过热-过电压冲击下高场超导复合材料微结构瞬态相变与失超传播

As one of the prominent materials for the high-field applications, the A15 phase Nb3Sn compound has great application prospects in International Thermonuclear Experimental Reactor (ITER), nuclear magnetic resonance (NMR) spectroscopy, and high energy physics(HEP). These magnets store a significant amount of energy due to the high ultimate operating currents. As a resistive transition(quench) occurs, the overheating and excessive voltages will be localized at the spot of the coil, causing the overheating and excessive voltages to be concentrated in a small area making it more intense and its effect more devastating to the high-field superconducting magnet. The increase of manufacturing level and design scale is hampered by our poor understanding of the transient behavior of the multifilamentary Nb3Sn composite, since the previous methods fails to yield correct results characterizing the strongly nonlinear process. The project aims to develop a micro-meso-macro-perspective to analyze the evolution of the material's microstructure and properties, which vary sharply with the rapid multiple-field environment change. The nonlinear features arising in the quick phase transition will be identified in detail and the nature of the multiscale coupling will be revealed. A quantitative characterization method accounting for the physical diversities and strong coupling over wide-range scales will be also proposed. The study will promote the process of the Nb3Sn material engineering application, and the results of which are promising to engineer optimized superconducting high magnetic field systems in large scale.

Nb3Sn高场超导复合材料主要应用于国际热核聚变实验反应堆、高能物理以及高场核磁共振波谱仪等磁体领域。失超瞬时释放出的巨大磁体能量，会导致超导线圈局部温度过高被烧毁和产生局部高电压击穿绝缘层，严重影响到高场超导磁体装置的安全稳定运行。由于对高场超导复合材料失超瞬态行为强非线性特征认识的不足，现有的半经验解析方法和数值模拟方法难以满足超导磁体的设计需求，制约了大型超导磁体制造水平的提升。本项目拟研究极速变化的多物理场环境下高场超导复合材料微结构组织演变和性能演化，揭示极端多物理场环境中其失超瞬态响应强非线性特征的多尺度耦合机制，提出从A15型晶体结构到材料微结构到宏观非均质超导复合材料的失超特性的跨尺度定量表征方法，建立准确有效的瞬态微-细-宏观多过程耦合的理论模型和数值算法。本项目的研究将提高对高场超导复合材料失超瞬态响应的认识和描述能力，为强磁场超导磁体装置的的制造提供有力的理论支撑。

超导磁体失超瞬时释放的巨大电磁能量会导致磁体局部温度过高被烧毁和产生局部高电压击穿绝缘层，本项目紧密围绕Nb3Sn超导体失超瞬态响应强非线性特征的机理和描述展开研究：以超导体临界性能多尺度多物理场耦合效应研究为起点，逐步深入探究超导相转变时电输运性能及力学性能突变，基于此建立考虑微结构相变的超导体失超瞬态响应模拟模型。以应变作用下Nb3Sn单晶电子结构演化切入解释并预测了Nb3Sn超导临界性能多尺度多物理场耦合效应，揭示了力学变形诱导超导临界性能衰减的影响因素及影响规律，建立了从Nb3Sn单晶体、多晶体到复合多晶体临界性能一致性分析的多尺度耦合模型。进而，基于超导相转变分析方法，建立了超导体超导相-正常相转变时电输运性能和弹性力学性能突变的解析模型，揭示了突变的特征和主导因素，理论模型刻画了温度和应力等环境因素对电阻率、弹性力学常数的影响规律。最后，基于多晶体有限元方法和瞬态热传导方程，借助对Nb3Sn超导体临界性能的多尺度多物理场耦合效应研究、Nb3Sn超导相转变时电输运/力学性能突变研究所发展的多尺度关联模型，建立了失超瞬态晶界局部热应力分析模型，模型虑及超导体微结构组织特征和性能演变，为揭示失超瞬态响应强非线性特征提供了基础。研究结果有助于提高对超导体失超瞬态响应的认识和描述能力，为强磁场超导磁体装备的制造和失超检测技术的发展提供理论支撑。