Cu-added Nb3Al multifilamentary superconductors having high Jc in high fields

The RHQT (rapid heating, quenching and transforming)-processed Nb ₃Al multifilamentary wire shows not only excellent strain tolerance but also 2-5 time higher J_c than those of the commercialized Nb₃Sn multifilamentary wires, and is being developed as a new practical superconductor. When the Nb/Al-2at%Cu microcomposite wire was rapidly heated and quenched, disordered A15 phase filaments were formed directly in stead of Nb-Al bcc supersaturated phase filament formation in the normal RHQT-process. With annealing at 700-800°C, its superconducting properties were improved drastically. The Cu-added Nb₃Al multifilamentary wire showed the maximum values of T_c=18.6 K and H_c2(4.2 K)=28.7 T, which are higher than the maximum values of T_c=17.9 K and H_c2(4.2 K)=25.8 T for the RHQT-processed Nb₃Al wire without Cu addition. In addition the new Nb₃Al superconductor showed higher J_c than that of the RHQT-processed Nb₃Al wire in high fields above 18 T. The maximum J_c is 360 A/mm² at 4.2 K and 21 T