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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

X-ray imaging and radiation transport effects on cylindrical implosions

Magnetization of inertial confinement implosions is a promising means of improving their performance, owing to the potential reduction of energy losses within the target and mitigation of hydrodynamic instabilities. In particular, cylindrical implosions are useful for studying the influence of a magnetic field, thanks to their axial symmetry. In this work, we present experimental results from cylindrical implosions on the OMEGA-60 laser using a 40-beam, 14.5 kJ, 1.5 ns drive and an initial seed magnetic field of B 0 = 30 T along the axes of the targets, compared with reference results without an imposed B-field. Implosions were characterized using time-resolved x-ray imaging from two orthogonal lines of sight. We found that the data agree well with magnetohydrodynamic simulations, once radiation transport within the imploding plasma is considered. We show that for a correct interpretation of the data in these types of experiments, explicit radiation transport must be taken into account.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1984

Hydrogen line ratios in Seyfert galaxies and low redshift quasars

New observations of the Lymal alpha radiation/hydrogen alpha radiation ratio in a set of X-ray selected active galactic nuclei and an archival study of International Ultraviolet Explorer (IUE) observations of Lymal alpha low redshift quasars and Seyfert galaxies have been used to form a large sample for studying the influence of soft X-rays on the enhancement of Balmer emission in the broad line region. In common models of broad line clouds, the Balmer lines are formed deep in the interior, largely by collisional excitation. Heating within the clouds is provided by soft X-ray radiation, while Lymal alpha is formed mainly by recombination after photoionization. The ratio Lymal alpha/Halpha is expected to depend weakly on the ratio of ionizing ultraviolet luminosity to X-ray luminosity (L sub UV/l sub x). If the Lymal alpha luminosity is used as a measure of L sub UV' a weak dependence of Lymal/H alpha on the X-ray luminosity is found similar to previous results.

Kriss, G. R.↗
NASA NTRS2002

Pulsar Polar Cap Heating and Surface Thermal X-ray Emission: Curvature Radiation Pair Fronts - 1

We investigate the effect of pulsar polar cap (PC) heating produced by positrons returning from the upper pair formation front. Our calculations are based on a self-consistent treatment of the pair dynamics and the effect of electric field screening by the returning positrons. We calculate the resultant X-ray luminosities and discuss the dependence of the PC heating efficiencies on pulsar parameters, such as characteristic spin-down age, spin period, and surface magnetic field strength. In this study we concentrate on the regime where the pairs are produced in a magnetic field by curvature photons emitted by accelerating electrons. Our theoretical results are not in conflict with the available observational x-ray data and suggest that the effect of PC heating should significantly contribute to the thermal x-ray fluxes from middle-aged and old pulsars. The implications for current and future x-ray observations of pulsars are briefly outlined.

Harding, Alice K.↗
NASA NTRS1983

Association between gradual hard X-ray emission and metric continua during large flares

X-ray radiation is used to study coronal phenomena in conjunction with meter wave observations during some large solar flares. It is found that metric flare continua and moving type IV bursts are associated with gradual and long lasting (a few tens of minutes) microwave and hard X-ray emissions. The detailed temporal analysis reveals that although metric and hard X-ray sources are located at very different heights, both kinds of emission result from a common and continuous/repetitive injection of electrons in the corona. The late part of the metric event (stationary type IV burst) is only associated with soft X-ray radiation. This indicates that the mean energy of the radiating electrons is lower during stationary type IV bursts than during the earlier parts of the event.

Klein, L.↗
NASA NTRS1978

Radiative transfer of X-rays in the solar corona

The problem of resonance scattering of X-ray emission lines in the solar corona is investigated. For the resonance lines of some helium-like ions, significant optical depths are reached over distances small compared with the size of typical coronal features. A general integral equation for the transfer of resonance-line radiation under solar coronal conditions is derived. This expression is in a form useful for modeling the complex three-dimensional temperature and density structure of coronal active regions. The transfer equation is then cast in a form illustrating the terms which give rise to the attenuation or enhancement of the resonance-line intensity. The source function for helium-like oxygen (O VII) under coronal conditions is computed and discussed in terms of the relative importance of scattering.

Acton, L. W.↗
NASA NTRS1992

Radiative-hydrodynamical simulations of X-ray burst-induced accretion disk coronae

A fully self-consistent radiative hydrodynamical algorithm developed earlier is used to study the 'steady' state coronae in order to simulate the response of the evaporated outflow to a time-dependent irradiation of the disk's surface. It is found that the burst definition is altered at both low and high inclination angles i. At i greater than or approximately equal to 45 deg, the detectable flux is enhanced (as much as 50 percent) by X-rays scattered into the line of sight from the radiation propagation through the corona, and (greater than or approximately equal to 30 percent) by X-rays reflected off the corona when i is less than or approximately equal to 45 deg.

Mella, Fulvio↗
NASA NTRS1981

Simultaneous X-ray, ultraviolet, optical, and radio observations of the flare star Proxima Centauri

Results of coordinated program of observations in the X-ray, UV, optical and radio regions of the dM5e flare star Proxima Centauri are presented. Simultaneous observations of the star were obtained on March 6 and March 7, 1979, by the Einstein Observatory IPC, the IUE SWP and LWR cameras at low dispersion, three ground-based optical telescopes in Australia and the Parkes 64-m radio telescope. A total of 10 radio bursts and six optical flares was detected during three nights of simultaneous radio and optical observations, which appear to be broadly correlated. A major X-ray flare event was detected with temperatures of 1.7 x 10 to the 7th and 1.2 x 10 to the 7th K during the rise and decay phases, respectively, respective X-ray fluxes of 3.0 x 10 to the -11th and 3.7 x 10 to the -11th ergs/sq cm per sec, and changes in spectral flux distribution. No radio, optical or UV flare emission corresponding to the X-ray flare was detected. The X-ray flare is interpreted in terms of an arch model with cooling predominantly by X-ray radiation, with an electron density of 1.0 x 10 to the 11th/cu cm during the decay phase and a total arch length comparable to the size of the star itself. The X-ray flare observed is thus more similar to a typical strong solar flare than heretofore seen on a flare star.

Haisch, B. M.↗
NASA NTRS2020

X-ray Evolution of the Nova V959 Mon Suggests a Delayed Ejection and a Non-Radiative Shock

X-ray observations of shocked gas in novae can provide a useful probe of the dynamics of the ejecta. Here we report on X-ray observations of the nova V959 Mon, which was also detected in GeV gamma-rays with the Fermi satellite. We find that the X-ray spectra are consistent with a two-temperature plasma model with non-solar abundances. We interpret the X-rays as due to shock interaction between the slow equatorial torus and the fast polar outflow that were inferred from radio observations ofV959 Mon. We further propose that the hotter component, responsible for most of the flux, is from the reverse shock driven into the fast outflow. We find a systematic drop in the column density of the absorber between days 60 and 140, consistent with the expectations for such a picture. We present intriguing evidence for a delay of around 40 d in the expulsion of the ejecta from the central binary. Moreover, we infer a relatively small (a few times 10−6Msun) ejecta mass ahead of the shock, considerably lower than the mass of 104K gas inferred from radio observations. Finally, we infer that the dominant X-ray shock was likely notradiative at the time of our observations, and that the shock power was considerably higher than the observed X-ray luminosity. It is unclear why high X-ray luminosity, closer to the inferred shock power, is never seen in novae at early times, when the shock is expected to have high enough density to be radiative.

Thomas Nelson↗
NASA NTRS1995

The neutral atomic phases of the interstellar medium

We calculate the thermal equilibrium gas temperature of the diffuse interstellar medium. Our method incorporates a new photoelectric heating rate from small grains and polycyclic aromatic hydrocarbons (PAHs) that accounts for a size distribution of particles extending from 100 to 3 A radius. We also include a detailed treatment of the ionization rates and heating due to the soft X-ray background and due to cosmic rays. Phase diagrams (thermal pressure P versus hydrogen density n) are presented for gas that is illuminated by local interstellar far-ultraviolet (FUV) and X-ray radiation fields. A stable two-phase medium is produced with thermal pressure in the range P/k approximately = to 10(exp 3-4) K/cc. We demonstrate that photoelectric heating from PAHs dominates in the warm neutral phase (WNM) and cold neutral phase (CNM). If the C II (158 micrometers cooling per hydrogen nucleus in the solar neighborhood represents an average value for the Galaxy, we predict L(sub CII) approximately = to 7 x 10(exp 7) solar luminosities from the CNM in the Galaxy, comparable to that observed by the Cosmic Background Explorer (COBE). We discuss the dependence of the results on absorbing column density, gas phase abundances, dust abundances and metallicity, FUV field, and the X-ray radiation field. These results will be useful in modeling the multiphase structure of high-velocity clouds in the halo, the interstellar matter (ISM) at other galactocentric radii, and the ISM in external galaxies and galactic nuclei.

Wolfire, M. G.↗
DOE OSTI2020

3D Printable Polymers for Radiological Applications

Additive manufacturing of polymers is a widely used and growing technology throughout the DOE complex. Composite filaments for Fused Deposition Modeling (FDM) printers are commonly used to enhance material properties such as mechanical strength, operating temperature and chemical resistance. Radio luminescent properties were added to 3D filaments by impregnating clear poly(ethylene terephthalate)-glycol (PETG) with X-ray scintillator powder. X-ray scintillators have unique, narrow emission spectra which can be imaged with low light DSLR cameras, photomultiplier tubes, or spectrometers. Filament Production: 1. Pellets are loaded into the hopper. 2. Temperature and extrusion speed are set on extruder. 3. Extruder turned on and filament is pulled from nozzle along air path to cool. 4. Spooler drive speeds set. 5. Filament is inserted through Filameasure then guided along drive wheels and into traverse. 6. Parameters adjusted to obtain 1.75 mm diameter 7. Filament is inserted into spooler wheel. Traverse speed set and slip nut adjusted to make tight and even roll. From Raw Materials to Printed Part: Clear PETG pellets were dipped in ZnS:Cu scintillator powder to coat pellets. Coated and uncoated pellets were mixed together before inserting into hopper. Filament showed trace amounts of powder and luminesced under UV light. Powder distribution is random and not reproducible thus providing a unique identification marker potentially useful for national security applications. Multiple X-ray scintillators can be arranged in a panel to discriminate incident X-ray photon energies. Variable panel arrangement: pixelated, layered, solid from homogenous filament. Ratio of emission intensities. Response varies with incident photon energy. Spectrally separate scintillators. Scintillators: Yttrium Oxide Europium Doped - Red, Gadolinium Oxysulfide Terbium Doped - Green, Barium Magnesium Aluminate Europium Doped - Blue, Zinc Sulfide Copper Doped - Green. Powder concentrations will need to be increased in the filament for use in the energy discriminating panel. Homogeneity in the filament will be a challenge that can be solved by turning the pellets into a powder and mixing it with scintillator powder prior to extrusion. The panels will be tested using x-ray booths and button sources such as Am-241, Cs-137, and Co-60.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1995

ROSAT detection of diffuse hot gas in the edge-on galaxy NGC 4631

We present our ROSAT observation of the edge-on spiral galaxy NGC 4631, a nearby Sc/SBd galaxy best known for its extended radio halo. Because of the low foreground Galactic X-ray-absorbing gas column density, N(sub HI) approximately = 1.4 x 10(exp 20)/sq cm, this observation is sensitive to gas of temperature greater than or approximately = a few x 10(exp 5) K. We detected soft (approximately 0.25 keV) X-ray radiation out to more than 8 kpc above the midplane of the galaxy. The stongest X-ray emission in the halo is above the central disk, a region of about 3 kpc radius which shows high star formation activity. The X-ray emission in the halo is bordered by two extended filaments of radio continuum emission. We also found diffuse X-ray emission from hot gas in the galaxy's disk. The spectrum of the radiation can be characterized by a thermal plasma with a temperature of 3 x 10(exp 6) K and a radiative cooling rate of approximately 8 x 10(exp 39) ergs/sec. This rate is only a few percent of the estimated supernova energy release in the interstellar medium of the galaxy. Analysis of the X-ray spectrum shows evidence for the presence of a cooler (several times 10(exp 5) K) halo gas component that could consume a much larger fraction of the supernova energy. We found strong evidence for disk/halo interaction. Hot gas apparently blows out from supershells in the galaxy's disk at a rate of approximately 1 solar mass/yr. This outflow of hot gas drags magnetic field lines up in the halo and forms a magnetized gaseous halo. If the magnetic field lines are still anchored to the disk gas at large disk radii, the outflowing gas may be confined high above the disk by magnetic pressure. We have identified a strong X-ray source which coincides spatially with an H I supershell. However, the source is likely an extremely luminous X-ray binary with L(sub x)(0.1-2 keV) approximately = 5 x 10(exp 39) ergs/sec, which makes it a stellar mass black hole candidate.

Wang, Q. Daniel↗
DOE OSTI2022

Probing Distinctive Redox Mechanism in Ni-Rich Cathode Via Real-Time Quick X-Ray Absorption Spectroscopy

X-ray radiation damage on the measuring system has been a critical issue regularly for a long-time exposure to X-ray beam during the in operando characterizations, which is particularly severe when the applied X-ray energy is near the absorption edges (M, L, K, etc.) of the interest element. Here, to minimize the negative effects raised by beam radiation, we employ quick X-ray absorption spectroscopy (QXAS) to study the electrochemical reaction mechanism of a Ni-rich layered structure cathode for lithium-ion batteries. With the advanced QXAS technique, the electronic structure and local coordination environment of the transition metals (TMs) are monitored in-operando with limited radiation damage. Compared to the conventional step-mode X-ray absorption spectroscopy, the QXAS can provide more reliable oxidation state change and more detailed local structure evolutions surrounding TMs (Ni and Co) in Ni-rich layered oxides. By leveraging these advantages of QXAS, we demonstrated that the Ni dominates the electrochemical process with the Co being almost electrochemically inactive. Reversible Ni ions movement between TMs sites and Li sites is also revealed by the time-resolved QXAS technique.

25 ENERGY STORAGE↗
DOE OSTI2020

A Coupled Analysis of Atmospheric Mass Loss and Tidal Evolution in XUV Irradiated Exoplanets: The TRAPPIST-1 Case Study

Exoplanets residing close to their stars can experience evolution of both their physical structures and their orbits due to the influence of their host stars. In this work, we present a coupled analysis of dynamical tidal dissipation and atmospheric mass loss for exoplanets in X-ray and ultraviolet (XUV) irradiated environments. As our primary application, we use this model to study the TRAPPIST-1 system and place constraints on the interior structure and orbital evolution of the planets. We start by reporting on an ultraviolet continuum flux measurement (centered around ∼1900 Å) for the star TRAPPIST-1, based on 300 ks of Neil Gehrels Swift Observatory data, and which enables an estimate of the XUV-driven thermal escape arising from XUV photodissociation for each planet. We find that the X-ray flaring luminosity, measured from our X-ray detections, of TRAPPIST-1 is 5.6 × 10{sup −4} L {sub *}, while the full flux including non-flaring periods is 6.1 × 10{sup −5} L {sub *}, when L {sub *} is TRAPPIST-1's bolometric luminosity. We then construct a model that includes both atmospheric mass loss and tidal evolution and requires the planets to attain their present-day orbital elements during this coupled evolution. We use this model to constrain the ratio Q{sup ′}=3Q/2k{sub 2} for each planet. Finally, we use additional numerical models implemented with the Virtual Planet Simulator VPLanet to study ocean retention for these planets using our derived system parameters.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Rotationally Driven Ultraviolet Emission of Red Giant Stars

Main-sequence stars exhibit a clear rotation-activity relationship, in which rapidly rotating stars drive strong chromospheric/coronal ultraviolet and X-ray emission. While the vast majority of red giant stars are inactive, a few percent exhibit strong ultraviolet emission. Here we use a sample of 133 red giant stars observed by Sloan Digital Sky Survey APOGEE and Galaxy Evolution Explorer to demonstrate an empirical relationship between near-UV (NUV) excess and rotational velocity (v sin i). Beyond this simple relationship, we find that NUV excess also correlates with rotation period and with Rossby number in a manner that shares broadly similar trends to those found in M dwarfs, including activity saturation among rapid rotators. Our data also suggest that the most extremely rapidly rotating giants may exhibit so-called supersaturation, which could be caused by centrifugal stripping of these stars rotating at a high fraction of breakup speed. As an example application of our empirical rotation-activity relation, we demonstrate that the NUV emission observed from a recently reported system comprising a red giant with a black hole companion is fully consistent with arising from the rapidly rotating red giant in that system. Most fundamentally, our findings suggest a common origin of chromospheric activity in rotation and convection for cool stars from main sequence to red giant stages of evolution.

79 ASTRONOMY AND ASTROPHYSICS↗