高温超导薄膜临界电流密度的无损测量研究

The nondestructive measurement for critical current density of high temperature films

临界电流密度Jc是超导薄膜的一个重要参量,它可以衡量超导薄膜的功率承载能力。大面积高温超导薄膜制成后,其Jc需要被无损精确测量。文中提出了一种新的交流磁场下的高温超导薄膜临界态模型:(1)基于此模型对薄膜的临界电流密度进行了精确无损测量;(2)并将实验测量的三次谐波电压曲线进行拟合研究。首先,根据麦克斯韦方程和伦敦方程,计算外加直流磁场超导薄膜Meissner态下电流和磁场在薄膜内的分布;然后分析薄膜进入临界态后内部电流的变化,在考虑顶扎力作用的情况下,提出了临界态电流和磁场非均匀分布模型;最后根据其模型,推导出三次谐波电压的表达式。为了验证该理论,分别对四片超导薄膜在不同频率下进行了三次谐波和临界电流密度测量。实验结果表明:三次谐波电压的理论与实验曲线一致;与四点传输法的测量结果相比较,该方法测量超导薄膜临界电流密度的误差在5%左右,具有高精度、无损伤、方便快捷等优点。

The critical current density Jc is one of the most important parameters of HTS films in superconductor application such as superconducting filter and superconducting Josephson devices.In this paper,a new model was presented to describe inhomogeneous current distribution throughout the thickness of superconducting films applied with magnetic field.Using this model,（1）The critical current density was measured accurately;（2）The third-harmonic voltage was accurately calculated and fitted.The theoretic curve was consistent with the experiment result about measuring superconducting film especially when the third-harmonic voltage just exceeds zero.Jc-value of superconducting films determined by the method was also compared with results measured by four-probe transport method.The relative error was good result for non-destruction measurement for Jc.