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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Gaussian approximation of dispersion potentials for efficient featurization and machine-learning predictions of metal–organic frameworks

Energy-related descriptors in machine learning are a promising strategy to predict adsorption properties of metal–organic frameworks (MOFs) in the low-pressure regime. Interactions between hosts and guests in these systems are typically expressed as a sum of dispersion and electrostatic potentials. The energy landscape of dispersion potentials plays a crucial role in defining Henry’s constants for simple probe molecules in MOFs. To incorporate more information about this energy landscape, we introduce the Gaussian-approximated Lennard-Jones (GALJ) potential, which fits pairwise Lennard-Jones potentials with multiple Gaussians by varying their heights and widths. The GALJ approach is capable of replicating information that can be obtained from the original LJ potentials and enables efficient development of Gaussian integral (GI) descriptors that account for spatial correlations in the dispersion energy environment. GI descriptors would be computationally inconvenient to compute using the usual direct evaluation of the dispersion potential energy surface. Here, we show that these new GI descriptors lead to improvement in ML predictions of Henry’s constants for a diverse set of adsorbates in MOFs compared to previous approaches to this task.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

The role of detonation condensates on the performance of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) detonation

Thermochemical models of detonation are widely used to estimate energy delivery, but they are based on the assumption that the carbon-rich condensates (soot) formed during detonation are very similar to bulk carbon. Here, we present an analytic equation of state (EOS) based on experimental detonation data for soot formed during the detonation of triaminotrinitrobenzene (TATB)-based high explosives. X-ray photoelectron spectra of several detonation soots are used to determine the elemental nitrogen abundance, with surprisingly high values for TATB. The proposed TATB soot EOS is highly compressible at low pressures and shares some features of glassy carbon, exhibiting graphite- and diamond-like behavior as a function of pressure. We demonstrate the influence of formed soot on detonation performance, including a lowering of the detonation velocity at typical charge densities, and a more compressive product Hugoniot at overdriven conditions. The soot model improves the accuracy of thermochemical calculations for TATB-based explosives across a wide range of states. Detonation velocity predictions for HMX (cyclotetramethylene-tetranitramine)-TATB blends with 80% or more TATB content, as well predictions for 1,3-diamino-2,4,6-trinitrobenzene (DATB) and 3-nitro-1,2,4-triazol-5-one (NTO), which share some features with TATB, are also improved.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Spatiotemporal measurements of striations in a glow discharge’s positive column using laser-collisional induced fluorescence

Here we have observed the behavior of striations caused by ionization waves propagating in low-pressure helium DC discharges using the non-invasive laser-collision induced fluorescence (LCIF) diagnostic. To achieve this, we developed an analytic fit of collisional radiative model (CRM) predictions to interpret the LCIF data and recover quantitative two-dimensional spatial maps of the electron density, n e , and the ratios of LCIF emission states that can be correlated with T e with the use of accurate distribution functions at localized positions within striated helium discharges at 500 mTorr, 750 mTorr, and 1 Torr. To our knowledge, these are the first spatiotemporal, laser-based, experimental measurements of n e in DC striations. The n e and 447:588 ratio distributions align closely with striation theory. Constriction of the positive column appears to occur with decreased gas pressure, as shown by the radial n e distribution. We identify a transition from a slow ionization wave to a fast ionization wave between 750 mTorr and 1 Torr. These experiments validate our analytic fit of n e , allowing the implementation of an LCIF diagnostic in helium without the need to develop a CRM.

42 ENGINEERING↗
DOE OSTI2022

Evaluation of a novel mid-infrared pyrometer for dynamic material experiments

Temperature is a complicated thermodynamic parameter to measure in dynamic compression experiments. Optical pyrometry is a general-purpose “work-horse” technique for measuring temperature from a radiant surface on these experimental platforms. The optical pyrometry channels are commonly held to the visible or Near-Infrared spectrum, which provides high fidelity temperature measurement for shock temperature above ∼1200–1500 K. However, low temperature (T < 1200 K) dynamic material experiments, including low pressure or quasi-isentropic studies, as well as experiments with complex thermodynamic paths, require Mid-Infrared (Mid-IR) for high fidelity measurements. This article outlines the design, testing, and characterization of a novel Mid-IR pyrometer system that can be configured between 2.5 and 5.0 µm, suitable for lower temperature measurements and for increasing the fidelity and precision of higher temperature measurements. Experimental validation was done on two separate gas gun platforms, with two separate impact velocities, achieving temperatures between 450 and 1100 K.

Dutra, E. C. (ORCID:0000000167649195)↗
DOE OSTI2022

X-ray diffraction from shock driven Sn microjets

Here, in situ x-ray diffraction was performed on shock-generated microjets composed of Sn and Sn–4Ag. Under low pressure drives (~21 GPa), a significant fraction of the jet volume was found to be in the β-Sn phase, and these crystallites were much smaller than the initial grain size of the material. Significant quantities of amorphous (molten) material were observed for higher drive pressures (~25–35 GPa). The extent of melting at these pressures was greater than would be predicted for uniaxial shock loading. Diffraction patterns from the Sn–4Ag alloy showed a peak that is consistent with the expected Ag 3 Sn intermetallic phase. This peak remained evident under drive conditions where the sample was otherwise fully amorphous. This indicates a slushy or a mixed phase of liquid Sn and solid Ag 3 Sn. Given the eutectic character of this alloy, this observation is attributed to a kinetic limitation on the dissolution of Ag 3 Sn. This implies that a much broader range of drive conditions will lead to mixed phase jets and ejecta than would be predicted from the equilibrium melt boundary of such alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Toward direct spatial and intensity characterization of ultra-high-intensity laser pulses using ponderomotive scattering of free electrons

Spatial distributions of electrons ionized and scattered from ultra-low-pressure gases are proposed and experimentally demonstrated as a method to directly measure the intensity of an ultra-high-intensity laser pulse. Analytic models relating the peak scattered electron energy to the peak laser intensity are derived and compared to paraxial Runge–Kutta simulations highlighting two models suitable for describing electrons scattered from weakly paraxial beams (f#>5) for intensities in the range of 1018−1021 W cm−2. Scattering energies are shown to be dependent on gas species, emphasizing the need for specific gases for given intensity ranges. Direct measurements of the laser intensity at full power of two laser systems are demonstrated, both showing a good agreement between indirect methods of intensity measurement and the proposed method. One experiment exhibited the role of spatial aberrations in the scattered electron distribution, motivating a qualitative study on the effect. We propose the use of convolutional neural networks as a method for extracting quantitative information on the spatial structure of the laser at full power. We believe the presented technique to be a powerful tool that can be immediately implemented in many high-power laser facilities worldwide.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Physics and applications of dusty plasmas: The Perspectives 2023

Dusty plasmas are electrically quasi-neutral media that, along with electrons, ions, neutral gas, radiation, and electric and/or magnetic fields, also contain solid or liquid particles with sizes ranging from a few nanometers to a few micrometers. These media can be found in many natural environments as well as in various laboratory setups and industrial applications. As a separate branch of plasma physics, the field of dusty plasma physics was born in the beginning of 1990s at the intersection of the interests of the communities investigating astrophysical and technological plasmas. An additional boost to the development of the field was given by the discovery of plasma crystals leading to a series of microgravity experiments of which the purpose was to investigate generic phenomena in condensed matter physics using strongly coupled complex (dusty) plasmas as model systems. Finally, the field has gained an increasing amount of attention due to its inevitable connection to the development of novel applications ranging from the synthesis of functional nanoparticles to nuclear fusion and from particle sensing and diagnostics to nano-contamination control. The purpose of the present perspectives paper is to identify promising new developments and research directions for the field. As such, dusty plasmas are considered in their entire variety: from classical low-pressure noble-gas dusty discharges to atmospheric pressure plasmas with aerosols and from rarefied astrophysical plasmas to dense plasmas in nuclear fusion devices. Both fundamental and application aspects are covered.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Understanding electronic structure tunability by metal dopants for promoting MgB 2 hydrogenation

Hydrogen is a promising energy carrier, but its onboard application is limited by the need for compact, low-pressure storage solutions. Solid-state complex metal hydride systems, such as MgB 2 /Mg(BH 4 ) 2 , offer high storage capacities but suffer from sluggish kinetics and poor reversibility. One avenue for improving reactivity is to introduce metal dopants to alter electronic and atomic properties, but the role of these chemical additives remains poorly understood, particularly for the hydrogenation reaction. In this work, we used density functional theory calculations on model MgB 2 systems to rationalize the potential role of metal dopants in destabilizing B–B bonding within the MgB 2 lattice. We carried out detailed electronic structure analyses for 28 different metal dopant adatoms to identify properties that contribute to a dopant’s efficacy. Based on the simulation results, we propose that an intermediate ionic and covalent character of the bonds between adatoms and B atoms is desirable for facilitating charge redistribution, disrupting the B–B bond network, and promoting H 2 dissociation and H atom chemisorption on MgB 2 .

08 HYDROGEN↗
DOE OSTI2025

Dynamic response of 17-4 stainless steel as a function of manufacturing method and heat treatment

We present a series of plate-impact experiments on 17-4 stainless steel to study the effect of manufacturing method and heat treatment on the Hugoniot elastic limit (HEL), Hugoniot, phase transformation stress, and spallation strength. Two traditional manufacturing methods were considered, wrought processing and casting, as well as two additive manufacturing methods, laser powder-bed fusion (LPBF) and wire-fed electron beam (EBAM). For both LPBF and EBAM 17-4 stainless steel variants, two billets were printed, enabling the application of two unique heat treatments. The HEL stress depended heavily on the thermal history, with the HEL increasing after the formation of Cu-rich precipitates via heat treatment. The Hugoniot response both below and above the phase transition was unaffected by the manufacturing method or heat treatment. The phase transition stress depended heavily on the thermal history, with its variation being attributed to the presence of various microstructural features. This is supported by a marked increase in the phase transition stress after precipitation hardening. These results suggest that the notion of the phase transition stress being dictated by bulk composition is an oversimplification and the stress fields generated by the meso-scale structure are a dominant force. The spallation strength was lower in the cast material compared to all other 17-4 stainless steel variants due to the presence of brittle δ-ferrite inclusions. Additionally, a drop in the tensile strain-rate was observed in the spallation response above the phase transition stress, which was hypothesized to stem from the kinetics of the reversion to the low-pressure phase during spall.

Compressive stress↗
DOE OSTI2020

Viricidal and bactericidal exciplex barrier-discharge lamps

A brief review is presented of investigations performed in 2002 – 2020 on ultraviolet inactivation of bacteria, vital cells, and viruses by using excilamps. The excilamp models that have been developed at the Institute of High-Current Electronics, SB RAS are briefly described. Scientific data acquired by now show that excilamps on KrCl{sup *}, KrBr{sup *}, and XeBr{sup *} molecules are an alternative to low-pressure mercury lamps with respect to optical parameters. These sources of optical radiation exhibit a bactericidal effect, and emission of KrCl and KrBr excilamps demonstrates viricidal action. The latter is actual due to expansion of coronavirus disease. (paper)

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Cardinal: A Lower-Length-Scale Multiphysics Simulator for Pebble-Bed Reactors

This paper demonstrates a multiphysics solver for pebble-bed reactors, in particular, for Berkeley’s pebble-bed -fluoride-salt-cooled high-temperature reactor (PB-FHR) (Mark I design). The FHR is a class of advanced nuclear reactors that combines the robust coated particle fuel form from high-temperature gas-cooled reactors, the direct reactor auxiliary cooling system passive decay removal of liquid-metal fast reactors, and the transparent, high-volumetric heat capacitance liquid-fluoride salt working fluids (e.g., FLiBe) from molten salt reactors. This fuel and coolant combination enables FHRs to operate in a high-temperature, low-pressure design space that has beneficial safety and economic implications. The PB-FHR relies on a pebble-bed approach, and pebble-bed reactors are, in a sense, the poster child for multiscale analysis. Relying heavily on the MultiApp capability of the Multiphysics Object-Oriented Simulation Environment (MOOSE), we have developed Cardinal, a new platform for lower-length-scale simulation of pebble-bed cores. The lower-length-scale simulator comprises three physics: neutronics (OpenMC), thermal fluids (Nek5000/NekRS), and fuel performance (BISON). Cardinal tightly couples all three physics and leverages advances in MOOSE, such as the MultiApp system and the concept of MOOSE-wrapped applications. Moreover, Cardinal can utilize graphics processing units for accelerating solutions. In this paper, we discuss the development of Cardinal and the verification and validation and demonstration simulations.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2022

Particle trapping, size-filtering, and focusing in the nonthermal plasma synthesis of sub-10 nanometer particles

Low-pressure nonthermal flowing plasmas are widely used for the gas-phase synthesis of nanoparticles and quantum dots of materials that are difficult or impractical to synthesize using other techniques. To date, the impact of temporary electrostatic particle trapping in these plasmas has not been recognized, a process that may be leveraged to control particle properties. Furthermore, we present experimental and computational evidence that, during their growth in the plasma, sub-10 nm silicon particles become temporarily confined in an electrostatic trap in radio-frequency excited plasmas until they grow to a size at which the increasing drag force imparted by the flowing gas entrains the particles, carrying them out of the trap. We demonstrate that this trapping enables the size filtering of the synthesized particles, leading to highly monodisperse particle sizes, as well as the electrostatic focusing of the particles onto the reactor centerline. Understanding of the mechanisms and utilization of such particle trapping will enable the design of plasma processes with improved size control and the ability to grow heterostructured nanoparticles.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Self-organization in 1 atm DC glows with liquid anodes: current understanding and potential applications

Self-organization refers to the spontaneous generation of spatially or temporally organized patterns in an otherwise disordered system. Self-organization is ubiquitous in plasma physics particularly in the low-pressure regime as observed in astrophysical jets or plasma loaded flux loops that form on the surface of the Sun. In recent times, self-organization in atmospheric pressure plasmas has captured the attention of researchers. Its occurrence has been observed in DBD discharges as well as DC 1 atm glows with liquid electrodes. The mechanism of pattern formation is still not well understood. In this work, we briefly review the current understanding of pattern formation in DC glows with liquid anode, surveying past work, application areas, theories on mechanisms of formation from the context of reaction diffusion systems, current experimental work and computational progress towards predicting pattern formation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Electric field reversals resulting from voltage waveform tailoring in Ar/O 2 capacitively coupled plasmas sustained in asymmetric systems

The etching of nanometer scale high-aspect-ratio (HAR) features into dielectric materials in low pressure radio frequency excited plasmas is often accompanied by charge accumulation inside the features which can slow etching rates and produce distortions such as twisting. The intra feature charging is at least partially produced by differences in electron and ion energy and angular distributions (EADs). Positive ions, accelerated to high energies having narrow angular spreads by the sheath electric field, can penetrate deeply into HAR features. Electrons typically arrive at the wafer with nearly thermal and isotropic distributions and do not penetrate deeply into HAR features. These disparities lead to differential charging of the inside of the feature, which can lead to reductions in etch rate and feature distortion due to ion deflection. With in-creasing aspect ratio of features, charging challenges are expected to continue for the foreseeable future. In this work, the use of tailored voltage waveforms in geometrically asymmetric capacitively coupled plasmas sustained in Ar/O 2 at 40 mTorr was computationally investigated with the goal of shaping the EAD of electrons incident onto the substrate to address differential charging. The tailored waveform consisted of a sinusoidal wave and its higher harmonics with a fundamental frequency of 1 MHz. Further, we found that electric field reversals in the sheath and presheath can occur during the anodic portion of the cycle. The electric field reversal increases the energy and decreases the angular spread of electrons incident onto the substrate. The magnitude of the electric field reversal can be controlled by the phase angle of the even harmonics and the gas composition. Due to its electronegative nature, increasing mole fractions of O 2 impedes electron transport to the surface which further increases the electric field reversal.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Similarity properties in capacitive radio frequency plasmas with nonlinear collision processes

Abstract Similarity laws (SL) are essential for correlating the characteristics of plasmas at different dimensional scales, which have been validated for radio frequency (rf) discharges at low pressure but under limited conditions. In this work, we evaluate the effects of nonlinear collisions (e.g. stepwise ionization) on the similarity properties in capacitive rf discharges in argon across a wide range of pressure regimes via fully kinetic particle-in-cell simulations. The SL scalings of fundamental discharge parameters, e.g. the electron power absorption and electron energy probability function, are examined with and without nonlinear collisions, respectively. Without the nonlinear collisions, the similarity scalings are found to be rigorously valid. When the nonlinear collisions are considered, the similarity properties in rf discharges still exist approximately, which indicates that the violations caused by the nonlinear collisions are still minor in the studied cases. The reasons for the effectiveness of SL scalings with nonlinear collision processes are also discussed. The results from this study confirmed the validity of similarity transformations with more complex reaction kinetics, which may promote the applicability of the SL scalings for the design and fabrications of plasma devices.

Physics↗
DOE OSTI2021

94 GHz microplasma sustained by a photonic crystal

A photonic crystal (PhC) with a single vacancy sustains an argon microplasma at 94 GHz. The PhC consists of a 7 × 13 array of small alumina rods, each 250 μm in radius. The PhC has a forbidden bandgap from 70–105 GHz. The vacancy creates an internal electromagnetic resonance at 94 GHz that intensifies the electric field of an incident wave to 5 × 10 5 V m –1 . Breakdown of low-pressure argon gas (80 mbar) occurs and forms a stable, ellipsoidal plasma inside the crystal. The central core of the microplasma is probed using a 200 μm optical fiber inserted into the PhC. The rotational temperature of the CH molecule is estimated from a numerical fit of the plasma emission and is found to increase from 450–650 K with both pressure (200–1000 mbar) and incident wave power (100 mW–1100 mW). Under these conditions, the electron density increases with both power and pressure from 0.5–1.5 × 10 20 m –3 . Furthermore, this plasma density range brackets the electron plasma frequency at 94 GHz. The results are compared with a similar microplasma operating at 44 GHz.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Effects of macroparticle weighting in axisymmetric particle-in-cell Monte Carlo collision simulations

In this paper, the effects of macroparticle (MP) weighting on the plasma discharge, particularly near the centerline, are investigated using a two-dimensional axisymmetric particle-in-cell Monte Carlo collision (PIC/MCC) model. A variable MP weight according to the radial position of the MPs is employed to maintain sufficient number of MPs near the centerline of the plasma source. Finally, the plasma density obtained from the PIC/MCC simulations for low-pressure (25–100 mTorr) capacitively coupled plasmas is found to be artificially large when the MP weight near the centerline is not well resolved, demonstrating the need for particle convergence studies for axisymmetric PIC/MCC simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Recent progress in shattered pellet injection technology in support of the ITER disruption mitigation system*

Shattered pellet injection (SPI) has been selected as the baseline technology for the disruption mitigation (DM) system for ITER. Typical SPI utilizes cryogenic cooling to desublimate low pressure (<100 mbar) gases onto a cold zone within a pipe gun barrel, forming a cylindrical pellet. Pellets are dislodged from the barrel and accelerated using either a gas driven mechanical punch or high-pressure light-gas delivered by a fast-opening valve. SPI technology developed at Oak Ridge National Laboratory is currently deployed and operational on DIII-D, JET, and KSTAR. These SPI systems are used in experiments for physics scaling to ITER thermal mitigation and runaway electron dissipation/avoidance. The pellet sizes used for these machines are in the range of 4 to 12.5 mm in diameter with length to diameter ratios (L/D) of ~1.5. The current plan for ITER SPI is to utilize pellets that are 28.5 mm in diameter with an L/D of ~2. Furthermore, the large pellet sizes, high steady-state magnetic fields, and limitations of operating in a radiation environment render much of the current technology unusable. In addition to technology improvements, a deeper understanding of pellet material properties, formation, and release is being developed for implementation in future SPI designs, specifically ITER.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗