Vortex shaking study of REBCO tape with consideration of anisotropic characteristics

The second generation high temperature superconductor, specifically REBCO, has become a new research focus in the development of high-field (>25T) magnets. Previous research shows that for magnetized superconducting stacks and bulks the application of an AC field in plane with the circulating current will lead to demagnetization due to vortex shaking. This paper provides an in-depth study, both experimentally and numerically, to unveil the vortex shaking mechanism of REBCO stacks. A new experiment was carried out to measure the demagnetization rate of REBCO stacks exposed to an in-plane AC magnetic field. Meanwhile, 2D finite element models, based on the E-J power law, are used for simulating the vortex shaking effect of the AC magnetic field. Qualitative agreement was obtained between the experiment results and the simulation results. Our results show that the applied in-plane magnetic field leads to a sudden decay of trapped magnetic field in the first half shaking cycle, which is caused by the magnetic field dependence of critical current. Furthermore, the decline of demagnetization rate with the increase of tape number is found to be caused by the increase of trapped magnetic field in the stack, which weakens the shaking effect of the applied AC magnetic field. Further study concerning the frequency of the applied AC magnetic field shows that it has little impact on the demagnetization process. Our modeling tool and findings will provide guidance in the development of future shaking devices for REBCO magnets.第二代高温超导体（second generation high temperature superconductor），具体为REBCO，已成为高场（>25T）磁体研发领域的新研究热点。既往研究表明，对磁化超导叠片与块材施加与环流同平面的交流磁场时，会因涡旋抖动（vortex shaking）引发退磁效应。本文通过实验与数值模拟相结合的方式，对REBCO超导叠片的涡旋抖动机制展开深入研究。本研究开展了全新实验，对处于同平面交流磁场中的REBCO超导叠片的退磁速率进行测量；同时，基于E-J幂律（E-J power law）构建二维有限元模型，用于模拟交流磁场引发的涡旋抖动效应。实验结果与模拟结果实现了定性吻合。研究结果显示，施加的同平面磁场会在抖动周期的前半段引发被俘获磁场的骤降，该现象源于临界电流的磁场依赖性。此外，退磁速率随超导带材数量增加而降低的现象，源于超导叠片内被俘获磁场的提升，该提升会削弱外加交流磁场的抖动效应。针对外加交流磁场频率的进一步研究表明，其对退磁过程的影响极小。本研究的建模工具与研究结果，将为未来REBCO磁体用抖动装置的研发提供指导。