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

We measure the current voltage (I-V) 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_c) 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 (n) of the voltage-current relationship, V ~ In, 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_c 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_c and n that are indicative of these position-dependent microstructural/pinning property variations. We describe the applicability of this new n-value analysis to improved understanding of practical conductor performance and performance variability.