Evaluation of thermal strain induced in components of Nb
Sn strand during cooling
Suwa, Tomone*; Hemmi, Tsutomu*; Saito, Toru*; Takahashi, Yoshikazu*; Koizumi, Norikiyo*; Luzin, V.*; Suzuki, Hiroshi
; Harjo, S.

Nb
Sn strands, whose properties are very sensitive to stress/strain, are utilized for ITER cable-in-conduit conductor (CICC) of the central solenoids. The Nb
Sn strands experience temperature range of
1000 K from the temperature of the heat treatment with the initiation of the Nb
Sn reaction to the operation temperature of
4 K. Due to this large temperature range, large thermal strain is induced in the Nb
Sn filaments due to the differences between the coefficients of thermal expansion and Young's moduli of the components of the strand. Therefore, it is considered that initial performance of the CICC is influenced by the thermal strain on the Nb
Sn, and it is important to evaluate the strain state of the Nb
Sn strand at low temperature. In this study, the thermal strain of the components of free Nb
Sn strand was measured by neutron diffraction and stress/strain state was assessed from room temperature to low temperature. As the results of diffraction measurements, it was found that 0.111 % and 0.209 % compressive strain were generated in Nb
Sn filaments at 300 and 10 K, respectively.