The Trapped Flux Of YBCO Above The Maglev Field Of Bimodal Guidaway At Below 77K

Since the discovery of superconductivity by Onnes in 1911 and the high-temperature superconductors (HTSCs) in 1986, many investigations on superconducting material and its applications have been carried out. For the characteristic of self-stability of high-temperature superconducting (HTS) bulk in applied field there are many potential applications, such as Maglev vehicle, flywheel, bearing, motor, and so on.A lot of efforts have been done on high-temperature superconducting (HTS) Maglev, and many outstanding achievements emerged. However, with the rapid developing science and technology, for desiring of better levitation performance to promote Maglev application, more in-depth investigations must be done. The study in this paper is mainly on the flux trapping characteristic of bulk HTSC which affects levitation and guidance performance. The levitation performance and the trapped flux of bulk YBa₂Cu₃O_7-σ (YBCO) with two different permanent magnet guideways (PMGs) at the temperature of 77 k and below 77 k are investigated respectively.Firstly this paper compares the field distribution of two different structure PMGs and their field characteristic respectively and evaluates applied field influence on levitation performance by the experiment results on levitation force and guidance force at different gap and cooling height. The results illustrate that field horizontal component B_x contributes to the levitation force and the field vertical component B_z contributes to the guidance force. Because the force generate from the interaction of induced current in with applied field, for desiring large levitation force, the main induced current area of the bulk HTSCs should be possibly located in strong B_x region. In the same way, the induced current that generates guidance force should possibly flow restrainedly in strong B_z region. Moreover, the results show that the levitation performance of bulk YBCO above the bi-polar Halbach PMG is better than over the uni-polar PMG. A low-temperature experimental platform was built for the sake of studying the magnetic flux trapping characteristics of the bulk above the PMGs at the temperature below 77K, and a vacuum enclosure and its fixtures were designed for refrigerator. The magnetic flux trapping characteristics of the ring bulk over the bi-polar PMG was investigated experimentally. The flux trapping dependent with cool field height, the time, the temperature and the moving process is major research issues. The trapped flux increases with lowering temperature and decreasing field cooling height and reaches a plateau in 20 minutes after fully field-cooling at 77K-60K.