N-Value Analysis of Position-Dependent Property Variability in Long-Length Coated Conductors

Abstract

We measure the current voltage ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> ) characteristics of high temperature superconductor coated conductors (HTS CCs) as a function of magnetic field, magnetic field angle, temperature, and position along multi-meter length practical wires. The critical current ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) data are analyzed to determine conductor uniformity, for quality assurance, and for feedback to the manufacturing process when an off-normal process event has occurred. We report on an expansion of this analysis to include the behavior of the power law exponent ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> ) of the voltage-current relationship, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> ~ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In</i> , as a function of magnetic field amplitude and angle, temperature, and position for long CCs. American Superconductor recently identified as of interest H ||ab plane <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> variations observed in wires fabricated by the MOD/RABiTS process. These variations were confirmed by LANL to exist in a 13 m length of wire. We also found correlations between <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> that are indicative of these position-dependent microstructural/pinning property variations. We describe the applicability of this new <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> -value analysis to improved understanding of practical conductor performance and performance variability.