Superconducting-magnetic heterostructures: a method of decreasing AC losses and improving critical current density in multifilamentary conductors
Superconducting-magnetic heterostructures: a method of decreasing AC losses and improving critical current density in multifilamentary conductors
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DOI：
10.1088/0953-8984/21/25/254206
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发表时间：
2009-06-24
影响因子：
2.7
通讯作者：
Majoros, M.
中科院分区：
文献类型：
--
作者：
Glowacki, B. A.;Majoros, M.
磁性材料可以在宏观/微观尺度上作为磁性导流剂，也可以在纳米尺度上作为有效的钉住中心，帮助提高实际超导体的性能。数值模拟结果表明，由于细丝的解耦，磁屏蔽降低了自场条件下的交流损耗，同时提高了复合材料的临界电流。这种效应对涂层导体特别有利，其中超导体的各向异性特性被导体结构放大。然而，铁磁涂层通常与YBa2Cu3O7和（Pb, Bi）(2)Sr2Ca2Cu3O9导体在化学上不相容，因此必须使用缓冲层。相反，在MgB2导体中，铁基体可能与超导磁芯保持直接接触。超导磁异质结构的应用需要考虑所用超导材料的热稳定性和电磁稳定性。一方面，磁性材料降低了单个细丝上的临界电流梯度，但另一方面，它们往往降低了超导磁芯和冷媒之间的导热性，这可能会在热不稳定的情况下导致导体的破坏。提高超导导体临界电流密度的一种可能的纳米级方法是引入亚微米磁性钉钉中心。然而，必须控制磁性包裹体的体积密度和化学相容性，以避免抑制超导性能。
Magnetic materials can help to improve the performance of practical superconductors on the macroscale/microscale as magnetic diverters and also on the nanoscale as effective pinning centres. It has been established by numerical modelling that magnetic shielding of the filaments reduces AC losses in self-field conditions due to decoupling of the filaments and, at the same time, it increases the critical current of the composite. This effect is especially beneficial for coated conductors, in which the anisotropic properties of the superconductor are amplified by the conductor architecture. However, ferromagnetic coatings are often chemically incompatible with YBa2Cu3O7 and (Pb, Bi)(2)Sr2Ca2Cu3O9 conductors, and buffer layers have to be used. In contrast, in MgB2 conductors an iron matrix may remain in direct contact with the superconducting core. The application of superconducting-magnetic heterostructures requires consideration of the thermal and electromagnetic stability of the superconducting materials used. On one hand, magnetic materials reduce the critical current gradient across the individual filaments but, on the other hand, they often reduce the thermal conductivity between the superconducting core and the cryogen, which may cause destruction of the conductor in the event of thermal instability. A possible nanoscale method of improving the critical current density of superconducting conductors is the introduction of sub-micron magnetic pinning centres. However, the volumetric density and chemical compatibility of magnetic inclusions has to be controlled to avoid suppression of the superconducting properties.