Effects of Crack Size Distribution and Specimen Length on the Correlation between <i>n</i>-Value and Critical Current in Heterogeneously Cracked Superconducting Tape

Abstract

A Monte Carlo simulation study was carried out to reveal the effects of crack size distribution and specimen length on the correlation between n-value and critical current in heterogeneously cracked superconducting tapes. First, it was shown that, with increasing distribution width of crack size, the distribution widths of critical current and n-values increase, and, the average critical current-value and average n-value of specimens decrease. Also, it was shown that the decrease in average n-value with increase in distribution width of crack size is more intense than the decrease in average critical current-value and this feature is more pronounced in longer specimens. Then it was revealed that plural n-values can exist for one critical current value since the n-value of specimen was dependent on the positional relation among the voltage-current curves of the sections, of which specimen is constituted. This phenomenon could be described by the difference in the resistance value in the current shunting circuit by application of a single equivalent crack-current shunting model in which the cracks within a specimen are replaced by a single equivalent crack. Based on this result, an approach, in which the resistance value in the current shunting circuit is used to describe the upper-lower bounds and the center of n-value in the correlation diagram between n-value and critical current, was presented. It was shown that the correlation diagrams at various distribution widths of crack size and specimen lengths, obtained by simulation and experiments, are described well by this approach. [

Effects of Crack Size Distribution and Voltage Probe Spacing on Variation of Critical Current and <i>n</i>-Value along the Longitudinal Direction in Superconducting Tape with Cracks

“…We define the current transfer length as s (¹ L 0 ), I c and n-value of the sections in the non-cracked state as I c0 and n 0 , respectively, and the critical electric field for determining the critical current as E c (= 1 µV/cm in this work). We express the VI curve of the cracked section (L 0 = 1.5 cm) as 2,3,8,9,15,16) V…”

“…7,11,12) We have studied the I c and n-value of both coated and filamentary tapes 2,3,7,16) experimentally and analytically by applying a current shunting model at cracks. 10) We have been developing a Monte Carlo simulation method 8,9) combined with the current shunting model at cracks to systematically obtain a wide range of data about the effects of crack size distribution and specimen length on I c and n-values. We have shown that this simulation method 8,9) reproduces the experimental observation that the local information about critical current values in a specimen is diluted in longer specimens.…”

“…10) We have been developing a Monte Carlo simulation method 8,9) combined with the current shunting model at cracks to systematically obtain a wide range of data about the effects of crack size distribution and specimen length on I c and n-values. We have shown that this simulation method 8,9) reproduces the experimental observation that the local information about critical current values in a specimen is diluted in longer specimens. 22) In this work, we used the Monte Carlo method combined with the current shunting model to determine the effects of the crack size distribution and voltage probe spacing on the variation of critical current and n-value along the tape length.…”

Effects of Size of the Largest Crack and Size Difference among Cracks on Critical Current of Superconducting Tape with Multiple Cracks in Superconducting Layer

“…The relation of V c to I c , K eq and V RE and the relation of I c to L p,smallest and V RE in the smallest ligamentsection are expressed by eqs. (8) and (9) from eqs. (7) and (2), respectively: Current,…”

“…In the same way, substituting K eq = K eq,ave = N, I c = I c,lower,ave , L p,smallest = L p,smallest,ave and corresponding L-value into eqs. (8) and (9) From eq. (14), the effects of the difference in crack size among the sections on the increase in average REBCOtransported current in the ligament part, ¦I RE,ave , and the increase in average shunting current in the cracked part ¦I s,ave in the largest crack-section were evaluated.…”