Full-Process Verification of 3D Dummy Coil for HTS Stellarator Completed

The Institute of Plasma Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences (ASIPP) has, in collaboration with Hefei Xihe Superconducting Technology Co., Ltd. (Xihe Superconducting), successfully completed the full-process verification of a 3D dummy coil for high-temperature superconducting (HTS) stellarators. This achievement establishes a complete technical pathway from physical design to the engineering manufacturing of core components for advanced stellarators. The research team completed the physical design of an advanced stellarator and the key technology development for HTS 3D coils, verifying the entire manufacturing process. The project was funded by the Anhui Provincial Key Research and Development Program and ASIPP's self-funded forward-looking research projects.

Stellarators utilize a 3D non-axisymmetric magnetic field to achieve steady-state plasma operation without plasma current, thereby avoiding disruption risks. However, this requires extremely precise 3D geometry and manufacturing accuracy for the magnet system. In this collaboration, the ASIPP team led the physical design and coils design, completing a scheme for an advanced HTS stellarator with a 2-meter major radius and a 5-tesla central magnetic field. Key parameters achieved include a core alpha particle loss of less than 0.4%, a linear ballooning mode beta limit exceeding 4.2%, and an effective neoclassical transport ripple below 10⁻³. The joint team also finalized the engineering design for HTS 3D coils with a peak magnetic field of 16 teslas.

To address the manufacturing challenges, XiHe Superconducting developed a dedicated production line capable of spatial twist control for continuous 3D bending. ASIPP completed the cabling of CORC superconducting conductors, while XiHe Superconducting executed the winding, Vacuum Pressure Impregnation (VPI), and cryogenic testing of a full-scale (1:1) 6-pancake, 60-turn CICC-type HTS 3D dummy coil. The prototype, with a circumference of approximately 13 meters, utilized a hybrid filling of HTS CORC cables and dummy cables to optimize costs. Testing results confirmed a profile tolerance better than ±1.5 mm, a coil box cross-sectional error of ≤ ±1 mm, and a post-winding critical current (Ic) retention rate of ≥ 95%. Both cooling-down and energization tests were completed successfully on the first attempt.

This milestone validates the reliability of the entire manufacturing chain for complex HTS 3D coils, marking a substantial step forward in manufacturing capabilities for advanced HTS stellarators. ASIPP will continue to collaborate with partners to advance magnetic confinement fusion research.

Design of HTS 3D Coils for Advanced Stellarators.

Structure of HTS CORC Cables.

Winding and Encapsulation of HTS 3D Dummy Coil.

Vacuum Pressure Impregnation (VPI) of HTS 3D Dummy Coil.

Cryogenic Critical Current Testing of HTS 3D Dummy Coil.