Effective bending strain estimated from Ic test results of a D-shaped Nb3Al CICC coil fabricated with a react-and-wind process for the National Centralized Tokamak

Abstract Japan National Centralized Tokamak (NCT) is a superconducting tokamak proposed as a modification to JT-60U. As part of the R&D for the National Centralized Tokamak, a two-turn, approximately 2 m tall, D-shaped Nb 3 Al coil was wound and tested using a full-size cable-in-conduit conductor (CICC). The Nb 3 Al cable-in-conductor was bent following the heat treatment reaction with a maximum bending strain of 0.4% to simulate the react-and-wind fabrication. The comparison of the coil performance to the measured strand data shows that the effective axial strain of the conductor strands is essentially zero despite the 0.4% bending strain of the conductor. This suggests that the strands in the cable slipped relatively to each other during bending of the conduit, thus reducing the effective strain transmitted to the strands. This result is very encouraging for the low-cost fabrication of high-current-density fusion coils using the react-and-wind method.