Stability of the superconductive materials

Critical properties of a superconductor usable for design of the superconductive magnet was limited only to a curve between critical current density, Jc and magnet field, B at 4.2 K in most of cases. In this study, on the advanced A15 type compounds (Nb3Al, V3Ga, and so on) wire materials and Bi series oxides superconducting wire materials which are expected for next generation nuclear fusion reactor materials, their measurements and evaluations of three dimensional Jc-B-T superconductive critical surface containing temperature (T) and effect of mechanical strain ε on superconductive critical surface which is especially important at nuclear fusion reactor was evaluated at a viewpoint of pinning force in lines of magnet flux. In 1998 fiscal year, on a V3Ga wire material showing a peak effect interested from a viewpoint of stability of the superconductive materials, measurement and evaluation on its superconductive critical surface were carried out. As a result, it had a large meaning that stable positive temperature dependency of Jc against substantial temperature turbulence could be found out. And, it could also be elucidated that even at the Nb3Al wire material the most expected for the next generation nuclear fusion reactor material, it showed a remarkable peak effect of Jc like that in V3Ga when receiving high temperature heat treatment. Therefore, by effectively using the positive temperature dependency, and so on of Jc due to this peak effect, the Nb3Al would be a much unique material stable against not only electromagnetic force but also temperature turbulence. (G.K.)