Time-Evolution Simulation of Shielding Current Density in High-Temperature Superconductor

高温超导体的临界电流密度是高温超导体工程应用的重要参数之一。在这种意义上，非接触、非破坏性的方法被用来测量高温超导薄膜的临界电流密度，Claassen等人提出了电感法测量高温超导薄膜的临界电流密度。当在一个放置在薄膜上方的小线圈中施加交流电流时，他们监测线圈中感应的电压谐波。结果表明，当且仅当线圈电流的幅度超过一定限度时，才能检测到三次谐波电压。该结果意味着可以通过测量阈值电流来估算临界电流密度。另一方面，Ohshima等人提出了与电感法大不相同的永磁法。当将永磁体靠近高温超导薄膜时，他们测量了电磁场。 ...更多信息 作用在薄膜上的磁力。结果，他们发现最大排斥力近似与临界电流密度成正比。这种趋势意味着临界电流密度可以通过测量磁体和HTS薄膜之间的电磁相互作用来确定。在本研究中，已经开发了用于分析HTS薄膜中的屏蔽电流密度的时间演化的数值代码，并且通过使用该代码，电感法和永磁法都被数值再现。本研究的主要结论如下：1）对于临界电流密度小于0.25 MA/cm ^2的情况，电感法的准确度不超过3%。2）永磁法的数值模拟表明，最大排斥力与临界电流密度近似成正比。这些数值结果与Ohshima等人的实验结果定性一致。

As is well known, the critical current density is one of the most important parameters for engineering applications of the high-temperature superconductor (HTS). In this sense, the nondestructive and noncontact method has been desired for measuring the critical current density of the HTS thin film.Claassen et al. proposed the inductive method for measuring the critical current density in HTS thin films. While applying an ac current in a small coil placed just above a film, they monitored harmonics of the voltage induced in the coil. As a result, they showed that the third-harmonic voltage is detected if and only if amplitude of the coil current exceeds a certain limit. This result means that the critical current density can be estimated by measuring the threshold current.On the other hand, Ohshima et al. have proposed the permanent magnet method that is widely different from the inductive method. While bringing a permanent magnet closer to a HTS thin film, they measured the electromagn … More etic force acting on the film. As a result, they found that the maximum repulsive force is approximately proportional to the critical current density. This tendency implies that the critical current density can be determined by measuring the electromagnetic interaction between the magnet and the HTS film.In the present study, the numerical code has been developed for analyzing the time evolution of the shielding current density in the HTS thin film and, by use of the code, both the inductive method and the permanent magnet method have been reproduced numerically. Conclusions obtained in the present study are summarized as follows.1)For the case where the critical current density is below 0.25 MA/cm^2, an accuracy of the inductive method is not more than 3%. Otherwise, its accuracy is remarkably degraded.2)The numerical simulation of the permanent magnet method shows that the maximum repulsive force varies in approximate proportion to the critical current density. These numerical results agree qualitatively with the experimental ones by Ohshima et al. Less