REBCO Tapes with Enhanced Current Sharing Characteristics for Quench Mitigation

The remarkably superior current densities of RE-Ba-Cu-O (REBCO, RE = rare earth) tapes enable high power density and highly efficient electric machines that directly address the needs of the Navy’s Advanced Power Systems. At such high current densities sustained through just 1 µm thick film, the superconductor is susceptible to localized heating at defective spots that are invariably present in a long tape. Since each tape turn of coils comprising a superconducting device is typically insulated, the hot spots do not dissipate easily which causes a thermal runaway, leading to a catastrophic failure. Since the normal zone propagation velocity in REBCO is extremely small, the hot spots cannot be detected in time to prevent thermal runaway, leading to a catastrophic failure. While long tapes with uniform critical current are highly desirable to avoid such hot spots, methods to manage local defects in REBCO tapes have to be investigated. Unlike metallic superconductors like Nb3Sn which consists of thousands of fine filaments in each strand, the wide geometry of REBCO tapes is not conducive for easy current sharing between tapes in a stack. The objective of the proposed project is to develop defect tolerant REBCO tape stacks that promote current sharing between tapes to bypass current around local defects to reduce the possibility of quench and potential failure. In the proposed project, AMPeers LLC will work with the University of Houston to design, develop, and test superconducting tape architectures that are defect tolerant and provide pathways to shunt current around defects. Through simulation and experiment, we will optimize the tape architecture and maximize its potential to shunt current around artificially created defects. Current sharing between tapes will be tested to confirm the efficacy of the new defect tolerant REBCO tape architecture. Additionally, innovative in-line quality control (QC) tools will be used for real-time monitoring of tape quality during the manufacture of tapes in this project. Such in-line QC tools will help enable early detection and correction to eliminate defective regions in the tape during manufacturing. Finally, we will assess the uniformity of current of our tapes not only by measurements at 77 K, 0 T but also by 2D mapping of critical current in a magnetic field up to 5 T, over 100% of their length, by a new reel-to-reel scanning hall probe microscope (SHPM).