| In1986, due to the discovery of high temperature superconductor (HTSC), superconducting application exploration entered into a new era. Because of the inherent flux pinning properties of HTSCs, self-stable levitation can be realized in externally applied magnetic fields. This phenomenon prompted the use of bulk HTSC in many applications such as high temperature superconducting (HTS) Maglev bearings, HTS flywheel energy storage systems, HTS Maglev vehicle and so on. In these HTS Maglev application systems, it is common to obtain stable levitation with the random combination of bulk HTSC pieces subjected to an applied magnetic field. However, upon further studying, more and more researchers noticed the growth properties of the top-seeded melt-grown bulk HTSC, including the differences of trapped magnetic flux performance between growth sectors (GS) and growth sector boundaries (GSB) inside a bulk HTSC, which may impact the whole levitation performance in a magnetic field. As to the related calculation analyses, the growth properties have not been taken into account in the modeling and calculation of HTS Maglev systems. Hence, an accurate calculation and evaluation have not yet been achieved up until now, as well as the levitation performance and variation trends due to the HTSC growth properties in different applied magnetic fields. Therefore, further experimental work must take place to better understand the implications of the growth properties of top seeded melt-grown bulk HTSCs.This paper mainly experimentally investigated the growth of bulk HTSC in the HTS Maglev system. Firstly, I studied the growth properties on the levitation performance in a one-layer Maglev system. In this experiment, HTSC bulks were positioned in the highest possible magnetic field density position, Bz-max, above the Halbach permanent magnet guideway (PMG) surface. Comparisons were made according to the relative position relation between the GSB and the Bz-max position; an aligned GSB pattern (AGSBP) and a misaligned GSB pattern (MGSBP). By conducting typical levitation performance and relaxation measurements on the force between the HTSC and the PMG, it was found that the bulk array with AGSBP exhibited a better levitation performance than that of the MGSBP. And on this newly found basis, we also explored the growth properties on the levitation performance in a double-layered Maglev system. In the double-layer experiment, the positions of the HTSC bulks were positioned in a similar manner as that of the one-layered Maglev system. The array pattern of the lower-layer bulk with the AGSBP exhibited a better levitation performance. According to the relative position relation between the GSB of the upper-layer bulk and that of the lower-layer bulk, the array patterns of the upper-layer bulk were AGSBP and MGSBP. Results show that the bulk array with the AGSBP between the upper-layer bulks and the lower-layer bulks exhibited a better levitation performance than that of the MGSBP.Based on the above derived conclusions, we further optimized the thickness of the lower-layer bulks in the double-layered Maglev system. It turns out that the levitation performance of the double-layered bulk Maglev system with the AGSMP reached an optimum when the thickness of the lower-layer bulk was set to6mm.A main conclusion in my work is that the existence of an alignment growth properties effect on the trapped magnetic flux in HTSC bulks affects the levitation performance in the Maglev system. The levitation force of the studied Maglev system can either be enhanced or mitigated based on geometry optimazation. Via levitation performance studies of the one-layered and double-layered Maglev system, several optimum bulk HTSC array patterns were obtained as well as the optimum thickness of the lower-layer bulks. These results are helpful and will support a new perspective and methodology for the performance optimization of present HTS Maglev systems inclusive of HTS bearings as well as future modeling calculations of HTS Maglev systems. |
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