Multifilamentary high JE Bi2Sr2CaCu2Ox/Ag superconducting wires for high fields

High field magnets (>16 T) are required for next generation accelerators and upgrading existing facilities. Multifilamentary round Bi-2212/Ag wires have demonstrated many attractive features, such as high irreversibility field (Birr > 100T), isotropic electromagnetic performance, solenoid layer winding, highest engineering critical current density, JE, at fields higher than 20T and compatibility with conventional cabling and strand insulation methods makes them one of themost promising materials to enable high field superconducting magnets. Even though encouraging reports exist on suitability of Bi-2212/Ag multifilamentary wires, R&D efforts for high field magnets are focused on low temperature superconductors mostly due to availability in long continuous lengths having uniform properties. Improving properties and the piece-length of Bi-2212 superconductors is of highest importance for use of these materials as possible conductors in magnets for high energy particle colliders. The proposed Small Business Research Program addresses key challenges for demonstration scale (>1km lengths) wire for magnets with fields between 25 T to 50 T, as well as production scaling (> 3 km) in fields between 16 T to 25 T. The SBIR also focuses on improving JE of round multifilamentary wires, reduce flaws in long length conductors and reduce cost by improving yield. The narrow heat treatment window is one of the major limitations for making long wires, cables, and magnet coils. Current carrying capability of Bi-2212/Ag is very sensitive to maximum heat treatment temperature. This problem is magnified as wire diameter and filament size is reduced. Wire manufacturers face a tough challenge in maintaining furnace temperature uniformity needed to heat treat long length wires, cables and magnet coils. Maintaining furnace temperature uniformity adds cost and reduces performance in long wires. Relaxation of temperature constraints will improve performance and enable use of simpler heat treatment furnaces needed for commercial Bi-2212/Ag wires. Preliminary work at MMT indicates the maximum heat treatment window can be improved by changing the composition of the powder from the stoichiometric Bi2.17Sr1.95Ca0.90Cu2Ox composition to non- stoichiometric leading to formation of additional Alkaline Earth Cuprate phases. In this program, composition will be further optimized to increase the processing window while maintaining higher current carrying capability. Minimization of defects will occur due to an increased heat treatment window in processing long wire (~ 1 km) resulting in properties comparable to shorter wires (~ 100 m). Powder characteristics will also be improved to minimize filament non-uniformity as the diameter of wires is reduced from 1 mm to 0.8 mm. The Phase I approach proposed will be demonstrated in short length (~ 300 m) Bi-2212/Ag wires with diameters of 0.8-1.2 mm. Long length (<1 km) wires will be produced and tested in Phase II from the selected compositions. Successful completion of the proposed program will enable powder to be made with optimized composition and characteristics for long Bi-2212/Ag wires. Availability of commercial scale cost effective round Bi-2212/Ag is critical for developing high field magnets for next generation accelerators and high field (~30 T) NMR.