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This paper presents a change of magnetic flux trapped in the YBCO bulk magnet under thermal excursions. We have supposed a new cryocooler system for the high temperature superconducting(HTS) bulk magnet in which the thermal cycles are generated. From the past research, it was found that the trapped flux mainly deteriorated at the first temperature rise, but a large change of the trapped flux was not seen at the first temperature descent and following thermal cycles. Degradation of the trapped flux by the first temperature-rise was explained by using the bean model. Moreover we proposed the model which does not have a current distribution constant. In this paper, we examined a change of magnetic field in each part of the bulk in detail. In addition, we applied attention to the change of the trapped flux after the first temperature rise. Although there is no big change of the trapped flux after the first temperature-rise, it is decreasing slowly. This cause is considered as influence of the flux creep, but its decay is more rapid than usual. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

In development of a flywheel energy storage system, electric power loss reduction is expected by using superconducting bearings. However, for realization of superconducting bearing strong levitation force, rotation loss reduction and axial descent reduction are required. It is known with axial descent reduction technology that a preload method is effective, whereas by this method, the levitation force becomes quite small compared with the normal levitation. We confirmed the performance of the preload method by experiment using a YBCO superconducting electromagnet. The preload method is improved and a method, which does not change the rate of the force relaxation and makes the levitation force larger than the existing preload method is proposed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper presents a change of magnetic flux trapped in the YBa2Cu3Ox (YBCO) disk under thermal excursions. We have supposed a new cryocooler system for the high temperature superconducting (HTS) magnet in which the thermal cycles are generated. As a result, it can be found that the trapped flux deteriorated at the first temperature-rise stage, but it kept constant after the first temperature-fall stage. The deterioration at the first temperature-rise stage can be explained by the Bean’s model, but the result of the following stages can’t be explained by it. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]