第３高調波誘導法による高温超電導薄膜・コート線材の 臨界電流密度とn 値の磁界角度依存性の測定

抄録

Nondestructive, AC inductive methods detecting third-harmonic voltages are widely used to measure the distribution of local critical current densities Jc of superconducting films deposited on large-area single-crystal substrates. We have extended this method to determine the electric field E versus current density J relation and the n-value (index of the power-law E-J characteristics) by evaluating the dependence of Jc on measurement frequency. The method to determine Jc with an electric-field criterion has been established as an international standard. This convenient method can also be applied to coated conductors with metallic substrates. Magnetic-field angular dependent Jc measurements are possible, and such measurements are of practical importance in applying coated conductors to superconducting coils. They are also useful in investigating the flux pinning mechanism. In this focused review, we briefly introduce the measuring method that has been based on our long years of research, and describe the precautionary points when recent coated conductors with high critical currents per unit width are measured.