Buckling Behavior of Nb3Sn Strand Caused by Electromagnetic Force and Thermal Mismatch in ITER Cable-In-Conduit Conductor

Abstract

Recent experiments on the international thermonuclear experimental reactor Nb3Sn cable-in-conduit conductor have shown degradation in current-sharing temperature ( ${T_{cs}}$ ) over several thousand electromagnetic (EM) cycles. The destructive investigations on these specimens have found that the Nb3Sn strand buckled and cracked on the surface of the long twist pitch cable at the low EM load side. In order to discuss the strand buckling behavior, we propose a theoretical model to analyze the influences of twisting pitch, stainless steel tape width (wrap width), coverage rate, wrap stiffness, and friction factor on the buckling behavior of the Nb3Sn strand. The cases of Nb3Sn strand with and without EM loading are discussed, respectively. Moreover, a slip of the cable within jacket, which often reinforces the plastic deformation of the strand, is also considered in this study.