| Evaluating Superconducting YBCO Film Properties Using X-Ray Photoelectron Spectroscopy (Postprint) |
Feb 2012 |
11 pages |
| Authors:
Paul N Barnes; Justin C Tolliver; Timothy J Haugan; Sharmila M Mukhopadhyay; John T Grant; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIR/POWER DIV/MECHANICAL ENERGY CONVERSION BRANCH
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 | Initial results have been recently reported that suggest a potential correlation exists between the full-width-half-maximum (FWHM) of the Y(3d) peak obtained by x-ray photoelectron spectroscopy (XPS) and the critical current density a YBa2Cu3O7-x film can carry. In particular, the Y(3d5/2) demonstrated a stronger correlation. Transport currents were determined by the 4-point contact method using the 1?V/cm criterion. An apparent correlation was also suggested between the Y(3d) FWHM and ac loss ... |
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| Flux Pinning and Properties of Solid-Solution (Y,Nd)1+xBa2-xCu3O7-delta Superconductors (Preprint) |
Feb 2012 |
12 pages |
| Authors:
Timothy J Haugan; M E Fowler; Justin C Tolliver; Paul N Barnes; W Wong-Ng; L P Cook; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIR/POWER DIV/MECHANICAL ENERGY CONVERSION BRANCH
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| The effect of chemical composition variations on the flux pinning and physical properties of (Y,Nd)1+xBa2-xCu3O7-delta superconductors was studied in powders processed by solid-state reaction and equilibrated in air at 910 deg C. An extended region of single-phase assemblages was determined for compounds with Ba = 2.0 to 1.7 and Nd = 0 to 1.3. At 77 K, Ba substituted and (Y0.2Nd0.8)Ba2Cu3O7-delta compounds had enhanced pinning properties (normalized Jc(H)) than other ... |
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| Tuning Porosity of YBa2Cu3O7-delta Vicinal Films by Insertion of Y2BaCuO5 Nanoparticles (Postprint) |
Feb 2012 |
5 pages |
| Authors:
R L Emergo; J Z Wu; T J Haugan; P N Barnes; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIR/POWER DIV/MECHANICAL ENERGY CONVERSION BRANCH
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| High critical current density Jc is the most critical specification for high-temperature-superconductor-coated conductors as required by numerous electric power-related applications. This has motivated an intensive research effort on the effects of microstructure on Jc. By growing YBa2Cu3O7-delta YBCO films at a small vicinal angle, we have recently obtained a highly porous structure in these films accompanied with a significantly enhanced Jc. This result raises a challenging question on whether the ... |
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| Controlled Introduction of Flux Pinning Centers in YBa2Cu3O7-x Films during Pulsed-Laser Deposition (Postprint) |
Feb 2012 |
5 pages |
| Authors:
C Varanasi; P N Barnes; J Burke; J Carpenter; T J Haugan; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIR/POWER DIV/MECHANICAL ENERGY CONVERSION BRANCH
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| To introduce controlled random inclusion of nanometer-sized nonsuperconducting particulates in YBa2Cu3O7-x films for flux pinning enhancement, a special pulsed-laser-ablation YBa2Cu3O7-x target with a Y2BaCuO5 sector was made and the films were deposited on LaAlO3 substrates. Initial results showed that the films consist of 10-20 nm-sized precipitates. In a 0.5 micron thick film, a transport critical current density (Jc) 3 MA/sq cm at 77 K in self-field was measured. Magnetization Jc ... |
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| Crystal Chemical Substitutions of YBa2Cu3O7-d to Enhance Flux Pinning (Postprint) |
Feb 2012 |
21 pages |
| Authors:
T J Haugan; J C Tolliver; J M Evans; J W Kell; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIR/POWER DIV/MECHANICAL ENERGY CONVERSION BRANCH
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| A review of the physical properties and principles of chemical substitution of YBCO to enhance flux pinning was provided. Chemical substitution is a potential cost-effective method of introducing nano-size defections into the superconductor to provide significant enhancement of Jc. It is especially important to consider this as a method for flux pinning to achieve ultra-small defects 1-4 nm in size, that were show in this paper to be essential to ... |
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| Flux Pinning Effects of Y2O3 Nanoparticulate Dispersions in Multilayered YBCO Thin Films |
Feb 2012 |
10 pages |
| Authors:
T A Campbell; T J Haugan; P N Barnes; I Maartense; J Murphy; L Brunke; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIR/POWER DIV/MECHANICAL ENERGY CONVERSION BRANCH
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| The flux pinning effects of Y2O3 nanoparticulate inclusions in YBa2Cu3O7-delta (Y123 or YBCO) thin films using (Y2O3/Y123) x N multilayer structures were studied. The multilayer films were made with pulsed laser deposition (PLD) on SrTiO3 and LaAlO3 substrates with a Y2O3 nanoparticulate 'pseudo-layer' thickness ranging from 0.2 to 1.4 nm, and YBCO layer thickness varying from 7 to 50 nm. Scanning electron microscopy images showed well-defined nanoparticle formation on film ... |
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| YBa2Cu3O7-d Films with a Nanoparticulate Dispersion of Y2BaCuO5 for Enhanced Flux Pinning (Preprint) |
Feb 2012 |
6 pages |
| Authors:
Paul N Barnes; Timothy J Haugan; Srinivas Sathiraju; Julianna M Evans; Justin C Tolliver; Michael D Sumption; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIR/POWER DIV/MECHANICAL ENERGY CONVERSION BRANCH
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| A comparison study of YBa2Cu3O7-x (Y123) films incorporating a nano-particulate dispersion of second-phase Y2BaCuO5 (Y211) and Y123 films incorporating a material (X, not specified) more closely lattice matched with Y123 is given. The inclusion of the nano-particulate dispersion was for the purpose of increasing superconducting film's magnetic pinning strength with the resultant improved in-field critical current density. The Y211 particulate and X layered inclusions in the Y123 was accomplished with ... |
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| Growth of YBCO Thin Films on TiN(001) and CeO2-Coated TiN Surfaces |
Feb 2012 |
10 pages |
| Authors:
Paul N Barnes; Rand Biggers; Gregory Kozlowski; Chakrapani Varanasi; Iman Maartens; Rama Nekkanti; Tim Peterson; Timothy J Haugan; Ilwon Kim; Scott A Barnett; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIR/POWER DIV/MECHANICAL ENERGY CONVERSION BRANCH
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| Epitaxial growth of YBa2Cu3O7-x (YBCO) layers on TiN(0 0 1) surfaces was explored, both with and without CeO2 intermediate layers. The epitaxial TiN layers were grown on MgO(0 0 1) and textured Ni substrates. Thin CeO2 (200 nm thick) and YBCO (300 nm thick) layers were grown on TiN-coated MgO substrates, using pulsed laser deposition. While YBCO grown directly on TiN was of poor quality, a good epitaxial YBCO layer ... |
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| The Integration of YBCO Coated Conductors into Magnets and Rotating Machinery (Postprint) |
Feb 2012 |
9 pages |
| Authors:
G A Levin; P N Barnes; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIRECTORATE
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| The implementation of the second generation high-Tc superconductors in power applications, such as electrical transformers, motors and generators requires superconducting wires that are superior to copper Litz wires at cryogenic temperatures in terms of losses in time-varying magnetic field, as well as in engineering current density. Another problem is to find a way to make practical coils and armatures out of flat tape-like conductors with low bending strain tolerance. We ... |
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| SM and ND Substiturions in YBCO Films Produced through Metal Organic Deposition (Postprint) |
Feb 2012 |
8 pages |
| Authors:
B C Harrison; J Carpenter; and P N Barnes P Klenk; H Fang; C V Varanasi; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIRECTORATE
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| Epitaxial YBa2Cu3O7-x (YBCO) films were produced on non-buffered (100) single crystal LaAlO3 using the metal organic deposition (MOD) method with fluorinated metal acetates. In an effort to enhance the in-field performance of the films, Sm and Nd acetates were fractionally substituted for Y acetate in a series of precursor solutions to incorporate an array of nanoscale flux pinning centers in the post-annealed films. From measurements taken in the non-optimized films ... |
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| Time-Resolved Magneto-Optical Imaging of Y1Ba2Cu3O7-delta Thin Films in High-Frequency AC Current Regime (Postprint) |
Feb 2012 |
6 pages |
| Authors:
A Lucarelli; G Luepke; T J Haugan; G A Levin; P N Barnes; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIR/POWER DIV/MECHANICAL ENERGY CONVERSION BRANCH
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| We present a time-resolved magneto-optical (MO) imaging study of high-temperature superconductor (HTS) in a high-frequency alternating current (AC) regime. The evolution of the magnetic flux density distribution in YBa2Cu3O7-delta (YBCO) thin film samples is studied as a function of the phase of the applied AC current. A quantitative analysis of the data shows that the maxima of the AC current density is shifted from the edges further inside the sample, ... |
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| Minute Doping with Deleterious Rare Earths in YBa2Cu3O7-delta Films for Flux Pinning Enhancements (Postprint) |
Feb 2012 |
5 pages |
| Authors:
P N Barnes; J W Kell; B C Harrison; T J Haugan; C V Varanasi; M Rane; F Ramos; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIR/POWER DIV/MECHANICAL ENERGY CONVERSION BRANCH
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| To enhance the critical current density of YBa2Cu3O7-delta films, flux pinning centers are intentionally added to inhibit flux flow in applied magnetic fields. Here we provide an initial demonstration that the incorporation of very minor additions 1% of Y as opposed to the 10%-40% in standard substitutions of typically deleterious rare earths into high quality YBa2Cu3O7-delta thin films provides significant improvement of the film's in-field current density. This is accomplished ... |
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| Pr Doped YBCO Films Produced by Pulsed Laser Deposition (Postprint) |
Feb 2012 |
8 pages |
| Authors:
B C Harrison; Joseph W Kell; Paul N Barnes; Timothy J Haugan; Chakrapani V Varanasi; Iman Maartense; Manisha V Rane; Frank Ramos; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIR/POWER DIV/MECHANICAL ENERGY CONVERSION BRANCH
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| Pr doped YBa2Cu3O7-d targets with composition Y1-xPrxBa2Cu3O7-d where x = 0.0001, 0.001, 0.01, and 0.1 were prepared from oxide powders and used to deposit thin films by pulsed laser deposition using conditions previously optimized for pure YBa2Cu3O7-d. The Pr dopant was found to be dispersed throughout the film by secondary ion mass spectrometry and the doped films had an increased density of nanoparticles on the surface. The pinning force of ... |
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| Nanoparticulate Flux Pinning Centers for YBa2Cu3O7-delta Films (Postprint) |
Feb 2012 |
5 pages |
| Authors:
Paul N Barnes; Joseph W Kell; Brandon C Harrison; Timothy J Haugan; Jack L Burke; Chakrapani V Varanasi; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIR/POWER DIV/MECHANICAL ENERGY CONVERSION BRANCH
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| YBa2Cu3O7-delta high temperature superconductors can maintain fairly high critical current densities (Jc) with increasing magnetic field. This in-field performance can be further improved upon by incorporating nanoparticulate magnetic flux pinning centers into the superconductors. This short paper briefly discusses and compares recent efforts by the U.S. Air Force Research Laboratory to incorporate insulating nanoparticles into the YBCO superconducting thin films by pulsed laser deposition. |
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| Impact of Edge-Barrier Pinning in Superconducting Thin Films (Postprint) |
Feb 2012 |
5 pages |
| Authors:
W A Jones; M J Mullins; P N Barnes; T J Haugan; F J Baca; R L Emergo; J Wu; J R Clem; DAYTON UNIV OH
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| It has been suggested that edge-barrier pinning might cause the critical current density (Jc) in bridged superconducting films to increase. Subsequent work indicated that this edge-barrier effect does not impact bridges larger than 1 micrometers. However, we provide a theoretical assessment with supporting experimental data suggesting edge-barrier pinning can significantly enhance Jc for bridges of a few microns or even tens of microns thus skewing any comparisons among institutions. As ... |
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| Use of Ultrasonic Force Microscopy to Image the Interior Nanoparticles in YBa2Cu3O7-x Films (Postprint) |
Feb 2012 |
6 pages |
| Authors:
Chakrapani V Varanasi; Vijay Nalladega; S Sathish; Timothy J Haugan; Paul N Barnes; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIRECTORATE
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| Nanoparticles present in the interior of YBa2Cu3O7-x (YBCO) films were successfully imaged for the first time by using an ultrasonic force microscope (UFM), which can also operate as a conventional atomic force microscope (AFM). Nanoparticles of Y2BaCuO5 and BaSnO3 were introduced into YBCO films using pulsed laser ablation to improve critical current density via enhanced flux pinning. The scanning speed and ultrasonic frequencies in the range of 300?500 kHz were ... |
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| Time Resolved Magneto-Optical Imaging in High Frequency AC Currents of YBa2Cu3O7-delta Thin Films (Postprint) |
Feb 2012 |
8 pages |
| Authors:
Andrea Lucarelli; Alexander Frey; Ran Yang; Gunter Luepke; Timothy J Haugan; George A Levin; Paul N Barnes; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIRECTORATE
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| We present a time-resolved magneto-optical (MO) imaging study of high-temperature superconductor (HTS) in high-frequency alternating current (AC) regime. The evolution of the magnetic flux density distribution in YBa2Cu3O7-delta (YBCO) thin film samples is studied in small steps of the phase of the applied AC current. The flux distribution at 10 K exhibits instabilities including flux jumps and flux creep. A quantitative analysis of the data allows us to obtain the ... |
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| 11.72-sq cm Active-Area Wafer Interconnected PiN Diode Pulsed at 64 kA Dissipates 382 J and Exhibits an Action of 1.7 MA(sup 2)-s |
30 Jan 2012 |
5 pages |
| Authors:
M Snook; H Hearne; Ty McNutt; N El-Hinnawy; V Veliadis; B Nechay; S Woodruff; R S Howell; David Giorgi; Joe White; NORTHROP GRUMMAN SYSTEMS CORP LINTHICUM MD ELECTRONIC SYSTEMS
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| The Silicon carbide (SiC) device area is presently limited by material and processing defects. To meet the large current handling requirements of modern power conditioning systems, the paralleling of a large number of devices is required. This can increase costs and complexity through wafer dicing, device soldering, the inclusion of ballast resistors, and the formation of multiple wire bonds. Furthermore, paralleling numerous discrete devices increases package volume and weight and ... |
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| High Temperature Superconducting State in Metallic Nanoclusters and Nano-Based Systems |
Oct 2011 |
12 pages |
| Authors:
Yury N Ovchinnikov; LANDAU INST FOR THEORETICAL PHYSICS MOSCOW (RUSSIA)
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| Main goal of project is the search of new materials with high temperature of the superconducting transition (order of room temperature). Main investigation objects are special nanoclusters with shell structure of the electron spectrum. The goal is investigation of the possibility of building of nets (two and three dimensional) from nanoclusters with high value of the superconducting transition temperature and possessing of possibility to transfer high value of transport current ... |
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| TCAD Analysis of Heating and Maximum Current Density in Carbon Nanofiber Interconnects |
Sep 2011 |
87 pages |
| Authors:
Jason A Brunton; NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF ELECTRICAL AND COMPUTER ENGINEERING
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| As devices shrink, the current density through interconnects increases proportionally making new materials a necessity for industry growth. Carbon nanofiber (CNF) and carbon nanotube's (CNT) potential for high current density make them a possible replacement for metal contacts. Learning the limitations of CNFs and CNTs is important if they are to be used in next-generation electronics. As current density increases, heat is generated throughout the CNF structure. This heating eventually ... |
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| Does the Altered Expression of Ion Channels Give Rise to the Enhanced Excitability of Neurons Isolated from Nf1 +/- Mice? |
Sep 2011 |
20 pages |
| Authors:
Grant Nicol; INDIANA UNIV AT BLOOMINGTON SCHOOL OF MEDICINE
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| We reported previously that sensory neurons isolated from mice with a heterozygous mutation of the Nf1 gene (Nf1+/-) exhibited greater excitability and increased sodium current densities compared to wildtype mice. This raises the question as to whether the increased current density resulted from post-translational modifications or increased expression of sodium channels. Quantitative real-time PCR was used to measure expression levels of the nine different voltage-gated sodium channel alpha subunits and ... |
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| Holmium Doped Solid State Laser Resonantly Pumped and Q-Switched by Novel GaSb-Based Photonic Devices |
31 Aug 2011 |
22 pages |
| Authors:
STATE UNIV OF NEW YORK AT STONY BROOK DEPT OF ELECTRICAL ENGINEERING
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| A highly efficient Ho3+-doped fluoride glass fiber laser operating at 2.08 micrometers is demonstrated using nearly resonant pumping at 1.94 micrometers by GaSb-based diode lasers. A maximum slope efficiency of 78% and output power above 500 mW were obtained. Asymmetric laser heterostructure was developed to improve beam properties of GaSb-based diode lasers. Multimode 100-micrometers-wide ridge waveguide lasers with 40 degrees fast axis beam divergence demonstrated output power of about 1.5 ... |
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| Development of RF Sensor Based on Two-Cell Squid |
15 JUL 2011 |
23 pages |
| Authors:
Fengbin Song; Ming He; Alexey Ustinov; KARLSRUHE INST OF TECHNOLOGY (GERMANY)
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| The RF directional sensor based on phase-sensitive detection using two sorts of Josephson parametric amplifiers has been analyzed and investigated experimentally. To construct the Josephson parametric amplifier, we use a SQUID (either single-cell SQUID or two-cell SQUID) embedded in a superconducting coplanar waveguide. We operated the circuit at a frequency of several GHz and measured the amplitude response of the SQUID-based Josephson parametric amplifier. Nonlinearity and flux tunability in the ... |
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| Current and Density Observations of Packets of Nonlinear Internal Waves on the Outer New Jersey Shelf |
May 2011 |
16 pages |
| Authors:
William J Teague; Hemantha W Wijesekera; W E Avera; Z R Hallock; NAVAL RESEARCH LAB STENNIS DETACHMENT STENNIS SPACE CENTER MS OCEANOGRAPHY DIV
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| Closely spaced observations of nonlinear internal waves (N LI Ws) were made on the outer continental shelf off New Jersey in June 2009. Nearly full water column measurements of current velocity were made with four acoustic Doppler current profilers (ADCPs) that were moored about 5 km apart on the bottom along a line approximately normal to the bathymetry between water depths of 67 and 92 m. Density profiles were obtained ... |
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| Photophysical Properties of Aromatic and Antiaromatic Porphyrinoids |
14 APR 2011 |
21 pages |
| Authors:
Dongho Kim; YONSEI UNIV SEOUL (KOREA SOUTH) DEPT OF CHEMISTRY
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| This is the report of an investigation of the photophysical properties of various Huckel or Mobius (anti)aromatic porphyrinoids such as expanded porphyrins, porphycenes, etc. using theoretical calculations and various spectroscopic methodologies in conjunction with the topology transformation between aromatic and antiaromatic porphyrinoids by conformational control vial solvent change and redox chemistry. |
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| Gamma-ray Irradiation Effects on InAs/GaSb-based nBn IR Detector |
Jan 2011 |
10 pages |
| Authors:
Vincent M Cowan; Christian P Morath; Seth M Swift; Stephen Myers; Nutan Gautam; Sanjay Krishna; AIR FORCE RESEARCH LAB KIRTLAND AFB NM SPACE VEHICLES DIRECTORATE
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| IR detectors operated in a space environment are subjected to a variety of radiation effects while required to have very low noise performance. When properly passivated, conventional mercury cadmium telluride (MCT)-based infrared detectors have been shown to perform well in space environments. However, the inherent manufacturing difficulties associated with the growth of MCT has resulted in a research thrust into alternative detector technologies, specifically type-II Strained Layer Superlattice (SLS) infrared ... |
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| Low Temperature Noise Measurement of an InAs/GaSb-based nBn MWIR Detector |
Jan 2011 |
9 pages |
| Authors:
Vincent M Cowan; Christian P Morath; Stephen Myers; Nutan Gautam; Sanjay Krishna; AIR FORCE RESEARCH LAB KIRTLAND AFB NM SPACE VEHICLES DIRECTORATE
|
| Recent experiments on conventional p-on-n and n-on-p Type II superlattices (SLS) infrared detectors still indicate larger than theoretically predicted dark current densities, despite the well known suppression of the Auger recombination mechanism. Rather, dark current in SLS is thought to still be limited by trap-assisted tunneling in the depletion region and surface leakage currents resulting from lack of fully passivated mesa sidewalls. An emerging infrared detector technology utilizing a unipolar, ... |
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| Nanocomposite Prepared from In Situ Grafting of Polypyrrole to Aminobenzoyl-Functionalized Multiwalled Carbon Nanotube and Its Electrochemical Properties |
Jan 2011 |
10 pages |
| Authors:
In-Yup Jeon; Hyun-Jung Choi; Loon-Seng Tan; Jong-Beom Baek; ULSAN NATIONAL INSTITUTE OF SCIENCE AND TECHNOLOGY (KOREA SOUTH)
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| We reported the functionalization of multiwalled carbon nanotube (MWCNT) with 4-aminobenzoic acid by a direct Friedel-Crafts acylation reaction in a mild polyphosphoric acid (PPA)/phosphorous pentoxide (P2O5) medium. The resulting 4- aminobenzoyl-functionalized MWCNT (AF-MWCNT) was used as a platform for the grafting of polypyrrole (PPy) in ammonium persulfate (APS)/aqueous hydrochloric acid solution to produce PPy-grafted MWCNT (PPy-g-MWCNT) composite. After dedoping with alkaline treatment, PPy-g-MWCNT displayed 20 times higher electrical conductivity than ... |
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| Fundamental Questions About Superconductivity in the Pnictides (Former title: Electromagnetic and Nanostructural Studies of Rare Earth Copper Oxide Grain Boundaries Grain Boundaries in High Temperature Superconductors) |
30 Jun 2010 |
7 pages |
| Authors:
David C Larbalestier; Alex Gurevich; FLORIDA STATE UNIV TALLAHASSEE
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| In early 2008 the Hosono group at Tokyo Institute of Technology discovered high temperature superconductivity in a new extensive family of pnictides based on doped As-Fe. This exciting discovery encouraged us to transition our work on grain boundary studies of YBCO to this new class of superconductors. We showed that they indeed exhibit high critical temperatures Tc, extremely high upper critical fields Hc2, an irreversibility field H* close to Hc2, ... |
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| Experimentally Characterizing the Plume of a Divergent Cusped-Field Thruster |
24-Sep-2009 |
16 pages |
| Authors:
Manuel Martinez-Sanchez; Michael R Nakles; Hargus; William A Jr; Stephen R Gildea; AIR FORCE RESEARCH LAB EDWARDS AFB CA PROPULSION DIRECTORATE
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| Divergent cusped-field thrusters are electric propulsion devices characterized by a divergent, dielectric wall channel and a magnetic topology dominated by two magnetic cusps and a magnetic bottle near the anode. Initial testing results suggest that this technology may lend itself to miniaturization while providing improved lifetime performance over miniature Hall thruster designs. This paper presents results of detailed probing of the divergent cusped-field thruster plume using a faraday cup and ... |
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| Material Science and Physics of High-IC Coated Conductors |
02 Aug 2009 |
8 pages |
| Authors:
Judy Wu; KANSAS UNIV LAWRENCE DEPT OF PHYSICS
|
| Investigate issues affect Ics in thick film HTS coated conductors and develop schemes to improve the Ics. Understand the physics associated to the deparing current density Jd in HTS films. Develop diagnostic tools for investigation of instability of HTS coated conductors. This three-year project started on July 1, 2006 and finished on June 30, 2009. This final report summarizes the major progress made during the three year project period. Two ... |
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| Investigating the Electrothermal Characteristics of a Gate Turn Off Thyristor During Turn-Off Using SILVACO ATLAS(TM) |
Jun-2009 |
149 pages |
| Authors:
Gerald E Vineyard; NAVAL POSTGRADUATE SCHOOL MONTEREY CA
|
| This thesis presents data from a simulation study of the thermal and electrical characteristics of a Gate Turn Off (GTO) thyristor. At present, most of the research on GTO thyristors has focused on their use in power electronic systems at high switching frequencies. As a result, the behavior of GTO thyristors at very low switching frequencies is not well understood. Previous research projects have shown experimentally that GTO thyristors are ... |
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| An Elegant Low-cost Materials Solution for Achieving Low Insertion Loss, Affordable Tunable Filters for Next Generation Mobile Communications Platforms |
Apr-2009 |
18 pages |
| Authors:
M W Cole; E Ngo; R J Tan; ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD WEAPONS AND MATERIALS RESEARCH DIRECTORATE
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| The effect ultraviolet (UV)-assisted annealing on the structural, dielectric, and insulating properties of barium strontium titanate (BST) thin films was investigated. The material properties of BST films, prepared by RF sputter deposition, annealed via conventional thermal annealing and UV-assisted thermal annealing process protocols were compared and evaluated. The x-ray diffraction results showed contracted lattice constants and enhanced crystallinity for the RF sputtered BST films annealed via the UV-assist treatment. Isothermal-temporal ... |
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| Power Generation by Harvesting Ambient Energy with a Micro-Electromagnetic Generator |
Mar-2009 |
116 pages |
| Authors:
James Shields; AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING AND MANAGEMENT
|
| This thesis investigated the potential power output of micro-electromagnetic generators fabricated using typical microfabrication materials and techniques. The design was intended to eliminate the need for batteries in bio-implanted or remote electronic devices. Such a micro-generator could harvest ambient energy and power such devices inde?nitely. Using electromagnetic theory, designs for the magnet's stator coil and rotor magnets were optimized to produce maximum current density. A method for overlaying two evaporated ... |
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| An Analysis of Multiple Configurations of Next-Generation Cathodes in a Low Power Hall Thruster |
Mar-2009 |
151 pages |
| Authors:
John E Rotter; AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH GRADUATE SCHOOL OF ENGINEERING AND MANAGEMENT
|
| The research presented here is an effort to integrate an existing hollow cathode design with a low power production Hall thruster in multiple geometries. Both externally- and internally-mounted cathodes were fabricated and operated in conjunction with a Busek BHT-1500 Hall thruster. Three insert materials were evaluated; Cerium Hexaboride (CeB6), Lanthanum Hexaboride (LaB6), and impregnated tungsten. The thruster was operated at a single operating condition for all testing. The operating specifications ... |
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| Critical Current Density and Microstructure Variations in YBa2Cu3O7-x + BaSnO3 Films with Different Concentrations of BaSnO3 (Postprint) |
Dec 2008 |
9 pages |
| Authors:
C V Varanasi; J Burke; L Brunke; H Wang; J H Lee; P N Barnes; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIR/POWER DIV/MECHANICAL ENERGY CONVERSION BRANCH
|
| Previous work on YBa2Cu3O7-x (YBCO) + BaSnO3 (BSO) films with a single composition showed significant critical current density (Jc) improvements at higher fields but lowered Jc in low fields. A detailed study on BSO concentrations provided here demonstrates that significant Jc enhancement can occur even up to 20 mol% BSO inclusion, where typical particulate inclusions in these concentrations degrade the YBCO performance. YBCO + BSO films were processed on (100) ... |
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| Carbon Nanotube Field Emission Devices With Integrated Gate for High Current Applications |
Aug-2008 |
5 pages |
| Authors:
Niemann; 2 Jeremy 1; /Silan; 2 Jessica L 1; /Killian; 4 3; Darrell L Kevin; NATIONAL AERONAUTICS AND SPACE ADMINISTRATION MOFFETT FIELD CA AMES RESEARCH CENTER
|
| We present a fabrication technique for the integration of a gate electrode with an array of carbon nanotube (CNT) emitters. These gated cathode structures have high emission current density and may be utilized in X-ray tubes, traveling wave tubes, and ion propulsion systems. The CNT emitters are grown directly on polished bulk metal substrates and are comprised of CNT bundles that are vertically aligned and can be uniformly produced over ... |
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| Lifetime of Sodium Beta-Alumina Membranes in Molten Sodium Hydroxide |
JUL 2008 |
18 pages |
| Authors:
Gudmundur Gunnarsson; ICELAND UNIV REYKJAVIK TECHNOLOGICAL INST OF ICELAND
|
| Sodium metal can be made by electrolysis of molten sodium hydroxide in sodium Beta-alumina membrane electrolysis cells. However, there are some uncertainties about the lifetime of the sodium Beta"-alumina membranes in contact with molten sodium hydroxide. The main objective of this project is to address these uncertainties and to study if the properties of the membrane degrade upon long term contact with molten sodium hydroxide. Electrolysis cells were designed, but ... |
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| High Current Density Cathodes for Future Vacuum Electronics Applications |
30 MAY 2008 |
28 pages |
| Authors:
CALABAZAS CREEK RESEARCH INC SAN MATEO CA
|
| This final report summarizes the achievements at Calabazas Creek Research, Inc. and Massachusetts Institute of Technology to develop and demonstrate techniques for fabricating high current density cathodes using scandium to lower the emission work function. Several techniques were investigated for depositing scandium on and beneath the surface of cathode emitters with techniques for replenishing that removed by normal surface erosion processes. Results indicate that several techniques can successfully provide the ... |
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| Investigation of the Current Turn-off Characteristics of a GTO Thyristor in an Inductive Pulse Forming Network |
02-May-2008 |
112 pages |
| Authors:
Gerald E Vineyard; NAVAL ACADEMY ANNAPOLIS MD DEPT OF ELECTRICAL ENGINEERING
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| The project investigated of the current interruption capability of Gate Turn Off (GTO) thyristors, specifically, factors that had potential to increase the amount of current that could safely be turned off. A series of GTO thyristors were used in an inductive pulse forming circuit to interrupt varying amounts of current. The test circuit consisted of a high-voltage capacitor bank, a wire-wound inductor, the GTO thyristor with control circuitry, and instrumentation ... |
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| Enhanced Field Emission Properties from Carbon Nanotube Emitters Grown on NiCr Alloy Surfaces with Grain Boundary Effect |
Apr-2008 |
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| Authors:
Setha Yim; Richiro Ohta; Jessie L Killian; Nathaniel B Zuckerman; Emily Allen; Cattien V Nguyen; ELORET CORP MOFFETT FIELD CA NASA AMES RESEARCH CENTER
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 | Carbon nanotubes (CNTs) are known to have exceptional field emission properties such as low turn-on voltage and high current density. Nilsson et al. reported that field emission properties depend highly on the density of the CNT films. The CNTs must have low density in order to minimize electrostatic field screening from neighboring nanotubes. At the same time, the CNT films must have a high number of emitting sites to achieve ... |
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| Field Emission Properties of Carbon Nanotube Pillar Arrays Patterned Directly on Metal Alloy Surfaces |
Apr-2008 |
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| Authors:
Mahmud Rahman; M Meyyappan; Cattien V Nguyen; Jessica L Killian; Darrell L Niemann; Nathaniel Zuckerman ;Jeremy Silan; Bryan P Ribaya; ELORET CORP MOFFETT FIELD CA NASA AMES RESEARCH CENTER
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| Carbon nanotube pillar arrays (CPAs) for cold field emission were fabricated using a conventional photolithography process, and the geometry of these arrays was studied and the effect of pillar height on field emission was quantified. Our CPA samples achieved turn-on fields as low as 0.9 V/micrometer and stable current densities of 10 mA/cm(2) at applied field lower than 6V/micrometer. |
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| Electromagnetic Characterization of YBa2Cu3O7-Delta Thin Films with Calcium Doping for Bi-Crystal Grain Boundary Conductivity Enhancement (Postprint) |
08 Feb 2008 |
8 pages |
| Authors:
Richard A Kleismit; Gregory Kozlowski; Angela L Campbell; Timothy J Haugan; Rand R Biggers; Paul N Barnes; Timothy L Peterson; Iam Maartense; Simon C Hopkins; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIR/POWER DIV/MECHANICAL ENERGY CONVERSION BRANCH
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| The objective of this study was to examine the transport properties of two YBa2Cu3O7-delta thin films with (Y0.9Ca0.1)2BaCuO5 additions deposited on vicinal SrTiO3 6 deg. bi-crystal substrates and to investigate the possible correlations between spatial calcium distribution and local electromagnetic properties across bi-crystal grain boundaries using evanescent microwave microscopy (EMM) and atomic force microscopy (AFM). The samples under consideration differed in transport critical current measurements by a factor of two ... |
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| A Study of Spectral Element and Discontinuous Galerkin Methods for the Navier-Stokes Equations in Nonhydrostatic Mesoscale Atmospheric Modeling: Equation Sets and Test Cases |
2008 |
31 pages |
| Authors:
F. X. Giraldo; M. Restelli; NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF APPLIED MATHEMATICS
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| We present spectral element (SE) and discontinuous Galerkin (DG) solutions of the Euler and compressible Navier-Stokes (NS) equations for stratified fluid flow which are of importance in nonhydrostatic mesoscale atmospheric modeling. We study three different forms of the governing equations using seven test cases. Three test cases involve flow over mountains which require the implementation of non-reflecting boundary conditions, while one test requires viscous terms (density current). Including viscous stresses ... |
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| Performance of Carbon/Polytetrafluoroethylene (PTFE) Air Cathodes from pH 0 to 14 for Li-Air Batteries |
DEC 2007 |
18 pages |
| Authors:
Michelle B. Marx; Jeffrey A. Read; ARMY RESEARCH LAB ADELPHI MD SENSORS AND ELECTRON DEVICES DIRECTORATE
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| The purpose of this project was to construct an inexpensive air cathode free of catalyst that is capable of functioning in both acidic and basic electrolytes. The performance of an uncatalyzed air cathode for use in a Li-Air battery was evaluated over the pH range from 0 to 14. This study was undertaken to determine if air cathodes constructed solely from carbon black and polytetrafluoroethylene (PTFE) can function at a ... |
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| Enhancement and Angular Dependence of Transport Critical Current Density in Pulsed Laser Deposited YBa2Cu3O7-x+BaSnO3 Films in Applied Magnetic Fields (Postprint) |
25 Sep 2007 |
7 pages |
| Authors:
C V Varanasi; J Burke; L Brunke; H Wang; M Sumption; P N Barnes; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIR/POWER DIV/MECHANICAL ENERGY CONVERSION BRANCH
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| YBa2Cu3O7-x (YBCO) films with nanoparticles of BaSnO3 (BSO) were processed using pulsed laser ablation of a special target made with dual phase sectors of YBCO and BSO. Transport critical current density (Jct) of these YBCO+BSO films in applied magnetic fields and angular dependence of Jct on the applied field orientation was measured. It was observed that in the YBCO+BSO films, the Jct (H c orientation) increased considerably as compared to ... |
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| Imaging the Spatial Distribution of Transport Currents and the Phenomenon of Nanoscale Phase Separation Phenomenon in CMR Materials |
13 SEP 2007 |
5 pages |
| Authors:
Satyajit Banerjee; INDIAN INST OF TECH KANPUR DEPT OF PHYSICS
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| The aim of the proposal was to develop a magneto-optics imaging "MOI" set up which will enable the direct imaging of transport current distribution inside a variety of materials. The primary objective of the proposal was to enhance the sensitivity of the existing magneto-optical imaging setup developed in the PI's laboratory to optically image the self fields generated by transport currents sent through materials. Based on the above objective it ... |
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| Performance of Hybrid Eulerian-Lagrangian Semi-Implicit Time-Integrators for Nonhydrostatic Mesoscale Atmospheric Modeling |
SEP 2007 |
73 pages |
| Authors:
Thomas J. De Luca; NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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| In this thesis, the performance and accuracy of explicit, semi-implicit, and Hybrid Eulerian-Lagrangian Semi-Implicit (HELSI) time-integration methods for use in atmospheric modeling are examined. Four test cases are analyzed: A density current, an inertial gravity wave, a rising thermal bubble, and a hydrostatic mountain wave. Strict attention is paid to computational time, stability criteria, and accuracy. The project aims to show increased efficiency using the HELSI method over semi implicit ... |
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| On the Through-Thickness Critical Current Density of an YBa2Cu3O7-x Film Containing a High Density of Insulating, Vortex-Pinning Nanoprecipitates (Postprint) |
18 Jun 2007 |
5 pages |
| Authors:
S I Kim; F Kametani; Z Chen; A Gurevich; D C Larbalestier; T Haugan; P Barnes; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIR/POWER DIV/MECHANICAL ENERGY CONVERSION BRANCH
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| Using sequential ion milling the authors have studied the thickness dependence of the critical current density Jc(H) of a single crystal 1 micron thick YBa2Cu3O7-x thin film containing 5 vol % of insulating Y2BaCuO5 (Y211) nanoparticles in order to better understand how to obtain high critical currents in thick films. Except very near the interface where the defect density was enhanced, Jc(H) in the body of the film was uniform ... |
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| Current Sharing between Superconducting Film and Normal Metal (Postprint) |
18 Jun 2007 |
10 pages |
| Authors:
George A Levin; Paul N Barnes; John S Bulmer; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH PROPULSION DIR/POWER DIV/MECHANICAL ENERGY CONVERSION BRANCH
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| A two-dimensional model is introduced that describes DC current sharing between the superconducting and normal metal layers in a configuration typical of YBCO-coated conductors. The model is used to compare the effectiveness of a surround stabilizer and a more conventional one-sided stabilizer. When the resistance of the interface between the superconductor and the stabilizer is low enough, the surround stabilizer is less effective than the one-sided stabilizer in stabilizing a ... |
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Reports by Keyword(s)
CURRENT DENSITY
