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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Local site behavior of the 5$d$ and 4$f$ ions in the frustrated pyrochlore Ho 2 Os 2 O 7

The pyrochlore osmate Ho 2 Os 2 O 7 is a candidate material for a fragile J=0 local singlet ground state, however little is known regarding the single-ion behavior of either the Os or Ho ions. To address this we present polarized neutron powder diffraction (PNPD) and resonant inelastic x-ray scattering (RIXS) measurements that separately probe the local site behavior of the Os and Ho ions. The PNPD results are dominated by Ho 3+ scattering and the analysis reveals local site susceptibility behavior consistent with spin ice materials. Complimentary unpolarized neutron powder diffraction show an ordered spin ice ground state in an applied magnetic field. To isolate the Os 4+ single-ion behavior we present resonant inelastic x-ray scattering (RIXS) measurements at the osmium L-edge. Analysis of the RIXS spectra parameterize the spin-orbit coupling (0.35 eV), Hund’s coupling (0.27 eV) and trigonal distortion (-0.17 eV). Here, the results are considered within the context of a J=0 model and possible departures from this through structural distortions, excitonic interactions and 5d-4f interactions between the Os ion and the surrounding Ho lattice. The experimental methodology employed highlights the complimentary information available in rare earth based 5d pyrochlores from distinct neutron and x-ray scattering techniques that allow for the isolation and determination of the behavior of the different ions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Mirror dark sector solution of the Hubble tension with time-varying fine-structure constant

Here we explore a model introduced by Cyr-Racine et al. that resolves the Hubble tension by invoking a “mirror world” dark sector with energy density a fixed fraction of the “ordinary” sector of Λ+ cold dark matter. Although it reconciles cosmic microwave background and large-scale structure observations with local measurements of the Hubble constant, H 0 , the model requires a value of the primordial helium mass fraction, Y p = 0.170 ± 0.025, that is discrepant with observations and with the predictions of big bang nucleosynthesis. We consider a variant of the model with standard helium mass fraction but with the value of the electromagnetic fine-structure constant, α, slightly different during photon decoupling from its present value. If α at that epoch is lower than its current value by Δα ≃ -2 x 10 -5 , then we can achieve the same Hubble tension resolution as in the work by Cyr-Racine et al. but with consistent helium abundance. As an example of such time evolution of α, we consider a toy model of an ultralight scalar field, with mass m < 4 x 10 -29 eV, coupled to electromagnetism, which evolves after photon decoupling at redshift z ≃ 10 3 , and that with appropriate coupling appears to be consistent with late-time constraints on α variation and the weak equivalence principle.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Signatures of primordial energy injection from axion strings

Axion strings are horizon-size topological defects that may be produced in the early Universe. Ultralight axion-like particles may form strings that persist to temperatures below that of big bang nucleosynthesis. Such strings have been considered previously as sources of gravitational waves and cosmic microwave background (CMB) polarization rotation. In this work we show, through analytic arguments and dedicated adaptive mesh refinement cosmological simulations, that axion strings deposit a subdominant fraction of their energy into high-energy Standard Model (SM) final states, for example, by the direct production of heavy radial modes that subsequently decay to SM particles. This high-energy SM radiation is absorbed by the primordial plasma, leading to novel signatures in precision big bang nucleosynthesis, the CMB power spectrum, and gamma-ray surveys. In particular, we show that CMB power spectrum data constrains axion strings with decay constants f a ≲ 10 12 GeV , up to model dependence on the ultraviolet completion, for axion masses m a ≲ 10 − 29 eV ; future CMB surveys could find striking evidence of axion strings with lower decay constants. Published by the American Physical Society 2024

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1985

A model for the origin of high-energy cosmic rays

It is suggested that cosmic rays, up to the highest energies observed, originate in the Galaxy and are accelerated in astrophysical shock waves. If there is a galactic wind, in analogy with the solar wind, a hierarchy of shocks ranging from supernova shocks to the galactic wind termination shock is expected. This leads to a consistent model in which most cosmic rays, up to perhaps 10 to the 14th eV energy, are accelerated by supernova shocks, but that particles with energies of 10 to the 15th eV and higher are accelerated at the termination shock of the galactic wind. Intermediate energies may be accelerated by intermediate-scale shocks, and there may be larger scale shocks associated with the Local Group of galaxies.

Jokipii, J. R.↗
NASA NTRS1985

On the origin of high-energy cosmic rays

It is suggested that cosmic rays, up to the highest energies observed, originate in the Galaxy and are accelerated in astrophysical shock waves. If there is a galactic wind, in analogy with the solar wind, a hierarchy of shocks ranging from supernova shocks to the galactic wind termination shock is expected. This leads to a consistent model in which most cosmic rays, up to perhaps 10 to the 14th eV energy, are accelerated by supernova shocks, but that particles with energies of 10 to the 15th eV and higher are accelerated at the termination shock of the galactic wind. Intermediate energies may be accerelated by intermediate-scale shocks, and there may be larger scale shocks associated with the Local Group of galaxies.

Jokipii, J. R.↗
NASA NTRS1986

Photoionization in the halo of the Galaxy

The ionizing radiation field in the halo is calculated and found to be dominated in the 13.6-45 eV range by light from O-B stars that escapes the disk, by planetary nebulae at 45-54 eV, by quasars and the Galactic soft X-ray background at 54-2000 eV, and by the extragalactic X-ray background at higher energies. Photoionization models are calculated with this radiation field incident on halo clouds of constant density for a variety of densities, for normal and depleted abundances, and with variations of the incident spectrum. For species at least triply ionized, such as Si IV, C IV, N V, and O VI, the line ratios are determined by intervening gas with the greatest volume, which is not necessarily the greatest mass component. Column densities from doubly ionized species like Si III should be greater than from triply ionized species. The role of photoionized gas in cosmic ray-supported halos and Galactic fountains is discussed. Observational tests of photoionization models are suggested.

Bregman, Joel N.↗
NASA NTRS1997

Towards Inner Magnetosphere Particle and Field Models

We report on the initial stages of an effort to construct comprehensive empirical models of the plasma and fields in the inner magnetosphere. The models are based not only on archival data (e.g., SCATHA) but also on current spacecraft mission data (e.g., POLAR). In this component of the effort, we incorporate the recently archived data provided by the SCATRA (Spacecraft Charging AT High Altitude) satellite. The SCAT14A satellite was in a near-geostationary orbit and was in operation for more than a decade. In this paper, we focus on the SCATRA plasma and magnetic field data from approximately the first two years of operation. The time-series data are binned according to spatial location and geomagnetic activity. Examples of statistical, empirical models from this initial effort are presented; even the simply-constructed preliminary models reveal such subtle features as the previously reported warm (greater than 100 eV) plasma density enhancement near the magnetic equator.

Spence, H. E.↗
DOE OSTI2025

Dual-Baseline Search for Active-to-Sterile Neutrino Oscillations in NOvA

We report a search for neutrino oscillations to sterile neutrinos under a model with three active and one sterile neutrinos (3+1 model). This analysis uses the NOvA detectors exposed to the NuMI beam, running in neutrino mode. The data exposure, 13.6 × 10 20 protons on target, doubles that previously analyzed by NOvA, and the analysis is the first to use 𝜈 𝜇 charged-current interactions in conjunction with neutral-current interactions. Neutrino samples in the near and far detectors are fitted simultaneously, enabling the search to be carried out over a Δ⁢𝑚$^{2}_{41}$ range extending 2 (3) orders of magnitude above (below) 1 eV 2 . NOvA finds no evidence for active-to-sterile neutrino oscillations under the 3+1 model at 90% confidence level. New limits are reported in multiple regions of parameter space, excluding some regions currently allowed by IceCube at 90% confidence level. We additionally set the most stringent limits for anomalous 𝜈 𝜏 appearance for Δ⁢𝑚$^{2}_{41}$ ≤ 3 eV 2 .

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1985

Monte Carlo simulation of EAS generated by 10(14) - 10(16) eV protons

Detailed Monte Carlo simulations of extensive air showers to be detected by the Homestake Surface Underground Telescope and other similar detectors located at sea level and mountain altitudes have been performed for 10 to the 14th power to 10 to the 16th power eV primary energies. The results of these Monte Carlo calculations will provide an opportunity to compare the experimental data with different models for the composition and spectra of primaries and for the development of air showers. The results obtained for extensive air showers generated by 10 to the 14th power to 10 to the 16th power eV primary protons are reported.

Fenyves, E. J.↗
DOE OSTI2022

Precision measurement of Compton scattering in silicon with a skipper CCD for dark matter detection

Experiments aiming to directly detect dark matter through particle recoils can achieve energy thresholds of $\mathcal{O}(1\,\mathrm{eV})$. In this regime, ionization signals from small-angle Compton scatters of environmental $\gamma$-rays constitute a significant background. Monte Carlo simulations used to build background models have not been experimentally validated at these low energies. We report a precision measurement of Compton scattering on silicon atomic shell electrons down to 23$\,$eV. A skipper charge-coupled device (CCD) with single-electron resolution, developed for the DAMIC-M experiment, was exposed to a $^{241}$Am $\gamma$-ray source over several months. Features associated with the silicon K, L$_{1}$, and L$_{2,3}$-shells are clearly identified, and scattering on valence electrons is detected for the first time below 100$\,$eV. We find that the relativistic impulse approximation for Compton scattering, which is implemented in Monte Carlo simulations commonly used by direct detection experiments, does not reproduce the measured spectrum below 0.5$\,$keV. The data are in better agreement with $ab$$initio$ calculations originally developed for X-ray absorption spectroscopy.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Catlas: an automated framework for catalyst discovery demonstrated for direct syngas conversion

Catalyst discovery is paramount to support access to energy and key chemical feedstocks in a post fossil fuel era. Exhaustive computational searches of large material design spaces using ab initio methods like density functional theory (DFT) are infeasible. We seek to explore large design spaces at relatively low computational cost by leveraging large, generalized, graph-based machine learning (ML) models, which are pretrained and therefore require no upfront data collection or training. We present Catlas, a framework that distributes and automates the generation of adsorbate-surface configurations and ML inference of DFT energies to achieve this goal. Catlas is open source, making ML assisted catalyst screenings easy and available to all. To demonstrate its efficacy, we use Catlas to explore catalyst candidates for the direct conversion of syngas to multi-carbon oxygenates. For this case study, we explore 947 stable/metastable binary, transition metal intermetallics as possible catalyst candidates. On this subset of materials, we are able to predict the adsorption energy of key descriptors, *CO and *OH, with good accuracy (0.16, 0.14 eV MAE, respectively). Using the projected selectivity towards C 2+ oxygenates from an existing microkinetic model, we identified 144 candidate materials. For 10 promising candidates, DFT calculations reveal a good correlation with our assessment using ML. Finally, among the top elemental combinations were Pt–Ti, Pd–V, Ni–Nb, and Ti–Zn, all of which appear unexplored experimentally.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1978

Electrostatic emissions between electron gyroharmonics in the outer magnetosphere

Electrostatic emissions are often observed by spacecraft in the outer magnetosphere at frequencies between low electron gyroharmonics. The emissions include the well-known odd half-harmonic emissions as well as weaker emissions which occur near the electron plasma frequency. A scheme is constructed for classifying the emissions, and it is shown that a theoretical model which has been previously used to explain '3/2' emissions can be extended to the other classes of emissions. All of the emissions therefore appear to be generated by the same basic mechanism: an unstable electron plasma distribution consisting of cold electrons (below 100 eV) and hot loss cone electrons (about 1 keV). Each emission class is associated with a particular range of model parameters; the wide-band electric field data can thus be used to infer the density and temperature of the cold plasma component. The model predicts that gyroharmonic emissions near the plasma frequency require large cold plasma densities.

Hubbard, R. F.↗
NASA NTRS2018

Solar Wind Implantation Into the Lunar Regolith: Monte Carlo Simulations of H Retention in a Surface With Defects and the H2 Exosphere

The solar wind implants protons into the top 20–30 nm of lunar regolith grains, and the implanted hydrogen will diffuse out of the regolith but also interact with oxygen in the regolith oxides. We apply a statistical approach to estimate the diffusion of hydrogen in the regolith hindered by forming temporary bonds with regolith oxygen atoms. A Monte Carlo simulation was used to track the temporal evolution of bound OH surface content and the H2 exosphere. The model results are consistent with the interpretation of the Chandrayaan-1 M3 observations of infrared absorption spectra by surface hydroxyls as discussed in Li and Milliken (2017). Themodel reproduced the latitudinal concentration of OH by using a Gaussian energy distribution of f(U(o) = 0.5eV, U(w) = 0.078 – 0.1 eV) to characterize the activation energy barrier to the diffusion of hydrogen in space weathered regolith. In addition, the model results of the exospheric content of H2 are consistent with observations by the Lyman Alpha Mapping Project on the Lunar Reconnaissance Orbiter. Therefore, we provide support for hydroxyl formation by chemically trapped solar wind protons.

O. J. Tucker↗
DOE OSTI2021

Dynamic thermal behavior of polycrystalline LaB 6 hollow cathodes

Lanthanum hexaboride (LaB6) hollow cathodes have demonstrated a capability for long life operation, which is critical to many space exploration missions. Thermal characterization of LaB6 hollow cathodes has revealed lower than expected electron emitter temperatures when the cathode reaches a steady state. This phenomenon is observed at discharge currents ranging from 5 to 35 A and xenon mass flow rates of 5–25 SCCM in cathodes with three different orifice diameters. Thus, the currently accepted value of the work function for polycrystalline LaB 6 , 2.67 eV, does not describe well the emission characteristics of LaB6 hollow cathodes operating with internal gas discharges at a steady state. We use empirically measured temperatures combined with a model of the hollow cathode emitter and xenon discharge to estimate the value of the work function, yielding a value ranging from 2.1 to 2.44 eV. This lower work function value implies that LaB6 hollow cathodes are expected to have even longer lifetimes than previously anticipated, further establishing them as a more suited alternative to other conventional cathode technologies for the task of long duration travel. Direct measurements of the work function as a function of depth on a hollow cathode emitter using x-ray photoelectron spectroscopy and ion beam milling indicate that the work function decreases with depth. We postulate several mechanisms that could explain the observed work function enhancement. Altogether, our results have important implications to the design, study approach, and operation of LaB 6 cathodes and potentially other cathodes with hollow configuration. Finally, our work opens the question of why the work function is reduced upon interaction with Xe plasma.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2017

Work function reduction in lanthanum hexaboride hollow cathodes operated in gas discharges

Thermal characterization of lanthanum hexaboride (LaB6) hollow cathodes has revealed lower than expected electron emitter temperatures when the cathode reaches steady state. This phenomenon is observed at discharge currents ranging from 5 to 35 A and xenon mass ow rates of 5 to 25 sccm in cathodes with three di erent ori ce diameters. Thus, the accepted value of the work function for polycrystalline LaB6, 2.66 eV, does not describe well the emission characteristics of LaB6 hollow cathodes operating with internal gas discharges at steady state. The measured temperatures and a model of the hollow cathode emitter and xenon discharge were used to estimate the value of the work function in these experiments, yielding a value ranging from 2.1 - 2.44 eV. Measurements of the work function as a function of depth on a hollow cathode emitter using X-ray photoelectron spectroscopy and ion beam milling indicate that the work function in a thin layer near the emitting surface is lower than in the bulk material. We postulate that a lanthanum-rich emitting surface with a lower work function develops as a result of lanthanum recycling in the internal plasma.

Lopez Ortega, Alejandro↗
DOE OSTI2023

Development of Prototypical District-Scale Models

The U.S. has set the climate goal to achieve net-zero greenhouse gas emissions by 2050. District-scale solutions, which include scale-specific opportunities for energy and emissions savings, can be investigated and implemented to help accelerate decarbonization and progress toward this goal. However, there is currently a lack of district-scale models of buildings and community energy systems that can be used to evaluate potential district-scale technologies and strategies across a range of representative community types. This initial work aims to define and develop prototype district models that can be adapted to support the planning, design, and operation of buildings and energy systems in districts considering the complexity and interactions of diverse building loads, weather impacts, distributed energy resources (e.g., PV, EV, electric and thermal energy storage), electric and thermal grid systems, and pricing signals. An overall workflow for developing these prototype district models is established. Stakeholders and potential users of the prototype district models provided technical feedback. The specifications of the selected high priority districts were defined and documented in a scorecard format. An example prototype district model was implemented with the URBANopt platform workflows. A case study was performed to demonstrate the model application.

building energy modeling↗
DOE OSTI2023

Development of Prototypical District-Scale Models: Preprint

The U.S. has set the climate goal to achieve net-zero greenhouse gas emissions by 2050. District-scale solutions, which include scale-specific opportunities for energy and emissions savings, can be investigated and implemented to help accelerate decarbonization and progress toward this goal. However, there is currently a lack of district-scale models of buildings and community energy systems that can be used to evaluate potential district-scale technologies and strategies across a range of representative community types. This initial work aims to define and develop prototype district models that can be adapted to support the planning, design, and operation of buildings and energy systems in districts considering the complexity and interactions of diverse building loads, weather impacts, distributed energy resources (e.g., PV, EV, electric and thermal energy storage), electric and thermal grid systems, and pricing signals. An overall workflow for developing these prototype district models is established. Stakeholders and potential users of the prototype district models provided technical feedback. The specifications of the selected high priority districts were defined and documented in a scorecard format. An example prototype district model was implemented with the URBANoptTM platform workflows. A case study was performed to demonstrate the model application.

district↗
DOE OSTI2020

Global Electrification of Vehicles and Intertwined Material Supply Chains of Cobalt, Copper and Nickel

Electric vehicles (EVs) will be an important part of a low-carbon economy. Future EV adoption depends on overcoming multiple barriers, including charging infrastructure, sufficient electricity generation, and the availability of battery raw materials at acceptable costs, including cobalt, copper and nickel – which typically are co-produced. Various EV projections have been made, along with associated requirements for battery raw materials (demand). There have been separate assessments of the availability of raw materials (supply). However, integrated assessments of supply and demand and their interaction over time are lacking to support decision-making. Using a dynamic market model that reflects the co-produced nature of cobalt, copper and nickel production as well as recycling, we estimate global output of these three metals under different EV growth scenarios from 2020 to 2040. In this work, results suggest that starting in 2025, replacement demand for battery raw materials becomes important. Thus, estimates for future material demand that consider only demands from new EVs are incomplete and misleading. EV deployment and associated increased demand for raw materials will have a greater impact on prices for cobalt than nickel and, in turn, for nickel than copper. High EV deployment scenarios will be difficult to achieve without larger supplies of copper, nickel and cobalt than forthcoming under the conditions modeled here, which anticipates a six-year time lag between a demand increase and the expansion of metal-production capacity. Shortening battery lifetimes and improving collection and recycling rates increase secondary supply, but the extent to which these factors support additional EV deployment is mixed.

54 ENVIRONMENTAL SCIENCES↗