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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Preparation of 110K (Bi, Pb)-Sr-Ca-Cu-O superconductor from glass precursor

The Bi1.5Pb0.5Sr2Ca2Cu3O(x) glass, prepared by rapid quenching of the melt, showed T(sub g) of 383 C, crystallization temperature of approx. 446 C, melting temperature of approx. 855 C, and bulk density of 5.69 g/cu. cm. in air. The as-quenched glass was oxygen deficient. On heating in O2, it showed a slow, irreversible, and continuous weight gain starting at approx. 530 C. The influence of annealing conditions on the formation of various phases was investigated by XRD and electrical resistivity measurements. The 110K-T(sub c) phase did not form below 840 C. The amount of this phase increased with the sintering time at 840 C. A sample annealed at 840 C for 243 h in air and furnace cooled showed the highest T(sub c) (R=0) of 107.2 K and transition width delta T(sub c) (10 to 90 percent) of approx. 2 K.

Bansal, Narottam P.↗
NASA NTRS1991

Shielding and flux trapping properties of high temperature superconductors in the shape of hollow cylinders

Allowing for a field-dependent critical current density, the authors calculate the magnetic field that can be supported by hollow cylinders of varying wall thickness. An adiabatically stable field of 1.0 T can be shielded by or trapped in a cylinder with a wall thickness of 0.4 cm if the critical current density varies linearly with magnetic field and has a value of 104 A/sq cm at a field of 1.0 T. Such a current density appears to be within reach of present state-of-the-art melt-processed YBa2Cu3O7 (123) materials.

Israelsson, U. E.↗
NASA NTRS1990

Upcoming planetary missions and the applicability of high temperature superconductor bolometers

Past and present planetary exploration is briefly reviewed, and the planned 1996 Cassini mission to Saturn and Titan is examined. The CIRS experiment aboard Cassini, which will retrieve information on the atmospheres of Titan and Saturn, is discussed. Ongoing efforts to build a high-sensitivity, high-Tc bolometer that would greatly improve detection in Titan's atmosphere are addressed.

Brasunas, J.↗
NASA NTRS1991

Design and performance of a high-Tc superconductor coplanar waveguide filter

The design of a coplanar waveguide low-pass filter made of YBa2Cu3O(7-delta) (YBCO) on an LaAlO3 substrate is described. Measurements were incorporated into simple models for microwave CAD analysis to develop a final design. The patterned and packaged coplanar waveguide low-pass filter of YBCO, with dimensions suited for integrated circuits, exhibited measured insertion losses when cooled in liquid nitrogen superior to those of a similarly cooled thin-film copper filter throughout the 0 to 9.5 GHz passband. Coplanar waveguide models for use with thin-film normal metal (with thickness either greater or less than the skin depth) and YBCO are discussed and used to compare the losses of the measured YBCO and copper circuits.

Chew, Wilbert↗
NASA NTRS1992

NASA Space applications of high-temperature superconductors

The application of superconducting technology in space has been limited by the requirement of cooling to near liquid helium temperatures. The only means of obtaining these temperatures has been with cryogenic fluids which severely limit mission lifetime. The development of materials with superconducting transition temperatures above 77 K has made superconducting technology more attractive and feasible for employment in aerospace systems. Here, potential applications of high temperature superconducting technology in cryocoolers, remote sensing, communications, and power systems are discussed.

Heinen, Vernon O.↗
NASA NTRS1991

AMSAHTS 1990: Advances in Materials Science and Applications of High Temperature Superconductors

This publication is comprised of abstracts for oral and poster presentations scheduled for AMSAHTS '90. The conference focused on understanding high temperature superconductivity with special emphasis on materials issues and applications. AMSAHTS 90, highlighted the state of the art in fundamental understanding of the nature of high-Tc superconductivity (HTSC) as well as the chemistry, structure, properties, processing and stability of HTSC oxides. As a special feature of the conference, space applications of HTSC were discussed by NASA and Navy specialists.

Bennett, Larry H.↗
NASA NTRS1991

Effect of doping in the Bi-Sr-Ca-Cu-O superconductor

The results of the effect of doping on the superconducting transition in the Bi-Sr-Ca-Cu-O system are reported. Samples were prepared under identical conditions with varying types (Pb, Sb, Sn, Nb) and amounts of dopants. All samples consisted of multiple phases, and showed stable and reproducible superconducting transitions. Stabilization of the well known 110 K phase depends on both the type and amount of dopant. No trace of superconducting phase of 150 K and above was observed.

Akbar, S. A.↗
NASA NTRS1991

Vortex movement and magnetization of high Tc superconductors

The basic characteristics of the thermoactivated vortex mobility in Y1Ba2Cu3O7 are determined by measurement of the kinetics of magnetization in two time regimes. The analysis of the kinetics of the approach of the equilibrium results in the activation energy, while the measurement of the log-creep rate allows determination of the activated moment. It is shown that the movement of vortices can be regarded as the diffusion process.

Roytburd, A. L.↗
NASA NTRS1991

A technique to measure the thermal diffusivity of high Tc superconductors

High T(sub c) superconducting electrical current leads and ground straps will be used in cryogenic coolers in future NASA Goddard Space Flight Center missions. These superconducting samples are long, thin leads with a typical diameter of two millimeters. A longitudinal method is developed to measure the thermal diffusivity of candidate materials for this application. This technique uses a peltier junction to supply an oscillatory heat wave into one end of a sample and will use low mass thermocouples to follow the heat wave along the sample. The thermal diffusivity is calculated using both the exponential decay of the heat wave and the phase shift to the wave. Measurements are performed in a cryostat between 10 K and room temperature.

Powers, Charles E.↗
NASA NTRS1992

NASA space applications of high-temperature superconductors

The application of superconducting technology in space has been limited by the requirement of cooling to near liquid helium temperatures. The only means of attaining these temperatures has been with cryogenic fluids which severely limits mission lifetime. The development of materials with superconducting transition temperatures (T sub c) above 77 K has made superconducting technology more attractive and feasible for employment in aerospace systems. Potential applications of high-temperature superconducting technology in cryocoolers and remote sensing, communications, and power systems are discussed.

Vernon O. Heinen↗
NASA NTRS1991

Permanent magnets composed of high temperature superconductors

A study of persistent, trapped magnetic field has been pursued with high-temperature superconducting (HTS) materials. The main effort is to study the feasibility of utilization of HTS to fabricate magnets for various devices. The trapped field, when not in saturation, is proportional to the applied field. Thus, it should be possible to replicate complicated field configurations with melt-textured YBa2Cu3O7 (MT-Y123) material, bypassing the need for HTS wires. Presently, materials have been developed from which magnets of 1.5 T, at 77 K, can be fabricated. Much higher field is available at lower operating temperature. Stability of a few percent per year is readily attainable. Results of studies on prototype motors and minimagnets are reported.

Weinstein, Roy↗
NASA NTRS1990

Magnetism and electron pairing in high-Tc superconductors

Correlated wave functions are used for YBa2Cu3O(7-y) where epsilon(d)-epsilon(p) is about 0 for Cu3d- and 02p-electrons. The electrons are delocalized (metallic) for y less than 0.5 with weak and temperature-independent paramagnetism. In contrast, the systems are conventional antiferromagnetic insulators for y greater than 0.6 with a narrow y between 0.5 and 0.6 transition region. These results are in agreement with magnetic and neutron diffraction data.

Tsang, T.↗
NASA NTRS1993

High-Temperature-Superconductor Films In Microwave Circuits

Report discusses recent developments in continuing research on fabrication and characterization of thin films of high-temperature superconducting material and incorporation of such films into microwave circuits. Research motivated by prospect of exploiting superconductivity to reduce electrical losses and thereby enhancing performance of such critical microwave components as ring resonators, filters, transmission lines, phase shifters, and feed lines in phased-array antennas.

Bhasin, K. B.↗
NASA NTRS1990

High temperature superconductor materials and applications

Research on processing methods leading to a significant enhancement in the critical current densities (Jc) and the critical temperature (Tc) of high temperature superconducting in thin bulk and thin film forms. The fabrication of important devices for NASA unique applications (sensors) is investigated.

Doane, George B., III.↗
NASA NTRS1991

Study of magnetic bearings with high temperature superconductors, phase 3

Three areas related to the actively controlled radial magnetic bearing concepts are discussed. These areas are: (1) modification to the ac loss calculations of the 1990 report; (2) a continuous changing mechanism to compensate rotor current drop due to ac losses; and (3) design of a proof of principle experiment simulating the proposed bearing concept.

Eyssa, Y. M.↗
NASA NTRS1993

Studying the kinetics of magnetization in high Tc superconductors

We report the first microscopic maps of magnetic induction in YBa2Cu3O(7-x) crystals which directly show the dependence of flux flow on twin density, polytwin block, and twin boundary orientation. These maps were obtained by means of a recently-improved magneto-optical imaging technique. Pinning was lowest in untwinned regions and increasing with increasing twin density. Anisotropy in twin boundary pinning, defined as the ratio of the magnetic induction gradient across twin boundaries to that along twin boundaries, was 10 at 17 K; this ratio increased with increasing temperature. In polycrystals, twin boundaries also had a strongly anisotropic effect on flux flow into a grain from a grain boundary.

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