Curvature analysis of Nb ₃Sn strands in react and wind CIC Conductor for fusion magnets

The Cable-In-Conduit Conductor (CICC) is the most promising one for large scale fusion magnets. Now it has been adopted as conductors for ITER magnets. Although the conductor has good mechanical strength against large electromagnetic force, the performance is not so good because the Nb ₃Sn strands are fragile and the critical current density is sensitive to strain. Because conductor is composed of hundreds or thousands of strands which are twisted and become tangled, the strands experience extra-bending during energizing magnets. It seems so difficult to analyse plastic deformation of the strands of whole conductor. Our approach to calculate it is unique in terms of using structural mechanics called Beam Model based on the measured strand traces inside the conduit. The calculated traces provide us the local curvatures of strands under electromagnetic force. This leads to the evaluate the conductor performance such as I _c degradation.