曲げ変形により損傷を受けたBi2223超伝導複合テープにおける局所臨界電流の分布と試料全体の臨界電流との関係

Abstract

The damage extent and therefore the critical current are different from position to position in a long sample especially when the sample is deformed severely. In the present work, a 48 cm long Bi2223 composite tape bent by 0.7%, being composed of 48 elements with a length of 1 cm and of 8 parts with a length of 6 cm, was used as the test sample. The V-I curve, critical current and n-value were measured for the 48 elements, 8 parts and overall sample, and the relation of the distribution of the critical current of the elements to the critical current of the parts and overall sample and the sample length dependence of critical current were discussed. It was found that the critical current and n-value of parts and overall sample are described well by the voltage summation model which regards the parts and overall sample to be composed of a series circuit of elements. The critical current distribution of the elements was described by the bi-modal Weibull distribution function. Applying the simulation method, in which the estimated Weibull distribution function for the critical current of elements, the empirical relation between the critical current and n-value, the series circuit model for voltage generation and the Monte Carlo method were combined, the relation of average critical current to sample length could be described well. From these results and the features of the V-I curve of the damaged part, it was shown that the critical current and n-value decrease with increasing sample length and the extent of the decrease in critical current with sample length is dependent on the criterion for the definition of critical current.