Nb tube processed Nb3Al multifilamentary superconductors

In addition to microstructural studies, various characteristics of Nb tube processed Nb₃Al multifilamentary (MF) conductors needed in designing superconducting magnets are described. With decreasing Al core diameters of the Nb/Al composite, the formation rate of the A15 phase increased, and its lattice parameter decreased conversely. This was accompanied by an increase in T_c and H_c2 (4.2 K), suggesting that the small diffusion spacing between Nb and Al facilitates the formation of the metastable A15 phase with stoichiometric composition. On the other hand, both the 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 up to at least 1.4%, indicating the applicability of the react-and-wind method. The degradation in the J_c (4.2 K, 12 T) 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 of H_c2 by 2.5 T