Jelly-roll fabrication of Textured-Powder Bi-2212/Ag wire

Bi-2212/Ag wire has the capacity today to carry >1,000 Amps of current in a 1 mm wire in a magnetic field of >16 T, which should make it the conductor of choice in the dipole magnets for a future hadron collider in high- energy research. But the cost of Bi-2212/Ag wire today is prohibitive for its use in those magnets. The wire cost is dominated not by the Bi-2212 powder within, but by the large fraction (80% of wire cross section) that is silver! The silver fraction is driven by the limitations of the powder-in- tube process that is used today for manufacture of Bi-2212/Ag wire. ATC has pioneered a new process for wire fabrication that significantly enhances the local area ratio (LAR) of Bi-2212:Ag (and thereby the current density). ATC’s process technology builds upon recent advances in jelly- roll processing of Nb3Al in Japan, and upon ATC’s experience in forming textured-powder Bi- 2212 square rods with uniform properties, and upon ATC’s innovations for the fixturing and robotic formers for bending a heterogeneous assembly of superconducting wires while preserving its internal registration. ATC is developing a cable-in-conduit (CIC) conductor which can be made in versions using Nb3Sn and Bi-2212, which is designed for use in hybrid-coil magnets. It is expected that the jelly- roll Bi-2212/Ag wire should be well-suited for use in both Rutherford cables and CIC conductors. The process will be developed to form a channel plate in silver alloy using a 2-roll press on which the forming rollers are machined with the desired channel pattern. The channels will be filled with Bi-2212 powder in a controlled atmosphere. A cover plate will be applied, and the assembly will be compressed to seal the ribs between channels to the cover plate and to apply uniaxial compression to texture the powder cores. The sealed assembly will then be rolled transversely and sheathed to form a jelly-roll billet. The billet will be cold-extruded and then drawn to make fine-filament round wire. ATC’s jelly-roll process wouldenhancethecost- performance of Bi-2212 wire for three product applications: NMR spectroscopy for molecular medicine, direct-drive generators for wind turbines, and hybrid windings for the solenoids and toroids for fusion tokamaks. The jelly-roll process offers the promise of a path to make wire with Ag fraction ~1:1. The LAR enhancement offers two parallel benefits: reducing the cost of the wire, and increasing its performance so that the overall winding package is more compact and thereby more efficient.