Effects of Heterogeneous Cracking of Superconducting Layer on Voltage-Current Curve, Critical Current, and n-Value in High-Temperature Superconducting Layer-Coated Conductor Tape

Abstract

When high-temperature superconducting layer-coated conductors are exposed to high electromagnetic and/or mechanical stress and strain, the superconducting layer is damaged mainly by cracking. As cracking occurs heterogeneously, the critical current and n-value of a test specimen, which is composed of a series circuit of local sections, are dependent on the extent of cracking in local sections. In this work, the correlations of the extent of cracking in local sections with the critical current and n-value of the specimen were studied by modeling analysis. When one section is cracked, the critical current and n-value of the specimen decrease with increasing crack size. When multiple sections are cracked, the properties depend on the difference in crack size among the sections. When the crack size of the sections is similar, the critical current of the specimen decreases and the n-value increases as the number of cracked sections increases. This is caused by the increased voltage and the decreased shunting current at cracks. When there are large differences in the crack sizes of the sections, the section with the largest crack controls the voltage-current behavior of the specimen and determines the reduction in the critical current and n-value. For a given size of the largest crack, the critical current of the specimen is slightly higher and the n-value is lower when there is an intermediate difference in crack size among the sections than when there is a small difference in crack size, and the critical current is lower and the n-value is higher when there is an intermediate difference in crack size than when there is a large difference in crack size.