Testing and post-analysis of a 23.9 T conduction-cooled all-REBCO superconducting magnet

Abstract Conduction-cooled high-temperature superconducting magnets offer a promising route for high field magnets above 4.2 K. This study reports the testing and post-analysis of a 23.9 T conduction-cooled all-REBCO magnet. The magnet was successfully charged to 440 A, generating a central magnetic field of 23.9 T at 16 K, with a calculated peak field of 25.4 T in the windings. Then a thermal runaway quench happened and the temperature peak reached 290 K during the fast-discharging operation. The magnet was ramped to a maximum current of 420 A and generated 22.2 T central magnetic field in the following re-excitation operation. Post-disassembly examination revealed significant axial deformation of the coils caused by electromagnetic forces, which can lead to field degradation and increased quench risk. Further analysis of the post-quench conductor performance and stress distribution in the quench-originating coil suggests that a stress-assisted thermal runaway occurred during the quench. These findings indicate that axial compactness and electro-thermal margin should be carefully considered in magnet designs. Despite these challenges, the demonstrated high-field operation confirms the strong potential of conduction-cooled REBCO magnets for high-field applications.