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

A preliminary investigation of a new Nb-Ti-Ta (39wt%Nb, 44wt.%Ti, 17wt.%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(2), the highest 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(2), Large variations in precipitate size were produced in the microstructures, which have yet to be fully optimized. Quantitative analysis of the microstructures in a be-44 wt.%Ti-15 wt.%Ta alloy reveals a linear relationship between volume % of 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 suggest a high atomic number region adjacent to the grain boundaries after heat treatment.