Relation of Distribution of Local Critical Current to Overall Critical Current in Bi2223 Superconducting Composite Tape Damaged by Bending

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.

Statistical analysis of the distribution of critical current and the correlation ofnvalue to the critical current of bent Bi2223 composite tape

“…As an alternative distribution function that enables us to describe the distribution of the local critical current at ε B = 1.1% where the ln ln(1 − F) −1 versus ln(I c ) plot showed a concave shape (figure 5(d)), the bimodal Weibull distribution can be mentioned [26,31,41,42]. It has been found in our preceding work that this function can describe the experimental results at high ε B (≈1.0%) for the samples from other suppliers [26,31,41]. In the present work, as well as in our preceding work, it was attempted to apply the bimodal Weibull distribution function to the experimental results at ε B = 1.1%.…”

Sample-length dependence of the critical current of slightly and significantly bent-damaged Bi2223 superconducting composite tape

“…The frequency (probability density) calculated by equation ( 3) with the obtained parameters stated above is presented in figure 6, describing the measured one. The authors are carrying out similar experiments not only for the present sample but also for a different fabricationroute Bi2223-composite tape sample [32]. Recently, it was found that, when the sample is significantly damaged as in the present case for 1.0% bending, equation ( 3) is a useful tool for the description of the local critical current distribution.…”

“…On the other hand, the curve of 1.0%-bent elements with a downward convex shape in figure 5(a) indicates that, when the applied bending strain is high, equation ( 2) is not suitable for the description of the distribution. As an alternative distribution that enables us to describe the distribution of 1.0%bent elements, the multimodal Weibull distribution can be mentioned [31,32]. This function stems from the competing risk model and is applicable when plural causes of damage coexist.…”

“…An example of the distribution of the critical current of significantly bent-damaged elements with a 1 cm length, measured for a different fabrication-route Bi2223-composite tape sample[32]. (a) Weibull plot of the measured values and the estimated cumulative distribution function based on the bimodal Weibull distribution function (equation (3)).…”

Simulation on the relation of distribution of overall critical transport current to that of local one in bent-damaged Bi2223 superconducting composite tape

“…͑3͒ later͔. 24,37 The applicability of the three parameter and bimodal functions to the present experimental results ͑Fig. 3͒ was examined as follows.…”