PURPOSE: To enhance a critical current density without exerting any adverse effect of a thermal treatment on other structures by setting a diameter of an Nb filament at 1μm or smaller, and applying a thermal treatment at 500°C or lower for one day or longer.
CONSTITUTION: A quantity of Sn required for producing Nb3Sn is dispersed to be embedded in or between bundles so as to be located in the vicinity of an Nb filament. A diameter of the Nb filament is set 1μm or smaller, and a longtime thermal treatment is applied at a temperature of 500°C or lower for one day or more, where a material of structures other than the superconductive wire can be in an annealed state so as to prevent deterioration of mechanical strength. A critical current density Jc becomes higher as the temperature becomes lower than 500°C, and further, a high current density Jc can be obtained in a longer thermal treatment as the temperature becomes lower. The thermal treatment at 475-425°C for 40 to 180 days is preferable.
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TANAKA TOSHIKATSU
OGASAWARA TAKESHI
KOBAYASHI HISAYASU
YASOHAMA KAZUHIKO
KUBOTA YOJI
