Development of Stacks-in-Conduit Conductor (SICC) for High-Field HTS Magnets

To enable high-current, internally-cooled high temperature superconductors (HTS) for fusion magnets, we developed a Stacks-in-Conduit Conductor (SICC) manufacturing process and produced prototype conductors. The SICC consists of a densely stacked REBCO tape bundle enclosed in a metal conduit (jacket) with an internal coolant channel, combining the high current density of stacked HTS tapes with the robust mechanical support and cooling of a cable-in-conduit design. A four-step continuous fabrication line was established, including automated tape stacking, bundle restacking, helical reinforcement insertion, and multi-stage roll forming into a square cross-section. Using aluminum dummy bundles and stainless steel (STS) tape stacks, we carried out forming trials to analyze mechanical and geometrical characteristics. An initial single-helix internal support led to a “wiggling” surface defect on the jacket, but this was resolved by adopting a double-helix (two counter-wound copper spirals) that cancels asymmetric forces, yielding a smooth outer surface. Micro-focus X-ray CT imaging confirmed that the HTS tape bundle remains intact after forming. These results demonstrate a viable manufacturing route for HTS SICC, and provide key insights on mechanical reinforcement and process optimization. The developed techniques lay a foundation for future SICC prototypes using actual HTS tapes, moving toward high-field fusion magnet applications.