Effect of metallurgical history on ''J/sub c/(5T)'' in surface diffuse multifilamentary Nb3Sn

Data are presented of critical current density ''J/sub c/(5T)'' in a 5 T perpendicular magnetic field (and 10 T as well for selected samples) for multifilamentary Nb3Sn formed by Sn diffusion from a Cu--Nb composite's outer surface. The parameters varied are: composite diameter and Cu/Nb ratio, Sn percentage, filament diameter, reaction temperature, and time. The composite diameter varied from 0.254 to 0.08 mm; Cu/Nb volume ratio from 1.7 to 3; volume percentage of Sn from 2 to 13.8 percent; average filament diameter from 2 microns to 7 microns. The reaction temperature was varied between 550 to 7950C for different lengths of time, one to several thousand hours. A three-stage heat treatment was selected to formulate the basis for the reaction heat treatment map. The J/sub c/(5T) varied from 103 to greater than 3 x 105 A/cm2 over the entire composite cross section (Cu--Sn, Nb3Sn, Nb). The optimum performances were 38.8 A in 0.127 mm diam 1.9/1 Cu/ (Nb + Nb3Sn) composite at 5 T and 78 A in a 0.18 mm diam 3/1 Cu/ (Nb + Nb3Sn) at 5 T. 12 figures