Multifilamentary Nb-Hf/Cu-Sn-Ga Composite Wires

Abstract

Multifilamentary Nb3Sn superconductors have been developed for large-scale applications, such as fusion reactor magnets and high-energy particle accelerators. However, the composite-processed Nb3Sn conductors with pure niobium cores and a Cu-Sn matrix are required to have better high-field current-carrying capacities for these applications. Recently, several attempts have been made to improve the critical current density, Jc, of composite-processed Nb3Sn in high fields by an alloying addition to the core or to the matrix. The additions of titanium, zirconium, or tantalum have been reported to increase both the Nb3Sn layer growth rate and Jc in high magnetic fields.1–3 Gallium additions to the Cu-Sn matrix have been reported to raise the upper critical field, Hc2, of the Nb3Sn.4 Of the various alloying additions to the core and matrix, it has been revealed through studies on single-core and 19-core composite specimens that the simultaneous addition of hafnium to the core and gallium to the matrix is most effective for increasing Hc2 and Jc in high fields of the composite-processed Nb3Sn.5, 6 Thus it is of great interest to examine the possibility of practical use of multifilamentary Nb-Hf/Cu-Sn-Ga composites. We report here the effect of the simultaneous addition of hafnium to the core and gallium to the matrix on high-field superconducting properties of the composite-processed multifilamentary Nb3Sn superconductors.