Proximity effects and pinning properties in superconducting wires for ac use

为了充分了解交流用超导线材的交流损耗和临界电流，本文研究了不同丝径和不同基体的多芯超导线材的转变温度T_c和上临界场B_c<c2>及其与温度的关系。研究了灯丝尺寸和基体材料对T_c和B_c的影响<c2>。在GLAG理论框架下对实验结果进行了分析。进一步对<c2>结构上类似于多层线的超导超晶格中的B_2进行了理论分析。所得结果总结如下. T_c：当纤维尺寸df从1 μ m减小时，T_c从9.35 K减小到7.84 K，在df=0.07 μ m附近T_c显著减小，这归因于纤维与周围基体之间的邻近效应. B_<c2>：4.2 K时的B_值<c2>也随着df的减小而减小。GL参数Kappa GL随着df的减小而增加，范围从40到60。在<c2>具有不同扩散常数的两层交替堆积的超导超晶格中，平行于层平面<c2>和垂直于层平面的B_（？）特别地，平行于层平面的B的温度依赖性<c2>预期在温度下改变。

In order to get a sufficient knowledge of ac loss and critical current in superconducting wires for ac use, multifilamentary superconducting wires with various filament sizes and different matrixes are investigated on their transiton temperature T_c and upper critical field B_<c2> including its temperature dependence. Much attention has been directed to the effects of filament size and matrix material to T_c and B_<c2>. Experimental resultls were analyzed in the framework of the GLAG theory. Futher, a theroretical analysis of B_<c2> in superconducting superlattices which are similar to multilayr wires in structure, has been done. Obtained results are summarized as follows.1. T_c : As the filament size df of samples is decreased from 1 mu m, T_c generally decreases from 9.35 to 7.84 K.A marked decrease in T_c appears around df=0.07 mu m and is ascribed to the proximity effect between the filament and surrounding matrix.2. B_<c2> : Values of B_<c2> at 4.2 K also decrease with decreasing df. The GL parameter Kappa GL increases with decreasing df and ranges from 40 to 60. An increase in Kappa GL for finer filament samples may lighten the decrease in B_<c2>.In superconducting superlattices where two layrs with different diffusion constants alternately pile up, values of B_<c2> parallel and perpendicular to the layr planes are appreciably different. In particular, the temperture dependence of B_<c2> parallel to the layr planes are expected to change at a temperature.