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 applying an AC field in plane with the circulating current will lead to demagnetization due to vortex shaking. To unveil the vortex shaking mechanism of REBCO stacks, this paper provides an in-depth study, both experimentally and numerically,. 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 developed to simulate the vortex shaking effects. Qualitative agreement was obtained between the experiment results and the simulation results. Our results show that the in-plane magnetic field leads to a sudden decay of the trapped magnetic field in the first half shaking cycle, due to magnetic field dependence of the circulating current. Furthermore, the decline rate of demagnetization with the increase of tape number is due to the increase of trapped magnetic field in the stack. 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 useful guidance in the development of future shaking devices for REBCO magnets.
High-temperature superconductors from the REBCO (RE = rare earth) family have attained industrial production and their performance is continuously being enhanced. However, cabling technology for high-current (kA range) cables for magnet technology is still challenging and there are only few cable concepts available (CORC®, Roebel cable, twisted stack cable). Each of them exhibits different characteristics. In this paper we experimentally investigate CORC® cable produced in-house utilizing a copper tube former. Such a former offers a central cooling channel for partial or complete cable cooling by forced flow of coolant. We focus mainly on AC loss due to transporting AC current, an external applied AC magnetic field and their simultaneous action. In the case of transporting AC current we found indications that a large part of the total loss has its origin in eddy currents due to an axial magnetic field. For the investigation of magnetization AC loss, we prepared several samples with different configurations. In this case we found direct evidence for increasing AC loss due to losses in the metallic former. However, we also found that at low field amplitudes the magnetization AC loss of the complete cable is lower than the loss in the bare former. This is caused by shielding of the magnetic field by a superconductor, which was also confirmed by numerical simulations.
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