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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

A non-neutral generalized Ohm's law model for magnetohydrodynamics in the two-fluid regime

Here, a new non-neutral generalized Ohm's law (GOL) model for atomic plasmas is presented. This model differs from previous models of this type in that quasi-neutrality is not assumed at any point. Collisional effects due to ionization, recombination, and elastic scattering are included, and an expression for the associated plasma conductivity is derived. An initial set of numerical simulations are considered that compare the GOL model to a two-fluid model in the ideal (collisionless) case. The results demonstrate that solutions obtained from the two models are essentially indistinguishable in most cases when the ion–electron mass ratio is within the range of physical values for atomic plasmas. Additionally, some limitations of the model are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1991

Numerical simulation of the emission and motion of neutral and charged dust from P/Halley

The present numerical model for neutral or charged dust-particle distribution prediction in P/Halley encompasses the spatial and temporal variations of the plasma parameters and magnetic field. A significant difference is noted between results for neutral dust trajectories and the trajectories of charged dust particles with radii smaller than 0.1 micron. While most of the model and in situ mass spectra were in good agreement, there is a shortage of the lowest-mass model particles, as well as an offset of the total counting rate for two outbound mass spectra. A combination of two Lorentzian particle mass-density functions with a 100:1 ratio for the number of particles with the lower and higher density functions yielded the best agreement.

Ellis, Tracy A.↗
NASA NTRS1977

Atomic hydrogen escape rate due to charge exchange with hot plasmaspheric ions

Data on ion and electron temperatures and concentrations to several thousand kilometers of altitude were obtained from the Atmosphere Explorer C satellite for 1974 and to 850 km from Arecibo incoherent scatter radar measurements. These data were used to normalize diffusive equilibrium profiles. From these profiles and by using the neutral atmospheric model of Jacchia (1971) and a new hydrogen model, the charge-exchange-induced neutral hydrogen escape fluxes for equatorial and middle latitudes were calculated. The data confirm earlier estimates that the charge exchange loss is more important than Jeans escape for the earth. It is also found that inside the plasmapause this charge exchange process with hot plasmapheric ions is the major production and loss process for the satellite population in the hydrogen geocorona.

Maher, L. J.↗
NASA NTRS2010

Joint Composable Object Model and LVC Methodology

Within the Department of Defense, multiple architectures are created to serve and fulfill one or several specific service or mission related LVC training goals. Multiple Object Models exist across and within those architectures and it is there that those disparate object models are a major source of interoperability problems when developing and constructing the training scenarios. The two most commonly used architectures are; HLA and TENA, with DIS and CTIA following close behind in terms of the number of users. Although these multiple architectures can share and exchange data the underlying meta-models for runtime data exchange are quite different, requiring gateways/translators to bridge between the different object model representations; while the Department of Defense's use of gateways are generally effective in performing these functions, as the LVC environment increases so too does the cost and complexity of these gateways. Coupled with the wide range of different object models across the various user communities we increase the propensity for run time errors, increased programmer stop gap measures during coordinated exercises, or failure of the system as a whole due to unknown or unforeseen incompatibilities. The Joint Composable Object Model (JCOM) project was established under an M&S Steering Committee (MSSC)-sponsored effort with oversight and control placed under the Joint Forces Command J7 Advanced Concepts Program Directorate. The purpose of this paper is to address the initial and the current progress that has been made in the following areas; the Conceptual Model Development Format, the Common Object Model, the Architecture Neutral Data Exchange Model (ANDEM), and the association methodology to allow the re-use of multiple architecture object models and the development of the prototype persistent reusable library.

Rheinsmith, Richard↗
NASA NTRS1996

Studies for the loss of atomic and molecular species for Io

A summary is presented for research undertaken, physical insight gained, and new directives identified in this project. Significant enhancements for the SO2 neutral cloud model and its dissociative products (SO, O2, O, S) as well as its application to investigating the amount of SO2+ measured by the Voyager PLS instrument in the plasma torus inside of Io's orbit are discussed. New excitation rates for UV and visible emission lines were incorporated in the O and S neutral cloud models, and the very preliminary analysis of UV observations near Io acquired in 1992 by the Hubble Space telescope is discussed. Observations for O('D) 6300 A emission near Io, preliminary reduction of these observations, and an initial assessment of these observations are presented. The analysis of 1985 sodium eclipse and emission data for Io has been completed and is contained in a paper in the Appendix. A larger data set for 1987 sodium emission observations, which will provide a new base for more detailed future studies, is described. A preliminary discussion is also presented for the likely nature of neutral gas clouds for the outer three Galilean satellites.

Smyth, William H.↗
NASA NTRS1986

Interaction of the solar wind with interstellar neutral hydrogen - Three-fluid model

It is commonly assumed in models of the solar wind-interstellar neutral hydrogen interaction that the ionized interstellar particles are quickly assimilated into the solar wind proton population and 'become indistinguishable' from the original solar wind. This assumption leads to the prediction that the solar wind proton temperature should increase with radius in the outer heliosphere. This temperature increase has not been observed. It is pointed out that assimilation of the interstellar particles to the point of indistinguishability takes place on the very long Coulomb collision time scale, and is not expected to occur within the heliosphere. Results are presented of a three-fluid model of the solar wind which consists of comoving thermal populations of protons of solar origin, protons produced by ionization of interstellar hydrogen, and electrons. The steady-state results yield a solar wind with a 'core' proton distribution which cools adiabatically, and a 'halo' of interstellar pickup protons which is maintained near 10 to the 7th K by the energy input of continued ionization and pickup. Such a distribution will not be observed to manifest the temperature increase at large heliocentric distances which is predicted from a one-fluid analysis. Further time-dependent calculations show a strong correlation between the densities of the solar wind and the interstellar pickup protons. It is suggested that the interstellar pickup population may be observable by the Voyager plasma instruments in low resolution mode during periods of high solar wind density and low solar wind temperature.

Isenberg, P. A.↗
NASA NTRS1991

Formation of the infrared emission lines of Mg I in the solar atmosphere

A non-LTE radiative transfer investigation of the emission lines is conducted at 7 and 12 microns using a realistic atomic model for neutral magnesium. An average quiet sun atmospheric model is used to calculate emission-line profiles that resemble the observed ones, i.e., broad absorption troughs with narrow central emission, and significant limb brightening. The charge exchange rates are found to be significant, but the effects of high-n coupling between Mg and Mg(+) together with radiative low-n transitions are of greater importance. It is confirmed that the emission cores are formed no higher than the temperature minimum region, and that the emission is caused by non-LTE effects rather than by the chromospheric temperature rise. It is inferred from the model calculations that the line core is sensitive to magnetic fields located almost 400 km above those measured in ordinary magnetograms; the gas pressure decreases 20-fold between these two heights.

Chang, E. S.↗
NASA NTRS1994

F2 peak electron density at Millstone Hill and Hobart: Comparsion of theory and measurement at solar maximum

This paper compares the observed behavior of the (F2) layer of the ionosphere at Millstone Hill and Hobart with calculations from the field line interhemispheric plasma (FLIP) model for solar maximum, solstice conditions in 1990. During the study period the daily F(sub 10.7) index varied by more than a factor of 2 (123 to 280), but the 81-day mean F(sub 10.7) (F(sub 10.7 A)) was almost constant near 190. Calculations were performed with and without the effects of vibrationally excited N2 (N(sup *)(sub 2) which affects the loss rate of atomic oxygen ions. In the case without N(sup *)(sub 2) there is generally good agreement between the model and measurement for the daytime, peak density of the F region (NmF2). Both the model and the measurement show a strong seasonal anomaly with the winter noon densities a factor of 3 to 4 greater than the summer noon densities at Millstone Hill and a factor of 2 greater at Hobart. The seasonal anomaly in the model is caused by changes in the neutral composition as given by the mass spectrometer and incoherent scatter (MSIS) 86 neutral density model. There is generally little or no increase in the observed noon NmF2 as a function of daily F(sub 10.7) except at Millstone Hill in winter. In contrast to the generally good agreement between model and data at noon, the model badly underestimates the density at night at Millstone Hill at all seasons. At Hobart the model reproduces the nighttime density variations well in both winter and summer. The international reference ionosphere (IRI) model generally provides a good representation of the average behavior of noon NmF2 and hmF2 but because the data show a lot of day-to-day variability, there are often large differences. The FLIP model is able to reproduce this variability when hmF2 is specified. The IRI model peak densities are better than the FLIP densities at night, but the IRI model does not represent the Millstone Hill summer data very well at night in 1990.

Richards, P. G.↗
DOE OSTI2024

Modeling resistance to the broadly neutralizing antibody PGT121 in people living with HIV-1

PGT121 is a broadly neutralizing antibody in clinical development for the treatment and prevention of HIV-1 infection via passive administration. PGT121 targets the HIV-1 V3-glycan and demonstrated potent antiviral activity in a phase I clinical trial. Resistance to PGT121 monotherapy rapidly occurred in the majority of participants in this trial with the sampled rebound viruses being entirely resistant to PGT121 mediated neutralization. However, two individuals experienced long-term ART-free viral suppression following antibody infusion and retained sensitivity to PGT121 upon viral rebound. Here, we develop mathematical models of the HIV-1 dynamics during this phase I clinical trial. We utilize these models to understand the dynamics leading to PGT121 resistance and to identify the mechanisms driving the observed long-term viral control. Our modeling highlights the importance of the relative fitness difference between PGT121 sensitive and resistant subpopulations prior to treatment. Specifically, by fitting our models to data, we identify the treatment-induced competitive advantage of previously existing or newly generated resistant population as a primary driver of resistance. Finally, our modeling emphasizes the high neutralization ability of PGT121 in both participants who exhibited long-term viral control.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Fluid and hybrid simulations of the ionization instabilities in Hall thruster

Low-frequency axial oscillations in the range of 5–50 kHz stand out as a pervasive feature observed in many types of Hall thrusters. While it is widely recognized that the ionization effects play the central role in this mode, as manifested via the large-scale oscillations of neutral and plasma density, the exact mechanism(s) of the instabilities remain unclear. To gain further insight into the physics of the breathing mode and evaluate the role of kinetic effects, a one-dimensional time-dependent full nonlinear low-frequency model describing neutral atoms, ions, and electrons is developed in full fluid formulation and compared to the hybrid model in which the ions and neutrals are kinetic. Both models are quasi-neutral and share the same electron fluid equations that include the electron diffusion, mobility across the magnetic field, and the electron energy evolution. The ionization models are also similar in both approaches. Further, the predictions of fluid and hybrid simulations are compared for different test cases. Two main regimes are identified in both models: one with pure low-frequency behavior and the other one, where the low-frequency oscillations coexist with high-frequency oscillations in the range of 100–200 kHz, with the characteristic time scale of the ion channel fly-by time, 100–200 kHz. The other test case demonstrates the effect of a finite temperature of injected neutral atoms, which has a substantial suppression effect on the oscillation amplitude.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1990

Recent advances in magnetospheric substorm research

More than two decades of magnetospheric exploration have led to a reasonably clear morphological picture of geomagnetic substorms, which is often summarized in terms of the near-earth neutral line model of substorms. Although this qualitative theory is quite comprehensive and explains a great many observations, it is hard pressed to explain both recent observations of consistently earthward flow within 19 RE and also the prompt onset of magnetic turbulence at 8 RE at the time of substorm onset. Other theories have recently been proposed which tend to be more quantitative, but which explain a more limited number of substorm observations. The challenge seems to be to understand the esential physics of these various quantitative theories and integrate them into a larger structure such as provided by the near-earth neutral line model.

Fairfield, D. H.↗
DOE OSTI2022

Deep modeling of plasma and neutral fluctuations from gas puff turbulence imaging

The role of turbulence in setting boundary plasma conditions is presently a key uncertainty in projecting to fusion energy reactors. To robustly diagnose edge turbulence, we develop and demonstrate a technique to translate brightness measurements of HeI line radiation into local plasma fluctuations via a novel integrated deep learning framework that combines neutral transport physics and collisional radiative theory for the 3 3 D - 2 3 P transition in atomic helium with unbounded correlation constraints between the electron density and temperature. The tenets for experimental validity are reviewed, illustrating that this turbulence analysis for ionized gases is transferable to both magnetized and unmagnetized environments with arbitrary geometries. Based on fast camera data on the Alcator C-Mod tokamak, we present the first two-dimensional time-dependent experimental measurements of the turbulent electron density, electron temperature, and neutral density, revealing shadowing effects in a fusion plasma using a single spectral line.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Deep modelling of plasma and neutral fluctuations from gas puff turbulence imaging

The role of turbulence in setting boundary plasma conditions is presently a key uncertainty in projecting to fusion energy reactors. To robustly diagnose edge turbulence, we develop and demonstrate a technique to translate brightness measurements of HeI line radiation into local plasma fluctuations via a novel integrated deep learning framework that combines neutral transport physics and collisional radiative theory for the $3^3 D - 2^3 P$ transition in atomic helium. The tenets for experimental validity are reviewed, illustrating that this turbulence analysis for ionized gases is transferable to both magnetized and unmagnetized environments with arbitrary geometries. Based upon fast camera data on the Alcator C-Mod tokamak, we present the first 2-dimensional time-dependent experimental measurements of the turbulent electron density, electron temperature, and neutral density revealing shadowing effects in a fusion plasma using a single spectral line.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1981

One-dimensional models of quasi-neutral parallel electric fields

Parallel electric fields can exist in the magnetic mirror geometry of auroral field lines if they conform to the quasineutral equilibrium solutions. Results on quasi-neutral equilibria and on double layer discontinuities were reviewed and the effects on such equilibria due to non-unique solutions, potential barriers and field aligned current flows using as inputs monoenergetic isotropic distribution functions were examined.

Stern, D. P.↗
NASA NTRS1992

A hybrid flow model for charged and neutral particles around spacecraft in Low Earth Orbit

A flow simulation for charged and neutral particles around spacecraft is given that combines the fully coupled effects of neutral particle flow, plasma flow, electromagnetic field effects, and spacecraft charging. The simulation allows for chemically reacting flows (associative ionization, dissociation, and chain exchange) and for thermal accommodation at a spacecraft surface. The solution procedure was applied to several types of flows with orbital altitudes ranging from 250 km to 500 km. Excellent agreement with previously verified computational algorithms was obtained for both the neutral and charged particle cases. Results for the full flow simulation are presented for altitudes of 250 km and 500 km.

Justiz, Charles R.↗
NASA NTRS1984

Cometary atmospheres: Modeling the spatial distribution of observed neutral radicals

The Monte Carlo particle trajectory model for the saptial distribution of cometary radicals was modified to include the heliocentric distance dependence of the parent molecule velocity, and the heliocentric velocity dependence for CN fluorescence and radiation pressure. Available data on the observed spatial distributions of cometary radicals were studied and a preliminary comparison of newly published data from previous studies is discussed.

Combi, M. R.↗