Quench Analysis and Experiments on Nb3Sn Superconducting Magnet Half-Length Prototype

The Institute of Modern Physics (IMP) at the Chinese Academy of Science (CAS) is building a Nb ₃ Sn magnet for utilization in a fourth-generation superconducting electron cyclotron resonance ion source (FECR) for the High Intensity heavy ion Accelerator Facility (HIAF). A half-length prototype of the magnet, comprising two axis solenoid coils and a sextupole coil with a cold iron yoke, has been developed to validate the technology of the Nb ₃ Sn superconducting magnet. The construction of the magnet presents a significant challenge due to the complex structure and properties of the Nb ₃ Sn conductor, necessitating quench protection. To tackle this challenge, quench simulations and experiments were conducted using OPERA-Quench and STEAM-LEDET. Based on the simulation results, a protection circuit was designed to ensure the safety of the magnet. Subsequently, the protection circuit underwent testing through a series of experiments. However, some quench events were inadequately protected against due to interference from voltage sparks caused by flux jump, resulting in gradual degradation of the magnet. The estimated adiabatic hot-spot temperature during these events reached 549 K, which is likely responsible for the observed degradation. Additionally, the impact of the utilizing of Metrosil varistors on quench protection is also under investigation.