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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2008

Electron Impact Ionization: A New Parameterization for 100 eV to 1 MeV Electrons

Low, medium and high energy electrons can penetrate to the thermosphere (90-400 km; 55-240 miles) and mesosphere (50-90 km; 30-55 miles). These precipitating electrons ionize that region of the atmosphere, creating positively charged atoms and molecules and knocking off other negatively charged electrons. The precipitating electrons also create nitrogen-containing compounds along with other constituents. Since the electron precipitation amounts change within minutes, it is necessary to have a rapid method of computing the ionization and production of nitrogen-containing compounds for inclusion in computationally-demanding global models. A new methodology has been developed, which has parameterized a more detailed model computation of the ionizing impact of precipitating electrons over the very large range of 100 eV up to 1,000,000 eV. This new parameterization method is more accurate than a previous parameterization scheme, when compared with the more detailed model computation. Global models at the National Center for Atmospheric Research will use this new parameterization method in the near future.

Fang, Xiaohua↗
NASA NTRS2023

Direct Observation of Electron Temperature Anisotropy Localized to One Separatrix during Electron-Only Magnetic Reconnection in a Laboratory Plasma

Anisotropic electron heating, Te∥/Te⊥ > 1 (relative to the local magnetic field) during electron-only magnetic reconnection with a large guide field is directly measured in a laboratory plasma through multi-dimensional incoherent Thomson scattering measurements of the electron velocity distribution function. The preferentially parallel electron heating is localized to one separatrix in the reconnection plane and anisotropies of 1.5 are observed. The localization of the heating to one separatrix and the anisotropy are reproduced with a 2D particle-in-cell simulation. The characteristics of the anisotropic heating are consistent with predictions for electron energization by the parallel reconnection electric field under strong guide field. The effective electron temperature is found to increase throughout the outflow region, a possible indication of the effects of collisions and the fully 3D nature of magnetic reconnection in the experiment.

Peiyun Shi↗
NASA NTRS2024

Comparative Observations of the Outer Belt Electron Fluxes and Precipitated Relativistic Electrons

Relativistic electron precipitation (REP) refers to the release of high‐energy electrons initially trapped in the outer radiation belt, which then precipitate into Earth's upper atmosphere, contributing significantly to the rapid depletion of radiation belt electron flux. This study presents a statistical analysis of REP observations collected by the Calorimetric Electron Telescope (CALET) experiment aboard the International Space Station from 2015 to the present day. Specifically, the analysis utilizes count rates acquired from the two top scintillators constituting the top charge detector, each sensitive to electrons with energies above 1.5 and 3.4 MeV, respectively. Analysis of CALET data reveals a previously unreported semi‐annual variation in the occurrence of REP events. REP periodicities resemble those observed for trapped electron fluxes in the outer belt. Furthermore, their amplitude follows the overall trend of solar wind high‐speed streams and the solar activity.

Sergio E. Vidal-Luengo↗
DOE OSTI2025

Differential Ligation Alters Electronic State and Coupling Signals of Iron-Sulfur Clusters in Flavin-Based Electron Bifurcation

Flavin-based electron bifurcation (FBEB) is employed by microorganisms for controlling pools of redox equivalents by reversibly splitting electron pairs into high- and low-energy levels from an initial midpoint potential. Our ability to harness this phenomenon is crucial for biocatalytic design which is limited by our understanding of energy coupling in the bifurcation system. In Pyrococcus furiosus, FBEB is carried out by the NADH-dependent ferredoxin:NADP+-oxidoreductase (NfnSL), coupling the uphill reduction of ferredoxin in NfnL to the downhill reduction of NAD+ in NfnS from oxidation of NADPH. Flanking the bifurcating flavin are two site-differentiated iron-sulfur clusters; the nearest is a glutamate-ligated [4Fe-4S] cluster in NfnL. Recent biochemical experiments substituting the native glutamate with cysteine led to loss of coupling between the uphill and downhill pathways, in contrast to the tight thermodynamic coupling in the native system. To understand how this decoupling is biochemically manifested by the cysteine-substituted [4Fe-4S] in NfnL, we employed electron paramagnetic resonance (EPR) spectroscopy to identify changes in electronic architecture and square wave voltammetry (SWV) to probe thermodynamic shifts produced by the substitution. We observed notable g-value shifts in the EPR for the cysteine-substituted iron-sulfur cluster in addition to significant downward shifts in the redox potential, as well as the disappearance of several low-field signals observed in the native NfnSL complex. These results suggest the site-differentiated glutamate residue facilitates higher spin states in the [4Fesingle bond4S] cluster to bridge energetic gaps in electron transfer to the bifurcating flavin in the native complex, preventing unwanted short-circuiting seen in the cysteine-substituted complex.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2022

A 2D Kaleidoscope of Electron Heat Fluxes Driven by Auroral Electron Precipitation

Electron heat flux is an important value for ionospheric space weather modeling networks. Utilizing the 2D array of Time History of Events and Macroscale Interactions during Substorms all-sky-imager (ASI) observations, Gabrielse et al. (2021, https://doi.org/10.3389/fphy.2021.744298) described a new method that estimates the auroral scale sizes of intense precipitating electron energy fluxes and their mean energies during two substorms on 16 February 2010. These parameters in combination with SuperThermal Electron Transport code were used to develop a new methodology to calculate electron thermal fluxes from data inputs in 2D during one of the substorms at 09:40:00 UT across Canada and Alaska. To test the effect of various precipitation lifetimes on electron heat flux values, boxcar averages ranging from 0 to 900 s were applied to the ASI data. These data are then combined with the newly developed kinetic simulation to determine the thermal fluxes associated with the observed diffuse and discrete precipitation.

Electron precipitation in aurora↗
DOE OSTI2025

Valence Electron Distributions from Sub-Angstrom Convergent Beam Electron Diffraction

Modern aberration-corrected scanning transmission electron microscopes can acquire four-dimensional data sets (“4D STEM”) by recording convergent beam electron diffraction (CBED) patterns, using precisely positioned, sub-angstrom probes. Here, we demonstrate that these patterns can probe the site symmetry, atomic displacements, and valence electron distributions at individual atomic columns. To this end, 4D STEM CBED patterns were acquired from SrTiO 3 single crystals and compared with patterns calculated using scattering potentials derived from density functional theory. Here, we show that an aspherical valence electron charge build-up at the oxygen sites causes intensity asymmetries in the low-angle scattering portion of the patterns. Using strained SrTiO 3 films containing subtle polar displacements within nanometer-sized domains, it is shown that the high-angle scattering portion in each pattern is sensitive to atomic displacements.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Kinetics for the reaction between the solvated electron and dissolved oxygen in n-dodecane from 2.5 to 40 °C

Temperature-controlled, time-resolved picosecond electron pulse radiolysis was utilized to measure the rate of reaction between the solvated electron (eS–) and dissolved oxygen in n-dodecane solutions from 2.5 to 40 °C for the first time. At 20.0 °C, the reaction rate was determined to be k(eS– + O2) = (4.54 ± 0.21) × 1010 M-1 s-1, with an activation energy of Ea = 14.4 ± 1.3 kJ mol-1. These newly determined kinetic parameters are important for predicting and managing the effects of aerated environments on the degradation of organic solvents used in nuclear fuel reprocessing technologies.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2024

Proton-Coupled Electron Transfer Mechanisms for CO 2 Reduction to Methanol Catalyzed by Surface-Immobilized Cobalt Phthalocyanine

Immobilized cobalt phthalocyanine (CoPc) is a highly promising architecture for the six-proton, six-electron reduction of CO 2 to methanol. This electroreduction process relies on proton-coupled electron transfer (PCET) reactions that can occur by sequential or concerted mechanisms. Immobilization on a conductive support such as carbon nanotubes or graphitic flakes can fundamentally alter the PCET mechanisms. We use density functional theory (DFT) calculations of CoPc adsorbed on an explicit graphitic surface model to investigate intermediates in the electroreduction of CO 2 to methanol. Our calculations show that the alignment of the CoPc and graphitic electronic states influences the reductive chemistry. These calculations also distinguish between charging the graphitic surface and reducing the CoPc and adsorbed intermediates as electrons are added to the system. This analysis allows us to identify the chemical transformations that are likely to be concerted PCET, defined for these systems as the mechanism in which protonation of a CO 2 reduction intermediate is accompanied by electron abstraction from the graphitic surface to the adsorbate without thermodynamically stable intermediates. Furthermore, this work establishes a mechanistic pathway for methanol production that is consistent with experimental observations and provides fundamental insight into how immobilization of the CoPc impacts its CO 2 reduction chemistry.

Adsorption↗
DOE OSTI2025

Sensing Few Electrons Floating on Helium with High-Electron-Mobility Transistors

We report on low-frequency measurements of few electrons floating on superfluid helium using a bespoke cryogenic cascode amplifier circuit built with off-the-shelf GaAs high-electron-mobility transistors (HEMTs). We integrate this circuit with a charge-coupled device (CCD) to transport the electrons on helium and characterize its performance. Here, we show that this circuit has a signal-to-noise ratio (SNR) of ~ 2 $\frac{e}{√Hz}$ at 102 kHz, an order of magnitude improvement from previous implementations, and provides a compelling alternative to few electron sensing with high-frequency resonators.

Charge-Coupled Devices↗
DOE OSTI2024

Exploring electron-beam induced modifications of materials with machine-learning assisted high temporal resolution electron microscopy

Directed atomic fabrication using an aberration-corrected scanning transmission electron microscope (STEM) opens new pathways for atomic engineering of functional materials. In this approach, the electron beam is used to actively alter the atomic structure through electron beam induced irradiation processes. One of the impediments that has limited widespread use thus far has been the ability to understand the fundamental mechanisms of atomic transformation pathways at high spatiotemporal resolution. Here, we develop a workflow for obtaining and analyzing high-speed spiral scan STEM data, up to 100 fps, to track the atomic fabrication process during nanopore milling in monolayer MoS 2 . An automated feedback-controlled electron beam positioning system combined with deep convolution neural network (DCNN) was used to decipher fast but low signal-to-noise datasets and classify time-resolved atom positions and nature of their evolving atomic defect configurations. Through this automated decoding, the initial atomic disordering and reordering processes leading to nanopore formation was able to be studied across various timescales. Using these experimental workflows a greater degree of speed and information can be extracted from small datasets without compromising spatial resolution. This approach can be adapted to other 2D materials systems to gain further insights into the defect formation necessary to inform future automated fabrication techniques utilizing the STEM electron beam.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A new synthetic correlation electron cyclotron emission diagnostic for validating nonlinear gyrokinetic simulations of electron temperature turbulence

To validate nonlinear gyrokinetic simulations of electron temperature turbulence, the experimental correlation electron cyclotron emission (CECE) measurements are to be compared using a synthetic CECE diagnostic, which generates modeled CECE measurement quantities by implementing realistic measurement parameters (e.g., spatial and wavenumber resolutions, radial location, etc.) to nonlinear gyrokinetic simulations. In this work, we calculate the radial and vertical spatial and wavenumber transfer functions, which are defined by the electron cyclotron emission emissivity radial profile and vertical probing antenna pattern, respectively. These transfer functions are applied to nonlinear gyrokinetic simulations of electron temperature turbulence using the continuum gyrokinetic code. A simultaneous comparison of the experimental electron temperature turbulence power spectrum and root-mean-square (RMS) level, as well as the radial correlation length with the new synthetic CECE diagnostic at a core location ρ ∼ 0.75 in an L-mode DIII-D tokamak plasma, is presented. Here, the preliminary result shows that the synthetic CECE output underestimates the RMS level by ∼42% and overestimates the radial correlation length by ∼40%.

Cyclotron radiation↗
DOE OSTI2025

Towards Mitigating Electron Beam-Induced Damage in MOFs Using Low Dose Electron Microscopy for In-Situ Room-Temperature Measurements

Metal-Organic Frameworks (MOFs) have emerged as a versatile class of materials with applications in gas storage and separation, catalysis, and drug delivery [1]. Understanding their damage mechanisms in under various environmental conditions is crucial for optimizing performance and stability [2]. This study employs a combination of Length Structural Coherence (LSC) analysis in electron scattering and Electron Energy Loss Spectroscopy (EELS) to elucidate the damage mechanisms in two representative MOFs. MIL101(Fe), and MIL101(Cr). Here, the primary objective is to reveal structural and chemical changes that occur under electron beam irradiation in Scanning Transmission Electron Microscopy (STEM), both in the pristine state and during in-situ CO and CO 2 adsorption. By combining LSC in Radial Distribution Function (RDF) analysis with EELS, comprehensive insights into the nanoscale alterations are obtained and correlated to the electron dose rate.

dos Santos, Gabriel T. [Northwestern University, E↗
NASA NTRS1971

Impurity color centers in quartz and trapped electron dating - Electron spin resonance, thermoluminescence studies.

Investigation of impurity-related electron-hole traps that are known to be sensitive to ionizing radiations. Electron spin resonance (ESR) equivalent natural doses were determined for the Al hole trap in virgin specimens; the doses agreed with estimates based on published data for the Ge electron trap. The 0.17 deg/sec 180 and 300 C thermoluminescence (TL) peaks in natural specimens were found to have activation energies approximately correct for the Ge trap. The 300 C peak was also found to be correlated with annealing of the Ge electron resonance in gamma-irradiated, step-annealed specimens. Although the 300 C peak occurs in virgin specimens, the corresponding natural Ge electron resonance was not observed.

Mcmorris, D. W.↗
NASA NTRS1972

Measurements of electron-bremsstrahlung coincidence rates at intermediate electron energies

Coincidence rates have been measured for inelastically scattered electrons and their associated bremsstrahlung for bombarding energies of 0.20 and 0.15 MeV. Measurements were made for an electron angle of 45 deg and a photon angle of 20 deg. Inelastic electron energies of 0.15 and 0.16 MeV were considered for an incident energy of 0.2 MeV and an inelastic electron energy of 0.12 MeV was considered for an incident energy of 0.15 MeV. To observe the trend with atomic number, Al and Au targets were used. The experimental cross section differentials in photon and electron angles and energy were found to be smaller than the predictions of the Bethe-Heitler theory.

Rester, D. H.↗
NASA NTRS1974

Electron-impact excitation of the low-lying electronic states of formaldehyde

Electron-impact excitation has been observed at incident electron energies of 10.1 and 20.1 eV to the first five excited electronic states of formaldehyde lying at and below the 1B2 state at 7.10 eV. These excitations include two new transitions in the energy-loss range 5.6-6.2 eV and 6.7-7.0 eV which have been detected for the first time, either through electron-impact excitation or photon absorption. The differential cross sections of these new excitations are given at scattering angles between 15 and 135 deg. These cross-section ratios peak at large scattering angles - a characteristic of triplet - singlet excitations. The design and performance of the electron-impact spectrometer used in the above observations is outlined and discussed.

Chutjian, A.↗
NASA NTRS1983

Evolution of electron and proton temperatures in a flaring loop. I - A case of thermal heating of electrons

A temperature difference between electrons and protons produced in a flaring loop was investigated experimentally by adopting a one-fluid, two-temperature model instead of a single-temperature model. Consideration was given to the case in which flare energy is released in the form of heating of electrons located in the top part of the loop. In this case, a large temperature difference appears in the corona in the energy-input phase of the flare. When the material evaporated from the chromosphere fills the corona, the temperature difference in the loop begins to shrink rapidly from below. Eventually, in the loop apex, the proton temperature exceeds the electron temperature mainly due to cooling of the electrons by conduction down the loop and heating of the protons by compression of the ascending material. In the late phase of the flare (about 15 min from the flare onset), the temperature difference becomes less than 2 pct of the mean temperature of electrons and protons at every point in the loop.

Nagai, F.↗
NASA NTRS1985

The downshift of electron plasma oscillations in the electron foreshock region

Electron plasma oscillations in the earth's electron foreshock region are observed to shift above and below the local electron plasma frequency. As plasma oscillations shift downward from the plasma frequency, their bandwidth increases and their wavelength decreases. Observations of plasma oscillations well below the plasma frequency are correlated with times when ISEE 1 is far downstream of the electron foreshock boundary. Although wavelengths of plasma oscillations below the plasma frequency satisfy k x lambda-De approximately 1 the Doppler shift due to the motion of the solar wind is not sufficient to produce the observed frequency shifts. A beam-plasma interaction with beam velocities on the order of the electron thermal velocity is suggested as an explanation for plasma oscillations above and below the plasma frequency. Frequency, bandwidth, and wavelength changes predicted from the beam-plasma interaction are in good agreement with the observed characteristics of plasma oscillations in the foreshock region.

Fuselier, S. A.↗
NASA NTRS1985

s-wave threshold in electron attachment - Observations and cross sections in CCl4 and SF6 at ultralow electron energies

The threshold photoionization method was used to study low-energy electron attachment phenomena in and cross sections of CCl4 and SF6 compounds, which have applications in the design of gaseous dielectrics and diffuse discharge opening switches. Measurements were made at electron energies from below threshold to 140 meV at resolutions of 6 and 8 meV. A narrow resolution-limited structure was observed in electron attachment to CCl4 and SF6 at electron energies below 10 meV, which is attributed to the divergence of the attachment cross section in the limit epsilon, l approaches zero. The results are compared with experimental collisional-ionization results, electron-swarm unfolded cross sections, and earlier threshold photoionization data.

Chutjian, A.↗