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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Systematic Comparison of Photoionized Plasma Codes with Application to Spectroscopic Studies of AGN in X-Rays

Atomic data and plasma models play a crucial role in the diagnosis and interpretation of astrophysical spectra, thus influencing our understanding of the Universe. In this investigation we present a systematic comparison of the leading photoionization codes to determine how much their intrinsic differences impact X-ray spectroscopic studies of hot plasmas in photoionization equilibrium. We carry out our computations using the Cloudy, SPEX, and XSTAR photoionization codes, and compare their derived thermal and ionization states for various ionizing spectral energy distributions. We examine the resulting absorption-line spectra from these codes for the case of ionized outflows in active galactic nuclei. By comparing the ionic abundances as a function of ionization parameter, we find that on average there is about 30 deviation between the codes in where ionic abundances peak. For H-like to B-like sequence ions alone, this deviation in is smaller at about 10 on average. The comparison of the absorption-line spectra in the X-ray band shows that there is on average about 30 deviation between the codes in the optical depth of the lines produced at log 1 to 2, reducing to about 20 deviation at log 3. We also simulate spectra of the ionized outflows with the current and upcoming high-resolution X-ray spectrometers, on board XMM-Newton, Chandra, Hitomi, and Athena. From these simulations we obtain the deviation on the best-fit model parameters, arising from the use of different photoionization codes, which is about 10 to40. We compare the modeling uncertainties with the observational uncertainties from the simulations. The results highlight the importance of continuous development and enhancement of photoionization codes for the upcoming era of X-ray astronomy with Athena.

plasmas – atomic processes – atomic data – t↗
NASA NTRS2000

Error Estimates for Emission Lines in the Hydrogen and Helium Isosequences

Emission lines from hydrogen and helium isosequence are among tile strongest in X-ray spectra; they will soon be used to measure the temperature, density, and equilibrium state of collisionally excited, astrophysical plasmas. We have created a new plasma code, APEC, which calculates the emission from such a plasma. APEC calculates the line emission from the direct electron and proton excitation rate and the radiative and dielectronic recombination rate. We show how different collisional plasma codes give varying emissivities for some strong lines of O VII and Fe XXVI, where direct excitation is the. primary effect. This variation is partly due to simple differences in the plasma code. However, the primary reason is that much work remains to be done on experimental and theoretical calculations of the, atomic rates. Large (approximately 50%) differences exist even for excitation rates for hydrogenic ions.

Smith, R. K.↗
NASA NTRS2010

Rapid Variability Generated at Relativistic Shocks Simulated by Particle-in- Cell Code

Plasma instabilities excited in collisionless shocks are responsible for particle acceleration. We have investigated the particle acceleration and shock structure associated with an unmagnetized relativistic electronpositron jet propagating into an unmagnetized electron-positron plasma. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a partially developed hydrodynamic-like shock structure. In the leading shock, electron density increases by a factor of about 3.5 in the simulation frame. Strong electromagnetic fields are generated in the trailing shock and provide an emission site. These magnetic fields contribute to the electrons transverse deflection behind the shock. We calculate the radiation from deflected electrons in the turbulent magnetic fields. Radiation from electrons near the trailing shock will be variable due to fluctuations of density and electromagnetic fields. The properties of this radiation may be important for rapid variability in relativistic jets such as AGN jets and blazars.

Nishikawal, Ken-Ichi↗
NASA NTRS1992

Spacecraft-plasma interaction codes: NASCAP/GEO, NASCAP/LEO, POLAR, DynaPAC, and EPSAT

Development of a computer code to simulate interactions between the surfaces of a geometrically complex spacecraft and the space plasma environment involves: (1) defining the relevant physical phenomena and formulating them in appropriate levels of approximation; (2) defining a representation for the 3-D space external to the spacecraft and a means for defining the spacecraft surface geometry and embedding it in the surrounding space; (3) packaging the code so that it is easy and practical to use, interpret, and present the results; and (4) validating the code by continual comparison with theoretical models, ground test data, and spaceflight experiments. The physical content, geometrical capabilities, and application of five S-CUBED developed spacecraft plasma interaction codes are discussed. The NASA Charging Analyzer Program/geosynchronous earth orbit (NASCAP/GEO) is used to illustrate the role of electrostatic barrier formation in daylight spacecraft charging. NASCAP/low Earth orbit (LEO) applications to the CHARGE-2 and Space Power Experiment Aboard Rockets (SPEAR)-1 rocket payloads are shown. DynaPAC application to the SPEAR-2 rocket payloads is described. Environment Power System Analysis Tool (EPSAT) is illustrated by application to Tethered Satellite System 1 (TSS-1), SPEAR-3, and Sundance. A detailed description and application of the Potentials of Large Objects in the Auroral Region (POLAR) Code are presented.

Mandell, M. J.↗
NASA NTRS1992

Performance of a plasma fluid code on the Intel parallel computers

One approach to improving the real-time efficiency of plasma turbulence calculations is to use a parallel algorithm. A parallel algorithm for plasma turbulence calculations was tested on the Intel iPSC/860 hypercube and the Touchtone Delta machine. Using the 128 processors of the Intel iPSC/860 hypercube, a factor of 5 improvement over a single-processor CRAY-2 is obtained. For the Touchtone Delta machine, the corresponding improvement factor is 16. For plasma edge turbulence calculations, an extrapolation of the present results to the Intel (sigma) machine gives an improvement factor close to 64 over the single-processor CRAY-2.

Lynch, V. E.↗
NASA NTRS1994

Collisional-Radiative Nonequilibrium and Precursor Effects in a Nitrogen Shock Wave

Improvements to a plasma code with a Collisional-Radiative (CR) non-equilibrium model are made, allowing for a more accurate description of the physical processes. The code allows for non-Boltzmann distributions of the electronic excited states by convecting separately each excited state, as a pseudo-specie. Each molecular state has also its own vibrational temperature, while a global rotational temperature is assumed. The free electron temperature is different from those of the excited states, and the electron heat conduction is also included. The CR model also uses a unique coupling between chemistry and vibrational energy (C-V coupling), which is fully coherent, and has the property of establishing thermal equilibrium as well as chemical equilibrium, on its own. We have also included a coupling between electronic excitations and vibrational energy (X-V coupling), which can have a strong influence on the vibrational temperature of some states. The recent improvements include the multi- temperature dependence of the chemical rates for associative ionization, as well as the estimation of the internal energies transferred during this process. Additionally, the distribution of energy into different translational modes (electron and heavy particles) is now correctly modeled. This provides a very rapid heating mechanism for the free electrons, since it is found that the electrons are generated with an average thermal energy of the same order as the heavy particle translational energy. This effect was observed by Gorelov et al in a recent paper, and lead to pronounced peaks in electron temperature immediately behind the shock. We will attempt ro reproduce this phenomenon. The last modification concerns the inclusion of the radiative terms into the calculations, thus enabling us to observe the effect of radiative losses and radiation transport. Preliminary tests have shown that the radiative losses are not negligible, i.e. the shock velocity drops when the radiative emission is included. In addition, we have observed some precursor excitation and ionization phenomena. These may be important at high shock velocities, and this will be investigated in detail. Precursor phenomena were also observed (in air) by Gorelov et al, and our results (for pure nitrogen) will be qualitatively compared with theirs.

Cambier, Jean-Luc↗
NASA NTRS2003

XMM-Newton and Chandra Observations of the Galaxy Group NGC 5044: Evidence for Limited Multiphase Hot Gas - 1

Using new XMM and Chandra observations, we present an analysis of the temperature structure of the hot gas within a radius of 100 kpc of the bright nearby galaxy group NGC 5044. A spectral deprojection analysis of data extracted from circular annuli reveals that a two-temperature model (2T) of the hot gas is favored over single-phase or cooling flow (M = 4.5 +/- 0.2 solar mass/yr) models within the central approx.30 kpc. Alternatively, the data can be fitted equally well if the temperature within each spherical shell varies continuously from approx.T(sub h) to T(sub c) approx. T(sub h)/2, but no lower. The high spatial resolution of the Chandra data allows us to determine that the temperature excursion T(sub h) approaches T(sub c) required in each shell exceeds the temperature range between the boundaries of the same shell in the best-fitting single-phase model. This is strong evidence for a multiphase gas having a limited temperature range. We do not find any evidence that azimuthal temperature variations within each annulus on the sky can account for the range in temperatures within each shell. We provide a detailed investigation of the systematic errors on the derived spectral models considering the effects of calibration, plasma codes, bandwidth, variable NH, and background rate. We find that the RGS gratings and the EPIC and ACIS CCDs give fully consistent results when the same models are fitted over the same energy ranges for each instrument. The cooler component of the 2T model has a temperature (T(sub c) approx. 0.7 keV) similar to the kinetic temperature of the stars. The hot phase has a temperature (T(sub h) approx. 1.4 keV) characteristic of the virial temperature of the solar mass halo expected in the NGC 5044 group. However, in view of the morphological disturbances and X-ray holes visible in the Chandra image within R approx. equals 10 kpc, bubbles of gas heated to approx.T(sub h) in this region may be formed by intermittent AGN feedback. Some additional heating at larger radii may be associated with the evolution of the cold front near R approx. 50 kpc, as suggested by the sharp edge in the EPIC images. Subject headings: cooling flows - galaxies: formation - galaxies: halos - intergalactic medium - X-rays: galaxies: clusters

Buote, David A.↗
NASA NTRS2012

Doubly-Shadowed Regions in Lunar Polar Craters: Hydrogen Accumulation in the Presence of Recursive Plasma Wakes

Permanently shadowed regions (PSRs) of the Moon have been identified as unique environments of extreme cold and comprise a natural cold trap for sequestering volatiles [Paige et al. 2010]. The diverse chemical composition of the LCROSS impact plume provided evidence for a volatile-rich and chemically-complex PSR environment [Cola prete et al. 2010, Schultz et al. 2010]. Additionally, the polar electrostatic environment is highly complex, with the possibility of strong, localized electric fields that divert solar wind ions directly into polar cold traps [Farrell et al. 2010, Zimmerman et al. 2011]. Thus, regional plasma physics processes couple directly with volatile sequestration. In the present work, kinetic simulations show that recursive plasma wake structure arises in the presence of step-like topographic features (Le. doubly-shadowed craters). Combining the plasma code with a numerical sputtering model demonstrates that solar wind protons can be either a hydrogen source via implantation or a volatile loss mechanism via sputtering, depending on properties of the regolith and solar wind. The present model provides a novel theoretical pathway toward understanding the lunar surface/solar wind physical and chemical interactions for complex topography near the poles.

Zimmerman, Michael I.↗
NASA NTRS2012

A New Method to Constrain Supernova Fractions Using X-ray Observations of Clusters of Galaxies

Supernova (SN) explosions enrich the intracluster medium (ICM) both by creating and dispersing metals. We introduce a method to measure the number of SNe and relative contribution of Type Ia supernovae (SNe Ia) and core-collapse supernovae (SNe cc) by directly fitting X-ray spectral observations. The method has been implemented as an XSPEC model called snapec. snapec utilizes a single-temperature thermal plasma code (apec) to model the spectral emission based on metal abundances calculated using the latest SN yields from SN Ia and SN cc explosion models. This approach provides a self-consistent single set of uncertainties on the total number of SN explosions and relative fraction of SN types in the ICM over the cluster lifetime by directly allowing these parameters to be determined by SN yields provided by simulations. We apply our approach to XMM-Newton European Photon Imaging Camera (EPIC), Reflection Grating Spectrometer (RGS), and 200 ks simulated Astro-H observations of a cooling flow cluster, A3112.We find that various sets of SN yields present in the literature produce an acceptable fit to the EPIC and RGS spectra of A3112. We infer that 30.3% plus or minus 5.4% to 37.1% plus or minus 7.1% of the total SN explosions are SNe Ia, and the total number of SN explosions required to create the observed metals is in the range of (1.06 plus or minus 0.34) x 10(exp 9), to (1.28 plus or minus 0.43) x 10(exp 9), fromsnapec fits to RGS spectra. These values may be compared to the enrichment expected based on well-established empirically measured SN rates per star formed. The proportions of SNe Ia and SNe cc inferred to have enriched the ICM in the inner 52 kiloparsecs of A3112 is consistent with these specific rates, if one applies a correction for the metals locked up in stars. At the same time, the inferred level of SN enrichment corresponds to a star-to-gas mass ratio that is several times greater than the 10% estimated globally for clusters in the A3112 mass range.

Observations↗
NASA NTRS1975

Applications of numerical codes to space plasma problems

Solar wind, earth's bowshock, and magnetospheric convection and substorms were investigated. Topics discussed include computational physics, multifluid codes, ionospheric irregularities, and modeling laser plasmas.

Northrop, T. G.↗
NASA NTRS1985

Self-consistent simulation of plasma interactions with secondary-emitting insulators

A cylindrical particle-in-cell (PIC) plasma simulation code applicable to plasma densities encountered in low Earth orbit (LEO) is described. The simulated geometries include that of a plain disk and a disk surrounded by a dielectric. Both configurations are mounted upon a ground plate in contact with a plasma environment. Techniques allowing simulation of dielectric charging using PIC time scales are discussed. Current versus voltage characteristic curves are calculated and the results are compared to experimental data.

Brandon, S. T.↗
NASA NTRS2000

Testing Models of Resonant Compton Scattering in X-Ray Pulsars

Over the performance period covered by the grant, the principal investigator modified a Monte Carlo Compton scattering code to model the propagation of x-rays through the magnetosphere of accreting neutron stars. These modifications were made to enable the author to compare the observations of x-ray pulsars to theoretical models of the system. The original code was designed to study relativistic plasmas with one of two geometries: a plane parallel plasma with a differential relativistic bulk velocity, and a static spherically symmetric plasma.- This code did not treat gravitational bending or bulk motion in the magnetosphere of a neutron star. Under the grant, the author incorporated code to trace light paths in a Schwarzschild metric. The code was modified to keep track of the photon polarization during propagati on. The investigator also modified the code so that bulk motion in an axisymmetric system is treated properly. An approximate treatment for resonant Compton scattering was added to the code. Finally, code was added that creates model observables that can be compared to observations, such as projected x-ray emission maps and energy-dependent light curves. Comparison to observations is now commencing.

Brainerd, Jerome J.↗
NASA NTRS2000

Cloudy 94 and Applications to Quasar Emission Line Regions

This review discusses the most recent developments of the plasma simulation code Cloudy and its application to the, emission-line regions of quasars. The longterm goal is to develop the tools needed to determine the chemical composition of the emitting gas and the luminosity of the central engine for any emission line source. Emission lines and the underlying thermal continuum are formed in plasmas that are far from thermodynamic equilibrium. Their thermal and ionization states are the result of a balance of a vast set of microphysical processes. Once produced, radiation must, propagate out of the (usually) optically thick source. No analytic solutions are possible, and recourse to numerical simulations is necessary. I am developing the large-scale plasma simulation code Cloudy as an investigative tool for this work, much as an observer might build a spectrometer. This review describes the current version of Cloudy, version 94. It describes improvements made since the, release of the previous version, C90. The major recent, application has been the development of the "Locally Optimally-Emitting Cloud" (LOC) model of AGN emission line regions. Powerful selection effects, introduced by the atomic physics and line formation process, permit individual lines to form most efficiently only near certain selected parameters. These selection effects, together with the presence of gas with a wide range of conditions, are enough to reproduce the spectrum of a typical quasar with little dependence on details. The spectrum actually carries little information to the identity of the emitters. I view this as a major step forward since it provides a method to handle accidental details at the source, so that we can concentrate on essential information such as the luminosity or chemical composition of the quasar.

Ferland, Gary J.↗
NASA NTRS1994

Application of the coded long-pulse technique to plasma line studies of the ionosphere

Recently, the coded long-pulse radar technique was tested at Arecibo Observatory, Puerto Rico using photoelectron-enhanced plasma lines in the daytime ionosphere. The technique immediately proved to be a powerful diagnostic tool for studying natural ionospheric phenomena. Our initial observations indicate that extremely accurate measurements of absolute electron density (0.01 to 0.03% error bars) can be achieved with an altitude resolution of 150 m and a temporal resolution of approx. 2 s. In addition, the technique provides information about electron density structure within a 150-m altitude cell and yields parameters from which the energy spectrum of suprathermal electrons (equal to or greater than 5 eV) can be deduced. Our earliest measurements are used to illustrate applications of the coded long-pulse technique to several aeronomic/ionsospheric areas of current interest. These include studies of neutral wave motions in the lower thermosphere, measurements of ion composition in the F(sub 1) region/upper ionosphere, and investigations of electron-gas thermal balance and photoelectron energy loss processes. The technique can be utilized to examine irregularity formation in the F region, probe electron acceleration processes in ionospheric modification experiments, verify the magnetic field dependence of Langmuir wave damping, and more generally test higher order corrections suggested for the Langmuir dispersion relation. It is anticipated that the latter tests will facilitate measurements of ionospheric currents.

Djuth, Frank T.↗
NASA NTRS2006

New Software for Predicting Charging of Spacecraft

Charging System Analyzer Program (Nascap-2K) is a comprehensive update, revision, and extension of several NASA and Air Force codes for predicting electrical charging of spacecraft. Nascap-2K integrates the capabilities and models included in four independent programs: NASCAP/LEO for low-Earth orbits, NASCAP/GEO for geosynchronous orbits, POLAR for auroral charging in polar orbits, and DynaPAC (Dynamic Plasma Analysis Code) for time-dependent plasma interactions. While each of the earlier codes works well for the range of problems for which it was designed, by today s standards these codes are difficult to learn, cumbersome to use, and overly restrictive in their geometric modeling capabilities. Nascap-2K incorporates these models into a single software package that includes spacecraft surface modeling, spatial gridding, environmental specifications, calculating scripting, and post-processing analysis and visualization. The provided material properties database includes values from earlier programs as well as values from recent measurements. Development of Nascap-2K continues with future capabilities to include interactions with dense plasma such as those produced by electric propulsion.

Mandell, Myron↗
NASA NTRS1977

A simulation model of time-dependent plasma-spacecraft interactions

A plasma simulation code is presented that models the time-dependent plasma properties in the vicinity of a spherical, charged spacecraft. After showing agreement with analytic, steady-state theories and ATS-6 satellite data, the following three problems are treated: (1) transient pulses from photoemission at various emission temperatures and ambient plasma conditions, (2) spacecharge limited emission, and (3) simulated plasma oscillations in the long wavelength limit.

Rothwell, P. L.↗
NASA NTRS1981

Computer code for charge-exchange plasma propagation

The propagation of the charge-exchange plasma from an electrostatic ion thruster is crucial in determining the interaction of that plasma with the associated spacecraft. A model that describes this plasma and its propagation is described, together with a computer code based on this model. The structure and calling sequence of the code, named PLASIM, is described. An explanation of the program's input and output is included, together with samples of both. The code is written in ASNI Standard FORTRAN.

Robinson, R. S.↗