NB TUBE PROCESSED NB3AL MULTIFILAMENTARY SUPERCONDUCTORS

In addition to microstructural studies, various characteristics of Nb tube processed Nb3Al MF conductors needed in designing superconducting magnets are described. With decreasing Al core diameters of Nb/Al composite, the formation rate of A15 phase increased and its lattice parameter decreased conversely. This was accompanied by an increase in T(c) and H(c)2(4.2K), suggesting that the small diffusion spacing between Nb and Al facilitates to form the metastable A15 phase with stoichiometric composition. On the other hand, both the n value of V-I curve and its field dependence decreased with decreasing Al core diameter below 50 nm, which suggests the sausaging of Al filaments in the heavily cold-worked sample. The reversible bending strain range was at least up to 1.4% which is much larger than that of Nb3Sn, indicating the applicability of the react and wind method to Nb3Al superconducting magnet. Degradation in J(c)(4.2K, 12T) of the solenoid with 1.8% winding strain was about 20%. A decrease in temperature from 4.2 to 1.8 K caused an increase H(c2) by 2.5 T.