Further Studies of Transverse Stress Effects in Cable-In-Conduit Conductors

Abstract

The effect of transverse stress on critical current has been examined for Cable-In-Conduit Conductors (CICCs) containing three active superconducting composite strands in cables containing a total of 21 strands. In measurements of this type reported previously, only soft copper was used for the inactive strands, allowing the possibility that peaking of stresses at strand cross-over points were avoided by deformation of the copper strands during CICC fabrication and testing. In the present experiments, the degree of critical current degradation was measured as a function of applied load for various void fractions for cable patterns using stainless steel wires as the inactive strands. The reduction of critical current, expressed as a function of load divided by the projected area of the core of the superconducting composite strand, was found to be similar to that observed in cables containing copper inactive strands. All the CICCs tested show a higher sensitivity to transverse stress as compared to single wires. At compressive loads of 50 MPa or less, the region of interest to magnet designers, the critical current is, at worse, 79% of the critical current in unloaded samples. The sensitivity to transverse load is a function of CICC void fraction, lower void fractions having less susceptibility to degradation. The results of this investigation indicate that the performance of large magnets employing CICC designs need not be seriously degraded due to transmitted or self-induced Lorentz loads.