极高场无绝缘内插超导磁体失超后性能退化及应力集中问题研究

Extremely high magnetic fields play a vital role on the development of modern science and technology. Non-insulated insert coil wound by ReBCO HTS tapes, with the advantages of high thermal conductivity, well thermal stability and no need of active protection, is the first choice for being a high field insert coil. Recent experiments show that high field insert under 24 T in liquid helium quenches rapidly before reaching the 0.1μV/cm quench criterion, which is quite different to ReBCO coils under low magnetic field, besides, insert coil shows performance degradation after the quench. The mechanism still remains unclear, which may be caused by the stress concentration on the ReBCO tape during the manufacture process. .This project takes the quench anomaly as the breakthrough point, studies the quench propogation characteristics via parameters such as magnetism, heat, voltage, current etc., establishes detailed and effective physical model for quench propogation in extremely high non-insulated ReBCO insert coil, simulates the stress distribution inside the ReBCO coil with fine FEA numerical analysis techniques, precisely predicts the stress/strain behavior in the insert coil, as so to develop more effective and suitable coil structure to overcome electromagnetic stress, cold contraction stress and local stress concentration caused by crossover distortion. The aim of this project is mainly to perfect the the magnet stucture and construction techniques suitable for insert coils with high operation stability in extremely high magnetic fields, and provides theoretical foundation and technical reserve for high-stability extremely high field magnets.

极高磁场环境对发展现代科学技术作用重大。采用ReBCO超导带材绕制的无绝缘内插线圈具有传热性能好、热稳定性好、无需主动保护等优点，是极高场内插线圈的首选。最近实验发现液氦浸泡的内插线圈在24T高场下，在没达到0.1μV/cm的失超判据时快速失超，这与低场下测试情况有很大不同，其发生机理仍不明晰，且内插线圈失超后性能有所退化，可能与内插线圈建造过程中的ReBCO带材应力集中有关。本项目以极高场内插磁体的失超异常现象为切入点，通过磁、热、电压、电流等参量来研究内插线圈的失超传播规律，建立详细而有效的失超传播物理模型，采用精细有限元数值分析技术仿真内插线圈内部的应力分布关系，精确预测磁体的应力和应变行为，发展更加有效、适用的线圈结构，克服电磁应力、冷收缩应力、crossover扭曲等造成的局部应力突变，完善高稳定度的极高场内插磁体结构和建造工艺，为发展高稳定度的极高场磁体提供理论基础和技术储备。

极高磁场超导磁体对现代科学技术发展作用重大。采用REBCO超导带材绕制的无绝缘内插线圈具有传热性能好、热稳定性好、无需主动保护等优点，是极高场内插线圈的首选。但是极高磁场超导磁体失超发生机理仍不明晰，线圈失超后性能退化与REBCO带材应力集中有关。为深入理解极高磁场超导磁体失超机理和性能退化机制，本项目开展了以下工作内容：. 1）对REBCO导体的瞬态扰动物理模型和数学模型进行了分析，针对极高场内插磁体的失超规律，定量研究了极高场内插磁体的电流分布规律和磁场、电流、电压等参量之间的关系，同时采用大尺度分析模型模拟磁体在通电、降温过程中的应力应变，找出磁体的应力集中点，针对焊接接头部分进行了应力分析，设计了特殊的焊接接头保护装置。. 2）建立了无绝缘磁体的多场耦合失超模型，为极高场内插磁体的设计和尽限安全设计提供理论支撑。结合磁体的结构特点与二代高温超导带材机电特性，提出一种减小不平衡力的保护方式，使得内插磁体因失超导致的瞬时增加应力降低了67%，该技术为后续建造的极高场超导磁体安全运行提供保障。. 3）分析了REBCO 内插线圈在不同材料下高场内插磁体的应力分布情况，对线圈绕制应力、磁体降温过程的冷收缩应力和通电励磁的电磁力作用对导线应力状态进行了详细分析，并根据分析结果优化了高场内插线圈根据计算分析结果优化极高场内插磁体的工艺参数和技术方案；针对双饼线圈 crossover 扭曲时的形变，设计了特种绕线骨架用以保护导线的扭曲过线位置，极大地缓解了其在高场情况下的应力集中问题。. 前述研究成果用于设计和建造的超导磁体实现了32.35T超导磁体的世界最高磁场记录，获取了大量宝贵的REBCO线圈在≥32T磁场下的运行数据，实现了极高场内插磁体的理论分析和建造技术的突破，为我国的超导强磁装备技术奠定了坚实的理论和技术基础。