Microstructure and superconducting properties comparison of bronze and internal tin process Nb3Sn strands for ITER

The long multifilamentary Nb3Sn strands for international thermonuclear experimental reactor (ITER) have been successfully fabricated by bronze and internal Sri process, respectively. Adopted in this work, the bronze process Nb3Sn strand with a Cu/non-Cu area ratio of 1:1.09 and the internal tin process strand with a Cu/non-Cu area ratio of 1:1.15 were designed. The microstructure details of two kinds of strands before and after heat treatment have been investigated by scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDX). The non-Cu J(c) (12 T, 4.2 K) value of 752 A/mm(2) for bronze process strand and 1185 A/mm(2) for internal tin process strand have been obtained. The influence of microstructure on transport property of strands has been discussed. (C) 2009 Elsevier B.V. All rights reserved.