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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 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Distinguishing S ± and S ++ Electron Pairing Symmetries by Neutron Spin Resonances in Superconducting NaFe 0.935 Co 0.045 As

A determination of the superconducting (SC) electron pairing symmetry forms the basis for establishing a microscopic mechansim for superconductivity. For iron pnictide superconductors, the s ± -pairing symmetry theory predicts the presence of a sharp neutron spin resonance at an energy below the sum of hole and electron SC gap energies (E ≤ 2Δ). Although the resonances have been observed for various iron pnictide superconductors, they are broad in energy and can also be interpreted as arising from the s ++ -pairing symmetry with E ≥ 2Δ. Here we use inelastic neutron scattering to reveal a sharp resonance at E = 7 meV in the SC NaFe 0.935 Co 0.045 As (T c = 18 K). By comparing our experiments with calculated spin-excitations spectra within the s ± and s ++ -pairing symmetries, we conclude that the resonance in NaFe 0.935 Co 0.045 As is consistent with the s ± -pairing symmetry, thus eliminating s ++ -pairing symmetry as a candidate for superconductivity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Interaction Induced Staggered Spin-Orbit Order in Two-Dimensional Electron Gas

Decoupling spin and charge transports in solids is among the many prerequisites for realizing spin electronics, spin caloritronics, and spin-Hall effect. Beyond the conventional method of generating and manipulating spin current via magnetic knob, recent advances have expanded the possibility to optical and electrical method which are controllable both internally and externally. Yet, due to the inevitable presence of charge excitations and electrical polarizibility in these methods, the separation between spin and charge degrees of freedom of electrons remains a challenge. Here we propose and formulate an interaction induced staggered spin-orbit order as a new emergent phase of matter. We show that when some form of inherent spin-splitting via Rashba-type spin-orbit coupling renders two helical Fermi surfaces to become significantly nested, a Fermi surface instability arises. To lift this degeneracy, a spontaneous symmetry breaking spin-orbit density wave develops, causing a surprisingly large quasiparticle gapping with chiral electronic states, with no active charge excitations. Since the staggered spin-orbit order is associated with a condensation energy, quantified by the gap value, destroying such spin-orbit interaction costs sufficiently large perturbation field or temperature or de-phasing time. BiAg2 surface state is shown to be a representative system for realizing such novel spin-orbit interaction with tunable and large strength, and the spin-splitting is decoupled from charge excitations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Summary of Booster Development and Qualification Report

This report outlines booster development work done at Los Alamos National Laboratory from 2007 to present. The booster is a critical link in the initiation train of explosive assemblies, from complex devices like nuclear weapons to conventional munitions. The booster bridges the gap from a small, relatively sensitive detonator to an insensitive, but massive, main charge. The movement throughout the explosives development community is to use more and more insensitive explosive components. With that, more energy is needed out of the booster. It has to initiate reliably, promptly, powerfully and safely. This report is divided into four sections. The first provides a summary of a collaborative effort between LANL, LLNL, and AWE to identify candidate materials and uniformly develop a testing plan for new boosters. Important parameters and the tests required to measure them were defined. The nature of the collaboration and the specific goals of the participating partners has changed over time, but the booster development plan stands on its own merit as a complete description of the test protocol necessary to compare and qualify booster materials, and is discussed in its entirety in this report. The second section describes a project, which began in 2009 with the Department of Defense to develop replacement booster formulations for PBXN-7. Replacement of PBXN-7 was necessary because it contained Triaminotrinitrobenzene (TATB), which was becoming unavailable to the DoD and because it contained Cyclotrimethylenetrinitramine (RDX), which was sensitive and toxic. A LANL-developed explosive, Diaminoazoxyfurazan (DAAF), was an important candidate. This project required any replacement formulation be a drop-in replacement in existing munitions. This project was timely, in that it made use of the collaborative booster development project, and had the additional constraint of matching shock sensitivity. Additionally it needed to be a safety improvement, and a performance improvement, especially at cold temperatures. The requirements of this project necessitated novel test development and a different approach to ranking booster qualities. Results of this project have been documented to the DoD and the relevant portions are included within. The third section of this booster report outlines testing related to main charge initiation merit. Initiability can be evaluated by looking at critical diameter, run distance, and shock sensitivity. Once a booster is initiated, it needs to be powerful enough to initiate the main charge symmetrically and evenly. Main charge initiability is evaluated directly by observing detonation wave symmetry, curvature, and first break out over the surface of a charge. Furthermore it must be insensitive to accidents and insults, and safe and reliable across a range of temperatures. These effects, tests, and results will be discussed individually in the context of DAAF and other explosives similarly tested. The last section provides a conclusion and summary of our experimental work and recommendations for the path forward. References and additional supporting documentation and results are provided in the appendices at the end of this report.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Mastering Uncertainty and Risk at Multiple Time Scales in the Future Electrical Grid

Today's electrical grids enjoy a relatively clean separation of spatio-temporal scales yielding a compartmentalization of grid design, optimization, control and risk assessment allowing for the use of conventional mathematical tools within each area. In contrast, the future grid will incorporate time-intermittent renewable generation, operate via faster electrical markets, and tap the latent control capability at finer grid modeling scales; creating a fundamentally new set of couplings across spatiotemporal scales and requiring revolutionary advances in mathematics techniques to bridge these scales. One example is found in decade-scale grid expansion planning in which today's algorithms assume accurate load forecasts and well-controlled generation. Incorporating intermittent renewable generation creates fluctuating network flows at the hourly time scale, inherently linking the ability of a transmission line to deliver electrical power to hourly operational decisions. New operations-based planning algorithms are required, creating new mathematical challenges. Spatio-temporal scales are also crossed when the future grid's minute-scale fluctuations in network flows (due to intermittent generation) create a disordered state upon which second-scale transient grid dynamics propagate effectively invalidating today's on-line dynamic stability analyses. Addressing this challenge requires new on-line algorithms that use large data streams from new grid sensing technologies to physically aggregate across many spatial scales to create responsive, data-driven dynamic models. Here, we sketch the mathematical foundations of these problems and potential solutions.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2012

Science Campaign-1 Pulsed Power Efforts [Slides]

The PHELIX portable pulsed-power driver is discussed. It is composed of two air-insulated, single Marx modules capable of storing 300 kJ of electrical energy. The Marx are cable coupled to a toroidal transformer with a 4:1 winding ratio. The experimental load is located at the center of the transformer. The components are mounted in a 8’x10’x18’ boxcar which can be moved in and out of the beam line at the LANL proton radiography facility and prevents EMI within the facility. PHELIX has successfully completed two liner implosion experiments with full diagnostic return from flash X-ray imaging, optical Faraday load current, and multi-channel PDV. Computational modeling with both the legacy 1D MHD code RAVEN and the LANL ASC-LAP FLAG code show good agreement with data.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

High Energy-Density Materials with Fast Energy Release: Molecular scale shock response of explosives (DTRA Basic Research Final Report 2012)

The principle goal of this $\$$150K/yr, 3-yr. project was to experimentally measure the time evolution of shock induced chemistry in the explosive RDX. Since direct measurements of shock induced chemistry in RDX, or any other explosive, have eluded researchers for several decades, new techniques had to be developed. Transient absorption was coupled to laser shock loading to probe the possible role of electronic excitations in the chemistry of RDX. Transient absorption signatures turned out to be a good indication of the relative degree of chemical reaction versus time, but were not conclusive regarding whether electronic excitation was an important factor in shock initiation. Preliminary efforts to sensitize shock induced chemistry with ultraviolet pulsed excitation were performed, but are not yet conclusive. The bulk of the effort of the project was directed at development of femtosecond stimulated Raman spectroscopy (FSRS) as a diagnostic of temperature in the presence of chemistry. This effort was significantly more difficult than initially anticipated. While we had planned to apply the method to single shot laser experiments, the sensitivity achieved during the project duration was insufficient to measure the sub-nanogram amounts of material shocked. Despite the difficulties applying this measurement to our current small scale laser shock experiments, it shows significant promise for measurements where there is more volume of material shocked. We have established the theoretical framework and experimentally validated FSRS as a sub-picosecond molecular vibrational temperature measurement diagnostic. We have also followed the shock induced chemistry of RDX through transient absorption spectroscopy and established the shock stresses required to achieve sub-nanosecond reaction rates. The project led to 3 peer reviewed journal articles, 4 conference proceedings, 3 invited talks at conferences, 2 contributed talks at conferences, and a number of other presentations.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Zone Refining for Low Loss Plutonium Purification

In an effort to enhance plutonium purification capabilities at Los Alamos National Laboratory, further develop of the currently existing zone refining capabilities is needed to create a functional low loss processing option in support of programmatic and materials science research activities. Currently, the most effective process for converting impure plutonium dioxide (~96% pure) to high-purity plutonium metal (>99.9%), consists of the following steps: (1) reducing the dioxide to an impure Plutonium metal with calcium metal in molten calcium chloride, (2) casting the impure metal into an anode and (3) electrorefining the impure metal to produce high-purity plutonium metal. The final step in this method is only 83% efficient as compared to the >95% efficiency of the other processing steps. Other more efficient processing methods are desirable to enhance current purification activities, thereby, reducing waste generation and conserving precious materials in need of purification. Although zone refining has been used extensively to purify many lanthanides and actinides, its usefulness in purifying plutonium has yet to be fully realized.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Sesame Equation of State Number 2100 for Scandium

An equation of state (EOS) for scandium has been constructed using the OpenSesame code and was placed in the SESAME library as material number 2100. The cold curve was constructed with a Mie-Grüneisen model fitted to the high pressure Hugoniot data and to the zero pressure bulk sound speed, the nuclear contribution was calculated from JD Johnson nuclear model and the electronic thermal contribution from the Thomas-Fermi-Dirac statistical model. The EOS behaves reasonably well over a wide range of densities, pressures and temperatures, and compares fairly with the available experimental data. Of the 5 solid phases present in scandium at room temperature, however, only the first one, the hcp phase, is assumed to occur. Also the transition to bcc at room pressure just before melting is ignored. We plan to construct a multiphase EOS as the next step. The purpose of the present calculation was mostly for learning purposes, as is reflected by the way the report is written.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Dynamical crossover between the infinite-volume and empty-lattice limits of ultra-cold fermions in 1D optical lattices

Unlike typical condensed-matter systems, ultra-cold atoms loaded into optical lattices allow separate control of both the particle number and system size. As a consequence, there are two distinct "thermodynamic” limits that can be defined for these systems: i) ’’infinite-volume limit” at constant finite density, and ii) "empty-lattice limit” at constant particle number. To probe the difference between these two limits and their crossover, we consider a partially occupied lattice and study the transport into the unoccupied region of non-interacting fermions and fermions interacting at the mean-field level. In the infinite-volume limit, a finite steady-state current emerges. On the other hand, in the empty-lattice limit there is no finite steady-state current. By changing the initial filling, we find a smooth crossover between the two limits. Our predictions may be verified using available experimental tools and demonstrate a fundamental difference between isolated small systems such as ultra-cold atoms and conventional condensed-matter systems.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2012

Electron Microscopy Laboratory MST-6: Instruments and Capabilities [Slides]

The Electron Microscopy Laboratory (EML) is a lab-wide facility, overseen by MST-6, that is available for use by qualified users. In FY12 the EML service contract costs were covered by funds from LDRD, BES, NE and other programs. Users can be trained to use the equipment independently or work collaboratively with other trained users or EML staff. Users are charged for the labor portion of their training. Most electron microscopy is done by staff or post-docs but some students are performing microscopy, particularly SEM. In the Materials Science Complex (MSC), there are two optical microscopes, two scanning electron microscopes (SEM’s), a SEM/ FIB (a SEM with a focused ion beam (FIB) column added), three transmission electron microscopes (TEM’s) and sample preparation equipment.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Final Report, DOE grant DE-FG02-99ER45780, "Indirect Excitons in Coupled Quantum Wells"

The is the final technical report for this project, which was funded by the DOE from 1999 to 2012. The project focused on experimental studies of spatially indirect excitons in coupled quantum wells, with the aim of understanding the quantum physics of these particles, including such effects as pattern formation due to electron-hole charge separation, the Mott plasma-insulator transition, luminescence up-conversion through field-assisted tunneling, luminescence line shifts due to many-body renormalization and magnetic field effects on tunneling, and proposed effects such as Bose-Einstein condensation of indirect excitons and phase separation of bright and dark indirect excitons. Significant results are summarized here and the relation to other work is discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Neutron Scattering Studies of Classical and Quantum Fluids in Porous Media

This is an annual and the final report on DE-FG02-03ER46038 (ER46680) following a no cost extension of DE-FG02-03ER46038 from February 16, 2016 to November 15, 2016. The report period is February 16, 2016 to November 15, 2016. The contract DE-FG02-03ER46038 (ER46680) was closed on November 15, 2016. The contract institution is the University of Delaware, address: Room 210, Hullihen %%@ Hall, University of Delaware, Newark, DE 19716. The Principal Investigator is Henry R. Glyde, Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (email: glyde@udel.edu). The Administrative Point of Contact is Dale S. Weiss Tel: 302 831 3634 dsweiss@udel.edu. The DOE Program is the Office of Basic Energy %%@ Sciences, U.S. Department of Energy, Germantown Building, 1000 Independence Ave., SW Washington, DC 20585. The program manager is Dr. P. Thiyagarajan, Neutron Scattering SC-22.2/ Germantown Bldg., Tel: 301-903-9706, email: P. Thiyagarajan@Science.DOE.GOV.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Collective Energy Transport of Excitons in Two-dimensional Materials

Electronic thermal transport and thermoelectric measurements are pursued in this project to obtain unique insights into the unusual collective energy transport behaviors in two-dimensional (2D) heterostructures. Electronic thermal transport and thermoelectric measurements are essential techniques for characterizing bulk superconductors by probing the heat-carrying quasi-particles. Thermoelectric and electronic thermal transport measurements are expanded in this work beyond bulk systems to probe interactions among electrons, holes, and phonons in 2D heterostructures. In one experiment, a microbridge platform is advanced to demonstrate field-effect resistive-thermometry measurements of the electronic thermal conductivity of graphene heterostructures. Together with first principles theoretical calculations and analytical models, the experimental results suggest that tunable electron coupling with flexural phonons provides a knob to control quantum matters in graphene heterostructures with broken reflection symmetry. In another experiment, the Seebeck coefficient (S) is measured to probe interlayer interactions in electron-hole bilayers that are predicted to give rise to the emergence of a variety of correlated states. As a measure of the entropy, the measured S reveals the signature of electric injection of interlayer excitons in transition metal dichalcogenide (TMD) structures.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Four-dimensional electrical conductivity monitoring of stage-driven river water intrusion: Accounting for water table effects using a transient mesh boundary and conditional inversion constraints

Our paper describes and demonstrates two methods of providing a priori information to the surface-based time-lapse three-dimensional electrical resistivity tomography (ERT) problem for monitoring stage-driven or tide-driven surface water intrusion into aquifers. First, a mesh boundary is implemented that conforms to the known location of the water table through time, thereby enabling the inversion to place a sharp bulk conductivity contrast at that boundary without penalty. Moreover, a nonlinear inequality constraint is used to allow only positive or negative transient changes in EC to occur within the saturated zone, dependent on the relative contrast in fluid electrical conductivity between surface water and groundwater. A 3-D field experiment demonstrates that time-lapse imaging results using traditional smoothness constraints are unable to delineate river water intrusion. The water table and inequality constraints provide the inversion with the additional information necessary to resolve the spatial extent of river water intrusion through time.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗