超電導体技術開発の動向

Abstract

The application of superconductivity is a key to produce a number of breakthroughs in a vast area of science and technology covering new energy systems, computer electronics, medical diagnosis, high-speed transportations, high-energy particle accelerators, etc. The recent discovery of high Tc oxide superconductors may provide a more positive prospect for the future development of the superconductivity technology. In the area of metallic superconductors, the development of ultrafine filamentary wires for AC use, which may bring about a large impact in electrical engineering, is being carried out. The high-field performance of Nb3Sn wires has been significantly improved by the Ti-doping, and multifilamentary (Nb, Ti)3Sn wires capable of generating fields up to 17 T have become commercially available. The development of Nb3Al and other superconductors with high-field performance superior to that of (Nb, Ti)3Sn is also being proceeded using new fabrication technologies.The application of techniques elaborated the fabrication of metallic superconductors, e.g. powder process using metal sheath, solidification process, diffusion process and high-rate deposition process has been attempted for the processing of high-Tc oxide superconductors. Ag-sheathed BPSCCO tapes show a Jc (77K, OT) of 3×104/cm2, and keep nearly the same Jc at 25T and 4.2K. The solidification process has achieved an encouraging result for obtaining enough Jc in bulk high-Tc oxides. Superconducting tubes coated with a thick YBCO layer, promising for cavities and magnetic shieldings, have been fabricated by a plasma spraying process. Meanwhile, large Jc's at 77K and high magnetic fields have been obtained in thin oxide films prepared by different physical and chemical deposition processes. Various problems to be solved, e.g. homogenization, densification, crystal orientation and introduction of pinning centers, for improving Jc in bulk high-Tc oxides are also described in this article.