Sample-length dependence of the critical current of slightly and significantly bent-damagedBi2223 superconducting composite tape

Abstract

The local critical current along a sample length is different from position to position in along sample, especially when the sample is damaged by externally applied strain. In thepresent work, we attempted to reveal the relation of the distribution of the localcritical current to overall critical current and the sample-length dependence ofcritical current for slightly and significantly damaged Bi2223 composite tapesamples. In the experiment, 48 cm long Bi2223 composite tape samples, composedof 48 local elements with a length of 1 cm and 8 parts with a length 6 cm, werebent by 0.37 and 1.0% to cause slight and significant damage, respectively. TheV–I curve, criticalcurrent (1 µV cm−1 criterion) and n value were measured for the overall sample as well as for the local elements and parts. Itwas found that the critical current distributions of the 1 cm elements at 0.37 and 1.0%bending strains are described by the three-parameter- and bimodal Weibull distributionfunctions, respectively. The critical current of a long sample at both bendingstrains could be described well by substituting the distributed critical current andn value of the short elements into the series circuit model for voltage generation. Also themeasured relation of average critical current to sample length could be reproduced well in thecomputer by a Monte Carlo simulation method. It was shown that the critical current andn value decrease with increasing sample length at both bending strains. The extent ofthe decrease in critical current with sample length is dependent on the criterionof the critical current; the critical current decreases only slightly under the1 µV cm−1 criterion which is not damage-sensitive, while it decreases greatly withincreasing sample length under damage-sensitive criteria such as the1 µV one.