Analysis of the degradation characteristics and causes of the HTS insert magnet after quenching in the 32.4T test

The quench of a superconducting magnet in a high magnetic field environment causes irreversible damage to the magnet. A 32.4 T completely superconducting magnet consisting of a low-temperature superconducting (LTS) external magnet and a high-temperature superconducting (HTS) inserting magnet was developed and tested. The LTS external magnet quickly discharged after quenching when the system’s peak center magnetic field reached 32.4 T. The inserting magnet, particularly the Coil 1 magnet on the magnet’s innermost side, was damaged due to the quick current change in the LTS external magnet. This created a significant current inside the HTS magnet due to the mutual inductance effect. The overcurrent caused the degradation of Coil 1 magnet. The continuous critical current of DP69, DP80, DP85, and DP94 in the magnet was measured to investigate the degradation. Numerous circular burn sites in areas of degraded critical current were observed by optical and scanning electron microscopy (SEM). To analyze the causes of the degradation, a dynamic coupling model of LTS and HTS magnet during quench was developed. The simulation outcomes indicated that the locations exhibiting high hoop stress correspond to those where the normalized critical current density is observed to be notably low, proving that excessive hoop stress is the main reason for the critical current degradation in the coils. Furthermore, the model quantified the turn-to-turn loss in the Coil 1 magnet during the quenching process of the LTS magnet. It offered potential evidence for the circular burn-through points in the superconducting layer.