Strain-driven electro-mechanical performance of twisted stacked-tape double casing conductors for high-field fusion magnets

Abstract High-temperature superconducting cables are being developed for high-field magnets operating above 20 T. The high current densities and magnetic fields produce significant Lorentz forces that can cause irreversible conductor degradation. In this high-load environment, achieving complete solidification of the conductor is a promising approach. However, such high-stress-resistant conductors are more vulnerable to strain-induced degradation, as individual strands are more likely to experience additional bending and twisting strains when being assembled into a full cable. This study presents a double-casing conductor (DCC) with a twisted stacked-tape cable (TSTC) configuration, designed as a fundamental sub-cable unit for future high-field, high-current fusion magnets. The DCC incorporates two copper casings and utilizes the vacuum soldering process, providing improved mechanical stability and reduced voids. To validate its performance comprehensively, we systematically investigated the electro-mechanical properties of the DCC under axial tension, bending and torsion. The irreversible strain threshold of the DCC (0.37%) and its safe mechanical operating limits (bending radius <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>&gt;</mml:mo> </mml:mrow> </mml:math> 300 mm, twist pitch <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>&gt;</mml:mo> </mml:mrow> </mml:math> 500 mm) align well with the stringent requirements of the CFETR central solenoid (20 T, 50 kA), where large Lorentz forces necessitate exceptional strain tolerance. Moreover, the bent-then-solder process effectively reduces strain-induced degradation, further enhancing the conductor’s mechanical integrity. These results confirm the robustness of the DCC and its suitability as a sub-cable unit for next-generation high-field fusion magnets. The identified irreversible stress limits and strain thresholds meet the stringent requirements of fusion reactor applications, laying a solid foundation for scaling up DCC-based cables and supporting their feasibility in future fusion energy systems.