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Abstract
High-Temperature Superconductors (HTS) are widely recognized for their efficiency and minimal energy loss, making them essential in industries such as power transmission, energy storage, and electronics. Nevertheless, the challenge of maintaining a consistent critical current (Ic) along HTS tapes has posed a significant obstacle to their broad commercialization. Quantifying the uniformity of critical current over long HTS tapes is a complex research problem due to the inherent uncertainty of critical current and its dynamic evolution. In this study, we introduce an innovative approach using the Roughness-based Uniformity Metric (RUM) for assessing the uniformity of Ic. By integrating the roughness measure of functional regression with 1D fused lasso, this study aims to achieve two key objectives: (1) accurately measuring the uniformity of the critical current, and (2) automatically monitoring and detecting the drop-out event with statistical control charts. By employing the roughness measure of functional regression for uniformity assessment and applying 1D fused lasso for smoothing, our method enhances the precision in detecting changes in the critical current. We demonstrate the effectiveness of the proposed approach through uniformity modeling and monitoring on three different HTS tapes. The proposed method are also compared with the conventional uniformity metric, e.g., the coefficient variation.
Keywords Roughness-based Uniformity Metric, Quality Modeling and Monitoring, Superconductor Manufacturing
1. Introduction
Recent advancements in High-Temperature Superconducting (HTS) tapes have unlocked considerable potential in various emerging technologies, ranging from ultra-sensitive sensing and quantum measurement instruments to superconducting energy storage systems [1]. The pivotal role of the Metal Organic Chemical Vapor Deposition (MOCVD) process has been instrumental in fabricating long-length HTS tapes [2]. These tapes are critical for the high-field applications of superconductors, demanding cost-effective production with uniform performance over extended lengths. However, ensuring this uniformity poses a significant challenge, given the spatial heterogeneity influenced by a myriad of process parameters and growth conditions.
In-line quality control tools have been employed to monitor the quality and process parameters of superconducting tapes during manufacturing. An essential quality indicator that has emerged is the critical current, a measure of the tape's ability to conduct electricity without resistance [3]. The uniformity of critical current along the tape is crucial for its application, with nonuniform behaviors manifesting as spatial variability and abrupt dropouts. These substantial critical current dropouts...