Novel YBCO Coated Filaments for Superconducting Magnets

Due to the high aspect ratio, alternative current (AC) loss is a severe problem for the traditional coated conductors (CCs) on metal tapes. Cutting wide CC tapes into small strips to reduce aspect ratio can minimize AC loss. However, technology limitations remain. Also, substrate magnetic and eddy current losses are unavoidable in the current CC technologies. Further, from the application stand point, customers need thin wires or multi-filament to bundle into cables rather than wide tape CCs. Recently, YBCO on sapphire fiber is under developing but because of the crystal structure and mismatch there are many limitations (such as surface usage is only about 50%, huge mismatch 12%, YBCO thickness limitation, and the growth orientation is less favorable) to grow YBCO on sapphire fibers. SrTiO3, LaAlO3 and/or YSZ substrates are among the best for YBCO deposition and can be grown into fibers with aspect ratio close to 1. No buffer or very simple buffer required will greatly reduce processing cost. In particular, YBCO on these fibers can form ideal superconducting filament and easily bundled into cables. High Jc and thick YBCO film guarantee high Je with extremely low AC loss for low aspect ratio and non-magnetic, non-conductive nature of the substrates. In addition solution approach, a very low cost approach, is the best fit for outer surface coating and can be scaled up readily. Commercial applications and other benefits: The research proposed in Phase I, if carried out, will provide a novel approach for fabrication of cuprate coated conductors. By using faceted fiber as substrate, the fiber coated conductor may lead to a revolution in HTS wire fabrication industry. Fiber coated conductor with aspect ratio close to 1 will be ideal in making multiple filament superconducting cable with extremely low AC loss. The breakthrough in the proposed approach will provide a scalable technology for low AC loss high Je HTS wire fabrication, which is critical for applications where the Je and AC loss are the major concern, for example, magnet, motors, transformers, and generators. It will be also beneficial to other HTS cable industries. We anticipate success in Phase I research and scale up in Phase II and III.