Study on resistance distribution between superconducting strand and a copper sleeve in a CICC joint considering three-dimensional strand path

A Cable-in-Conduit-Conductor (CICC) is a composite conductor consisting of many superconducting strands twisted in multiple steps. The CICC has the characteristics which make it suitable for fusion magnets, but lower critical current than expected have been observed in some experiments. The resistance distribution between the strand and the copper sleeve in a "Wrap Joint" is expected to be inhomogeneous and to affect the current distribution and the critical current in the CICC. We measured the DC resistance distribution between the strand and the copper sleeve in a simple model Wrap Join at liquid helium temperature and observed an inhomogeneous resistance distribution. A 3-D strand path calculated by considering the manufacturing process of CICC and an algorithm from previous work were used to evaluate the resistance distributions between the strand and the copper sleeve. The calculated and measured resistance distributions showed the same overall trends. The homogeneity of the resistance distribution between the strand and the copper sleeve is strongly dependent on whether the strand is in direct contact with the copper sleeve or not. Maximizing the number of direct contacts between the strand and the copper sleeve of the "Wrap Joints" was effective for reducing any possible current imbalances.