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The critical current density jC is one of the most important parameters of high-temperature superconductors (HTS). Although the standard four-probe method has been widely used for measuring jC, it requires the heat-treat process of a HTS sample. This process may lead to the degradation of the HTS characteristics. For this reason, a contactless method has been desired for measuring the critical current density. As the contactless measurement method of the critical current density jC, Claassen et al. proposed the inductive method [1]. While an ac current I(t) = I0sin2πft is applied in an N-turn coil placed just above a HTS thin film, they measured the harmonic voltage induced in the coil. As a result, they found that the third-harmonic voltage suddenly develops when the coil current I0 exceeds the threshold current IT. In addition, they showed that jC can be calculated from IT. On the other hand, Ohshima et al. have proposed the permanent magnet method [2]. While moving a permanent magnet up and down above a HTS film, they measured the electromagnetic force acting on the film. As a result, they found that the maximum repulsive force FM is roughly proportional to jC. This result implies that jC can be estimated from the measured value of FM. A numerical code has been developed for determining the time evolution of the shielding current density in a HTS thin film. By using the code, two kinds of the contactless methods are investigated numerically. The results of computations show that, in the inductive magnet, the third-harmonic voltage suddenly develops above a certain limit of the coil current I0. This tendency qualitatively agrees with Claassen’s experimental results. In addition, it is found that, even if the center of the magnet is located at the film edge, the maximum repulsive force FM is almost proportional the critical current density jC in the permanent magnet method (see Fig. 1). This means that the jC-distribution can be determined from these relationships between jC and FM.

Numerical Simulation of Contactless Methods for Measuring jC Distribution of High Temperature Superconducting Thin Film