Superconducting Nb₃Sn magnets have composite structures consisting of Nb₃Sn multi-filaments, cooper, and epoxy resin. The complicated strain states due to different thermal expansion coefficients for Nb₃Sn and matrix materials and high Lorentz force will cause significant degradation of critical current density J_c of Nb₃Sn wires, thereby having a substantial impact on the thermomagnetic instabilities in the superconducting magnets. So, it is highly needed to explore the effects of strain on thermomagnetic instabilities with numerical simulations. We theoretically analyze the effects of Cu/SC (superconductor) ratio, strain, and the field ramp functional form on flux jumps in composite Nb₃Sn wires inside the superconducting coil to obtain more accurate results. Considering the composite multi-filamentary structures, we find that a lower Cu/SC ratio leads to higher temperature peaks, and a larger proportion of Cu causes higher voltage peaks. Moreover, the strain significantly causes a higher frequency of flux jumps and higher voltage peaks. The temperatures recover to working temperature more difficultly, and SC wires quench earlier in the presence of strain. For the ramping magnetic field with a jagged ramp form, it is interesting that few flux jumps and temperature jumps occur at the decreasing branch, whereas frequent flux jumps can be observed promptly again when the applied current exceeds the pre-existing peak value. Our simulated results agree very well with experimental observations in Nb₃Sn coils. Additionally, unlike the pulsed flux jumps observed in linear ramp cases, giant and prolonged flux jumps are observed at the increasing branch under linear field ramp with additional sinusoidal field oscillations, when the applied current is sufficiently large. Reverse voltage signals are also observed during a decreasing branch, which can be revealed by the variations of current, magnetic field, and temperature distributions. The findings in this paper provide new insights into understanding and exploring the complex flux jumps in composite Nb₃Sn wires with multi-filaments.

超导 Nb ₃ Sn 磁体具有由 Nb ₃ Sn 多丝、铜和环氧树脂组成的复合结构。_{由于 Nb 3} Sn 和基体材料的不同热膨胀系数和高洛伦兹力导致的复杂应变状态将导致Nb _{3 Sn 线的临界电流密度}J _c显着降低，从而对超导磁体中的热磁不稳定性产生重大影响. 因此，非常需要通过数值模拟来探索应变对热磁不稳定性的影响。我们从理论上分析了 Cu/SC（超导体）比、应变和场斜坡函数形式对复合 Nb 中通量跳跃的影响₃超导线圈内的 Sn 线以获得更准确的结果。考虑到复合多丝结构，我们发现较低的 Cu/SC 比会导致更高的温度峰值，而更大比例的 Cu 会导致更高的电压峰值。此外，应变显着导致更高频率的通量跳跃和更高的电压峰值。温度更难以恢复到工作温度，并且 SC 线在存在应变的情况下更早淬火。对于呈锯齿状斜坡形式的斜坡磁场，有趣的是，在下降分支处很少发生通量跳跃和温度跳跃，而当施加的电流超过预先存在的峰值时，可以立即再次观察到频繁的通量跳跃。我们的模拟结果与 Nb 中的实验观察结果非常吻合_3个锡线圈。此外，与在线性斜坡情况下观察到的脉冲通量跳跃不同，当施加的电流足够大时，在线性场斜坡下的增加分支处观察到巨大和长时间的通量跳跃，并伴有额外的正弦场振荡。在递减分支期间也观察到反向电压信号，这可以通过电流、磁场和温度分布的变化来揭示。本文的研究结果为理解和探索具有多丝的复合 Nb ₃ Sn 线中的复杂通量跳跃提供了新的见解。