Development of NbTi conductor for high field applications

The processing parameters of NbTi for use in magnetic fields above 10 Tesla at temperatures of 4.2 K and lower have been optimized. In particular, the time, temperature and number of heat treatments as well as the amount of cold work reduction have been analyzed for approximately 100 samples. Two alloy compositions, namely Nb-46.5 wt. pct. Ti and Nb-55 wt. pct. Ti, were used in this program. In all cases, the lower titanium concentration alloy had the superior performance at high fields. Superconductor critical current densities greater than 1 × 10⁵A/cm²were measured for Nb-46.5% Ti in fields as high as 11 Tesla at a temperature of 1.5 K. Such a current density is typical of fields of 6 or 7 Tesla at 4.2 K. Many of the results at reduced temperature compared very favorably with those of Nb3Sn at 4.2 K. For example, at 12 T and 2 K, conductor current densities of 2.7 × 10⁴A/cm²are found for NbTi. At 12 T and 4.2 K, a typical conductor current density of Nb3Sn is less than 2.5 × 10⁴A/cm². A small coil containing 100 meters of wire was operated in the bore of a Bitter magnet. At 1.5 K the coil operated without quenching with a maximum field at the windings in excess of 14 Tesla. Based on these results, NbTi operating at reduced temperatures appears to be a good alternative to Nb3Sn for conductor in high field magnets.