Design and characterization of a low-resistance joint for TSTC-CICC conductors

Abstract

Abstract

Abstract Reliable low-resistance joints are a critical enabling technology for high-current superconducting magnet systems across fusion, high-field research, and accelerator applications. This work develops an indium-mediated mechanically compressed joint for helically-slotted twisted stacked-tape cable-in-conduit conductors (TSTC-CICCs), aiming to achieve joint resistances in the tens of nanohms without post-fabrication high-temperature soldering. The joint performance is systematically investigated through four-terminal electrical measurements at 77 K, complemented by a three-dimensional coupled mechanical-electrical finite-element model that incorporates pressure-dependent interfacial contact resistivity. Experimental results show that increasing the bolt torque from 60 to 160 N•m reduces the joint resistance from approximately 34 to 31 nΩ for cores prepared with water-based flux, and from 47 to 39 nΩ for those with oil-based flux, with the reduction saturating above 120 N•m. The numerical model, calibrated against measurements, reveals that the saturation behavior originates from a nonuniform contact pressure distribution, where further compression primarily raises local pressure in already-contacted zones rather than expanding the effective current-transfer area. These findings demonstrate that the proposed compression joint provides a viable low-resistance solution for TSTC-CICC conductors, and identify a practical assembly torque range of 120-140 N•m for the present configuration. The combined experimental and modeling framework offers a transferable methodology for designing and optimizing mechanically compressed joints in CICC-type high-temperature superconducting conductors.