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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Perturbative model for the saturation of energetic-particle-driven modes limited by self-generated zonal modes

We present a simplified energy-conserving approach to incorporate wave–wave nonlinear effects within the framework commonly used to describe wave–particle nonlinearities. In particular, the effects of zonal mode (ZM) generation on the determination of the saturation amplitude of energetic particle (EP)-driven Alfvénic instabilities is studied. The model assumes that the zonal perturbations grow at a rate twice that of the original (pump) wave, consistent with a beat-driven (or force-driven) generation mechanism. The evolution and saturation of the mode amplitude are investigated both analytically and numerically within our reduced model assumptions, in both the collisionless and scattering-dominated regimes. These studies underscore the crucial role of sources and sinks in capturing the impact and the role of beat-driven zonal perturbations on mode evolution. In the realistic case of saturation set by sources and sinks, we discuss the role of a finite amplitude ZM in reducing microturbulent particle scattering, thus limiting the energy source for the resonant mode. We then discuss comparisons between the model’s predictions and simulation results. The model reproduces key features observed in gyrokinetic simulations as the reduction in saturated mode amplitude and the onset of wave–wave nonlinear effects as functions of mode growth rate and amplitude. Thanks to its simplicity, it can be readily implemented into codes based on reduced models, thereby improving their predictive capability for strongly driven instabilities.

Alfvén eigenmodes↗
DOE OSTI2025

Impact of charge-density-wave pattern on the superconducting gap in Vanadium-based kagome superconductors

Kagome metals AV 3 Sb 5 (A = K, Rb, Cs) provide a compelling platform to explore the interplay between superconductivity (SC) and charge-density-wave (CDW) orders. While distinct CDW orders have been identified in K/RbV 3 Sb 5 versus CsV 3 Sb 5 , their influence on the SC order parameter remains unresolved. Here, we investigate low-energy quasiparticle excitations in AV 3 Sb 5 , uncovering a striking difference in SC gap anisotropy: K/RbV 3 Sb 5 exhibit fully gapped, nearly isotropic s-wave states, in contrast to the strongly anisotropic SC gap in CsV 3 Sb 5 . Impurity scattering introduced via electron irradiation in K/RbV 3 Sb 5 has a minimal impact on low-energy excitations, and it induces an increase in the SC transition temperature T c , consistent with more isotropic s-wave SC competing with CDW order. Our theoretical analysis attributes the observed SC gap anisotropy differences to distinct CDW modulation patterns: the star-of-David structure unique to CsV 3 Sb 5 preserves van Hove singularities near the Fermi level, promoting anisotropic s-wave SC with enhanced T c via bond-order fluctuations. These findings establish a systematic framework for understanding the interplay between SC and CDW orders in AV 3 Sb 5 , driven by electron correlations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2020

Radiative Heating Rate Profiles over the Southeast Atlantic Ocean during the 2016 and 2017 Biomass Burning Seasons

Marine boundary layer clouds, including the transition from stratocumulus to cumulus, are poorly represented in numerical weather prediction and general circulation models. Further uncertainties in the cloud structure arise in the presence of biomass burning carbonaceous aerosol, as is the case over the southeast Atlantic Ocean where biomass burning aerosol is transported from the African continent. As the aerosol plume progresses across the southeast Atlantic Ocean, radiative heating within the aerosol layer has the potential to alter the thermodynamic environment and therefore the cloud structure; however, limited work has been done to quantify this along the trajectory of the aerosol plume in the region. The deployment of the First Atmospheric Radiation Measurement Mobile Facility in support of the Layered Atlantic Smoke Interactions with Clouds field campaign provided a unique opportunity to collect observations of cloud and aerosol properties during two consecutive biomass burning seasons during July through October of 2016 and 2017 over Ascension Island (7.96 °S, 14.35 °W). Using observed profiles of temperature, humidity, and clouds from the field campaign, alongside aerosol optical properties from MERRA-2 as input for the Rapid Radiation Transfer Model, profiles of the radiative heating rate due to aerosols and clouds were computed. Radiative heating is also assessed across the southeast Atlantic Ocean using an ensemble of back trajectories from the Hybrid Single Particle Lagrangian Integrated Trajectory Model. Idealized experiments using the Rapid Radiation Transfer Model with and without aerosols and a range of values for the single scattering albedo demonstrate that shortwave heating within the aerosol layer above Ascension Island can locally range between 2 and 8 K per day depending on the aerosol optical properties, though impacts of the aerosol can be felt elsewhere in the atmospheric column. When considered under clear conditions, the aerosol has a cooling effect at the TOA and based on the observed cloud properties at Ascension Island, the cloud albedo is not large enough to overcome this. Shortwave radiative heating due to biomass burning aerosol is not balanced by additional longwave cooling, and the net radiative impact results in a stabilization of the lower troposphere. However, these results are extremely sensitive to the single scattering albedo assumptions in models.

Allison B. Marquardt Collow↗
DOE OSTI2025

Large radiation back-flux from Monte Carlo simulations of fusion neutron–material interactions

Abstract Fusion power reactors will generate intense neutron fluxes into plasma-facing and structural materials (SMs). Radiation back-fluxes, generated from neutron–material interactions under these fluxes, can dramatically impact the plasma dynamics, e.g. by seeding runaway electrons during disruptions via Compton scattering of background electrons by wall-emitted gamma radiation. Here, we quantify these back-fluxes, including neutrons, gamma rays, and electrons, using Monte Carlo calculations for a range of SM candidates and first wall (FW) thicknesses. The radiation back-flux magnitudes are remarkably large, with neutron and gamma radiation back-fluxes on the same order of magnitude as the incident fusion neutron flux. Electron back-fluxes are two orders of magnitudes lower, but are emitted at sufficiently high energies to impact the sheath and boundary plasma dynamics. Material configuration plays a key role in determining back-flux magnitudes. The SM chiefly determines the neutron back-flux magnitude, while the FW thickness principally attenuates the gamma ray and electron back-fluxes. In addition to prompt back-fluxes, which are emitted immediately after fusion neutrons impact the surface, significant delayed gamma ray and electron back-fluxes arise from nuclear decay processes in the activated materials. These delayed back-flux magnitudes range from 2% to 7% of the prompt back-fluxes, and remain present during transients when fusion no longer occurs. During disruptions, build-up of delayed gamma radiation back-flux represents potential runaway electron seeding mechanisms, posing additional challenges for disruption mitigation in a power reactor compared with non-nuclear plasma operations. This work highlights the impact of these radiation back-fluxes plasma performance and demonstrates the importance of considering back-flux generation in materials selection for fusion power reactors.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1978

The tektite problem

Small glassy pebbles, called tektites, are found in widely scattered locations around the world. These tektites appear much like volcanic glass obsidian, but their chemical composition is different from that of any terrestrial lava and they contain far less water and none of obsidian's characteristic microcrystals. No one has ever found the mother lode of a field of tektites. They cannot, therefore, be the product of terrestrial volcanism. Recently acquired knowledge about the moon's surface confirms earlier indications that tektites cannot be bits of lunar soil propelled to the earth by the impact of meteorites on the moon. According to one of two remaining possibilities tektites are bits of terrestrial sedimentary rock excavated by meteorites striking the earth's surface, melted by the heat of impact, and congealed into glass as they travel above the atmosphere to the scattered sites where they are found. The other possibility is that tektites are the remains of gobs of lava fired at the earth by volcanic activity on the moon.

Okeefe, J. A.↗
DOE OSTI2022

Progress in Understanding Short-Range Structure in Nuclei: An Experimental Perspective

High-energy electron scattering is a clean, precise probe for measurements of hadronic and nuclear structure and plays a key role in understanding the role of high-momentum nucleons (and quarks) in nuclei. Jefferson Lab has dramatically expanded our knowledge of the high-momentum nucleons generated by short-range correlations, providing sufficient insight to model much of their impact on nuclear structure in neutron stars and in low- to medium-energy scattering observables, including neutrino oscillation measurements. These short-range correlations also seem related to the modification of the quark distributions in nuclei, and efforts to improve our understanding of the internal structure of these short-distance and high-momentum configurations in nuclei will provide important input on a wide range of high-energy observables.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Understanding how minority relativistic electron populations may dominate charge state balance and radiative cooling of a post-thermal quench tokamak plasma

Minority relativistic electron populations can occur in a range of complex plasmas. Of specific interest is when runaway electrons form among the presence of high-atomic-number ion species in a tokamak plasma discharge. It has been recently demonstrated that ion charge state distributions and radiation losses at low bulk electron temperatures can be dominated by relativistic electrons, even though their density is orders of magnitude lower. Furthermore, this was attributed to the relativistic enhancement of electron impact inelastic cross sections. In this work, we provide a closer inspection of the atomic physics underpinning this effect. We also demonstrate the consequences of runaway enhanced scattering on post-disruption tokamak fusion discharges with neon and argon impurities present. Effects on charge state distributions, radiation and spectral characteristics, and reduced-order modeling considerations are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1996

[MODIS Investigation]

Our first activity is based on delivery of code to Bob Evans (University of Miami) for integration and eventual delivery to the MODIS Science Data Support Team. As we noted in our previous semi-annual report, coding required the development and analysis of an end-to-end model of fluorescence line height (FLH) errors and sensitivity. This model is described in a paper in press in Remote Sensing of the Environment. Once the code was delivered to Miami, we continue to use this error analysis to evaluate proposed changes in MODIS sensor specifications and performance. Simply evaluating such changes on a band by band basis may obscure the true impacts of changes in sensor performance that are manifested in the complete algorithm. This is especially true with FLH that is sensitive to band placement and width. The error model will be used by Howard Gordon (Miami) to evaluate the effects of absorbing aerosols on the FLH algorithm performance. Presently, FLH relies only on simple corrections for atmospheric effects (viewing geometry, Rayleigh scattering) without correcting for aerosols. Our analysis suggests that aerosols should have a small impact relative to changes in the quantum yield of fluorescence in phytoplankton. However, the effect of absorbing aerosol is a new process and will be evaluated by Gordon.

Abbott, Mark R.↗
NASA NTRS1984

Lunar origin: role of giant impacts

The explanation that lunar origin involved giant impacts remains attractive. Large planetesimals are consistent with current accretion models, and may have been widely scattered in the early solar system; their existence is a reasonable, assumption in Moon origin models. Isotopic data require the Moon's formation primarily from local material resembling Earth's upper mantle, not material from elsewhere in the solar system. Giant impacts are stochastic, class predictable events that would provide the required type of ejected Earth mantle material without requiring large moons to form near other planets (a problem with less stochastic processes). Such material may have mixed with incoming meteorites during lunar formation, affecting lunar chemistry.

Hartmann, W. K.↗
NASA NTRS1985

Lunar Origin: Role of Giant Impacts

The explanation that lunar origin involved giant impacts remains attractive. Large planetesimals are consistent with current accretion models, and may have been widely scattered in the early solar systems; their existence is a reasonably, assumption in Moon origin models. Isotopic data require the Moon's formation primarily from local material resembling Earth's upper mantle, not material from elsewhere in the solar system. Giant impacts are stochastic, class predictable events that would provide the required type of ejected Earth mantle material without requiring large moons to form near other planets (a problem with less stochastic processes). Such material may have mixed with incoming meteorites during lunar formation, affecting lunar chemistry.

Hartmann, W. K.↗
DOE OSTI2020

Final Technical Report for DE-FG02-86ER45268

This work addresses several key issues for understanding the unusual superconductivity in IBS, already shown to be technologically useful materials. 1a). Are reactive gasses like fluorine, chlorine, or water vapor behaving simply as electron donors to cause the superconductivity (at T conset =21 K) in undoped IBS like BaFe 2 As 2 ? 1b). Does exposure to fluorine increase T c in electron-doped IBS materials that are underdoped, e. g. Ba(Fe 0.96 Co 0.04 ) 2 As 2 ? 1c). Can fluorine as a reactive electron-donor, with its relatively greater ease of introduction into the lattice, be used as a rapid tool to search for superconductivity in new materials under investigation? Method of investigation: Using electron probe microanalysis, x-ray photoemission spectroscopy, and dynamical mean field theory calculations, we found that fluorine substitutes for As in the BaFe 2 As 2 lattice, and should therefore behave as an electron donor. We will F-dope Ba(Fe 0.96 Co 0.04 ) 2 As 2 and several new compounds under investigation for superconductivity upon doping to determine fluorine’s effect. Potential impact: If – like for fluorine - a brief exposure to hydrogen indeed causes superconductivity to a depth of 10 microns, this technique could be useful in creating long lengths of superconducting tape without the chemical aggressiveness of fluorine. Using the F ion, which substitutes for As - away from the Fe planes, in underdoped IBS like Ba(Fe 0.96 Co 0.04 ) 2 As 2 may form optimally doped IBS with less impurity scattering of the superconducting Fe 3d electrons resulting in improved superconducting properties. Another potential impact is the speed of checking for superconductivity in new materials under investigation for superconductivity upon doping. 2. What are the effects of Be substitution into IBS, beginning with FeSe and its derivatives (FeSe 1-x S x and FeSe 1-x Te x ) and BaFe 2-x Co x As 2 ? Method of investigation: We recently succeeded in adding Be to the FeSe lattice and found, surprisingly, a factor of four improvement of the low temperature residual resistivity ratio, consistent with improved electronic ordering. Using single crystal x-ray diffraction and x-ray dispersive spectroscopy, determine the concentration and location of the Be dopant. Using resistivity, determine if there is improvement in the residual resistivity achieved by Be doping in the FeSe derivatives (using AlCl 3 :KCl flux growth) and Co-doped BaFe 2 As 2 (using self-flux single crystal growth). Measuring resistivity under strain, determine the changes of the nematic susceptibility at the structural ordering transition causes by the increase in electronic order caused by Be doping in FeSe. Potential impact: Further understanding of IBS, including FeSe which - under physical pressure - has a T c increase to 40 K and -prepared as a monolayer - has a T c reported to be over 100 K. 3. In collaboration, prepare light atom compounds involving Be and look for high pressure-induced superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

A global study of hygroscopicity-driven light-scattering enhancement in the context of other in situ aerosol optical properties

The scattering and backscattering enhancement factors (ƒ(RH) and ƒ b (RH)) describe how aerosol particle light scattering and backscattering, respectively, change with relative humidity (RH). They are important parameters in estimating direct aerosol radiative forcing (DARF). In this study we use the dataset presented in Burgos et al. (2019) that compiles ƒ(RH) and ƒ b (RH) measurements at three wavelengths (i.e., 450, 550 and 700 nm) performed with tandem nephelometer systems at multiple sites around the world. We present an overview of ƒ(RH) and ƒ b (RH) based on both long-term and campaign observations from 23 sites representing a range of aerosol types. The scattering enhancement shows a strong variability from site to site, with no clear pattern with respect to the total scattering coefficient. In general, higher ƒ(RH) is observed at Arctic and marine sites, while lower values are found at urban and desert sites, although a consistent pattern as a function of site type is not observed. The backscattering enhancement ƒ b (RH) is consistently lower than ƒ(RH) at all sites, with the difference between ƒ(RH) and ƒ b (RH) increasing for aerosol with higher ƒ(RH). This is consistent with Mie theory, which predicts higher enhancement of the light scattering in the forward than in the backward direction as the particle takes up water. Our results show that the scattering enhancement is higher for PM 1 than PM 10 at most sites, which is also supported by theory due to the change in scattering efficiency with the size parameter that relates particle size and the wavelength of incident light. At marine-influenced sites this difference is enhanced when coarse particles (likely sea salt) predominate. For most sites, ƒ(RH) is observed to increase with increasing wavelength, except at sites with a known dust influence where the spectral dependence of ƒ(RH) is found to be low or even exhibit the opposite pattern. The impact of RH on aerosol properties used to calculate radiative forcing (e.g., single-scattering albedo, ω 0 , and backscattered fraction, b) is evaluated. The single-scattering albedo generally increases with RH, while b decreases. The net effect of aerosol hygroscopicity on radiative forcing efficiency (RFE) is an increase in the absolute forcing effect (negative sign) by a factor of up to 4 at RH = 90 % compared to dry conditions (RH < 40 %). Because of the scarcity of scattering enhancement measurements, an attempt was made to use other more commonly available aerosol parameters (i.e., ω 0 and scattering Ångström exponent, α sp ) to parameterize ƒ(RH). The majority of sites (75 %) showed a consistent trend with ω 0 (higher ƒ(RH = 85 %) for higher ω 0 ), while no clear pattern was observed between ƒ(RH = 85 %) and αsp. This suggests that aerosol ω 0 is more promising than α sp as a surrogate for the scattering enhancement factor, although neither parameter is ideal. Nonetheless, the qualitative relationship observed between ω 0 and ƒ(RH) could serve as a constraint on global model simulations.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Plasma dynamics, instabilities and OH generation in a pulsed atmospheric pressure plasma with liquid cathode: a diagnostic study

Abstract While plasma–liquid interactions have been an important focus in the plasma research community, the impact of the strong coupling between plasma and liquid on plasma properties and processes remains not fully understood. In this work, we report on the impact of the applied voltage, pulse width and liquid conductivity on the plasma morphology and the OH generation for a positive pulsed DC atmospheric pressure plasma jet with He–0.1% H 2 O mixture interacting with a liquid cathode. We adopted diagnostic techniques of fast imaging, 2D laser induced fluorescence of OH and Thomson scattering spectroscopy. We show that plasma instabilities and enhanced evaporation occur and have a significant impact on the OH generation. At elevated plasma energies, it is found that the plasma contracts due to a thermal instability through Ohmic heating and the contraction coincides with a depletion in the OH density in the core due to electron impact dissociation. For lower plasma energies, the instability is suppressed/delayed by the equivalent series resistor of the liquid electrode. An estimation of the energy flux from the plasma to the liquid shows that the energy flux of the ions released into the liquid by positive ion hydration is dominant, and significantly larger than the energy needed to evaporate sufficient amount of water to account for the measured H 2 O concentration increase near the plasma–liquid interface.

Physics↗
DOE OSTI2025

Self-Consistent Relativistic Electron Scattering using the Sherlock Scattering Model for X-ray Diagnostics

We present on a new, self-consistent, arbitrary-temperature Romberg integration scheme for modeling electron scattering in materials in a LANL Lagrangian Shock Hydro (LSH) code. Electron beam-target interactions are fundamental to a wide range of scientific and technological applications. When high-energy electron beams hit their target, they may scatter, deposit energy, or ionize the source. These processes govern the behavior and outcomes in nanotechnology manufacturing, electron microscopy, and modern X-ray diagnostics. Simulating these interactions is essential for interpreting experimental results, predicting material responses, and designing efficient tools and experiments. At Los Alamos, this is done using a LSH code, which is a multi-dimension, multi-material, massively parallel, multi-physics code used to simulate applications from asteroid impacts to electron beam interactions. By effectively and efficiently modeling the way that electrons scatter from the beam we can bolster these simulations and more accurately predict experimental outcomes. The model currently implemented in the LSH of interest is based on work by Papp and does not self-consistently preserve momentum in the slightly relativistic regime; here we adopt a model proposed by Braams and Karney and implement a Romberg integration scheme to compute the diffusion tensor. In this paper we will provide background on the Braams-Karney diffusion tensor as well as the Romberg integration scheme we employed to numerically solve for it. We will show that our integration scheme is accurate in solving for the set of scalar potentials used to re-express the diffusion tensor in differential form, and in solving for the diffusion coefficients in the larger LSH code. By using this diffusion tensor rather than the existing Papp one, and numerically integrating it with a Romberg method, we produce much more accurate, self-consistent results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2019

Modeling Atmosphere-Ocean Radiative Transfer: A PACE Mission Perspective

The research frontiers of radiative transfer (RT) in coupled atmosphere-ocean systems are explored to enable new science and specifically to support the upcoming Plankton, Aerosol, Cloud ocean Ecosystem (PACE) satellite mission. Given (i) the multitude of atmospheric and oceanic constituents at any given moment that each exhibits a large variety of physical and chemical properties and (ii) the diversity of light-matter interactions (scattering, absorption, and emission), tackling all outstanding RT aspects related to interpreting and/or simulating light reflected by atmosphere-ocean systems becomes impossible. Instead, we focus on both theoretical and experimental studies of RT topics important to the science threshold and goal questions of the PACE mission and the measurement capabilities of its instruments. We differentiate between (a) forward (FWD) RT studies that focus mainly on sensitivity to influencing variables and/or simulating data sets, and (b) inverse (INV) RT studies that also involve the retrieval of atmosphere and ocean parameters. Our topics cover (1) the ocean (i.e., water body): absorption and elastic/inelastic scattering by pure water (FWD RT) and models for scattering and absorption by particulates (FWD RT and INV RT); (2) the air-water interface: variations in ocean surface refractive index (INV RT) and in whitecap reflectance (INV RT); (3) the atmosphere: polarimetric and/or hyperspectral remote sensing of aerosols (INV RT) and of gases (FWD RT); and (4) atmosphere-ocean systems: benchmark comparisons, impact of the Earth's sphericity and adjacency effects on space-borne observations, and scattering in the ultraviolet regime (FWD RT). We provide for each topic a summary of past relevant (heritage) work, followed by a discussion (for unresolved questions) and RT updates.

Chowdhary, Jacek↗
DOE OSTI2023

Light-Induced Structural Dynamics and Charge Transport in Layered Halide Perovskite Thin Films

The dynamic nature of the metal halide perovskite lattice upon photoexcitation plays a vital role in their properties. Here we report an observation of light-induced structure dynamics in quasi-2D Ruddlesden–Popper phase perovskite thin films and its impact on the carrier transport properties. By a time-resolved X-ray scattering technique, we observe a rapid lattice expansion upon photoexcitation, followed by a slow relaxation over the course of 100 ns in the dark. Theoretical modeling suggests that the expansion originates from the lattice’s thermal fluctuations caused by photon energy deposition. Power dependent optical spectroscopy and photoconductivity indicate that high laser powers triggered a strong local structural disorder, which increased the charge dissociation activation energy that results in localized transport. Finally, our study investigates the impact of laser energy deposition on the lattices and the subsequent carrier transport properties, that are relevant to device operations.

2D perovskites↗
NASA NTRS1989

Principles and procedures for determining absolute differential electron-molecule (atom) scattering cross sections

Procedures and calibration techniques for measuring the absolute elastic and inelastic differential cross sections (DCS) for electron impact on molecular (atomic) species are described and illustrated by examples. The elastic DCS for the molecule under study is first determined by calibration against helium using the relative flow technique. The second step involves the production of energy-loss spectra for the instrument response function, the unfolding of overlapping inelastic structures and the normalization of inelastic intensities to the elastic cross sections. It is concluded that this method of determining absolute differential electron-molecule (atom) scattering cross sections is generally applicable and provides reliable results.

Nickel, J. C.↗