高场CICC导体分流温度的退化机理研究

The Tokamak magnet is the main component of the ITER project. The toroidal field (TF) and the center solenoid (CS) are made of cable in conduit conductor (CICC) which are made of Nb3Sn superconducting strands. The conductors, working at the cryogenic and high magnetic field, not only need to endure tens of thousands of electromagnetic cycling loads, but also thermal loading caused by thermal mismatch between different materials. The ITER organization proposed the parameter of current sharing temperature (Tcs) to measure the stability of the conductor under electromagnetic and thermal cyclic loads. In recent years, the short-pitch CS CICC samples proposed by ITER was tested in SULTAN, showed that the current sharing temperature of this kind of conductor keeps constant even increases with the number of electromagnetic cycles, and solved the problem of current sharing temperature degradation found in the early years, experimentally. However, this experimental result is contrary to the exsisting theoretical models. Therefore, we are aiming at the mechanism of current sharing temperature degradation of CICC conductor under electromagnetic and thermal cyclic loads, establishing the theoretical model of the relationship between current sharing temperature and mechanical deformation. The ultimate goal of this project is to make out the change of CICC conductor under electromagnetic and thermal cycling loads. In order to make some contribution to the construction of China Fusion Engineering Testing Reactor in the near future.

托克马克磁体是国际热核聚变堆(ITER)的核心部件，其环向场(TF)线圈和中心螺线管(CS)均采用Nb3Sn材料制备的管内电缆导体(CICC)绕制。导体在极低温强磁场环境下不仅需要承受数万次的高电磁力循环载荷作用，还有材料间热失配引起的热载荷作用。ITER组织提出分流温度的概念旨在对导体在循环电磁热载荷作用下的稳定性进行评价。目前，SULTAN中心测试结果显示，短节距导体分流温度随电磁循环加载次数保持不变或呈现上升的趋势，从实验上成功的解决了ITER组织早年发现的循环载荷引起分流温度退化这一难题。但是，该实验结果与现有的理论预测结果相反。本项目将瞄准循环电磁热载荷作用下CICC导体分流温度退化这一前沿课题开展相应的实验与理论研究，建立导体分流温度与力学变形相关联的理论模型，从而揭示CICC导体在电磁热循环载荷作用下的力学响应规律，为我国独立建造热核聚变堆提供相关参考依据。

超导电缆导体分流温度的退化机理研究是超导磁体科学和技术的关键问题，也是电磁固体力学研究领域的前沿课题。本项目采取自下而上的方法，从超导材料、绞线结构和多环境场加载等多方面出发对超导临界参数退化深入研究。主要完成了以下几个方面的工作：（1）基于微纳工艺制备方法和超低温多场耦合测试系统，模拟晶界弱连接制备了不同几何结构的超导岛链薄膜，实验观测超导薄膜在电-磁-热多场耦合作用下的非线性行为，进一步揭示了超导材料输运性能退化的微观物理机制。（2）针对超导复合材料如股线、多层超导带材等，基于晶界能理论，揭示了超导材料力电行为及退化规律的微观机制，有效分析了超导薄膜、股线、带材等实际工程材料力电耦合行为。（3）针对管内电缆导体多级绞缆结构在复杂多场载荷作用下的响应规律，建立了可预测绞缆等效热膨胀系数，等效模量，单股、多股、全尺寸绞线滑移屈曲、输运性能退化等非线性力电行为的理论框架和计算方法。研究结果对评估超导磁体的有效性能以及预测超导电缆的失效行为具有重要的科学意义和工程价值。