Development of high performance multifilamentary Nb-Ti-Ta superconductor for LHC insertion quadrupoles

A preliminary investigation of a new Nb-Ti-Ta (39 wt.Nb, 44 wt.Ti, 17 wt.Ta) alloy has been investigated as a possible material for application at 1.9 K and 10.5 T in the insertion quadrupoles of LHC, 1550 A/mm/sup 2/, the highest $9 yet reported critical current density at 10.5 T (1.9 K), was achieved in a monofilament of this material. The initial multifilamentary production strand produced a lower 10.5 T (1.9 K) critical current density of 1370 A/mm/sup 2/. $9 Large variations in precipitate size were produced in the microstructures, which have yet to be fully optimized. Quantitative analysis of the microstructures in a Nb-44 wt.Ti-15 wt.Ta alloy reveals a linear relationship between $9 volume 554330f alpha -Ti precipitate and critical current density at 5 T and 8 T (4.2 K). The increase in critical current with precipitate volume is less than for Nb-47 wt.Ti. High resolution FESEM electron backscatter images $9 suggest a high atomic number region adjacent to the grain boundaries after heat treatment. (18 refs).