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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 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

DSMC simulations of polarized atomic beam sources including magnetic fields

In recent decades a lot of work has been done to understand and optimize the output of polarized atomic beam sources. However, there are many effects which prevent a complete analytic description of the system. Now, a DSMC (Direct Simulation Monte Carlo ) simulation based on OpenFOAM 1.7.1 using Birds algorithm is set up. So far, the simulated particles have been given spin and a generic utility to include arbitrary magnetic fields has been created. The equation of motion in every timestep is solved by a fourth order Runge-Kutta scheme. In this contribution, we describe promising first results of the simulations. Additionally a tool to measure the collision age has been created. Further effects to be included are recombination on the walls and spin exchange collisions. After that an algorithm will be included to optimize the output of the atomic beam source.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

ON THE IONIZATION OF LUMINOUS WMAP SOURCES IN THE GALAXY: CONSTRAINTS FROM He RECOMBINATION LINE OBSERVATIONS WITH THE GBT

Murray and Raham used the Wilkinson Microwave Anisotropy Probe (WMAP) free-free foreground emission map to identify diffuse ionized regions (DIRs) in the Galaxy. It has been found that the 18 most luminous WMAP sources produce more than half of the total ionizing luminosity of the Galaxy. We observed radio recombination lines (RRLs) toward the luminous WMAP source G49.75-0.45 with the Green Bank Telescope near 1.4 GHz. Hydrogen RRL is detected toward the source but no helium line is detected, implying that n{sub He{sup +}}/n{sub H{sup +}}< 0.024. This limit puts severe constraint on the ionizing spectrum. The total ionizing luminosity of G49 (3.05 Multiplication-Sign 10{sup 51} s{sup -1}) is {approx}2.8 times the luminosity of all radio H II regions within this DIR and this is generally the case for other WMAP sources. Murray and Rahman propose that the additional ionization is due to massive clusters ({approx}7.5 Multiplication-Sign 10{sup 3} M{sub Sun} for G49) embedded in the WMAP sources. Such clusters should produce enough photons with energy {>=}24.6 eV to fully ionize helium in the DIR. Our observations rule out a simple model with G49 ionized by a massive cluster. We also considered 'leaky' H II region models for the ionization of the DIR, suggested by Lockman and Anantharamaiah, but these models also cannot explain our observations. We estimate that the helium ionizing photons need to be attenuated by {approx}>10 times to explain the observations. If selective absorption of He ionizing photons by dust is causing this additional attenuation, then the ratio of dust absorption cross sections for He and H ionizing photons should be {approx}>6.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

A COMPREHENSIVE SURVEY OF HYDROGEN CHLORIDE IN THE GALAXY

We report new observations of the fundamental J = 1-0 transition of HCl (at 625.918 GHz) toward a sample of 27 galactic star-forming regions, molecular clouds, and evolved stars, carried out using the Caltech Submillimeter Observatory. Fourteen sources in the sample are also observed in the corresponding H{sup 37}Cl J = 1-0 transition (at 624.978 GHz). We have obtained clear detections in all but four of the targets, often in emission. Absorptions against bright background continuum sources are also seen in nine cases, usually involving a delicate balance between emission and absorption features. From RADEX modeling, we derive gas densities and HCl column densities for sources with HCl emission. HCl is found in a wide range of environments, with gas densities ranging from 10{sup 5} to 10{sup 7} cm{sup -3}. The HCl abundance relative to H{sub 2} is in the range of (3-30) x 10{sup -10}. Comparing with the chlorine abundance in the solar neighborhood, this corresponds to a chlorine depletion factor of up to {approx}400, assuming that HCl accounts for one-third of the total chlorine in the gas phase. The [{sup 35}Cl]/[{sup 37}Cl] isotopic ratio is rather varied, from unity to {approx}5, mostly lower than the terrestrial value of 3.1. Such variation is highly localized, and could be generated by the nucleosynthesis in supernovae, which predicts a {sup 37}Cl deficiency in most models. The lower ratios seen in W3IRS4 and W3IRS5 likely confine the progenitors of the supernovae to stars with relatively large mass ({approx}>25 M{sub sun}) and high metallicity (Z {approx} 0.02).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Dependence of Cosmological Constraints on Gray Photometric Zero-point Uncertainties of Supernova Surveys

Abstract Type Ia supernova (SN) measurements of the Hubble constant, H 0 ; cosmic mass density, Ω M ; and dark energy equation-of-state parameter, w , rely on heterogeneous SN surveys across three decades of observation. These distinct surveys may have undiagnosed, relative photometric zero-point errors. We determine the sensitivities of the SH0ES+Pantheon+ cosmological constraints to unknown gray systematics in the photometric zero-point calibration between the 19 surveys that comprise the Pantheon+ SN compendium. Varying the surveys’ gray zero-points simultaneously with cosmological parameters, we determine that the SH0ES+Pantheon+ measurement of H 0 is robust against gray intersurvey photometric miscalibration. Specifically, uncalibrated intersurvey systematics could represent a source of uncertainty no larger than 0.39 km s −1 Mpc −1 for H 0 . This modest increase in H 0 uncertainty could not account for the 7 km s −1 Mpc −1 “Hubble tension” between the SH0ES measurement of H 0 and the Planck ΛCDM-based inference of H 0 . However, the SH0ES+Pantheon+ best-fit values of Ω M and w are not robust against gray zero-point error, slipping by up to 0.16 and −0.63. Because measurements of Ω M and w depend on intrasurvey cross-band calibration, the hypothetical gray miscalibration underestimates the sensitivity of these measurements to zero-point miscalibration. Because the Pantheon+ compendium contains many surveys that share low- z Hubble flow (HF) and Cepheid-paired SNe, intersurvey photometric calibration errors do not significantly impede the joint use of SH0ES and Pantheon+ to measure H 0 to 1% accuracy. However, H 0 constraints that rely on one HF survey but numerous galactic distance calibration surveys are susceptible to intersurvey photometric miscalibration.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

What happened to the moon? A lunar history mission using neutrons

The ages of lunar rocks can be determined using the {sup 40}Ar -{sup 39}Ar technique that can be used in-situ on the moon if a neutron source, a noble gas mass spectrometer and a gas extraction and purification system are brought to the lunar surface. A possible instrument for such a task is ISAGE, which combines a strong {sup 252}Cf neutron source and a compact spectrometer for in-situ dating of e.g. the South Pole Aitken impact basin or the potentially very young basalts south of the Aristachus Plateau. In this paper, the design of the neutron source will be discussed. The source is assumed to be a hollow sphere surrounded by a reflector, a geometry that provides a very homogeneous flux at the irradiation position inside the sphere. The optimal source geometry depending on the experimental conditions, the costs of transportation for the reflector and the costs of the source itself are calculated. A minimum {sup 252}Cf mass of 1.5 mg is determined. (authors)

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2011

Production of a high brightness H{sup -} beam by charge exchange of a hydrogen atom beam in a sodium jet

Production of H{sup -} beams for applications in accelerators via charge exchange of a high brightness hydrogen neutral beam in a sodium jet cell is experimentally studied in a joint experiment by the Brookhaven National Laboratory (BNL) and the Budker Institute of Nuclear Physcis (BINP). In the experiment, a hydrogen atomic beam with an energy 3-6 keV, an equivalent current up to 5 A and a pulse duration 200 microseconds is used. Initial results demonstrate that an H{sup -} beam with a current 36 mA, an energy 5 keV and {approx}0.15 cm{center_dot}mrad normalized emittance was obtained. The recirculating sodium jet target with an entrance aperture 2 cm, which was developed for the BNL optically pumped polarized ion source, is used in the experiment. To increase the H{sup -} beam current, geometric focusing of the hydrogen neutral beam will be used in the future experiments. In addition, the effects of H{sup -} beam space-charge and sodium-jet stability will be studied to determine the basic limitations of this approach. The atomic beam is produced by charge exchange of a proton beam in a pulsed hydrogen target. The proton beam is formed by an ion source with a four-electrode multiaperture ion-optical system with small-size apertures. The plasma emission surface is formed by the plasma expansion from an arc plasma generator. The transverse ion temperature at the emission surface is 0.2 eV.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Templated vanadium tellurites: Identifying the effects of low density attractions on inorganic layer topology

Exploration of the NH 4 VO 3 /Na 2 TeO 3 /2,4,6-triaminopyrimidine/H 2 O system yielded the formation of two new phases, [C 4 H 8 N 5 ][VO 3 ] and [C 4 H 8 N 5 ] 2 [V 2 Te 2 O 10 ]. Phase selection in this system is largely dictated by the tellurium concentration during reaction. Differences in the [V 2 Te 2 O 10 ] n 2n- layer topologies in [C 4 H 8 N 5 ] 2 [V 2 Te 2 O 10 ] and two related phases, [C 6 H 16 N 2 ][V 2 Te 2 O 10 ] and [C 5 H 14 N 2 ][V 2 Te 2 O 10 ] were probed using noncovalent interaction energy ratios. These ratios allow for one to directly visualize and quantify differences in intermolecular interaction strengths between compounds. The presence or absence of π - π stacking interactions between organic ammonium cations in [C 4 H 8 N 5 ] 2 [V 2 Te 2 O 10 ] and two related phases, [C 6 H 16 N 2 ][V 2 Te 2 O 10 ] and [C 5 H 14 N 2 ][V 2 Te 2 O 10 ] is the source of layer connectivity differences. These π - π interactions between 2,4,6-triaminopyrimidinium cations in [C 4 H 8 N 5 ] 2 [V 2 Te 2 O 10 ] dictate their orientations between [V 2 Te 2 O 10 ] n 2n- layers, and direct the locations of hydrogen-bonding interactions. Effects associated with reactant concentrations, charge density matching and intermolecular interactions were probed using composition space analyses, Iterative Hirshfeld partial atomic charge, molecular surface area calculations and noncovalent interaction index calculations, respectively.

noncovalent interaction energy ratios↗
DOE OSTI2014

Transmission spectroscopy of the hot Jupiter WASP-12b from 0.7 to 5 μm

Since the first report of a potentially non-solar carbon-to-oxygen ratio (C/O) in its dayside atmosphere, the highly irradiated exoplanet WASP-12b has been under intense scrutiny and the subject of many follow-up observations. Additionally, the recent discovery of stellar binary companions ∼1'' from WASP-12 has obfuscated interpretation of the observational data. Here we present new ground-based multi-object transmission-spectroscopy observations of WASP-12b that we acquired over two consecutive nights in the red optical with Gemini-N/GMOS. After correcting for the influence of WASP-12's stellar companions, we find that these data rule out a cloud-free H{sub 2} atmosphere with no additional opacity sources. We detect features in the transmission spectrum that may be attributed to metal oxides (such as TiO and VO) for an O-rich atmosphere or to metal hydrides (such as TiH) for a C-rich atmosphere. We also reanalyzed NIR transit-spectroscopy observations of WASP-12b from HST/WFC3 and broadband transit photometry from Warm Spitzer. We attribute the broad spectral features in the WFC3 data to either H{sub 2}O or CH{sub 4} and HCN for an O-rich or C-rich atmosphere, respectively. The Spitzer data suggest shallower transit depths than the models predict at infrared wavelengths, albeit at low statistical significance. A multi-instrument, broad-wavelength analysis of WASP-12b suggests that the transmission spectrum is well approximated by a simple Rayleigh scattering model with a planet terminator temperature of 1870 ± 130 K. We conclude that additional high-precision data and isolated spectroscopic measurements of the companion stars are required to place definitive constraints on the composition of WASP-12b's atmosphere.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Coated boron layers by boronization and a real-time boron coating using impurity powder dropper in LHD

In Large Helical Device (LHD), diborane (B 2 H 6 ) is used as a standard boron source for boronization, which is assisted by helium glow discharges. In 2019, a new Impurity Powder Dropper (IPD) system has been installed and is under evaluation as a real-time wall conditioning technique. In LHD), which is a large size heliotron device, an additional helium (He) glow discharge cleaning (GDC) after boronization has been operated for a reduction of hydrogen recycling from coated boron layers, and this operational time of 3 h was determined by spectroscopic data during glow discharges. A flat hydrogen profile is obtained on the top surface of coated boron on the specimen exposed to boronization, the result suggests a reduction of hydrogen at the top surface by He-GDC. Trapped oxygen in coated boron was obtained by boronization, and the coated boron, which has boron-oxide, on the first wall by B-IPD was also shown. Finally, considering the difference in coating areas between B 2 H 6 boronization and B-IPD operation, it would be most effective to use the IPD and B 2 H 6 boronization coating together for optimized wall conditioning.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗