To support large currents in multifilamentary superconductors based on niobium-titanium alloys, a fine scale substructure is required within the superconductor wire. To produce substructure of the order of 100A, the conventional multifilamentary superconductor fabrication technology requires a rather large number of tedious processing steps. Typically a 5 inch diameter niobium-titanium alloy ingot is mechanically worked through extrusion and wire drawing, until 5 micrometers diameter filaments are obtained. The chemical inhomogeneity in the starting ingots that arises due to segregation of alloying elements during solidification is often deleterious to the superconductor properties. An altogether new manufacturing route for the preparation of multifilamentary superconductors is proposed, which has the potential of producing superconductors with improved characteristics, and significantly lower cost. The approach involves preparing continuous superconductor filaments, typically 40 micrometers thick, directly from the melt. Such thin filaments, when extracted from the melt experience high solidification rates. The high solidification rates lead to a chemically homogeneous microstructure with extremely fine grain sizes and sub-structures of the order of 100A. This project will address the feasibility of obtaining desirable microstructures for flux pinning and high critical current density. This development will obviate all the processing steps requiring extensive mechanical deformation. Approaches to incorporate the superconductor filaments prepared directly from the melt, into composite wires will also be explored. The work will result in significant property improvements in fine multifilamentary composite niobium-titanium superconductors, and considerable cost reduction in the production of such wires. The material will be suitable for a wide range of applications including dipoles and quadrapoles for future high energy accelerator magnets.
