Abstract
A (Nb, Ti)3Sn superconductor with high critical current density (Jc) for a 1GHz NMR magnet has been developed on the base of a so-called bronze process by using a matrix of Cu-15 wt% Sn-0.3 wt% Ti. To investigate the effects of increase in tin content on Jc and n value, another conductor with a conventional matrix of Cu-13 wt% Sn-0.3 wt% Ti was fabricated for comparison. The developed conductor showed a distinct increase in Jc in comparison with the conventional one. Based on microscopic investigations, the obtained improvement in Jc was attributed to an increase in reacted layer thickness and a decrease in grain size. The dependence of high field Jc on heat treatment conditions was also examined in relation to flux pinning. It then turned out that the Jc of the developed (Nb, Ti)3Sn conductor in high fields of over 20T depends on the upper critical field rather than on the microstructures of (Nb, Ti)3Sn. The developed conductor showed a Jc of 102A/mm2 and n values of about 40 at 1.8K and 21T, fulfilling all target values in the preliminary design of a 1GHz NMR magnet.
