A new superconducting wire developed at the Department of Energy's (DOE) Oak Ridge National Laboratory (ORNL) may pave the way for the future manufacture of practical conductors for electric power applications.
"This research innovation has tremendous significance," said James Daley, manager of DOE's Superconductivity Systems Program. "We now have a new path to the goal we've pursued since the 1986 Nobel Prize-winning discovery - a superconducting wire that can be used in motors, generators and other energy systems while operating at liquid nitrogen temperatures."
ORNL researchers have produced a roll-textured, buffered metal, superconducting tape with a critical current density of 300,000 amperes per square centimeter in liquid nitrogen. Standard household wires typically carry less than 1,000 amperes per square centimeter. An ampere is a unit of electric current.
Researchers developed a method for fabricating the wire by employing the process of rolling-assisted biaxial textured substrates, or RABiTS(TM). The process conditions the substrate upon which superconductors can be formed and provides the underlying foundation for the wire. RABiTS(TM) enables the superconducting materials to have a high degree of grain alignment in all directions along the wire, allowing for more efficient current flow through the superconductor.
Superconductors have virtually no resistance to electric current, offering the possibility of new electric power equipment with improved energy efficiency, smaller size and lower operating costs than today's devices. These systems could help reduce the U.S. requirements for new power plants as electricity demand is expected to double by the year 2030.
The ORNL team, composed of the Solid State, Metals and Ceramics, and Chemical and Analytical Sciences divisions, developed substrates for the wire that are chemically compatible with high-temperature superconductors and exhibit sharp biaxial texture. Texture refers to the alignment of the atomic planes within the wire.
The nickel base metal tapes are textured using special rolling and heat treatment procedures at ORNL. No further surface treatments, such as polishing, are used. A buffer layer technology, developed specifically for these substrates, is used to provide a chemical barrier between the nickel and the superconductor while maintaining the texture. The high-temperature superconductor yttrium-barium-copper-oxide (YBCO) is then deposited on the RABiTS(TM) conditioned surface by pulsed-laser deposition. The high-current sample was three millimeters wide and 15 millimeters long.
"These special substrates will enable the next generation of high-temperature superconducting wires to be used in transmission cables, transformers, current limiters, motors and generators - anywhere large amounts of electricity are produced, transmitted or distributed to customers," said Robert Hawsey, director of ORNL's Superconductivity Technology Center.
The ORNL process provides opportunities for the development of high-current conductors using all oxide superconductor families. The important opportunity offered by this technology is the operation of electric power devices in liquid nitrogen cooled systems.
The Superconductivity Technology Center is one of three national sites funded by DOE's Office of Utility Technologies. The center implements DOE's national program to develop the technology necessary for U.S. industry to proceed to commercialization of high-temperature superconducting electric power products.
"We are extremely pleased that a combination of fundamental materials science supported by the Office of Basic Energy Sciences, and applied research supported by the Office of Energy Efficiency and Renewable Energy has resulted in the development of materials processing methods for high-temperature superconducting wires which can carry the substantial electric currents needed for practical applications," said William Oosterhuis, chief of the Solid State Physics and Materials Chemistry Branch in DOE's Office of Basic Energy Sciences.
ORNL, one of DOE's multiprogram national research and development facilities, is managed by Lockheed Martin Energy Research Corp.