Conductor Technology Research Articles

Progress in solution-based YBCO coated conductor

Solution-based YBCO and buffer layers on deformation–textured Ni or Ni-based alloys have been developed as a low-cost coated conductor technology for high temperature superconducting wire. For short samples, J c values of up to 2.1 MA/cm 2 for 0.4 μm films were measured at 77 K, self-field. Using CeO 2 buffered YSZ single crystals, J c values of up to 5 MA/cm 2 for 0.4 μm films and 2.5 MA/cm 2 for 1.2 μm films can be obtained by such a solution-based YBCO process. Differences in the J c performance of different metal substrate samples are possibly related to a-axial grain growth.

Progress towards a low-cost coated conductor technology

Progress in the development of an economically and technically viable YBCO coated conductor technology for HTS wire using deformation-textured buffered substrates and solution-deposited superconductor layers is reported. Biaxially textured Ni substrates have been fabricated using a deformation texturing process. Epitaxial oxide buffer layers have been deposited by a combination of e-beam deposition and magnetron sputtering. Epitaxial YBCO films have been grown using a trifluoroacetate solution precursor. The resulting composite conductors have critical current densities approaching 2 MA/cm 2 at 77K in self-field. Critical current densities of 4.5 MA/cm 2 have been also obtained on CeO 2 buffered YSZ single crystal substrates, demonstrating performance parity with vacuum deposited YBCO films.

Advances in YBCO-coated conductor technology

Processes for producing both the yttrium-stabilized zirconia (YSZ) template film by ion beam-assisted deposition (IBAD) and the YBa 2Cu 3O x (YBCO) superconducting film by pulsed laser deposition (PLD) at 1-m lengths have achieved I c values of 122 A and J c values of 1 MA/cm 2. Improvements have been made in all stages of the process. Variations of I c along the length of the 1-m samples stimulated development of a new in-field I c measurement capability. The use of MgO as an IBAD template film has made great progress and can potentially decrease the time to produce the template film by more than an order of magnitude. A combination of electrical and microstructural investigations is being made to understand and improve the properties of the YBCO-coated conductors.

Low-cost YBCO coated conductor technology

Deformation-textured, non-silver substrates, and solution-baseddeposition of buffer and superconductor layers offer routes to a low-cost YBCOcoated-conductor technology for high-temperature superconducting wire. Severalsignificant steps towards such a technology are reported here: asolution-based Gd2O3 seed buffer layer was deposited by aweb-coating technique over a metre-length tape of deformation-textured nickelwith excellent texture and uniformity. Also, short full-stack samples withYBCO performance up to 0.8 MA cm-2 at 77 K were prepared atOak Ridge National Laboratory (ORNL) and American Superconductor (ASC) using aCeO2/YSZ/CeO2 buffer sequence on textured nickel and atrifluoroacetate (TFA) precursor YBCO process; in this case the buffers aredeposited by e-beam and magnetron sputtering.

HTS high field magnets

Recent progress on HTS high field magnet technology is reviewed. This paper covers HTS conductor technology for high field application, superconducting-joint technology and design and fabrication technologies for stacked-pancake and solenoid magnets. In addition, the typical transport properties of the developed magnets will be reviewed, including driven and persistent mode operation with superconducting closed circuits.

HTS wire at commercial performance levels

Short rolled multifilamentary BSCCO-2223 oxide-powder-in-tube (OPIT) wire has reached a core critical current density J/sub c/ over 73,000 A/cm/sup 2/ (77 K, self-field, 1 /spl mu/V/cm) in multiple samples, with engineering (full-cross-section) current density J/sub c/ of 22,800 A/cm/sup 2/ (77 K, self-field, 1 /spl mu/V/cm). Regular production wires several hundred meters long show average engineering current density over 10,000 A/cm/sup 2/ (77 K, self-field, 1 /spl mu/V/cm), a benchmark for commercial electric power applications such as cables and motors. Cost studies indicate that cost-performance below $10/kA-m is attainable for full-scale production levels, Next-generation YBCO-123 coated conductor technology offers further potential cost-performance improvements.

Structural optimization of the superconducting outsert of a 45-T hybrid magnet

The National High Magnetic Field Laboratory (NHMFL), Tallahassee, Florida, in collaboration with the Francis Bitter National Magnet Laboratory, MIT, is constructing a 45 T hybrid magnet system using cable-in-conduit conductor (CICC) technology for the superconducting coils. In this technology, superconducting wires are cabled and placed in a steel conduit that acts as the principal load-bearing member of the solenoid. In this paper, a structural optimization of the CICC is performed with the aim of reducing the coil mass required to generate the same field strength. The constraints for the optimization are the upper limits values (allowable limits) for the three state variables: the average and peak values of equivalent von Mises stress, and hoop strain. Different geometric and material options were analyzed for optimum performance. Global-local finite element technique was used to conduct the stress analysis. First, a global analysis, using effective material properties, was performed; followed by a local structural analysis. This procedure was iteratively applied until one of the state variables just reached its allowable limit, thus yielding the optimized design. Significant reductions were achieved in mass and stored energy of the magnet as a result of the optimization. © 1997 Elsevier Science Limited

Materials selection and processing issues pertinent to the fabrication of a large magnet by the insulate-wind-react-impregnate technique

The 45 T hybrid magnet system under construction for the National High Magnetic Field Laboratory will contain three superconducting coils using cable-in-conduit conductor technology. Two of these will use Nb 3Sn wire and will be fabricated by the insulate-wind-react-impregnate technique. Critical issues are the selection of the fabric with which the conductor will be wrapped before winding, removal of the fabric sizing (which may leave carbon residue), suppression of oxygen in the heat-treatment vessel (because of the sensitivity of the Incoloy 908 conduit to cracking due to stress-accelerated grain-boundary oxidation) and full impregnation of the interstices of the windings for good structural and electrical insulation integrity. The challenge in this task is that all requirements must be met simultaneously. We report on the test programme to verify that the selected materials and processes will be successful when applied to fabrication of the final coils.

Coupled electromagnetic structural analysis of a DC magnet for a MHD power generator

A coupled electromagnetic and nonlinear structural analysis of a 4.5 tesla superconducting MHD dipole magnet is presented. The magnet design combines the latest in cable-in-conduit conductor (CICC) technology, a novel quasi-momentless support configuration, and finite element modeling to demonstrate the viability of this retrofit magnet concept. With the conductor participating as a major structural element, the support system is greatly simplified, and the overall cost and risk of the magnet system is reduced. Two and three-dimensional models are used to evaluate the concept and demonstrate how the full simulation is accomplished in one ANSYS computer run. >

A design for the superconducting outsert of a 45-T hybrid magnet system using cable-in-conduit conductors

A part of the mission of the new NHMFL is to have available for users in 1995 a hybrid magnet system capable of producing at least 45-T steady field on axis in a 33-mm working bore. Approximately 31 T of the combined field will be produced by a water-cooled insert. The superconducting outsert, which combines NbTi and Nb/sub 3/Sn conductor technologies, will provide more than 14 T. The authors describe an option for this superconducting outsert based on the cable-in-conduit-conductor (CICC) approach, where cabled strands of conductor are contained in intimate contact with helium coolant inside a strong steel sheath that also acts as distributed structure. A departure from the usual practice for CICC technology is in the application of static Hell cooling, which simultaneously provides higher conductor performance and nearly passive extraction of the rather modest heat loads during normal operation of the magnet system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The impact of fusion on superconducting magnet development in Europe

Within the European fusion programmes the need for the development of superconducting magnets is recognized since about 20 years and strong programmes with several important milestones have been successfully executed. In all phases an early involvement of industry in close collaboration with the laboratories was essential. This was and is seen as a benefit for both sides in using the know-how from or for all other areas of superconductivity applications. Many basic areas of superconducting magnet technology have been improved remarkably by the fusion magnet development, as e.g. optimized SC wires, complex conductors with low AC losses, cable-in-conduit conductor technology, 1.8 K cooling technique and forced-flow He-I cryogenics, vacuum impregnation of large windings, low-temperature high-voltage capability of windings and leads, force transmitting embedment of the coil in thick cases and many other important details. The achieved state of the art facilitated the conceptual design of the W 7-X stellarator with advanced SC coils to a large extent and accelerates required prototype testing because existing facilities can be used. The programmes are still continued towards the manufacturing of NET/ITER model coils and their testing in TOSKA.

Energy-dispersive x-ray microanalysis in the earth sciences

The electron microprobe analyser (EMPA) is used extensively for the analysis of the constituent minerals in rocks and the samples generated by experimental petrology apparatus. These analyses, combined with the results of field observations and data from other analytical techniques, are used in petrogenetic studies and hence in the determination of planetary formation and evolution. In turn, this knowledge helps the mining industry in their mineral exploration programs.In the 1960s almost all geological usage of the EMPA was confined to the x-ray spectrometry of L3-K lines of elements of atomic number 11 through 30 (Na through Zn). By the end of this decade semi conductor technology had advanced so that these x-ray lines could be resolved using a lithium-drifted silicon detector working as an energy dispersive spectrometer (EDS). Quantitative EDS software was developed in the early 1970s and it became possible to perform major element analyses of silicates, oxides, carbonates and sulphides using a scanning electron microscope (SEM) fitted with an EDS.

Nb/sub 3/Sn multifilamentary superconductors: an updated comparison of different manufacturing routes

Bronze route Nb/sub 3/Sn conductors can be designed to exhibit the best performance in terms of uniformity as measured by the n value and as needed for persistent mode operation. When designed for low magnetization and low hysteresis losses bronze route conductors exhibit the best combination of critical current density, effective filament diameter, and hysteresis losses. The filament coupling losses can be kept small due to the high resistivity of the bronze and the good twistability of the wires. It is concluded that the fabrication technology and reliability of bronze route conductors have reached high standards which cannot readily be achieved with other fabrication technologies.

Problems and challenges of Super Conductor Technology in India

Problems and challenges of Super Conductor Technology in India

Recent developments in NbTi superconductors at Vacuumschmelze

Superconductors based on NbTi have been recently the most widely used conductors for superconducting magnet. The fabrication technology of monofilamentary and multifilamentary conductors in a Cu matrix has reached a very high standard mainly in conjunction with the applications in analytical measuring techniques using nuclear magnetic resonance (NMR) and in medicine using magnetic-resonance imaging (MRI). The specific requirements of NbTi for the fields of NMR/MRI, particle accelerator technology, nuclear fusion, and power generators are briefly discussed. The state of the art of conductor technology is described by presenting the parameters and the performance of conductors produced or developed for recently completed or ongoing projects. Areas for further research and development are identified. >

Design of Aggressive Superconducting TFCX Magnet Systems

An investigation of several fundamental limits of machine design indicate that a machine fitting the specifications of the Tokamak Fusion Core Experiment (TFCX) can be built with both a superconducting toroidal field (TF) coil set and a plasma major radius of less than 3.2 m. This small size is achieved by accepting a peak nuclear heat load of 50 (kW)(m/sup -3/) in the TF coin inner leg while operating at a 10-T maximum field with a current density of 35 (A)(mm/sup -2/) in the winding pack. This performance, high by traditional standards, is justified based on developments in forced flow conductor technology using Nb/sub 3/Sn composite superconductors.

High-resolution microscopy of a GTB-type Rb-Nb-oxide

Synthesis of specific tunnel compounds has recently been stimulated by their potential application in both cation storage and ionic conductor technologies. However, the theoretical understanding of these compounds is insufficient to be predictive about the tunnel retentivity for various cations. At present HREM seems to be the most practical method of examining this experimentally when, as in the present case, several different types of tunnels are competing for the available cations.A new type of structure in the Rb-Nb-O system, named GTB by Bhide and Gasperin, was first analysed by Gatehouse et al using single crystal x-ray diffraction. It was found to have the tetragonal framework structure indicated schematically in Figure 1, in which corner-linked NbO6 octahedra form 4, 5, 6 and 7-sided tunnels. A similar structure was later found by Bhide and Gasperin in the Tl-Nb-O system. The cell dimensions of the Rb-compound are: a = 27.49 Å; c = 3.96 Å. The composition of the framework is Nb54O146.

Progress in and Technology of Low-Cost Silver Containing Thick-Film Conductors

Thick-film materials have been proved to possess economic, processing, and functional advantages over other technologies in the high-volume production of miniaturized circuits. Inherent in the adoption of thick-film technology for increasingly diverse applications has been the ability of thick-film materials suppliers to provide progressive performance improvements at lower cost concurrent with circuit manufacturer's needs. Since the first major commercial thick-film adoption in the early sixties when IBM adopted platinum-gold conductors and palladium-silver resistors in their 360 computers, rapid technological advances over the last decade have produced an increasing variety of hybrid circuits and networks. The wide adoption of thick-film technology in all segments of the electronic industry has placed increasing demands on performance and processing latitude. The development of low-cost silverbearing conductors is outlined and the evolution of technology improvements to present day systems is described. Initially the deficiencies of early Pd/Ag conductors are reviewed, particularly solder leach resistance and degradation of soldered adhesion following hightemperature storage, and focus is placed on the first Pd/Ag system which overcame these problems. Extension of this technology and subsequent improvements in both binders and vehicles to fulfill adhesion requirements to AI <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> substrates of Varying chemistries and to meet demands for high-speed printing are described also. In the second segment an overview of the present understanding of thickfilm conductor composites from a mechanistic point of view is given. The various types of binder systems commonly employed in conductors are discussed in terms of how they effect a bond between the sintered metal and the substrate, and the advantages and disadvantages of each type. Metallurgical aspects of conductor/solder connections are considered and their effects on bond reliability following exposure to high temperature are discussed. Rbeological considerations of paste design are presented and related to printing performance. In the final segment newer low-cost high-performance materials systems that have evolved over the past two years are considered. The technologies of each system are reviewed in terms of metallurgy, binder, and vehicle. Important functional properties are presented to illustrate cost/performance trade-offs. Special emphasis is given to a recently developed Ag conductor which has outstanding soldered adhesion even after 1000 h of storage at 150°C.