Numerical Investigation on Accuracy and Resolution of Contactless Methods for Measuring <i>j</i><sub>C </sub>in High-Temperature Superconducting Film: Inductive Method and Permanent Magnet Method

Abstract

The accuracy and the resolution of two types of the contactless methods for measuring the critical current density in a high-temperature superconducting (HTS) film have been investigated numerically. To this end, a numerical code has been developed for analyzing the shielding current density in the film with a crack. The results of computations show that the accuracy of two contactless methods is degraded remarkably due to the crack. Specifically, in the permanent magnet method, the maximum repulsive force acting on the film decreases when the magnet approaches near the crack. It is found that, even if the crack size is small, the maximum repulsive force decreases. This means that the crack can be detected. In the inductive method, although the threshold current decreases because of the crack, its value does not necessarily decrease for the case with a small crack size. In fact, the accuracy is not degraded when the inner radius of the coil contains the crack of the film. For this reason, we conclude that the smallest possible inner radius is preferable to detect the crack.