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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Nanoscale phase separation in epitaxial Cr-Mo and Cr-V alloy thin films studied using atom probe tomography: Comparison of experiments and simulation

Tailored metal alloy thin film-oxide interfaces generated using molecular beam epitaxy (MBE) deposition of alloy thin films on a single crystalline oxide substrate can be used for detailed studies of irradiation damage response on the interface structure. However, the presence of nanoscale phase separation in the MBE grown alloy thin films can impact the metal-oxide interface structure. Due to nanoscale domain size of such phase separation, it is very challenging to characterize by conventional techniques. Therefore, laser assisted atom probe tomography (APT) was utilized to study the phase separation in epitaxial Cr{sub 0.61}Mo{sub 0.39}, Cr{sub 0.77}Mo{sub 0.23}, and Cr{sub 0.32}V{sub 0.68} alloy thin films grown by MBE on MgO(001) single crystal substrates. Statistical analysis, namely frequency distribution analysis and Pearson coefficient analysis of experimental data was compared with similar analyses conducted on simulated APT datasets with known extent of phase separation. Thus, the presence of phase separation in Cr-Mo films, even when phase separation was not clearly observed by x-ray diffraction, and the absence of phase separation in the Cr-V film were confirmed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Electron energy distributions and electron impact source functions in Ar/N{sub 2} inductively coupled plasmas using pulsed power

In plasma materials processing, such as plasma etching, control of the time-averaged electron energy distributions (EEDs) in the plasma allows for control of the time-averaged electron impact source functions of reactive species in the plasma and their fluxes to surfaces. One potential method for refining the control of EEDs is through the use of pulsed power. Inductively coupled plasmas (ICPs) are attractive for using pulsed power in this manner because the EEDs are dominantly controlled by the ICP power as opposed to the bias power applied to the substrate. In this paper, we discuss results from a computational investigation of EEDs and electron impact source functions in low pressure (5–50 mTorr) ICPs sustained in Ar/N{sub 2} for various duty cycles. We find there is an ability to control EEDs, and thus source functions, by pulsing the ICP power, with the greatest variability of the EEDs located within the skin depth of the electromagnetic field. The transit time of hot electrons produced in the skin depth at the onset of pulse power produces a delay in the response of the EEDs as a function of distance from the coils. The choice of ICP pressure has a large impact on the dynamics of the EEDs, whereas duty cycle has a small influence on time-averaged EEDs and source functions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Complex oxide growth using simultaneous in situ reflection high-energy electron diffraction and x-ray reflectivity: When is one layer complete?

During layer-by-layer homoepitaxial growth, both the Reflection High-Energy Electron Diffraction (RHEED) intensity and the x-ray reflection intensity will oscillate, and each complete oscillation indicates the addition of one monolayer of material. However, it is well documented, but not well understood, that the phase of the RHEED oscillations varies from growth to growth and thus the maxima in the RHEED intensity oscillations do not necessarily occur at the completion of a layer. Here, we demonstrate this by using simultaneous in situ x-ray reflectivity and RHEED to characterize layer-by-layer growth of SrTiO 3 . We show that we can control the RHEED oscillation phase by changing the pre-growth substrate annealing conditions, changing the RHEED oscillation phase by as much as 137°. In addition, during growth via pulsed laser deposition, the relaxation times between each laser pulse can be used to determine when a layer is complete, independent of the phase of the RHEED oscillation.

36 MATERIALS SCIENCE↗
DOE OSTI2015

First experiments probing the collision of parallel magnetic fields using laser-produced plasmas

Novel experiments to study the strongly-driven collision of parallel magnetic fields in β ∼ 10, laser-produced plasmas have been conducted using monoenergetic proton radiography. These experiments were designed to probe the process of magnetic flux pileup, which has been identified in prior laser-plasma experiments as a key physical mechanism in the reconnection of anti-parallel magnetic fields when the reconnection inflow is dominated by strong plasma flows. In the present experiments using colliding plasmas carrying parallel magnetic fields, the magnetic flux is found to be conserved and slightly compressed in the collision region. Two-dimensional (2D) particle-in-cell simulations predict a stronger flux compression and amplification of the magnetic field strength, and this discrepancy is attributed to the three-dimensional (3D) collision geometry. Future experiments may drive a stronger collision and further explore flux pileup in the context of the strongly-driven interaction of magnetic fields.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Developments in time-resolved high pressure x-ray diffraction using rapid compression and decompression

Complementary advances in high pressure research apparatus and techniques make it possible to carry out time-resolved high pressure research using what would customarily be considered static high pressure apparatus. This work specifically explores time-resolved high pressure x-ray diffraction with rapid compression and/or decompression of a sample in a diamond anvil cell. Key aspects of the synchrotron beamline and ancillary equipment are presented here, including source considerations, rapid (de)compression apparatus, high frequency imaging detectors, and software suitable for processing large volumes of data. A number of examples are presented, including fast equation of state measurements, compression rate dependent synthesis of metastable states in silicon and germanium, and ultrahigh compression rates using a piezoelectric driven diamond anvil cell.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

X-ray imaging for studying behavior of liquids at high pressures and high temperatures using Paris-Edinburgh press

Several X-ray techniques for studying structure, elastic properties, viscosity, and immiscibility of liquids at high pressures have been integrated using a Paris-Edinburgh press at the 16-BM-B beamline of the Advanced Photon Source. In this paper, we report the development of X-ray imaging techniques suitable for studying behavior of liquids at high pressures and high temperatures. White X-ray radiography allows for imaging phase separation and immiscibility of melts at high pressures, identified not only by density contrast but also by phase contrast imaging in particular for low density contrast liquids such as silicate and carbonate melts. In addition, ultrafast X-ray imaging, at frame rates up to ~10 5 frames/second (fps) in air and up to ~10 4 fps in Paris-Edinburgh press, enables us to investigate dynamics of liquids at high pressures. Very low viscosities of melts similar to that of water can be reliably measured. These high-pressure X-ray imaging techniques provide useful tools for understanding behavior of liquids or melts at high pressures and high temperatures.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

Using multiple secondary fusion products to evaluate fuel ρR, electron temperature, and mix in deuterium-filled implosions at the NIF

In deuterium-filled inertial confinement fusion implosions, the secondary fusion processes D( 3 He,p) 4 He and D(T,n) 4 He occur, as the primary fusion products 3 He and T react in flight with thermal deuterons. In implosions with moderate fuel areal density (~ 5–100 mg/cm 2 ), the secondary D- 3 He reaction saturates, while the D-T reaction does not, and the combined information from these secondary products is used to constrain both the areal density and either the plasma electron temperature or changes in the composition due to mix of shell material into the fuel. The underlying theory of this technique is developed and applied to three classes of implosions on the National Ignition Facility: direct-drive exploding pushers, indirect-drive 1-shock and 2-shock implosions,and polar direct-drive implosions. In the 1- and 2-shock implosions, the electron temperature is inferred to be 0.65 x and 0.33 x the burn-averaged ion temperature, respectively. The inferred mixed mass in the polar direct-drive implosions is in agreement with measurements using alternative techniques.

42 ENGINEERING↗
DOE OSTI2015

Catalyst synthesis and evaluation using an integrated atomic layer deposition synthesis–catalysis testing tool

An integrated atomic layer deposition-catalysis (I-ALD-CAT) tool was developed, combining an ALD manifold with a plug-flow reactor system for the synthesis of supported catalytic materials by ALD and immediate evaluation of catalyst reactivity using gas-phase probe reactions. The I-ALD-CAT system can deliver gaseous reagents comprised of 12 different metal ALD precursors, 4 oxidizing or reducing agents, and 4 catalytic reaction feeds to either of the two plug-flow reactors. The system can employ reactor pressures and temperatures in the range of 10 -3 to 1 bar and 300–1000 K, respectively. Furthermore, the instrument is also equipped with a gas chromatograph and a mass spectrometer unit for the detection and quantification of volatile species from ALD and catalytic reactions. In this report, we demonstrate the use of the I-ALD-CAT tool for the ALD of platinum active sites and Al 2 O 3 overcoats, and evaluation of catalyst propylene hydrogenation activity.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

A method for the direct measurement of electronic site populations in a molecular aggregate using two-dimensional electronic-vibrational spectroscopy

Two dimensional electronic spectroscopy has proved to be a valuable experimental technique to reveal electronic excitation dynamics in photosynthetic pigment-protein complexes, nanoscale semiconductors, organic photovoltaic materials, and many other types of systems. It does not, however, provide direct information concerning the spatial structure and dynamics of excitons. 2D infrared spectroscopy has become a widely used tool for studying structural dynamics but is incapable of directly providing information concerning electronic excited states. 2D electronic-vibrational (2DEV) spectroscopy provides a link between these domains, directly connecting the electronic excitation with the vibrational structure of the system under study. In this work, we derive response functions for the 2DEV spectrum of a molecular dimer and propose a method by which 2DEV spectra could be used to directly measure the electronic site populations as a function of time following the initial electronic excitation. We present results from the response function simulations which show that our proposed approach is substantially valid. This method provides, to our knowledge, the first direct experimental method for measuring the electronic excited state dynamics in the spatial domain, on the molecular scale.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Compact spherical neutron polarimeter using high-T{sub c} YBCO films

We describe a simple, compact device for spherical neutron polarimetry measurements at small neutron scattering angles. The device consists of a sample chamber with very low (<0.01 G) magnetic field flanked by regions within which the neutron polarization can be manipulated in a controlled manner. This allows any selected initial and final polarization direction of the neutrons to be obtained. We have constructed a prototype device using high-T{sub c} superconducting films and mu-metal to isolate regions with different magnetic fields and tested device performance in transmission geometry. Finite-element methods were used to simulate the device’s field profile and these have been verified by experiment using a small solenoid as a test sample. Measurements are reported using both monochromatic and polychromatic neutron sources. The results show that the device is capable of extracting sample information and distinguishing small angular variations of the sample magnetic field. As a more realistic test, we present results on the characterization of a 10 μm thick Permalloy film in zero magnetic field, as well as its response to an external magnetic field.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Time-dependent analysis of visible helium line-ratios for electron temperature and density diagnostic using synthetic simulations on NSTX-U

Helium line-ratios for electron temperature (T{sub e}) and density (n{sub e}) plasma diagnostic in the Scrape-Off-Layer (SOL) and edge regions of tokamaks are widely used. Due to their intensities and proximity of wavelengths, the singlet, 667.8 and 728.1 nm, and triplet, 706.5 nm, visible lines have been typically preferred. Time-dependency of the triplet line (706.5 nm) has been previously analyzed in detail by including transient effects on line-ratios during gas-puff diagnostic applications. In this work, several line-ratio combinations within each of the two spin systems are analyzed with the purpose of eliminating transient effects to extend the application of this powerful diagnostic to high temporal resolution characterization of plasmas. The analysis is done using synthetic emission modeling and diagnostic for low electron density NSTX SOL plasma conditions by several visible lines. Quasi-static equilibrium and time-dependent models are employed to evaluate transient effects of the atomic population levels that may affect the derived electron temperatures and densities as the helium gas-puff penetrates the plasma. The analysis of a wider range of spectral lines will help to extend this powerful diagnostic to experiments where the wavelength range of the measured spectra may be constrained either by limitations of the spectrometer or by other conflicting lines from different ions.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

The molecular gradient using the divide-expand-consolidate resolution of the identity second-order Møller-Plesset perturbation theory: The DEC-RI-MP2 gradient

We report an implementation of the molecular gradient using the divide-expand-consolidate resolution of the identity second-order Møller-Plesset perturbation theory (DEC-RI-MP2). The new DEC-RI-MP2 gradient method combines the precision control as well as the linear-scaling and massively parallel features of the DEC scheme with efficient evaluations of the gradient contributions using the RI approximation. We further demonstrate that the DEC-RI-MP2 gradient method is capable of calculating molecular gradients for very large molecular systems. A test set of supramolecular complexes containing up to 158 atoms and 1960 contracted basis functions has been employed to demonstrate the general applicability of the DEC-RI-MP2 method and to analyze the errors of the DEC approximation. Moreover, the test set contains molecules of complicated electronic structures and is thus deliberately chosen to stress test the DEC-RI-MP2 gradient implementation. Additionally, as a showcase example the full molecular gradient for insulin (787 atoms and 7604 contracted basis functions) has been evaluated.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Spectral survey of helium lines in a linear plasma device for use in HELIOS imaging

Fast visible cameras and a filterscope are used to examine the visible light emission from Oak Ridge National Laboratory’s Proto-MPEX. The filterscope has been configured to perform helium line ratio measurements using emission lines at 667.9, 728.1, and 706.5 nm. The measured lines should be mathematically inverted and the ratios compared to a collisional radiative model (CRM) to determine T{sub e} and n{sub e}. Increasing the number of measurement chords through the plasma improves the inversion calculation and subsequent T{sub e} and n{sub e} localization. For the filterscope, one spatial chord measurement requires three photomultiplier tubes (PMTs) connected to pellicle beam splitters. Multiple, fast visible cameras with narrowband filters are an alternate technique for performing these measurements with superior spatial resolution. Each camera contains millions of pixels; each pixel is analogous to one filterscope PMT. The data can then be inverted and the ratios compared to the CRM to determine 2-dimensional “images” of T{sub e} and n{sub e} in the plasma. An assessment is made in this paper of the candidate He I emission lines for an imaging technique.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Control of secondary electrons from ion beam impact using a positive potential electrode

Secondary electrons emitted when an ion beam impacts a detector can amplify the ion beam signal, but also introduce errors if electrons from one detector propagate to another. A potassium ion beam and a detector comprised of ten impact wires, four split-plates, and a pair of biased electrodes were used to demonstrate that a low-voltage, positive electrode can be used to maintain the beneficial amplification effect while greatly reducing the error introduced from the electrons traveling between detector elements.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Power increases using wind direction spatial filtering for wind farm control: Evaluation using FLORIS, modified for dynamic settings

As wind energy plays a growing role in the energy sector, new methods for controlling wind turbines and wind farms to maximize performance are garnering industry interest. A developing body of research treats the entire wind farm as a control system, with individual turbines acting as agents in a network, allowing farm-level objectives to be considered. Two promising developments in this research are wake steering control, which seeks to increase the power generated at a wind farm by directing the wakes of upstream turbines away from downstream ones, and communication-based spatial filtering, which seeks to improve the quality of information used by turbine- and farm-level controllers by combining measurements of the wind field collected at the individual turbines. The latter method has been shown to improve the estimates of wind direction at the turbines; however, the resulting potential for increased power capture warrants further investigation. With this paper, we begin to address this gap by combining wake steering with wind direction spatial filtering. To do so, we present a preliminary method for assessing the power capture of dynamic controllers using wind farm codes designed for time-averaged simulation. This allows us to generate results much more rapidly than would be possible using high-fidelity wind farm simulators and may be useful in many wind farm control design applications.

17 WIND ENERGY↗
DOE OSTI2024

Source shape estimation for neutron imaging systems using convolutional neural networks

Neutron imaging systems are important diagnostic tools for characterizing the physics of inertial confinement fusion reactions at the National Ignition Facility (NIF). In particular, neutron images give diagnostic information on the size, symmetry, and shape of the fusion hot spot and surrounding cold fuel. Images are formed via collection of neutron flux from the source using a system of aperture arrays and scintillator-based detectors. Currently, reconstruction of fusion source geometry from the collected neutron images is accomplished by solving a computationally intensive maximum likelihood estimation problem via expectation maximization. In contrast, it is often useful to have simple representations of the overall source geometry that can be computed quickly. In this work, we develop convolutional neural networks (CNNs) to reconstruct the outer contours of simple source geometries. We compare the performance of the CNN for penumbral and pinhole data and provide experimental demonstrations of our methods on both non-noisy and noisy data.

Machine learning, neutron imaging, source reconstr↗