Properties and performance of the multifilamentary Nb3Sn with Ti addition processed by the Nb tube method

MF Nb3Sn conductors made by titanium added niobium tube process have been developed for use in high fields. Composites, consisting of Nb-1. Owt.%Ti tube with a copper sheathed tin core inside and a high conductivity copper tube outside, were stacked together up to 264 filaments, then drawn to the final sizes without any intermediate annealings. As workability was further improved by the titanium addition, it was possible to decrease the Cu/SC ratio for the conductor down to 0.67 and to increase the tin concentration up to 30 wt.% in Cu-Sn inside the filament. An enhanced layer growth rate and a slightly increased grain size of Nb3Sn were observed in the titanium added conductors. compared with those made by use of pure Nb tube. The critical current density at high fields, which was more sensitive for heat-treatment condition, was superior to that of the other conventional processed conductors. Especially, the conductors with 30 % tin content have high critical current density for Nb3Sn layer and an excellent field dependence of critical current density without copper: 1550 A/mm²at 10 T, 600 A/mm²at 15 T and 350 A/mm²at 17 T. The critical current was also measured in the temperature range 1.88 - 4.2 K. A coil, aiming at 14 T, was fabricated using the conductor with .25 % tin to assure high level performance in practical situations.