人工柱状孔对块体高温超导体俘获场的影响
Modification of the trapped field in bulk high-temperature superconductors as a result of the drilling of a pattern of artificial columnar holes
摘要：
在沿c轴人工钻孔的大块高温超导体中检查了捕获的磁场。通过数值模型和霍尔探针映射技术研究和比较了孔图案对磁化强度的影响。为了这个目的，我们考虑两个散装YBCO样品与一个矩形的横截面，每个被钻六个孔安排在一个矩形晶格（样品I）或在一个中心的矩形晶格（样品II）。对于数值分析，考虑三种不同的模型来计算捕获通量：（i）二维（2D）Bean模型，其忽略退磁效应和磁通蠕变，（ii）2D有限元模型，其忽略退磁效应，但以E-J幂律的形式结合磁弛豫，以及（iii），三维有限元分析，考虑到样品的有限高度和磁通蠕变效应。对于实验分析，通过在钻孔过程之前和之后执行的霍尔探针映射来测量样品表面上方的捕获的磁通量密度。钻孔样品中的最大陷获磁通密度小于普通样品中的最大陷获磁通密度。发现具有居中矩形晶格的样品II的磁化下降最小。这一结果得到了数值模型的证实。在每个样品中，使用三种不同模型独立计算的相对液滴具有良好的一致性。如实验所观察到的，在样品II中计算的磁化降是最小的，并且其相对值与测量值相当。相比之下，样品（1）中测得的磁化强度下降远大于模拟预测的磁化强度下降，这很可能是由于钻孔过程中微观结构的变化。
英文摘要：
The trapped magnetic field is examined in bulk high-temperature superconductors that are artificially drilled along their c-axis. The influence of the hole pattern on the magnetization is studied and compared by means of numerical models and Hall probe mapping techniques. To this aim, we consider two bulk YBCO samples with a rectangular cross-section that are drilled each by six holes arranged either on a rectangular lattice (sample I) or on a centered rectangular lattice (sample II). For the numerical analysis, three different models are considered for calculating the trapped flux: (i), a two-dimensional (2D) Bean model neglecting demagnetizing effects and flux creep, (ii), a 2D finite-element model neglecting demagnetizing effects but incorporating magnetic relaxation in the form of an E-J power law, and, (iii), a 3D finite element analysis that takes into account both the finite height of the sample and flux creep effects. For the experimental analysis, the trapped magnetic flux density is measured above the sample surface by Hall probe mapping performed before and after the drilling process. The maximum trapped flux density in the drilled samples is found to be smaller than that in the plain samples. The smallest magnetization drop is found for sample II, with the centered rectangular lattice. This result is confirmed by the numerical models. In each sample, the relative drops that are calculated independently with the three different models are in good agreement. As observed experimentally, the magnetization drop calculated in the sample II is the smallest one and its relative value is comparable to the measured one. By contrast, the measured magnetization drop in sample (1) is much larger than that predicted by the simulations, most likely because of a change of the microstructure during the drilling process.
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