Analysis of Nb3Sn strand microstructure after full-size SULTAN test of ITER TF conductor sample

The study of defects generated in superconducting filaments of Nb3Sn strands under electromagnetic and thermal cycling was carried out for the TFRF3 cable-in-conduit-conductor ( CICC) sample that passed final testing in the SULTAN test facility. The TFRF3 sample was manufactured for the qualification of the RF Toroidal Field ( TF) CICC. The strand samples were taken from different locations in the cross-section of TFRF3 and different positions along its axis in relation to background magnetic field. Qualitative and quantitative analysis of defects were carried out using metallographic analysis of images obtained by Laser Scanning Microscope. We analyzed number, type, and distribution of defects in filaments of the Nb3Sn strand samples extracted from different petals of TFRF3 in dependence on the strand location in the cross-section ( the center of petal, nearby the spiral, nearby the outer jacket) in the high field zone ( HFZ). The results about the defects amount and their distribution are presented and discussed. (C) 2015 The Authors. Published by Elsevier B.V.