Second Generation Superconducting Cable with Exfoliated YBCO Filaments

High temperature superconducting YBCO wire technology has a significant potential to become the wire of choice for Helium-free magnet systems. Helium-free magnet systems are attracting more interest as the world supply of Helium is depleted. Currently the wire is manufactured as a thin, 1 micron, superconducting layer deposited on a 1 cm wide 100 microns thick metal substrate. Due to this geometry a magnet wound from the wire suffers from high losses. Brookhaven Technology Group BTG) will partner with AMSC Corp. to develop and demonstrate the feasibility of a new type of a cable bundled from exfoliated YBCO filaments. The approach is based on our recent successful experiments on stress-induced exfoliation of YBCO filaments. The filaments were demonstrated to retain up to 90% of the original critical current. We will develop technology for bundling filaments into a narrow, 2-3 mm diameter, cable with up to 20% fill factor. The cable is symmetric: both sides of the superconductor layer are in contact with the metal stabilizer. This geometry will deliver significantly improved quench stability of the cable and enhance the traditionally low c-axis yield strength and cleavage strength of YBCO wires up to at least 50 MPa both. The cabling process will use the well-developed 2G wire production steps with the cost reduction coming from the substrate re-cycling. In Phase I we will fabricate short coupons of the cable and conduct electrical and mechanical tests in order to determine suitability of the proposed cable for superconducting magnet applications. The information gained during this testing will be used to de-risk the pilot cable production system that we plan to build in Phase II. In Phase II we will develop a system for production of 10s of meters of the new cable. A test coil will be wound from the new cable using a transposition method that reduces AC loss of the coil by a factor of 5 as compared with a coil wound using 10 mm wide YBCO wire. The test coil will be used to solidify the value proposition of the technology. The commercialization process will follow Lean methodology. Our cable technology will provide a pathway for efficient and economical high-temperature superconducting magnets operating > 20 K. Such a magnet could be cooled by conduction, thus not requiring a supply of Helium. High temperature of operation ensures that the materials comprising the magnet have high approximately 50 times more than at 4.2 K) specific heat. This makes the high-temperature magnet quench-resistant. Quench-resistant magnets can be ramped faster, are more efficient and reliable. These features are very appealing for many applications outside the particle physics facilities. For example, there is a large market for MRI machines in countries with undeveloped Helium re-fill infrastructure. A conduction-cooled, persistent magnet would be a highly desirable product for this market.