Development of Nb3Al/Cu Multifilamentary Superconductors

Abstract

The Nb3A1 superconductor has been expected to the application under the high field, such as the one for International Thermo-nuclear Experimental Reactor (ITER), on the point of superior characteristics of Ic under stress. The present status of the development of Nb3A1 superconducting wires manufactured by the Jelly-Roll process is presented in this paper. The recent development has achieved the Nb3A1 superconductor stabilized by the copper matrix with a high critical current density and a low hysteresis loss. In the development, the microstructure of Nb-Al compound phases, each identified by EDS, are observed. The volume of each Nb-Al phase calculated by the Image Analysis System is discussed in terms of its dependence of Jc. With a non-copper critical current density of more than 550 A/mm² at 12T, the wire features excellent high field characteristics, for example μ0Hc2 is 21.5T. Also, this wire has less degradation of Ic by strain compared to Nb3Sn. Hysteresis losses in the wire was measured by the magnetization method. For the field perpendicular to the wire length, it was shown that the effective filament diameter is almost equal to the actual filament diameter (21μm). On the other hand, the hysteresis loss for the parallel field was around one-fourth as large as that for the perpendicular one, corresponding to an effective filament diameter of approximately 8 µm. The 40kA-class cable-in-conduit conductor was fabricated to demonstrate its applicability to fusion magnets. The critical current test of the conductor proves that the capacity of 40kA is attained at 11.2T. The practical 10kA-–100m class long length cable-in-conduit conductor, of which conduit is Titanium, was fabricated first in the world.