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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 73 records · Page 4

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NASA NTRS1985

Simulation of the electron acoustic instability in the polar cusp

A computer simulation of the beam-driven electron acoustic instability in the polar cusp is used to investigate the temporal evolution of typical cusp electron distribution functions in self-consistently generated wave fields. The simulation results are compared with linear, second-order, and nonlinear theory. The behavior of the instability over a range of plasma parameters, such as beam speed and the cold electron density, is shown. The saturation mechanism of the instability is examined, and the relevance of the results for observations of cusp hiss are discussed.

Lin, C. S.↗

NASA NTRS1985

Simulation of non-linear bearing forces for post-stability investigation

Different types of bearing designs were developed to improve dynamic properties of rotor-bearing systems. Elliptical bearings, multisleeve bearings, tilting pad and other designs such as herringbone groove were utilized to increase resistance to the onset of self excited vibrations. Experimental trials are costly, two alternative methods are used to gain a qualitative insight. The first one creates mathematical model and applies both a digital or an analog computer simulation. The second one investigates phenomena occurring on the laboratory rig with the bearing replaced by an electronic simulating device, working in a feedback loop, which produces forces,which are functions of journal displacement and velocity. The simulated hydrodynamic forces are produced according to assumed characteristics matched to the bearing type. The principal benefit of the analog simulation is that nonlinear characteristics of a subsystem are precisely identified and mathematical methods applied for a wide class of problems are checked on the experimental installation.

Parszewski, Z. A.↗

NASA NTRS1990

Simulation studies of electron acceleration by ion ring distributions in solar flares

A 2.5-dimensional fully relativistic EM, particle-in-cell code (PIC) is used to investigate a potential electron acceleration mechanism in solar flares. The free energy is provided by ions which have a ring velocity distribution about the magnetic-field direction. Ion rings may be produced by perpendicular shocks, which could in turn be generated by the super-Alfvenic motion of magnetic flux tubes emerging from the photosphere or by coronal mass ejections. Such ion distributions are known to be unstable to the generation of lower hybrid waves, which have phase velocities in excess of the electron thermal speed parallel to the field and can, therefore, resonantly accelerate electrons in that direction. The simulations show the transfer of perpendicular ion energy to energetic electrons via lower hybrid wave turbulence. With plausible ion ring velocities, the process can account for the observationally inferred fluxes and energies of non-thermal electrons during the impulsive phase of flares.

Mcclements, K. G.↗

NASA NTRS1990

Re-forming supercritical quasi-parallel shocks. I - One- and two-dimensional simulations

The process of reforming supercritical quasi-parallel shocks is investigated using one-dimensional and two-dimensional hybrid (particle ion, massless fluid electron) simulations both of shocks and of simpler two-stream interactions. It is found that the supercritical quasi-parallel shock is not steady. Instread of a well-defined shock ramp between upstream and downstream states that remains at a fixed position in the flow, the ramp periodically steepens, broadens, and then reforms upstream of its former position. It is concluded that the wave generation process is localized at the shock ramp and that the reformation process proceeds in the absence of upstream perturbations intersecting the shock.

Thomas, V. A.↗

NASA NTRS2016

Fast Simulation of the NICER Instrument

The NICER mission uses a complicated physical system to collect information from objects that are, by x-ray timing science standards, rather faint. To get the most out of the data we will need a rigorous understanding of all instrumental effects. We are in the process of constructing a very fast, high fidelity simulator that will help us to assess instrument performance, support simulation-based data reduction, and improve our estimates of measurement error. We will combine and extend existing optics, detector, and electronics simulations. We will employ the Compute Unied Device Architecture (CUDA2) to parallelize these calculations. The price of suitable CUDA-compatible multi-gigaflop cores is about $0.20/core, so this approach will be very cost-effective.

gEDA↗

NASA NTRS1995

Structure of the magnetopause inferred from one-dimensional hybrid simulations

The structure of the magnetopause is investigated by studying the interaction between two plasmas with solar wind and magnetospheric properties. Both Hall-MHD and hybrid (particle ions and fluid electrons) simulations are performed to compare and contrast the nature of the solutions in the fluid and the kinetic limits. It is shown that, in accordance with previous studies, the fluid solutions consist of multiple discontinuities and waves such as slow shocks and waves, as well as contact and rotational discontinuities. In contrast, the kinetic solutions consist of fewer discontinuities and include non-MHD boundaries. The difference between the two types of solutions are attributed to the absence of contact surfaces in collisionless plasmas and the possible Landau damping of slow waves. The kinetic solutions are found to be in a much better agreement with magnetopause observations, which have shown little evidence for the presence of slow shocks or contact discontinuities. The results of kinetic calculations suggest that the presence of a small but finite normal component of the magnetic field allows for the mixing of magnetosheath and magnetospheric plasmas and may, in part, be responsible for the formation of the boundary layer even during the periods of northward interplanetary magnetic field. These results also show that the necessary changes in the fields and the plasma parameters across the magnetopause do not occur simultaneously (i.e., in the same spatial location). As such, the magnetopause cannot be viewed as a single boundary but instead is a region which includes both abrupt and gradual changes in the fields and plasma parameters.

Omidi, N.↗

NASA NTRS1995

Diffusion at the magnetopause: Hybrid simulations

Electromagnetic wave generation and resulting cross-field diffusion of plasma are considered at a tangential discontinuity, which characterizes the magnetopause for northward interplanetary magnetic field. Two-dimensional hybrid (particle ions, massless fluid electrons) simulations, in which the tangential discontinuity is generated self-consistently via a stream-stream interaction, are used to show that wave growth occurs when the ambient magnetic field is predominantly perpendicular to the direction of the density gradient. Low-frequency (much less than ion gyrofrequency) waves, with amplitudes delta B/B less than or equal to 0.2 and anticorrelated density fluctuations delta n/n less than or equal to 0.6, are generated at the discontinuity, resulting in cross-field diffusion that is comparable to the Bohm rate. Both the fluctuation level and the lack of ion heating in the calculations are consistent with observations at the magnetopause. The magnitude of the diffusion is considered in the presence of numerical effects and in the context of the inferred diffusion rate at the magnetopause. The relation of the low-frequency waves and their consequences to faster growing, short-wavelength waves due to the lower hybrid drift instability is also addressed. The overall conclusion of this initial study is that diffusion due to low frequency waves is not likely to be a major effect at the magnetopause.

Winske, D.↗

NASA NTRS1992

Electron acceleration by Alfven waves in the magnetosphere

The self-consistent electron kinetics of Alfven waves on the electron inertial scale is studied using a 2D hybrid-kinetic description. The ions follow a fluid description for Alfven waves at frequencies below the ion cyclotron frequency. The parallel electron dynamics is treated kinetically using particle-in-cell techniques. In this model, the electron plasma mode is eliminated, and only the physics of the Alfven waves is retained. At sufficiently large amplitudes, it is found that oblique Alfven waves break due to finite electron inertia in a cold plasma. The consequence of wave breaking is the formation of an electron beam which can be unstable to the beam-plasma instability. The electrons supporting the parallel current thermalize into a non-Maxwellian distribution with an energetic tail up to several keV, assuming a reasonable magnetospheric Alfven speed. In hot plasma simulations, electron trapping is the principal mechanism of electron acceleration. It is proposed that wave breaking or electron trapping of oblique Alfven waves at 1 R(E) can result in electron acceleration and may explain some observed auroral phenomena.

Hui, C.-H.↗

DOE OSTI2025

Carrier Localization and Spontaneous Formation of Two-Dimensional Polarization Domain in Halide Perovskites

Halide perovskites are known for their rich phase diagram and superior performance in diverse optoelectronics applications. The latter property is often attributed to the long electron-hole recombination time, whose underlying physical mechanism has been a long-standing controversy. In this Letter, we investigate the transport and localization properties of electron and hole carriers in a prototypical halide perovskite (CsPbBr 3 ), through ab initio tight-binding nonadiabatic dynamics approach for large-scale (tens of nm size) supercell calculations, to simulate electron and ion dynamics on the same footing. Here, we found distinct structural, lattice polarization, and electron-phonon coupling properties at low (below 100 K) and high temperatures, consistent with experimental observations. In particular, at low temperature we find spontaneous formation of polar grain boundaries in the nonpolar bulk systems, which result in two-dimensional polarization patterns that serve to localize and separate electrons and holes. We reveal phonon-assisted variable-range hopping mostly responsible for low-temperature transport, and their characteristic frequency correlates with temperature-dependent phonon power spectrum and energy oscillation frequency in nonadiabatic dynamics. We answer the critical questions of long electron-hole recombination lifetime at low temperature and offer the correlation among polarization domains, electron-phonon couplings, and photocarrier dynamics.

Carrier generation & recombination↗

NASA NTRS1972

Neutral winds implied by electron content observations during the 7 March 1970 solar eclipse.

Measurements of columnar electron content using geostationary satellite signals were made at several of our observatories throughout the U.S., during the 7 March 1970 solar eclipse. The ionospheric response to the solar eclipse was simulated in a computer. Discrepancies between observed and simulated electron content behaviors can be greatly reduced by assuming the existence of plausible neutral winds originated by the eclipse in the F-region heights.

Almeida, O. G.↗

NASA NTRS1987

Telescience - Concepts and contributions to the Extreme Ultraviolet Explorer mission

It is shown how the contradictory goals of low-cost and fast data turnaround characterizing the Extreme Ultraviolet Explorer (EUVE) mission can be achieved via the early use of telescience style transparent tools and simulations. The use of transparent tools reduces the parallel development of capability while ensuring that valuable prelaunch experience is not lost in the operations phase. Efforts made to upgrade the 'EUVE electronics' simulator are described.

Marchant, Will↗

NASA NTRS1972

Test report: Vibration testing of the electron/proton spectrometer structural test unit

The structural test unit of the electron-proton spectrometer was tested to a random vibration spectra and to a sinusoidal resonant search to comply with the requirements of a verification plan for the spectrometer. The test item consisted of mass simulated electronic and printed circuit boards mounted in a flight type electronic housing. The arrangement, center of gravity, and weight were as proposed for flight units.

Vincent, D. L.↗

DOE OSTI2025

Modeling and Characterizing the electron backscatter in a cylindrical anode-based distributed X-ray source

Upcoming advancements in computed tomography architectures warrants the investigation of new X-ray source designs and the impacts that electron backscatter can have on these designs. One such design being investigated is a distributed, cylindrical anode-based X-ray source. For such a distributed X-ray source, we developed a modeling pipeline for simulating electron optics and transport to characterize the quality of the primary X-ray beam and the electron backscatter behavior. We report our results on the energy distributions of the bremsstrahlung spectra; electron backscatter ratio; and spatial, temporal, and energy distributions of backscattered electrons that return to the anode.

46 - INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AN↗

NASA NTRS1992

Gas-exposure enhanced Na* emission from Na-rich surfaces

The optical emission attributed to electronically desorbed excited sodium atoms from NaCl and Na-evaporated surfaces is shown to be enhanced by exposure of the surface to gaseous CO2 and N2. This is the first observation of enhancement of electron-simulated desorption of substrate atoms caused by the exposure of surfaces to gaseous molecules which do not contain the desorbed atoms. The large amount of excited-sodium yield at 60 K provides evidence for nonexistence of the secondary-electron excitation of thermally desorbed ground sodium.

Xu, Jun↗

DOE OSTI2025

How the choice of exchange–correlation functional affects DFT-based simulations of the hydrated electron

Hydrated electrons are anionic species that are formed when an excess electron is introduced into liquid water. Building an understanding of how hydrated electrons behave in solution has been a long-standing effort of simulation methods, of which density functional theory (DFT) has come to the fore in recent years. The ability of DFT to model the reactive chemistry of hydrated electrons is an attractive advantage over semi-classical methodologies; however, relatively few density functional approximations (DFAs) have been used for the hydrated electron simulations presented in the literature. Here, we simulate hydrated electron systems using a series of exchange–correlation (XC) functionals spanning Jacob’s ladder. We calculate a variety of experimental and other observables of the hydrated electron and compare the XC functional dependence for each quantity. We find that the formation of a stable localized hydrated electron is not necessarily limited to hybrid XC functionals and that some hybrid functionals produce delocalized hydrated electrons or electrons that react with the surrounding water at an unphysically fast rate. Here, we further characterize how different DFAs impact the solvent structure and predicted spectroscopy of the hydrated electron, considering several methods for calculating the hydrated electron’s absorption spectrum for the best comparison between structures generated using different density functionals. None of the dozen or so DFAs that we investigated are able to correctly predict the hydrated electron’s spectroscopy, vertical detachment energy, or molar solvation volume.

Ab-initio molecular dynamics↗

NASA NTRS2018

Laboratory Measurements of X-ray Emission from Highly Charged Argon Ions

Uncertainties in atomic models will introduce noticeable additional systematics in calculating the flux of weak dielectronic recombination (DR) satellite lines, affecting the detection and flux measurements of other weak spectral lines. One important example is the Ar xvii Heβ DR, which is expected to be present in emission from the hot intracluster medium of galaxy clusters and could impact measurements of the flux of the 3.5 keV line that has been suggested as a secondary emission from a dark matter interaction. We perform a set of experiments using the Lawrence Livermore National Laboratory's electron beam ion trap (EBIT-I) and the X-ray Spectrometer quantum calorimeter (XRS/EBIT) to test the Ar xvii Heβ DR origin of the 3.5 keV line. We measured the X-ray emission following resonant DR onto helium-like and lithium-like Argon using EBIT-I's Maxwellian simulator mode at a simulated electron temperature of T(e) = 1.74 keV. The measured flux of the Ar xvii Heβ DR lined is too weak to account for the flux in the 3.5 keV line, assuming reasonable plasma parameters. We, therefore, rule out Ar xvii Heβ DR as a significant contributor to the 3.5 keV line. A comprehensive comparison between the atomic theory and the EBIT experiment results is also provided.

Esra Bulbul↗

NASA NTRS1986

Simulations of high Mach number perpendicular shocks with resistive electrons

A simulation code which models the ions as microparticles and the electrons as a resistive massless fluid is employed to study the structure of high Mach number perpendicular shocks. It is found that stable stationary shock solutions can be obtained for Alfven Mach numbers (M sub A) between 5 and 60 for upstream plasmas where the ratio of the plasma pressure to the magnetic pressure is 1, providing that the upstream resistive diffusion length is much smaller than the ion inertial length. For much larger resistive diffusion lengths, the magnetic field overshoot is damped, and the imbalance in the electron momentum equation results in a periodic fluctuation of the fraction of reflected ions. In the limit of M sub A of less than 10, the magnetic overshoot and the fraction of reflected ions increase with increasing M sub A, while at higher Mach numbers the fraction of reflected ions peaks at about 40 percent and the magnetic field overshoot increases at a much slower rate. Electron inertial effects are also considered.

Quest, K. B.↗

DOE OSTI2025

Intrinsic Defect-Induced Local Semiconducting-to-Metallic Regions Within Monolayer 1T-TiS2 Displayed by First-Principles Calculations and Scanning Tunneling Microscopy

Using density functional theory (DFT) and scanning tunneling microscopy (STM), the intrinsic point defects, formation energy, and electronic structure of 1T-TiS2 were investigated. Defect systems include single-atom vacancies, interstitial and adatom additions, and direct atomic substitution. Using a collective approach for analyzing realistic systems for point defect investigation, we provide a more straightforward comparison to the experimental measurements, reproducing more realistic environmental conditions related to thin film growth. STM images are compared to computationally simulated electron density images to identify specific geometries that result from favorable point defects. DFT suggests that titanium interstitials are the most energetically favorable intrinsic defect, and sulfur vacancies are more likely to form than titanium vacancies within this realistic analysis, which is in agreement with STM data. A pristine, stoichiometric monolayer system is calculated to have a direct band gap of 0.422 eV, which varies based on local point defects. Local semiconducting-to-metallic electronic transitions are predicted to occur based on the presence of Ti interstitials.

Keeney, P. J.↗