some experimental investigations of the static and dynamic electromagnetic force characteristics in the high temperature superconductor levitation system under some different temperature cyclings and lateral moving velocity conditions, some new phenomena and characteristics are found, and the results are explained; The frozen-image model is also modified to fit the experimental results of influences of lateral moving of permanent magnet on the electromagnetic forces.Firstly, the influences of different cooling temperature on the hysteretic curves of levitation force versus gap between the bulk HTS and the PM under zero-field cooling (ZFC) are described. It is found that with the decreasing of cooling temperature, there exists a crossing phenomenon on the hysteretic curves of levitation force. Even though the hysteresis loop area decreases with the decreasing of cooling temperature and the maximum levitation force of each hysteretic curves of different cooling temperature increase and saturate under lower cooling temperature condition, the crossing area and the gap of crossing point increase with the decreasing of cooling temperature.Secondly, the influences of some temperature cycling on the levitation force relaxation is described. It is found that the levitation force continue to decrease when the temperature of superconductor is decreased continually from the initial cooling temperature during the relaxation, and it will increase with the increasing of temperature after the continual decreasing. According to these results, a temperature stabilization pretreatment method is presented. Another temperature cycling that increase the temperature from the initial cooling temperature under zero magnetic field condition and then go back to the initial cooling temperature also under zero magnetic field condition will show a fixed ratio between the decreased levitation force ranges of increasing and decreasing processes if the target value of increasing process for different initial cooling temperature cases are the same.Finally, the effects of the initial cooling height (CH) and the lateral moving speed on the levitation force and the lateral force in the levitation system are described. The measurement results show that for some cooling height after the symmetrical movement (from the CH to levitation height) the effects of lateral movement and lateral moving velocity on the levitation force are remarkable. The levitation force will decrease for higher CH and increase for lower CH after the lateral movement. The hysteresis loop area of levitation force increase with the increasing of lateral moving velocity for higher CH, and the hysteresis loop area have nearly no change for lower CH. The hysteresis loop area of lateral force for all CH have nearly no change with the increasing of lateral moving velocity. The frozen-image method has also be modified to simulate the results of above, that the lateral moving speed has significant effect on levitation force-lateral displacement hysteresis loop curves.