An Experimental and Analytical Study of Periodic and Aperiodic Fluctuations in the Critical Current of Long Coated Conductors

It is well known that the critical current of all coated conductors fluctuates along their length and from run to run for reasons that are seldom reported in detail and may not always be understood. Here, we report results obtained with a reel-to-reel transport and magnetization measurement apparatus that allows 77-K measurements with a resolution of about 20 and 1 mm, respectively. Analysis of these data assesses both periodic and random contributions to the critical current fluctuations. We find multiple sources of the fluctuations, and, thus, many different types of behavior. A very positive result is that fluctuations are definitely decreasing in more recent conductors. We show how to reveal fluctuations due to variations of the active cross section of the conductor (i.e., an IC variation) and to variations of the superconducting properties themselves. We found that the latter dominates in the vast majority of conductors studied.