Simulation of Quench Behavior in CS LTS Magnets for Next-Generation Fusion Devices With Time-Varying Operation

In the next generation of fusion devices, the central solenoid (CS) coil needs to withstand large alternating currents and rapidly changing magnetic fields to achieve plasma breakdown, configuration formation, and control. In this study, the quench behavior of a representative submodule (CS1U-LTS) is investigated under time-varying current and magnetic field conditions, where the local field ramp rate reaches approximately 2.5 T/s. This alternating operation mode significantly affects the stability of superconducting magnets. However, the current simulation of superconducting magnet quench is mostly based on the steady-state current and steady-state background field, which makes it difficult to reflect the quench propagation characteristics of superconductors under alternating conditions as the current and magnetic field intensity and direction change. To ensure the safe operation of the CS coils under alternating conditions, this article first analyzes the quench behavior in a reference case with constant peak current prior to an exponential discharge and determines the protection thresholds required to limit the hotspot temperature to below 150 K:200 mV voltage threshold and 0.5 s time threshold. The quench response at the positive and negative current peaks during time-varying operation is further analyzed. The results show that under the same protection conditions, the maximum temperature of the CS1U-LTS coil in alternating operation still meets the design requirements. In addition, this article compares the differences in quench propagation near the two peak points, revealing the impact of alternating operation on quench propagation behavior.