Tech Brief: Strong, round cross-sectioned high current density 2212 wire

First commercial High Temperature Superconductors (HTS) are all tape shaped (widths > 10 times thickness) because achieving useful current densities required them to be processed into tape form, even though this also makes it more problematic to use them in some important coil types.

Our product is the first HTS in commercially usable wire forms that can also be cabled into low loss coil windings. It is based on the 2212 (Bi₂Sr₂CaCu₂O₈) HTS material. Among HTS options, only 2212 can be processed to attain useful current densities in wire forms similar to low temperature superconductors (LTS), while surpassing them in field generating and operating temperature capability. We have determined that 2212 is also the only HTS that can be 1) cabled into low loss, high current configurations that are required for ac and ramped field applications, 2) most easily produced with the superconducting joints that are vital for many applications, and 3) scaled up and produced at lower cost than HTS tapes, provided it also meets strength requirements.

During the Phase I award period, we developed a testbed and used it to prove the feasibility of manufacturing strong round 2212 wire, including equipment and techniques to pre-form reinforcement strips followed by wrapping and diffusion bonding them to 2212 wires. In a series of tests, we demonstrated that these wires are strengthened as required, capable of being bent to small diameters and cabled so as to carry the same currents as unreinforced wires.

Our objective continues to be the development of strong round 2212 wires that are similar in form to proven commercial Nb₃Sn round wires, and that, by virtue of their forms, low losses, and superior current densities in high magnetic fields, offer advantages over HTS tapes, as well as MgB₂ and LTS wires in a number of important magnet systems, for example as field boosting coils in high field solenoid and particle accelerator quadrupole racetrack designs.

Long length production capability for producing strong, round, high Je, multifilament 2212 wire, will be established. Both wire and cable designs will also be advanced to enable fabrication of Bi2212-based HTS wires and cables to a wide range of operating current levels, tensile stress / load tolerances, and ramped / ac operation as well as persistent current modes. The suitability of these wire and cables for use in a variety of coils will be demonstrated by fabricating and testing solenoid and racetrack coils.