Unlocking the Potential of High-Temperature Superconductors

Superconductive Components, Inc.
Columbus, Ohio

For bulk applications of high-temperature superconductor materials, the entire superconducting structure must have essentially the same crystal orientation (a "single domain" or "texture") if the material's superconducting properties are to be retained. Until now, the largest single-domain melt-textured samples produced have been no more than one or two inches in diameter. For commercial applications like current leads, fault current limiters, high-energy-density motors, and energy storage devices, much larger structures are required. Because the technology needed to produce large structures for industrial applications has not been available, the tremendous practical potential of high-temperature superconductors has not materialized.

Now, in a dramatic breakthrough, researchers at Argonne have developed a new technology that permits the fabrication of large superconducting structures of any shape without limiting super-current flow. This method, called "superconducting welding," consists of joining individual, monolithic melt-textured pieces of yttrium-based copper oxide superconductor, YBa₂Cu₃O_x (called YBCO for short), by means of an intervening layer of thulium-based copper oxide superconductor, TmBCO. The new process maintains the oriented crystalline structure of melt-textured material across weld joints ("single-domain" superconductors). Appropriately treated, these joints form mechanically strong superconducting welds that can carry critical currents comparable with those in the original bulk materials.

This graphic shows how well the superconductor welding technique works on a ring of superconducting material. The left panel shows the magnetic field produced by a superconducting current circulating around the unbroken 12-mm diameter ring. In the center panel, the ring is cut, and the magnetic field drops as the electric current ceases to flow. In the right panel, the ring has been "welded" back together with the new process. To see a larger version of the graphic, click here.

Argonne's dramatic breakthrough offers major benefits for the electric-power industry:

• In all applications, YBCO superconducting materials significantly out-perform other superconductors operating at lower temperatures (such as bismuth-based BSCCO at 40 K, or even "conventional" superconductors at liquid-helium temperature, 4.2 K). High-performance YBCO materials joined by means of Argonne's superconducting welding method open the door to eventual widespread commercial use for these materials
• For motors and generators that incorporate superconducting components, the power density is estimated to be five times higher with YBCO-based rotor inserts. Better power density translates to more physically compact, as well as more cost-effective, applications.
• The use of single-domain material is a requirement for superconducting "wire." The costs of materials and manufacturing are significantly less, and performance is better, using YBCO rather than BSCCO materials. The electric-power industry can now embrace the YBCO alternative, made practical at last by the new joining technology.

Argonne's superconducting welding innovation is the key that has been neede. to unlock the potential of bulk high-temperature superconducting materials for widespread use in industry as high-current power-transmission leads, as well as in fault current limiters, motors and generators, and energy-storage devices. Argonne expects the new method to be adopted for commercial use at costs that will be far lower (in terms of dollars per kiloampere-meter of conductor) than those associated with existing techniques.

The superconducting welding method was developed under a cooperative research and development agreement (CRADA) with Superconductive Components (SCI), Columbus, Ohio. Argonne's work under the CRADA was supported by funding from the U.S. Department of Energy, Office of Science, Laboratory Technology Research Program. Additional research was funded by DOE's Office of Science, Basic Energy Sciences, Materials Science, and by the National Science Foundation, Science and Technology Center for Superconductivity.

Based on material prepared by Floyd Bennett of Argonne's Technical Services Division, and Richard Greb of Argonne's Office of Public Affairs.

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New Technique Does Super(conducting) Weld

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