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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Investigation of gas temperature measurements using ultraviolet excitation

A high resolution spectrographic study has been made of the nitrogen first negative system as induced by ultraviolet radiation. The radiation used in this experiment was the neutral helium resonance radiation at 584 A. Nitrogen molecules at approximately 300 K and at a pressure of one torr were ionized by the ultraviolet radiation with the aid of a windowless experimental configuration. The resulting nitrogen fluorescence was analyzed with sufficient resolution to enable study of the intensities of the R branch rotational lines of the 0-0 vibrational band of the first negative system. The data indicate that the induced population of the upper levels approximates a Boltzmann Distribution at the ambient temperature of the gas.

Ofelt, G. S.↗
NASA NTRS1976

Mass loss in red giants and supergiants

The circumstellar envelopes surrounding 13 late-type giants and supergiants have been studied using a homogeneous collection of high-resolution, photoelectric scans of strong optical resonance lines. Various properties of the envelopes, including the mass loss rate, dilution factor, hydrogen density, and degree of ionization, have been determined quantitatively.

Sanner, F.↗
NASA NTRS1981

The ultraviolet dayglow. IV - The spectrum and excitation of singly ionized oxygen

The emission line spectrum of singly ionized atomic oxygen (O II) dominates the day airglow spectrum in the extreme ultraviolet below 834 A. The strongest resonance line, at 834 A, is optically thick and an analysis of height profiles obtained from rocket observations between 140 and 265 km in specific viewing directions indicates that the principal excitation source is direct photoionization of neutral atomic oxygen. Strong emission at 538-539 A is most likely due to the quartet rather than the doublet transitions, which both occur at these wavelengths and which are not spectrally resolved in the data. The intensities of the weaker lines are consistent with recent laboratory measurements of transition branching ratios. Several strong O II lines near He I 584 produce severe contamination of low-altitude (less than 400 km) measurements of geocoronal helium emission made with thin-film broadband photometers.

Feldman, P. D.↗
NASA NTRS1986

Ultraviolet and visual variability of Theta CrB during a normal B-phase following a shell phase (1980-1985)

Based on far-UV and visual observations made between 1980 and 1985, the phenomena characterizing the end of a shell phase of Theta-CrB, and the normal B-phase following it, are described as part of a long-term study of Be stars. The strength, shape, and velocity of the C IV, Si IV, and Al III resonance lines, and the Fe III lines of low excitation, show associated variability patterns over the whole range of ionization observable in the IUE and visual spectra. The observed variability pattern consists of a one-year narrow-line stage where the lines show narrow absorption cores close to rest wavelength, a two-year series of abrupt changes between a weak and a strong line, and a damping out of these variations leaving the observed spectrum in a lower ionization state. The existence of a phase-lag between similar phenomena occurring in the superionized and subionized/normally ionized regions, is noted.

Doazan, V.↗
NASA NTRS1999

Recent Progress on the VASIMR

Experimental and theoretical studies on the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) have continued through a NASA led collaborative program involving several research groups. In the experimental area, performance characterization of the VASIMR helicon plasma source has been obtained over a portion of the parameter space, with helium and hydrogen propellant. Density (10(exp 18) - 10(exp 19)/ cubic meter) and temperature (5 eV) were measured at moderate degree of ionization in two separate experimental devices. Helicon design improvement and optimization will be discussed. Experiments with the ion cyclotron resonance heating (ICRH) subsection have begun and preliminary results will be discussed. Theoretical picture and integrated numerical simulation continue to be refined to account for the main physics elements of the VASIMR, including RF absorption and particle acceleration with subsequent detachment in the magnetic nozzle.

ChangDiaz, Franklin R.↗
NASA NTRS1995

On Ba(+) production in the CRIT 2 experiment

Analysis of partical data from the CRIT 2 experiment, studying Alfven's critical ionization velocity (CIV) effect, shows that the density of newly created ions (presumably Ba(+) from the shaped-charge beam) is consistent with the increase in total plasma density measured by the independent RF plasma probe on board (Swenson et al., 1990) at the most active time period. We model this ion production using the measured electron flux data and the neutral barium model of Stenbaek-Nielsen et al. (1990a). To identify the main source mechanisms which may contribute most to the barium ionization, a simple model for the barium ion density at the payload location is developed based on Liouvilles theorem. We estimate that the electron impact ionization is responsible for 90% of the barium ion production observed by CRIT 2 in the first release and up to 45% in the second release. By employing a two-state approximation calculation (Rapp and Francis, 1962), the Ba-O(+) charge exchange cross section is found to range from about 2.0 X 10(exp -17) sq cm at a velocity of 4 km/s to 2.0 X 10(exp -15) sq cm at a velocity of 20 km/s. This result suggests that the Ba-O(+) charge exchange is probably dominant among all the non-CIV ionization processes. By considering the charge exchange process in our density model, the barrium ion densities are calculated for the two releases on CRIT II. The comparison between the model results and the observed data is found to be resonably consistent if the cross sections, as calculated above, are multiplied by 0.3 for the first release and 1.0 for the second release. Our result suggests that the charge exchange process could be the most important non-CIV ionization mechanism in the CRIT II experiment and it should be considered carefully case by case in CIV experiments.

Liou, K.↗
NASA NTRS1974

Theoretical helium I emission-line intensities for quiescent prominences

Self-consistent solutions of the combined statistical equilibrium and transfer equations have been carried out for a rather complete multilevel, multi-ion model helium atom in model quiescent prominences. The excitation and ionization of both He I and He II were considered simultaneously, and detailed calculations of the radiative transfer in the resonance lines and ground-state continua of both these ions were made, allowing for the effects of overlapping hydrogen transitions. A large number of excited states have been included in the computation, so that a fairly comprehensive set of predicted subordinate line intensities are now available for comparison with observation. A preliminary comparison of the predicted values with published singlet/triplet ratio observations shows good agreement for all the pairs of lines considered.

Heasley, J. N.↗
NASA NTRS1976

Calculation of multiphoton ionization processes

We propose an accurate and efficient procedure in the calculation of multiphoton ionization processes. In addition to the calculational advantage, this procedure also enables us to study the relative contributions of the resonant and nonresonant intermediate states.

Chang, T. N.↗
NASA NTRS1980

Ultraviolet observations of 31 and 32 Cygni

Some observations of 31 and 32 Cygni, started in September 1978, at phases 0.62 and 0.17, respectively, are presented. The UV spectrum of 32 Cyg is described both qualitatively and quantitatively. Numerous lines of Si II, O I, C II, Al II and III and Fe II appear with P Cygni characteristics. The LWR-2275 image is dominated by the Mg II 2800 A resonance doublet and numerous Fe II lines in the 2200 - 2700 A region, all showing P Cygni profiles. More quantitatively, ionization modeling for the B star environs was made by comparing observed and computed equivalent widths to deduce density, temperature and turbulence values. At the projected separation between the stars, the log particle density obtained was 7.2, neglecting dust and molecule formation.

Stencel, R. E.↗
DOE OSTI2020

Probing the Electronic Structure of Warm Dense Nickel via Resonant Inelastic X-Ray Scattering

The development of bright free-electron lasers (FEL) has revolutionized our ability to create and study matter in the high-energy-density (HED) regime. Current diagnostic techniques have been successful in yielding information on fundamental thermodynamic plasma properties, but provide only limited or indirect information on the detailed quantum structure of these systems, and on how it is affected by ionization dynamics. In this work we show how the valence electronic structure of solid-density nickel, heated to temperatures of around 10 of eV on femtosecond timescales, can be probed by single-shot resonant inelastic x-ray scattering (RIXS) at the Linac Coherent Light Source FEL. The RIXS spectrum provides a wealth of information on the HED system that goes well beyond what can be extracted from x-ray absorption or emission spectroscopy alone, and is particularly well suited to time-resolved studies of electronic-structure dynamics.

36 MATERIALS SCIENCE↗
NASA NTRS1981

The interstellar medium and the highly ionized species observed in the spectrum of the nearby white dwarf G191-B2B

High-resolution spectra of the nearby (48 pc) white dwarf G191-B2B, obtained with the International Ultraviolet Explorer, reveal sharp resonance lines of N V, C IV, and Si IV. The origin of these features is most likely linked to the white dwarf, possibly being formed in an expanding halo around the star. Interstellar lines of C II, N I, Mg II, Si II, and Fe II are also seen in the spectrum. Analysis of these features indicates an average neutral hydrogen number density of 0.064 for this line of sight. In combination with the recent EUV and soft X-ray results, this is interpreted to mean that the interstellar medium in the most immediate solar vicinity is of the normal density n approximately equal to 0.1/cu cm of lower ionization, while just beyond it, at least in some directions, is a hot lower density plasma. These results are apparently in conflict with the model of the interstellar medium by McKee and Ostriker (1977) in its present form.

Bruhweiler, F. C.↗
DOE OSTI2025

2025 ASMS Investigation of the Collision-Induced Dissociation Mechanism of Protonated TODGA with IRIS

Title (20 words): Investigation of the Collision-Induced Dissociation Mechanism of Protonated TODGA with IRIS Introduction (120 words): One of the challenges facing wide-spread adoption of nuclear power is the development of efficient separation processes for used nuclear fuel. The molecules in separation processes are subjected to an extreme environment due to the high radiation fields from the used fuel and highly acidic media used for fuel dissolution, which results in significant molecular degradation, leading to reduced process efficiency. These degradation products must be identified and studied so mitigation strategies can be developed to maintain process efficiency. However, complex systems can have many degradation products, complicating identification. Untargeted analysis tools could be used to understand radiation chemistry in complex systems. However, this would necessitate improved understanding of the gas-phase fragmentation mechanisms of fuel cycle molecules like tetraoctyldiglycolamide (TODGA). Methods (120 words): The gas-phase fragmentation of protonated TODGA was investigated using collision-induced dissociation (CID), resonance ejection, and infrared ion spectroscopy (IRIS). CID and resonance ejection experiments were conducted using a Bruker Daltonics (Bremen, Gemany) SolariX XR fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. IRIS spectra of protonated TODGA and its two CID fragmentation products were measured using a modified Bruker amaZon Speed ETD 3D quadrupole ion trap mass spectrometer coupled to the Free Electron Lasers for Infrared eXperiments (FELIX) free electron laser. Measured spectra were compared with density functional theory (DFT) calculations using the Gaussian 16, Revision C.02 software package with the ?B97X-D functional and def2-TZVPP basis sets. Candidate structures were generated using the CREST 3.0 conformational sampling software tool. Preliminary Data (300 words): Collision-induced dissociation of protonated TODGA ([C36H73N2O3]+, m/z=581.562) results two fragment ions, one at m/z=340.285 assigned as [C20H38NO3]+ and the other at m/z=312.290, assigned as [C19H38NO2]+. Based on the assigned formula and the structure of protonated TODGA, the fragment at m/z=340.285 is likely formed from elimination of neutral dioctylamine. Comparison of the IRIS spectrum of m/z=340.285 with DFT predictions suggests it contains a ring structure, and is assigned as N-octyl-N-(6-oxo-1,4-dioxan-2-ylidene)octan-1-aminium. Based on this structure and the structure of protonated TODGA, we hypothesize this fragment formed from elimination of neutral dioctylamine followed by a ring closure mechanism. Comparison of the IRIS spectrum of the fragment at m/z=312.290 with DFT predictions also indicated the presence of a ring structure, assigned as N-(1,3-dioxolan-4-ylidene)-N-octyloctan-1-aminium. This product could be formed from elimination of carbon monoxide from the ring of m/z=340.285 as a sequential fragmentation or formed directly from protonated TODGA via elimination of neutral N,N-dioctylformamide followed by a ring closure. Resonance ejection experiments where m/z=340 was continuously ejected from the IRC cell showed no decrease in intensity of m/z=312.290 across several collision energies, suggesting that the later, direct formation mechanism, dominates. The location of the ionizing proton in protonated TODGA is important for modeling the fragmentation mechanisms. DFT calculations suggested that the position of bands involving the coupled vibrations of the amide C—N and C=O bonds in TODGA are the most sensitive to proton location. Evaluation of the IRIS spectrum of protonated TODGA suggests that the ionizing proton is located between the two amid oxygens. This protonation location was calculated to lie approximately 30 kJ/mol lower in energy than the next lowest energy location, with the proton located solely on one of the amide oxygens. Novel aspect (20 words): Infrared ion spectroscopy combined with resonance ejection experiments and density functional theory to probe the collision-induced dissociation mechanism of tetraoctyldiglycolamide.

37 - INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL C↗
DOE OSTI2020

Butyltin Keggin Ion with a Rare Four-Coordinate Ca Center

Alkyltin clusters are exploited in nanolithography for the fabrication of microelectronics. The alkyltin Keggin family is unique among Keggin clusters across the periodic table; its members appear to favor the lower-symmetry β and γ isomers rather than the highly symmetrical α and ε isomers. Therefore, the alkyltin Keggin family may provide important fundamental information about the formation and isomerization of Keggin clusters. In this study, we have synthesized and structurally characterized a new butyltin Keggin cluster with a tetrahedral Ca 2+ center, fully formulated [(BuSn) 12 (CaO 4 )(OCH 3 ) 12 (O) 4 (OH) 8 ] 2+ (β-CaSn 12 ). The synthesis is a simple one-step process. Extensive solution characterization including electrospray ionization mass spectrometry, small-angle X-ray scattering, and multinuclear ( 1 H, 13 C, and 119 Sn) nuclear magnetic resonance shows β-CaSn 12 is essentially phase-pure and stable. This differs from the previously reported Na-centered analogues that always form a mixture of β and γ isomers, with facile interconversion. Therefore, this study has clarified prior confusion over complex spectroscopic and crystallographic characterization of the Na-centered analogues. Density functional theory calculations showed the following stability order: γ-CaSn 12 < γ-NaSn 12 < β-CaSn 12 < β-NaSn 12 . The β analogue is always more stable than the γ analogue, consistent with experiment. Notable outcomes of this study include a rare tetrahedral Ca coordination, a Na-free alkyltin cluster (important for microelectronics manufacturing), and a better understanding of Keggin families built of different metal cations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Atomic and Molecular Physics in Strong Fields

In this project, we have investigated a broad range of atomic, molecular, and optical (AMO) processes of current significance in strong-field and ultrafast science and technology. The main goals are to develop new theoretical formalisms and accurate computational methods for ab initio and in-depth non-perturbative study of time-resolved multiphoton quantum dynamics and spectroscopy, very-high-order harmonic generation, optimal control of ultrafast attosecond pulse generation, and resonance-enhanced below threshold harmonics in intense ultrashort laser fields. We have worked on the following projects and we have published 20 top 15 % SCI journal articles during the last 3.5 years (Jan. 1, 2016 to June 30, 2019), including one article in top raking Physical Review Letters, and 3 articles in top ranking (Nature) Scientific Reports, and one Physical Review A article was chosen as Editors’ suggestion paper, etc. (a) Development of new time-dependent methods for accurate and efficient solution of multi-dimensional time-dependent Schrödinger equation and time-dependent density functional theory. (b) Non-perturbative treatment of very-high order (1000th – 5000th order) harmonic generation and broadband supercontinuum spectra from XUV to soft x-ray regime. (c) Development of synchrosqueezing transform (SST) for precision time-frequency analysis of electron multi-rescattering dynamics. (d) Exploration of the dynamical origin of resonance-enhanced near- and below-threshold harmonics. (e) Probing the high-order harmonics generation in disordered semiconductor. (f) Multiphoton ionization of one-electron relativistic diatomic quasi-molecules in strong laser fields. and, (g) New development of non-adiabatic density functional theory. The theoretical and simulation projects we have pursued are closely related to the ongoing experimental researches in several leading laboratories in the US and Europe, etc. It is expected that the outcome of this project will provide timely and significant new information and insight for the advancement of strong-field atomic and molecular physics and ultrafast science and technology.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1986

Double photon excitation of high-Rydberg atoms as a long-lived submillimeter detector

A method and apparatus for detecting submillimeter or IR radiation is disclosed. A rare gas, such as xenon, is supplied at its ground state via a pressurized cylinder and an adjustable leak valve into a cryogenically cooled detection area. The ground state of xenon is double photon excited to a particularized level of the Rydberg series by a resonance lamp and a laser. The doubly excited gas is then further excited by the radiation to be measured. A field ionization and an ion measurement indicative of the radiation intensity is achieved.

Chutjian, A. N.↗
NASA NTRS1989

Currents between tethered electrodes in a magnetized laboratory plasma

Laboratory experiments on important plasma physics issues of electrodynamic tethers were performed. These included current propagation, formation of wave wings, limits of current collection, nonlinear effects and instabilities, charging phenomena, and characteristics of transmission lines in plasmas. The experiments were conducted in a large afterglow plasma. The current system was established with a small electron-emitting hot cathode tethered to an electron-collecting anode, both movable across the magnetic field and energized by potential difference up to V approx.=100 T(sub e). The total current density in space and time was obtained from complete measurements of the perturbed magnetic field. The fast spacecraft motion was reproduced in the laboratory by moving the tethered electrodes in small increments, applying delayed current pulses, and reconstructing the net field by a linear superposition of locally emitted wavelets. With this technique, the small-amplitude dc current pattern is shown to form whistler wings at each electrode instead of the generally accepted Alfven wings. For the beam electrode, the whistler wing separates from the field-aligned beam which carries no net current. Large amplitude return currents to a stationary anode generate current-driven microinstabilities, parallel electric fields, ion depletions, current disruptions and time-varying electrode charging. At appropriately high potentials and neutral densities, excess neutrals are ionized near the anode. The anode sheath emits high-frequency electron transit-time oscillations at the sheath-plasma resonance. The beam generates Langmuir turbulence, ion sound turbulence, electron heating, space charge fields, and Hall currents. An insulated, perfectly conducting transmission line embedded in the plasma becomes lossy due to excitation of whistler waves and magnetic field diffusion effects. The implications of the laboratory observations on electrodynamic tethers in space are discussed.

Stenzel, R. L.↗
NASA NTRS1974

Highly ionized atoms observed with Copernicus

Based on high-resolution observations using the Princeton satellite/spectrometer on Copernicus the O VI doublet is discussed in detail, in conjunction with data for the resonance lines of N V, Si IV, and S IV reported in five stars. The temperature, density, and the possible extent of the O VI producing region are discussed. The ratio N(S IV)/N(O VI) is used to derive a lower limit to the temperature in the O VI producing region. In near pressure equilibrium with normal interstellar clouds and H II regions minimum densities are found to be consistent with a hot plasma.

York, D. G.↗