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A.L. Mbaruku and J. Schwartz, J. Appl. Phys. , 101 , 073913 (2007)

Statistical Analysis of the Electromechanical Behavior of AgMg Sheathed Bi 2 Sr 2 CaCu 2 O 8+ x Superconducting Tapes Using Weibull Distributions.

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A.L. Mbaruku and J. Schwartz, J. Appl. Phys. , 101 , 073913 (2007)

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  1. Statistical Analysis of the Electromechanical Behavior of AgMg Sheathed Bi2Sr2CaCu2O8+x Superconducting Tapes UsingWeibull Distributions AgMg sheathed Bi2Sr2CaCu2O8+x (Bi2212) is the leading conductor candidate for high field superconducting magnets generating 25 T and above. The manufacturing of Bi2212 conductors involves deformation and thermal processing, that can result in non-uniform properties which are largely due to manufacturing defects, even in well-controlled manufacturing processes. Consequently, the electrical and mechanical properties vary along the length of a conductor. Here, we report results from analyzing the electromechanical properties of Bi2212 tapes using a statistical approach. 24 samples were studied at strains of 0%, 0.25%, and 0.349% for a total of 72 samples and the probability of electrical and mechanical failures was then analyzed using two- and three-parameter Weibull distributions. It was found that the mechanical failure of these tapes is homogeneous, consistent with failure in the AgMg sheath, but that the electromechanical failure is inhomogeneous within the conductor and as a function of strain, indicating that this failure is dictated by failure in the inhomogeneous ceramic oxide superconducting filaments. The distribution function, plotted in terms of reliability (i.e., probability of non-failure), is shown in the figure. So, for example, while the traditional model of Bi2212 strain-dependence would suggest that the conductor will not be degraded at 0.25% strain, the statistical analysis shows that only about 20% of samples at this strain will continue to have the average, zero-strain critical current. This has important implications for the development and design of superconducting magnets. Cross-sectional image of the Bi2212 tape conductor used in this study. Reliability function of Bi2212 tape conductors as a function of applied strain. The curves indicate the probability that the conductor will carry the indicated critical current, Ic, at the corresponding strain, ε. A.L. Mbaruku and J. Schwartz,J. Appl. Phys., 101, 073913 (2007) This work supported by the National Science Foundation and the Office of Naval Research, PI: Justin Schwartz

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