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.