A research team led by KUANG Guangli and JIANG Donghui at the High Magnetic Field Laboratory of the Hefei Institutes of Physical Science of the Chinese Academy of Sciences (CHMFL), has developed a "pocket-type" high-temperature superconducting (HTS) coil, achieving a record combined magnetic field of 44.86 tesla.

The coil, wound using domestically produced REBa₂Cu₃O₇₋ₓ (REBCO) tapes, generated 28.20 T at zero field in a liquid helium bath and produced an additional 10.36 T inside the 34.5 T steady-state magnetic field of the WM5 water-cooled magnet. 

Steady high magnetic fields are critical for frontier research in materials science, physics, and biology, enabling scientists to observe new phenomena and explore new laws of matter. REBCO high-temperature superconducting material has become one of the optimal choices for developing devices that generate higher magnetic fields, owing to its high current-carrying capacity and favorable mechanical properties. 

In this work, the researchers adopted a no-insulation (NI) winding technique for the coil, and carried out a systematic optimized design addressing the electromagnetic, stress, and thermal challenges encountered during the high-field operation of the insert HTS coil. A laser dynamic tracking method was introduced during winding to ensure coil flatness and structural integrity. 

By adjusting the thickness of the tin layer and optimizing soldering temperature and pressure, the researchers developed an inner joint with a resistance as low as 65 nΩ·cm² at 77 K, which significantly reduced heat loss. 

To further enhance thermal stability, aluminum nitride was used as the insulating material to improve heat dissipation, and a flexible electrode connection method was applied to enhance stability under high fields.

This work lays a solid technical foundation for the development of even higher-field magnets in the future.

Test result of the HTS Coil under high field and its design schematic. (Image by JIANG Shili)