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

众所周知，临界电流密度是高温超导体(HTS)工程应用的重要参数之一。从这个意义上讲，非破坏性和非接触性的方法已经成为测量高温超导薄膜临界电流密度的理想方法。提出了测量高温超导薄膜临界电流密度的电感法。当他们在放置在薄膜上方的小线圈中施加交流电流时，他们监测了线圈中感应电压的谐波。结果，他们表明，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。这一结果意味着可以通过测量阈值电流来估计临界电流密度。提出了与感应法大相径庭的永磁法。在使永磁体更接近高温超导薄膜的同时，他们测量了电磁…更多的精神力量作用于这部电影。结果，他们发现最大排斥力与临界电流密度近似成正比。这一趋势意味着可以通过测量磁体与高温超导薄膜之间的电磁相互作用来确定临界电流密度。在本研究中，开发了用于分析高温超导薄膜中屏蔽电流密度的时间演化的数值程序，并利用该程序对感应法和永磁法进行了数值再现。1)对于临界电流密度小于0.25 mA/cm~2的情况，感应法的精度不超过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变化。这些数值结果与Ohshima等人的实验结果定性地吻合。较少

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