Evaluation of bending strain in NbSn strands of CIC conductor using neutron diffraction

Hemmi, Tsutomu*; Harjo, S.   ; Kajitani, Hideki*; Suwa, Tomone*; Saito, Toru*; Aizawa, Kazuya  ; Osamura, Kozo*; Koizumi, Norikiyo*

The superconducting property of NbSn strands is very sensitive to strain. The transverse electromagnetic loading has been considered as a major origin of the degradation of NbSn 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 NbSn 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 NbSn in the CICC. This paper shows that the bending strain in NbSn strands of CICCs can be determined by the neutron diffraction profile nondestructively and quantitatively.