Challenges in Continuous In-Field Critical Current Testing of High-Temperature Superconducting Tapes: Thermal and Mechanical Perspectives

—High-temperature superconductors (HTS) are essential for ultra-high-field applications requiring exceptional current-carrying capacity under extreme conditions. However, systematic characterization of critical current in long-length conductors remains challenging due to complex thermal, electromagnetic, and mechanical interactions during continuous testing. This study reports the development of a continuous in-field magnetization testing system for position-dependent critical current measurement in HTS tapes at 20 K under 7.5 T fields, enabling identification of performance-limiting regions that could compromise magnet stability. The system addresses two fundamental challenges inherent to cryogenic reel-to-reel testing. First, thermal management requires continuous cooling of a moving conductor to 20 K, achieved through liquid-nitrogen precooling combined with a 100 W@20 K Gifford-McMahon cryocooler. Second, screening currents in high fields generate Lorentz forces that induce twisting, bowing, and potential delamination. To mitigate these risks, we propose mechanical reinforcement and active current density suppression strategies. Numerical simulations reveal four primary failure modes: Frictional heating at guide interfaces, unstable equilibria causing deformation, transverse current-induced stresses at guide transitions, and unsupported forces in vertical spans. Our mitigation strategies include PTFE-coated guides to minimize friction, spring-loaded stabilization mechanisms to maintain tape alignment, and controlled pre-heating using the liquid nitrogen thermal jacket to suppress critical current at stress points. The experimental system is nearing completion. Preliminary validation at 65 K under 0.5 T demonstrates strong correlation between simulation-predicted mechanical instabilities and observed critical current variations during conductor transitions through the measurement region. These findings establish a robust foundation for quality assurance protocols essential to next-generation superconducting magnet applications.