Design, simulation, and experimental validation of a heat treatment system for CRAFT TF Nb3Sn coil: A critical step towards CFETR TF

Fusion reactors represent one of the ultimate solutions to humanity's energy challenge. China is accelerating the construction of the China Fusion Engineering Test Reactor (CFETR). In preparation, the Comprehensive Research Facility for Fusion Technology (CRAFT) project was initiated to tackle key engineering and technological challenges anticipated for CFETR. The fabrication of the CRAFT Toroidal Field (TF) magnet represents a critical milestone in the development of the CFETR superconducting magnet system. The CRAFT TF coil measures approximately 19.5 m in length, 11.5 m in width, and 1.1 m in height. This design introduces, for the first time, a unique graded winding and nesting structure that integrates superconducting coils of NbTi, ITER-grade Nb 3 Sn, and high-performance Nb 3 Sn. However, Nb 3 Sn must undergo a specific heat treatment (HT) process to form the superconducting A15 phase, and the reacted Nb 3 Sn wire is highly sensitive to stress and strain. Consequently, the TF coil fabrication follows the “wind-and-react” (W&R) manufacturing sequence. This paper details the design, simulation, and experimental validation of a full-argon protective atmosphere furnace system for the HT of the CRAFT TF Nb 3 Sn coil. With temperature uniformity maintained within ±5 °C across all holding stages, this result confirms the suitability of controlled atmosphere HT for meeting the stringent requirements of TFC in next-generation fusion reactors.