One of the prospective applications of high critical temperature superconductors is a superconducting magnet for the magnetically levitated (Maglev) train. Recent development shows that REBaCuO and LRE(light rareearth)BaCuO superconductors prepared by melt processes have a high critical current density at 77 K and high magnetic fields. LRE-B a-C U-0 bulk superconductors m elt-processed in a reduced oxygen atmosphere, named oxygen-controlledmelt-growth (OCMG) process are very promising for high field application as a superconducting permanent magnet with liquid nitrogen refrigeration. Compared to good quality melt-grown REB aCuO bulks, LREBaCuO bulks exhibit larger critical current densities in high magnetic fields and much improved irreversibility field at 77 K, implying that more effective flux pinning can be realized in a commercially feasible way. In this study, we discuss the possibility of a superconducting bulk magnet for a Maglev train. A preliminary design of the bulk magnet and also melt processing for REBaCuO and LREBaCuO bulk superconductors and their characteristic superconducting properties are presented.
We are investigating the possibility of using bulk magnets in the Maglev system. It is considered that bulk magnets for the Maglev system must be composed of numerous superconducting bulks arranged in rows and columns for each magnet pole because a bulk superconductor with a high critical current density doesn't have a sufficiently large size for Maglev magnet. Therefore, it is necessary to examine the flux-trapping characteristic of superconducting bulks arranged in array. Flux-trapping experiments are performed using the meltprocessed YBaCuO superconducting bulks arranged in rows and columns, in which each bulk individually has a magnetizing coil, and the bulks are magnetized by field cooling. It is found that, when the superconducting bulks are arranged in rows and columns, the trapped flux density and the generated magnetic field are smaller than those when a superconducting bulk is used alone. The rate of decreases in the trapped flux density and the generated magnetic field becomes larger with increases in the number of superconducting bulks arranged in array. The trapped flux decreases conspicuously in particular at a superconducting bulk surrounded by other superconducting bulks.
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