December 2010
Table of Contents
Material Development Within High Temperature Superconductivity
Brookhaven National Laboratory
Los Alamos National Laboratory
National Institute of Standards and Technology
MATERIAL DEVELOPMENT WITHIN HIGH TEMPERATURE SUPERCONDUCTIVITY
The mission of the DOE’s Office of Electricity Delivery and Energy Reliability is to lead national efforts to modernize the electric grid; enhance security and reliability of the energy infrastructure; and facilitate recovery from disruptions to energy supply. High-temperature superconductivity (HTS) power equipment has the potential to become a key twenty-first century technology for improving the capacity, efficiency, and reliability of our electric system. The deployment of HTS technologies will help in not only increasing current carrying capacity on the electric grid, especially in urban areas, but also in relieving overburdened cables elsewhere in local grids, thus helping to ensure continued delivery of safe and reliable power throughout the country.
As mentioned in the October 2010 newsletter, one of President Obama’s priorities is the Smart Grid. On November 17, 2010, U.S. Energy Secretary Steven Chu announced an investment of more than $19 million for five projects aimed at optimizing the nation’s electric grid. Together, these projects will apply technologies, tools, and techniques that are capable of transforming the electric grid into a system that is cleaner and more efficient, reliable, resilient, and responsive. The five projects also support the Administration's goal of building the infrastructure necessary to bring clean, low-cost energy sources to American homes and businesses.
Material development plays a critical role within the evolution of superconductivity. The primary requirement for electrical power applications is a strong and flexible high-temperature superconducting wire capable of carrying large currents in magnetic fields. The National Labs focus on research and technology while conducting fundamental studies necessary to support wire and systems development. Among their goals are improving the performance of HTS wire while reducing manufacturing costs and demonstrating the applicability and the potential benefits of superconductivity in electric power systems.
This newsletter highlights selected efforts of DOE’s National Laboratories and industry that support material development in superconductivity.
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ARGONNE NATIONAL LABORATORY (ANL)
The physics of vortices in superconductors is currently undergoing a major revision stimulated by new discoveries. In the last five years, many of the traditional concepts of vortex physics have been overthrown or found to be too limited to describe the new behavior. As vortex behavior is probed at ever deeper levels, novel phenomena are continuously discovered, which lead to new physical pictures of vortex behavior, to new experimental tools for probing this behavior, and to new theoretical concepts which often apply generally in condensed matter physics, well beyond their vortex origins. The issues in vortex physics fall into three categories: equilibrium phase diagrams, dynamics of driven phases, and technological applications. Argonne National Laboratory (ANL) develops forefront research in all these areas.
BSCCO Wire (ANL) |
ANL continues to develop magneto-optical imaging as a tool to characterize the local performance of composite BiSrCaCuO (BSCCO) wires and yttrium barium copper oxide (YBCO) thin and thick films on the scale of a few microns. ANL is developing shielding methods, which characterize the local pinning strength by examining the field penetration, and transport methods, which directly image the path and magnitude of transport currents within the superconductor. Both techniques are applied to commercially produced superconducting wires and coated conductors, as well as to the superconducting materials themselves in order to improve their performance. |
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BROOKHAVEN NATIONAL LABORATORY (BNL)
The Superconducting Magnet Division (SMD) at the Brookhaven National Laboratory (BNL) has been active in developing HTS technology for over a decade. It is not only the first major international laboratory to initiate an HTS magnet R&D program but also currently poses an unmatched experience in designing, building, and testing HTS coils and magnets. In addition, it has unique facilities for testing high current HTS wires, tapes, and cables in applied fields. A large number of coils with essentially all types of HTS available in reasonable lengths has been successfully built and tested. This includes solenoid and pancake coils made with Bi2212 Rutherford cable, Bi2212 tape, Bi2223 tape, YBCO tape, and MgB2 tape tested in a variety of magnet structures. The size of the BNL HTS program can be measured from the fact that so far, over 15 km length of conductor has been obtained (normalized to 4 mm tape equivalent). This is expected to reach to about 50 km in two years to fulfill the requirements of various programs that are already funded.
BNL has already built over 50 coils with the first generation (1G) HTS and over 25 coils with the second generation (2G) HTS for a wide range of applications. In some cases, the applications are either high field or high temperature and in other cases in between - namely medium field (2-3 T) and medium temperature (20-60 K). These programs help one another in developing a wider understanding of the field and allowing sharing of resources to carry out cost-effective R&D to overcome several technical challenges. |
Solenoid Coil (BNL) |
In addition, BNL has designed and built a flexible cryogen-free HTS magnet where the cooling is entirely obtained with cryo-coolers. This structure (consisting of six racetrack coils each made of ~100 meters of second generation HTS) is currently being tested.
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FLORIDA STATE UNIVERSITY (FSU)
Two different types of high-temperature superconductors (HTS) are being pursued for applications in superconducting magnets that are projected to exceed 30 T in the coming years: round wire Bi-2212 (Bi2Sr2CaCu2O8) and YBCO (YBa2Cu3O7) tape conductor.
Bi-2212 is unique among all HTS materials in that it is available as a round wire. However, processing is complex. Recent work has reduced leaks of Bi-2212 through the silver sheath around the HTS wires resulting in clean multi-Tesla magnets.
YBCO coils showed no degradation at stress levels (760MPa) that are twice that of the 32 T HTS magnet being constructed at the Magnet Lab. These high stresses are enabled by the substrate of high strength nickel-based alloy tape on which the YBCO is deposited.
The performance of Bi-2212 and YBCO, which have very different conductor forms, is being explored in R&D programs that investigate the stress, quench energy, fabrication, and performance limits for coils.
Bi-2212 must be reacted at almost 900C after winding to make it superconducting. YBCO tape grown on high strength alloy is supplied commercially, but as a single tape it is susceptible to debilitating local defects.
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LOS ALAMOS NATIONAL LABORATORY
The DOE program has evolved from the development of first generation BSCCO (Bi2223 and/or Bi2212) in the early 1990’s to almost exclusively the development of second-generation YBCO (coated conductor) tapes today. Superconductivity centers at Argonne, Oak Ridge, and Los Alamos National Laboratories (LANL) are partnering in the development of the second generation YBCO tapes.
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Other national laboratories also involved in the coated conductor development include Brookhaven, Sandia, National Institute of Standards and Technology, and the National Renewable Energy Laboratory. |
Major university collaborations in this area have involved groups at the University of Wisconsin (moved to Florida State University in mid-2006), the University of Houston, Stanford University, and the University of Kansas. This has led to a variety of new processing techniques. Simplistically, these tapes can be thought of as composed of a substrate, one or more buffer layers, and a YBCO coating. The substrate should be strong and flexible, and the buffer layer(s) should provide a good template for the YBCO coating.
The development of a viable HTS coated conductor wire technology involves microstructural control across multiple length scales in thick HTS films. This work targets materials development and vortex pinning issues in RE1Ba2Cu3Oy (REBCO: RE = Rare Earths) films for coated conductor applications across a wide range of temperature and fields. The overall approach of Los Alamos National Laboratory’s work deals with three areas of interest ubiquitous to the HTS community: the synergistic assembly of defects for optimized coated conductor performance; the development of new materials to improve overall coated conductor performance; and the manipulation of coated conductor anisotropy to conform to specific application conditions. In order to understand the general commonalities and properties of REBCO films irrespective of deposition process, the laboratory strives to obtain samples from a variety of sources beyond itself, including those produced by industrial collaborators at American Superconductor, SuperPower, STI, and university/laboratory collaborators at the University of Cambridge (UK), AFRL, and ORNL, and other institutions.
Goals set for FY2011 include delivering data and analysis of an industry-relevant, integrated materials system (template + process + enhanced REBCO film) for high-current applications in cables and fault-current limiters in which the pinning landscape/properties can be tuned for the specific field and temperature-dependent applications.
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NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY (NIST)
Copper-based high-temperature superconductors are created by taking a nonconducting material called a Mott insulator and either adding or removing some electrons from its crystal structure. As the quantity of electrons is raised or lowered, the material undergoes a gradual transformation to one that, at certain temperatures, conducts electricity utterly without resistance. Until now, all materials that fit the bill could only be pushed toward superconductivity either by adding or removing electrons – but not both.
NIST Center for Neutron Research (NIST) |
However, the new material tested at the NIST Center for Neutron Research (NCNR) is the first one ever found that exhibits properties of both of these regimes. A team of researchers from Osaka University, the University of Virginia, the Japanese Central Research Institute of Electric Power Industry, Tohoku University and the NIST NCNR used neutron diffraction to explore the novel material, known only by its chemical formula of YLBLCO. |
The material can only be made to superconduct by removing electrons. But if electrons are added, it also exhibits some properties only seen in those materials that superconduct with an electron surplus – hinting that scientists may now be able to study the relationship between the two ways of creating superconductors, an opportunity that was unavailable before this “ambipolar” material was found.
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OAK RIDGE NATIONAL LABORATORY
This year, Oak Ridge National Lab (ORNL) made significant strides toward achieving its FY2010 goals. In FY2009, ORNL showed for the first time that columnar defects can also be formed with double perovskite tantalates and niobates phases (Ba2RETaO6 and Ba2RENbO6 respectively). The Lab determined the effect of out-of-plane macrostrain and microstrain on Tc while also making correlations on strain as a function of BZO doping to understand the decrease in Tc in PLD YBCO films with BZO columnar defects and related it to the observed pinning in these films. ORNL also determined the effect of on self-assembly of columnar defects in YBCO films with BaMO3-type additions and found that a certain range of lattice mismatch gives the best results. |
Ideal cubic perovskite structure. |
Very high-performance HTS coatings are emerging from both base program research in developing ideal nanostructures for pinning enhancement and from newly improved commercial prototypes. This project conducts a combination of electrical transport and contactless magnetic-based techniques to broadly characterize and analyze the relevant superconductive properties as a function of temperature, magnetic field, orientation in field, and effective electric field level. ORNL has implemented new methodology in characterizing orientation-dependent critical currents, extended to parameter regimes that are otherwise highly problematic for laboratory scale techniques.
U.S. HTS wire manufacturers are now in a position to produce reasonable quality coated conductors in “pilot-scale” mode. In meeting the DOE cost target, however, it is necessary to further improve the HTS transport properties, especially in the presence of high applied magnetic fields. Improvements in the properties of the HTS coating require a thorough understanding of the pinning mechanisms and control of various combination of nanostructures, in order to further improve the in-field and angular dependent properties in REBCO.
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CONCLUSION
The efforts of DOE’s National Labs in the field of Material Development for Superconductivity have enabled the advancements of HTS. The Labs, in collaboration with universities and industry, have worked to continually develop new materials, reduce energy losses, and advance HTS applications. Their ultimate goal is to have HTS accepted commercially. In moving toward this goal, they work with industry to increase and enhance manufacturing production which lowers costs, thereby increasing its acceptance in the marketplace.
ABOUT THIS UPDATE
The High-Temperature "Superconductivity News Update" is compiled by Bob Lawrence & Associates, Inc. on behalf of the U.S. Department of Energy's superconductivity program and is issued periodically as events warrant.
Please let me know if you would like more information or have story ideas on any of these news items involving high-temperature superconductivity---a clean and capable new electricity technology for the 21st century.
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Thank you very much.
Ashley Thompson
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