Application of react-and-wind method to D-shaped test coil using the 20 kA Nb3Al conductor developed for JT-60SC

Using a 20 kA Nb₃Al cable-in-conduit (CIC) conductor, a two-turn D-shaped test coil with a height of 2.0 m and a width of 1.8 m was fabricated by a react-and-wind (R&W) method. After heat treatment, the conductor was formed to the D-shaped coil. Bending strain of the conductor is ±0.4% at critical current I_c test section. The I_c exceeded 31.4 kA at 7.3 T, 4.2 K. In spite of the stainless steel conduit, a critical current density J_c of 89% of the strand value was attained. The total strain of the D-shaped test coil was about -0.57%, the same as the triplex-CIC sample fabricated by a W&R method, indicating that bending did not influence the I_c. The I_c at 7.4 T, 5.6 K including the margin of 1 K exceeds the operational current. Therefore, it was concluded that the R&W method is quite appropriate for the toroidal field coil of JT-60SC.