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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 NTRS1995

Effects of Surface Treatments on Secondary Electron Emission from CVD Diamond Films

Secondary electron emission (SEE) properties of polycrystalline diamond films grown by chemical vapor deposition (CVD) were measured. The total secondary yield (sigma) from as-grown samples was observed to be as high as 20 at room temperature and 48 while heating at 700 K in vacuum. Electron-beam-activated, alkali-terminated diamond films have shown stable values of sigma as high as 60 when coated with CsI and similarly high values when coated with other alkali halides. Diamond coated with BaF2 had a stable sigma of 6, but no enhancement of the SEE properties was observed with coatings of Ti or Au. Hydrogen was identified to give rise to this effect in as-grown films. However, electron beam exposure led to a reduction in sigma values as low as 2. Exposure to a molecular hydrogen environment restored sigma to its original value after degradation, and enabled stable secondary emission during electron beam exposure. Atomic hydrogen and hydrogen plasma treatments were performed on diamond/Mo samples in an attempt to increase the near-surface hydrogen concentration which might lead to increased stability in the secondary emission. Raman scattering analysis, scanning electron microscopy, and Auger electron spectroscopy (AES) confirmed that hydrogen plasma and atomic hydrogen treatments improved the quality of the CVD diamond significantly. Elastic recoil detection (ERD) showed that heating as-grown diamond targets to 7OO K, which was correlated with an increase in sigma, removed contaminants from the surface but did not drive hydrogen from the diamond bulk. ERD showed that the hydrogen plasma treatment produced an increase in the hydrogen concentration in the near-surface region which did not decrease while heating in vacuum at 700 K, but no improvement in the SEE properties was observed.

Mearini, G. T.↗
NASA NTRS1989

Operating characteristics of a hydrogen-argon plasma torch for supersonic combustion applications

The residence time of the combustible mixture in the combustion chamber of a scramjet engine is much less than the time normally required for complete combustion. Hydrogen and hydrocarbon fuels require an ignition source under conditions typically found in a scramjet combustor. Analytical studies indicate that the presence of hydrogen atoms should greatly reduce the ignition delay in this environment. Because hydrogen plasmas are prolific sources of hydrogen atoms, a low-power, uncooled hydrogen plasma torch has been built and tested to evaluate its potential as a possible flame holder for supersonic combustion. The torch was found to be unstable when operated on pure hydrogen; however, stable operation could be obtained by using argon as a body gas and mixing in the desired amount of hydrogen. The stability limits of the torch are delineated and its electrical and thermal behavior documented. An average torch thermal efficiency of around 88 percent is demonstrated.

Barbi, E.↗
NASA NTRS1984

Pioneer 10 and Voyager Observations of the Interstellar Medium in Scattered Emission of the He 584 a and H Lya 1216 a Lines

The combination of Pioneer photometric and Voyager spectrometric observations of EUV interstellar-interplanetary emissions in the region beyond 5 A was applied to a determination of atomic hydrogen and helium densities. These density estimates obtained from direct measurement of scattered radiation depend on absolute calibration of the instruments in the same way as other earlier determinations based on the same method. However, the spacecraft data were combined with daily ll sun averages of the H Lyman 1216 A line obtained by the Solar Mesospheric Explorer satellite to obtain a measure of atomic hydrogen density independent of instrument absolute calibration. The method depends on observations of long and short term temporal variability of the solar line over a one year period, and the fact that the ISM is optically thick. The density estimates from preliminary work on these observations are H = 0.12/cu cm and H = .016/cu cm, giving a density ratio close to the cosmic abundance value in contrast to some earlier results indicating a depletion of atomic hydrogen. Estimates were obtained of galactic background emissions in the signals of both spacecraft.

Shemansky, D. E.↗
NASA NTRS1984

Pioneer 10 and Voyager observations of the interstellar medium in scattered emission of the He584 A and H Lya 1216 A lines

The combination of Pioneer photometric and Voyager spectrometric observations of EUV interstellar-interplanetary emissions in the region beyond 5 A was applied to a determination of atomic hydrogen and helium densities. These density estimates obtained from direct measurement of scattered radiation depend on absolute calibration of the instruments in the same way as other earlier determinations based on the same method. However, the spacecraft data were combined with daily full sun averages of the H Lyman 1216 A line obtained by the Solar Mesospheric Explorer satellite to obtain a measure of atomic hydrogen density independent of instrument absolute calibration. The method depends on observations of long and short term temporal variability of the solar line over a one year period, and the fact that the ISM is optically thick. The density estimates from preliminary work on these observations are H = 0.12 cu cm and H = .016 cu cm, giving a density ratio close to the cosmic abundance value in contrast to some earlier results indicating a depletion of atomic hydrogen. Estimates were obtained of galactic background emissions in the signals of both spacecraft.

Shemansky, D. E.↗
NASA NTRS1984

Pioneer 10 and Voyager Observations of the Interstellar Medium in Scattered Emission of the H 584 A and H Lya 1216 A Lines

The combination of Pioneer photometric and Voyager spectrometric observations of EUV interstellar-interplanetary emissions in the region beyond 5 AU have been applied to a determination of atomic hydrogen and helium densities. These density estimates obtained from direct measurement of scattered radiation depend on absolute calibration of the instruments, in the same way as other earlier determinations based on the same method. However. we have combined the spacecraft data with daily full sun averages of the H Lya 1216 A line obtained by the Solar Mesospheric Explorer (SME) satellite, to obtain a measure of atomic hydrogen density independent of instrument absolute calibration. The method depends on observations of long and short term temporal variability of the solar line over a 1 year period, and the fact that the ISM is optically thick. The density estimates from preliminary work on these observations are (H) = 0.12 cm(sup 2) and (He) = .016 cm(sup 2), giving a density ratio close to the cosmic abundance value, in contrast to some earlier results indicating a depletion of atomic hydrogen. We have obtained estimates of galactic background emissions in the signals of both spacecraft.

Shemansky, D. E.↗
NASA NTRS1994

Neutral hydrogen in the solar wind acceleration region

Observation of solar Ly alpha radiation scattered by coronal neutral hydrogen atoms can be used to investigate the acceleration region of the solar wind. In this paper we focus on the use of these observations to study Alfven waves, which can accelerate the solar wind plasma to flow speeds observed in high-speed streams if their amplitude at the coronal base is 20 km/s or larger. The wave amplitude is then larger than the proton thermal speed in the outer corona, so that the mean proton speed (averaged over a wave period) is significantly larger than the proton thermal speed. For low-frequency wave the hydrogen atoms follow the proton motion in the waves, while for higher frequencies the protons move relative to the neutrals. Nevertheless, in the higher frequency case, the rates for charge exchange and recombination are high enough to broaden the velocity distribution function of neutral hydrogen. Both the wave motion of the hydrogen atoms in low-frequency Alfven waves and the 'heating' by higher frequency waves lead to a broadening of the scattered solar Ly alpha line. For coronal base amplitues of 20 km/s, the line broadening increases with heliocentric distance beyond 4-5 solar radii.

Olsen, Espen Lyngdal↗
NASA NTRS1974

Compact hydrogenator

The development and characteristics of a hydrogenating apparatus are described. The device consists of a reaction chamber which is selectively permeable to atomic hydrogen and catalytically active to a hydrogenating reaction. In one device, hydrogen is pumped out of the reaction chamber while the reactant remains inside to remove molecular hydrogen so that more atomic hydrogen can pass through the walls. In another device, the reactant is pumped through the reaction chamber, and the hydrogen is removed from the material leaving the chamber. The reactant is then cycled through the chamber.

Simmonds, P. G.↗
NASA NTRS1988

UV resonance line dayglow emissions on earth and Jupiter

The similarities and differnces between atomic resonance line emissions on earth and Jupiter are studied. For earth, the scattering of the conservative atomic oxygen triplet transition at 1304 A and the nonconservative atomic oxygen sextuplet at 989 A is considered. For Jupiter, the scattering of the conservative atomic hydrogen doublet at 1216 A and the nonconservative atomic hydrogen doublet at 1026 A are addressed. Models are presented for the intensities of the emission features as seen from a distance of several planetary radii, using the same observational geometry for both earth and Jupiter. Variations of the line-integrated emissions across the disk and near the limb of each planet are examined in detail. Line profiles for the emission near the limb and at disk-center are also studied. The models reveal the importance of including inhomogeneities and temperature variations of the atmosphere in scattering models, and indicate that outer planet emissions previously interpreted as 'electroglow' may be solely due to resonant scattering of solar emissions.

Gladstone, G. Randall↗
NASA NTRS1991

Velocity measurements in a hydrogen arcjet using LIF

A new diagnostic developed to measure the axial velocity of atomic hydrogen in a 1-kW hydrogen-fueled arcjet thruster is reported. The technique is based on laser-induced fluorescence of the Balmer alpha transition (656 nm) in atomic hydrogen. A narrow-band CW ring dye laser scans the excitation spectrum permitting accurate determination of the absorption line shape and position. The velocity is derived from the Doppler-shifted line position. A spatially resolved velocity profile is presented with a peak velocity of 12.8 km/s at the arcjet centerline near the exit plane.

Liebeskind, John G.↗
NASA NTRS1972

The interstellar molecular hydrogen observed in the ultraviolet spectrum of delta Scorpii

Molecular hydrogen bands of the Lyman and Werner systems were observed in the ultraviolet, interstellar spectrum of delta Sco. The average molecular column density is given, and the average temperature of the gas of which the molecules are part is 47 K. Minimum and maximum gas temperatures are 25 and 98 K respectively. The ratio of the number of hydrogen atoms in molecular form to the total number of hydrogen atoms in either atomic or molecular form is 0.044 (+0.070, -0.018).

Smith, A. M.↗
NASA NTRS2003

Seasonal/Diurnal Mapping of Ozone and Water in the Martian Atmosphere

Ozone and water are key species for understanding the stability and evolution of Mars atmosphere; they are closely linked (along with CO, H, OH, and O) through photochemistry. Photolysis of water produces the OH radical (thought to catalyze reformation of CO2 from CO and O2) and atomic hydrogen (which reacts with O3 forming OH and O2). Atomic hydrogen also reacts with O2 (forming HO2), thereby reducing the amount of O2 available to reform O3 from collisions between O and O2. Hence ozone and water should be anti-correlated on Mars. Photolysis of O3 produces O2(a(sup 1) delta g) with 90% efficiency, and the resulting emission band system near 1.27 mm traces the presence and abundance of ozone. This approach was initially used to study ozone on Earth and then applied to Mars. In 1997, we measured several lines of the O2(a(sup 1) delta g) emission using CSHELL at the NASA IRTF; the O2(a(sup 1) delta g) state is also quenched by collisions with CO2. This quenching dominates at lower altitudes so that the detected emissions are used to detect ozone column densities above ~20 km. The slit was positioned N-S along Mars' central meridian resulting in a one-dimensional map of ozone. Nearly simultaneous maps may be made of water using CSHELL by detecting the v1 fundamental band of HDO near 3.67 microns and using the D/H ratio for Mars. This technique was used by DiSanti and Mumma. With CSHELL, measurements for both O2(a(sup 1) delta g) emissions and HDO absorptions can be made during the day or night. Since January, 1997, we have repeated these measurements at different times during the Martian year. For all of these dates, we have positioned the slit N-S along the central meridian; for some of these dates, we have also stepped the slit across the planet at 1 arc-sec intervals generating a 2-dimensional map. We have also positioned the slit E-W on Mars thus providing diurnal variations of ozone and water along the slit.

Novak, R. E.↗
NASA NTRS1972

Developable Images Produced by X-rays Using the Nickel Hypophosphite System. 1 X-ray Sensitive Salts

Twenty-eight crystalline salts were X-irradiated and treated with an ammoniacal nickel hypophosphite solution. Treatment (development) of six of the salts resulted in precipitation of nickel metal. The developable salts were four hypophosphites, sodium phosphite, and nickel formate. A mechanism is proposed for the process based on the postulate that micro amounts of hydrogen atoms are formed during the radiation step. During development, these hydrogen atoms cause the formation of nucleation sites of nickel metal. In turn, these sites catalyze further reduction of the nickel cations by the hypophosphite. The results are discussed in terms of application of the process to the formation of developable latent images.

May, C. E.↗
NASA NTRS1986

Development and evaluation of a 1 kW plasma torch ignitor for scramjets

A low power, uncooled plasma torch was tested in combination with a new injector design to study ignition and flameholding in hydrogen-fueled supersonic flows. Both semifree jet and ducted tests were conducted in a Mach 2 flow under simulated scramjet combustor conditions at 1 atmosphere static pressure and total temperatures between 1400 and 2800 R. The injector design incorporates a small upstream pilot fuel flow, a step for recirculation, and primary fuel injectors downstream of the recirculation region. Using a 1:1 volumetric mixture of hydrogen and argon, good performance at a simulated flight Mach number of 3.7 is found for a 1-kW torch which is located in the recirculation zone and fueled by the upstream pilot fuel injectors. Spectroscopic measurements verified the presence of hydrogen atoms in the torch exhaust, and it is suggested that hydrogen atoms are responsible for the ignition.

Wagner, Timothy C.↗
NASA NTRS1984

Particle excitation, airglow and H2 vibrational disequilibrium in the atmosphere of Jupiter

The extreme ultraviolet EUV emission produced by particle excitation of the hydrogen atmospheres of Jupiter and Saturn is examined using model calculations to determine the nature of the energy deposition process and the effect of such processes on atmospheric structure. Tasks ranging from examination of phenomenologically related processes on Saturn and Titan to analysis of experimental laboratory data required to allow accurate modeling of emissions from hydrogenic atmospheres are investigated. An explanation of the hydrogen H Ly(alpha) bulge in Jupiter's emission from the equatorial region is presented. It is proposed that Saturn, rather then Titan is the major source of the extended hydrogen cloud. The atomic hydrogen detected at the rings of Saturn may originate predominantly from the same source. A cross calibration is obtained between the Pioneer 10 EUV photometer and the Voyager EUV spectrometers, thus providing a direct measure of the temporal morphology of Jupiter between a minimum and a maximum in solar activity. Atomic and molecular data required for the research program are analyzed. An extrapolation of conditions in the upper atmospheres of Jupiter and Saturn produces a predicted condition at Uranus in terms of excitation and hydrogen escape rates that may be observed at Voyager-Uranus encounter.

Shemansky, D. E.↗
NASA NTRS1979

Theory of direct scattering of neutral and charged atoms

The theory for direct elastic and inelastic collisions between composite atomic systems formulated within the framework of the Glauber approximation is presented. It is shown that the phase-shift function is the sum of a point Coulomb contribution and of an expression in terms of the known electron-hydrogen-atom and proton-hydrogen-atom phase shift function. The scattering amplitude is reexpressed, the pure Coulomb scattering in the case of elastic collisions between ions is isolated, and the exact optical profile function is approximated by a first-order expansion in Glauber theory which takes into account some multiple collisions. The approximate optical profile function terms corresponding to interactions involving one and two electrons are obtained in forms of Meijer G functions and as a one-dimensional integral, and for collisions involving one or two neutral atoms, the scattering amplitude is further reduced to a simple closed-form expression.

Franco, V.↗