Neutron diffraction measurements of internal strain in NbSn cable-in-conduit conductors

Hemmi, Tsutomu; Harjo, S.   ; Ito, Takayoshi; Matsui, Kunihiro; Nunoya, Yoshihiko; Koizumi, Norikiyo; Takahashi, Yoshikazu; Nakajima, Hideo; Aizawa, Kazuya  ; Suzuki, Hiroshi  ; Machiya, Shutaro*; Oguro, Hidetoshi*; Tsuchiya, Yoshinori*; Osamura, Kozo*

Residual strain in conductors is caused by the difference in the coefficient of expansion between NbSn strands and the jacket over a temperature range of 5 - 923 K. The superconducting properties of strands vary significantly, depending on the strain. It is important to clarify the residual strain as part of the evaluation of superconducting performance. However, the residual strain of strands in the conductor has not been measured so far because of their complicated configuration and their location in a jacket. The engineering materials diffractometer "Takumi" in J-PARC can measure residual strain with a relative accuracy of around 0.02%, using neutron diffraction. In this study, the Takumi was applied to the measurement of residual strain in strands for the ITER TF conductor. Results indicate that the residual strain of strands in the conductor can be determined, thereby clarifying the mechanism of residual strain and its relationship to superconducting performance.