Evaluation of Bending Strain in Nb3Sn Strands of CIC Conductor Using Neutron Diffraction

The superconducting property of Nb3Sn strands is very sensitive to strain. The transverse electromagnetic loading has been considered as a major origin of the degradation of Nb3Sn cable-in-conduit conductors (CICCs) due to the local bending. Since the bending pitch is around 5 mm due to contacting of strands compacted by the electromagnetic transverse loading, there is a possibility of a large bending strain with small deflection of strands. The bending strain of the strands cannot be evaluated from only the small deflection obtained visually. Measuring bending strain of Nb3Sn strand in CICCs is important for evaluating the conductor performance. Neutrons, which have a large penetration depth, are a powerful tool to evaluate the internal strain of Nb3Sn in the CICC. This paper shows that the bending strain in Nb3Sn strands of CICCs can be determined by the neutron diffraction profile nondestructively and quantitatively.