Heat Treatment of Large Nb3Sn Coil for CRAFT TF

The fabrication of a prototype toroidal field (TF) coil for the Comprehensive Research Facility for Fusion Technology (CRAFT) represents a critical component of the China Fusion Engineering Test Reactor project. The CRAFT TF coil, characterized by its distinctive “D” shape, measures approximately 19.5 m in length, 11.5 m in width, and 1.1 m in height. The coil incorporates Nb₃Sn cable-in-conduit conductors in both its high-field and medium-field windings. Owing to the intense sensitivity of Nb₃Sn superconductors to stress and strain, the manufacturing process will adhere to the established “wind and react” methodology. Among the various manufacturing stages, heat treatment emerges as a pivotal step in the production of TF Nb₃Sn coil. We have engineered China's largest superconducting coil heat treatment facility, incorporating a fully argon-purged oven environment. This investigation primarily addresses the computational modeling and experimental validation of thermal gradients and fluid dynamics within the system. The design specifications, structural configuration, and processing parameters of the CRAFT TF heat treatment system have been experimentally validated. System performance evaluation demonstrates compliance with technical specifications, particularly in maintaining temperature uniformity within ±5 °C during the critical 650 °C stabilization phase.