Development of a measurement system for evaluating critical current characteristics in superconductor

The critical current density of a superconductor is the maximum value of current density that can flow through the superconductor with zero resistance. A detailed evaluation of this property is necessary for power system applications. The four-terminal and DC magnetization methods are often used to measure the critical current characteristics. However, in four-terminal method, it is difficult to measure successfully without a power supply that can output a large current when the critical current of the superconductor is large. Second, the DC magnetization method is difficult to measure accurately. Because the current paths in the oxide superconductor are complex, the value is obtained by averaging each different current path. In this study, we designed a measurement system using the AC inductive method, known as the Campbell method, to evaluate the critical current characteristics of superconductors in detail. The system was developed by using the programing tool of LABVIEW so that it can be operated semi-automatically. As the experiment target, a high-temperature oxide superconducting bulk was chosen. As a result of the measurement, the characteristic of external AC magnetic field amplitude vs. penetration depth of the AC magnetic flux in superconductor were obtained. In addition, it was confirmed that this measurement system allows detailed evaluations of the critical current characteristics, such as the critical current density flowing through the bulk can be calculated based on the differences in current paths of the oxide superconductor.