Magnetic hysteresis losses and critical current densities in submicron filament bronze-processed Nb3Sn wires

Submicron filament bronze-processed multifilamentary Nb3Sn wires with Cu-5at%Sn-X matrix and Nb-1at%Ta cores have been fabricated. The Ge content in bronze matrix is changed in the range from 0% to 1% for optimizing Ge content. The cross-sectional structure of wires was the central-Cu-stabilizer type to facilitate, by external Sn diffusion, improvement in critical current density, Jc, and hysteresis losses, Qh. The simultaneous addition of 0.25at%Ge to the bronze matrix and 1at%Ta to the Nb core enhances the non Cu Jc by 60%, and decrease the Qh by approximately 60%. By Sn plating, the non Cu Jc was improved by 10%, and the Qh was reduced by 5%. The formation of a thin layer richer in Ge is observed in the Nb3Sn layer and the matrix adjacent to the Nb3Sn layer, which may be effective for the improvements in Jc and Qh characteristics