Longitudinal Critical Current Profiles in Coated Conductors Examined by Transport and Magnetization Measurements

Abstract

Critical current ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> ) variations along the coated conductor (CC) have a significant impact on the conductor stability and quench behavior. In the direct current (DC) transport case, localized <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> minimum can lead to the formation of a region with a higher electric field. Joule heating in such a region can disable the operational functionality of the device. Then a sufficiently detailed knowledge of the longitudinal profile of the conductor <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> is in the first place necessary in assessing the conductor eligibility for a specific application. In the second place, it serves to design appropriate electro-thermal stabilization, securing an effective operation, and reducing the probability of conductor degradation during the quench. We report on the experimental investigation of longitudinal <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> homogeneity of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CC</i> observed by means of transport and magnetization measurements. Basic information is the CC data from the producer on <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> profiles obtained with ∼1-milimeter spatial resolution by Tapestar <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TM</sup> XL. We compare it with the result obtained by multi-channel DC transport measurement with 3-millimeter spatial resolution between neighboring contacts on a multiprobe device. Then the whole sample is characterized by a complex AC susceptibility experiment. We analyze possible causes of observed discrepancies between respective methods and discuss the relevance of various techniques for the determination of longitudinal <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> profiles in commercial CC.