Fabrication of large diameter external-diffusion processed Nb3Sn composites

Large diameter multifilamentary Nb3Sn composites have been fabricated by the external-diffusion process. Consideration of the phase relationship in the CuSn binary system, Sn diffusion kinetics and vacancy diffusion has led to the development of an appropriate Sn homogenization anneal. By correctly annealing the composites Sn flow and Kirkendall porosity may be controlled. The application of bronze electrodeposition has also been investigated and found to significantly reduce annealing times. These concepts have been applied successfully to 0.76 mm (0.030 in) diameter composites which have overall critical currents in excess of 7 × 10³amps/cm²at 17 Tesla.