Temperature dependence of critical current density of AC superconductor and the effect on AC quench current degradation

For the development of large-current-capacity AC superconducting cable, it is important to consider the temperature dependence of the critical current density of AC superconductors. To this end, critical current density was evaluated from the magnetization /spl Delta/M, measured by SQUID between 4.5 K and 7.5 K. This value was compared with that obtained by measurement of the same sample using the four-wire method between 4.2 K and 8.0 K, and a good agreement was observed. Therefore, the critical current density evaluated from /spl Delta/M could be considered as a transport critical current density. Also, it was confirmed to be degraded drastically with temperature rise. From simple evaluation, it is considered that the effect of this phenomenon cannot be ignored for AC quench current degradation of large-current-capacity AC superconducting cables, because of AC loss. The cause of this phenomenon is discussed using the pinning force dependence on temperature and magnetic field.<>