Demagnetisation by crossed fields in superconductors
Demagnetisation by crossed fields in superconductors
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DOI：
10.1088/1361-6668/aa52f2
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发表时间：
2017-03-01
影响因子：
3.6
通讯作者：
Coombs, Tim
中科院分区：
文献类型：
--
作者：
Campbell, Archie;Baghdadi, Mehdi;Coombs, Tim
本文研究了超导体在交叉场作用下俘获磁化强度的衰减。数值结果与Brandt和Mikitik（2002 Phys. Rev. Lett. 89027002），其解决了薄带超导体的问题。使用A配方的FlexPDE和H配方的COMSOL。一个带的横截面的纵横比为20的模拟结果表明，与理论的横向场大于横向穿透场的情况下，一个较小的。在后一种情况下，磁化强度如预测的那样饱和，然而，模拟显示在许多周期后缓慢衰减。在堆叠的YBCO带材的情况下，磁通线的移动是非常小的，并且研究了可逆运动的影响。对于非常薄的去耦带，这可以减少最初的衰减，但在非常大量的循环之后会导致稳定的衰减。对堆叠条带的模拟表明，衰减常数随条带数量近似线性增加。当与一个磁带的理论相结合时，这可以解释在以前的实验中观察到的非常缓慢的衰减。实验结果与理论和模拟定性一致，但显示出一些差异。然而，实验情况和理论之间存在许多差异，因此预期不会有很好的一致性。
A study has been made of the decay of the trapped magnetisation in superconductors when exposed to a crossed field. Numerical results have been compared with the theory of Brandt and Mikitik (2002 Phys. Rev. Lett. 89 027002) which solves the problem for a thin strip superconductor. FlexPDE with the A formulation and COMSOL with the H formulation were both used. Simulations of a strip with a cross section aspect ratio of 20 showed good agreement with theory both for the case of a transverse field larger than the transverse penetration field and for one smaller. In the latter case the magnetisation saturates as predicted, however the simulations show a slow decay after many cycles. In the case of stacked YBCO tapes the movement of flux lines is very small and the effects of the reversible motion were investigated. This can decrease the decay initially for very thin decoupled tapes, but cause a steady decay after very large numbers of cycles. Simulations on stacked strips showed that the decay constant increased approximately linearly with the number of strips. When combined with the theory for one tape this can explain the very slow decay observed in previous experiments. Experimental results were qualitatively in agreement with theory and simulations but showed some discrepancies. However there are a number of differences between the experimental situation and theory so good agreement is not expected.