The research and development programs in high-temperature superconductivity (HTS) at ORNL have both basic and applied components. The fundamental studies are supported predominantly by the DOE Office of Energy Research, at a funding level of about $ 1.1 M. The technology development work is focused on power applications of HTS, including wire development and systems design and evaluation. The latter include projects on HTS transformers and transmission cables for utility applications. This work is funded by the DOE Office of Energy Efficiency and Renewable Energy at an $8M level, including substantial funds-out and subcontracts to industry and universities in excess of $2.4M.
The basic research areas include the formation and characterization of HTS material and heterostructural samples and conductor prototypes. Work related to power applications is aimed at understanding fundamental mechanisms of current conduction and flux pinning the phenomenon that enables practical energy loss-free currents in superconductors. Flux pinning studies involve materials modification and characterization, including the introduction of controlled defect microstructures through tailored materials processing and by energetic particle irradiations. Efforts are also directed at synthesizing new bulk and deposited HTS and substrate materials that have novel and enabling characteristics. Techniques include HTS and ceramic film deposition by pulsed laser ablation, electron-beam evaporation, and magnetron sputtering. Principal characterization techniques include Z-contrast scanning electron microscopy, high-resolution four-circle x-ray diffractometry, ion beam spectroscopy, neutron scattering, and a variety of electrical transport and magnetic properties measurements. Significant contributions from basic studies have included the introduction of near-optimum flux pinning microstructures in various classes of HTS, leading to an understanding of the intrinsic limits to loss-free current conduction; the development of epitaxial oxide deposition directly on the surfaces of biaxially textured metals, leading to a new development program in coated conductors; the deposition of thick, high critical current density YBCO coating on these buffered metals; the characterization of atomic disorder at grain boundaries in HTS, leading to an improved understanding of poor current conduction across high-angle grain boundaries.
Close coupling between basic studies and technology development has helped promote a new world-wide initiative in the development of HTS coated conductors, now referred to by DOE as the "2nd Generation" of HTS wires. ORNL is helping to exploit different approaches to this deposition-based wire technology through six different industrial partnerships, including a four-way collaboration with 3M, Southwire Company, and Los Alamos National Lab. These Second-Generation tape conductors will enable operation at higher temperatures and magnetic fields by utilizing the superior properties of the YBa2Cu3O,7 (YBCO) HTS material.
In parallel with these developments are programs devoted to the design and testing of pre-commercial prototype superconducting systems, based on the "First Generation", BiSrCaCuO-based (BSCCO) HTS wire.
The first US HTS transformer (containing nearly 2 km of BSCCO wire) completed initial tests at Waukesha Electric Systems in March 1998. This team, also comprising Intermagnetics General Corporation and Rochester Gas and Electric, will develop a 5 MVA, three-phase transformer to be installed by Waukesha at their main plant in 2000. ORNL supports several R&D tasks in the program, including the design and analysis of cryogenic issues related to scale-up to 5 MVA, the development of 138/230-kV bushings, the design, fabrication and testing of prototype low ac loss windings, and the development, demonstration, and characterization of 138 kV/230 kV insulation concepts.
ORNL's HTS cable development partner, Southwire Co., is developing a three-phase, 30-m HTS cable that will be installed at their headquarters manufacturing plant in 2000. This year, a HTS 5-cable test facility will be completed in Oak Ridge for initial evaluations, including ac loss testing of 5-m lengths, and calorimetric benchmarking of electrical loss measurements. A substantial dielectrics research program is also under way, for tape, liquid nitrogen, and vacuum-based electrical insulation of devices.