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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Development of an apparatus for obtaining molecular beams in the energy range from 2 to 200 eV

The formation and detection of molecular beams obtained by charge exchange from a low-energy ion source is discussed. Dispersion in energy of the ion source was measured and problems concerning detection of neutral beams were studied. Various methods were used, specifically secondary electron emissivity of a metallic surface and ionization of a gas target with a low ionization voltage. The intensities of neutral beams as low as 10 eV are measured by a tubular electron multiplier and a lock-in amplifier.

Clapier, R.↗
NASA NTRS1969

Ionization of positive ions.

Binary encounter model for ionization by charged particle impact modified to evaluate cross section for ionization of positive ions by electron impact

Garcia, J. D.↗
NASA NTRS1972

Dynamics of the inverse pinch.

Experiments are performed on the plasma produced in a large inverse pinch using argon with no applied magnetic fields or preheating. A direct observation is made of the precursor ionization which initially raises the electron temperature and electrical conductivity. Calculations show that most of the mass is entrained in the current sheet, but that less than complete sweeping occurs at the lower velocities. The shock which is embedded in the current sheet closely resembles an ordinary gasdynamic shock. Consideration of the shock jump condition derived from the induction equation is shown to determine the frequent inability of the shock to separate from the current sheet.

Weisbach, M. F.↗
NASA NTRS1973

Magnetic control of the near equatorial neutral thermosphere.

Neutral density data between 400 and 500 km obtained with the Ogo 6 neutral mass spectrometer indicate that at all longitudes the daytime N2 and O densities have latitudinal minimums at the magnetic equator that are about 20 and 10%, respectively, below maximums observed between plus and minus 20 deg magnetic latitude. Our calculations suggest that this anomaly could result from latitudinal variations in ion drag associated with the 'equatorial anomaly' in F region ionization. At latitudes of enhanced electron density the energy flow from the dayside to the nightside of the earth is damped, and thus the amplitude of the temperature and density variations is enhanced, and the time of maximum is shifted to later local times.

Hedin, A. E.↗
NASA NTRS1973

Soft X-ray flare spectra

Large solar flares produce intense soft X-ray emission, indicating the existence of high temperature plasmas that coexist in time with the plasmas responsible for the normally observed brightenings in H-alpha. The time behavior of the X-ray flux, as revealed, for example, by ion chamber detectors on the series of Solrad monitoring satellites, appears to roughly mimic the intensity-time behavior of the H-alpha flare, insofar as start times, times of maximum flux, and approximate decay times are concerned. In recent years, soft X-ray spectra of both active regions and solar flares have been obtained by instruments flown on spacecraft such as the Orbiting Solar Observatory (OSO) series. The disbursing elements used were Bragg crystals, and in the 8 Angstrom region the resolution is typically approximately 1200. This paper discusses the observed characteristics of X-ray flare spectra and spectroscopic diagnostics for determining electron temperatures, electron densities, and departures from ionization equilibrium within the soft X-ray emitting plasma.

Doschek, G. A.↗
NASA NTRS1974

A multiwire proportional counter system for high energy astrophysics

Resolution tests of multiwire proportional counter delay line readout systems are reported. The system is being developed at NASA/JSC for use in a large balloon borne magnet spectrometer. The system is ultimately intended for use in Space Shuttle missions. Tests of two different types of delay line and associated electronics carried out in minimum ionizing particle beams (accelerator and sea level cosmic ray) are reported. Resolution performance is shown to be strongly dependent on type of gas mixture and in the case of inclined events upon the propagation velocity of the delay line. The resolution performance achieved for magic gas chamber filling (100 um at normal incidence) is far superior to any other state of the art technique capable of being applied to large geometry factor systems.

Lacy, J. L.↗
NASA NTRS1974

Line absorption studies of the interstellar gas near 1 million GHz

The Copernicus satellite now opens up the ultraviolet region for inspection, and the number of resonance lines which may be studied has increased from 6, seen in the visible, to more than 30. The distribution and properties of an important constituent of the interstellar gas, molecular hydrogen, can be studied in detail using this instrument. A more comprehensive picture may now be developed for element depletion factors, electron densities, and sources of ionization (UV photons, low energy cosmic and X-rays).

Jenkins, E. B.↗
NASA NTRS1979

Calculation of radiative properties of nonequilibrium hydrogen plasma

A computer program called NEQRAP is described that calculates the radiative properties of nonequilibrium ionized hydrogen. From the given electron temperature, electron density, and atom density values (which do not necessarily satisfy the equilibrium relationship) and intensities of incident radiation, the non-Boltzmann populations of electronic states are computed by solving the equation of quasi-steady-state population distribution. Emission and absorption coefficients are determined as functions of wavelength by invoking the principle of detailed balance between the upper and lower states of each radiative transition. Radiative transport through the medium is computed assuming a one-dimensional uniform slab. The rate of ionic reaction is also computed. When used on a sample case, the program shows that there is a large difference between the calculated intensities of radiation emitted by a bulk of equilibrium and nonequilibrium hydrogen. The accuracy of the program is estimated to be better than 10%.

Park, C.↗
NASA NTRS1981

Detectors for energies less than 10 MeV

In the energy domain 100 keV to 10 MeV, both crystal scintillations and semiconductors are widely used for gamma ray detectors in spectrometer systems. These detectors' operation depend on the fact that gamma rays lose energy by ionization in these materials and electrons and holes are produced. In the case of semiconductors, these electrons and holes are collected by an electric field, and they provide an electric signal that is a direct measure of the energy lost by the gamma ray in the material. Scintillation detectors depend on a further conversion of the energy lost in electron hole pair production to the production of photons. A photomultiplier tube measures the intensity of the photon flux, and an electrical pulse proportional to the photon intensity is produced at the photomultiplier output.

Source record↗
NASA NTRS1985

Spacecraft-induced plasma energization and its role in flow phenomena

Plasma instabilities induced by orbiting vehicles can cause many important phenomena ranging from electron and ion heating and suprathermal electron tail energization, to enhanced ionization and optical emissions. We outline the basic collective processes leading to plasma energization near plasma sheaths and in regions of neutral gas streaming through plasma, and discuss the role of the induced collective effects in producing the optical emission spectra.

Papadopoulos, K.↗
NASA NTRS1987

The formation of a double layer leading to the critical velocity phenomenon

The formation of a double layer is proposed as the mechanism which produces the critical velocity phenomenon. This hypothesis was examined qualitatively and it was found that the double layer can be a very efficient mechanism for transferring the kinetic energy of the neutral gas into the kinetic energy of electrons which, in turn, will ionize the neutral gas if the critical velocity was reached or exceeded.

Williams, A. C.↗
NASA NTRS1987

The formation of a double layer leading to the critical velocity phenomenon

The formation of a double layer is proposed as the mechanism which produces the critical velocity phenomenon. This hypothesis is examined qualitatively, and it is found that the double layer can be a very efficient mechanism for transferring the kinetic energy of the neutral gas into the kinetic energy of electrons which, in turn, will ionize the neutral gas if the critical velocity has been reached or exceeded.

Williams, A. C.↗
NASA NTRS1988

The outer atmospheres of the coolest M giants - Ultraviolet spectra of Rho Persei, 2 Centauri, g Herculis, Theta Apodis, and R Lyrae

New IUE observations of five M giants cooler than most studied previously have been obtained in order to study the variation of chromospheric properties with effective temperature. The ultraviolet spectrum lines of one of these stars, Rho Persei, are identified. The properties of the spectra of of the five stars are examined in detail, including the line widths and turbulence, the radial velocities of groups of lines, the structure in the Mg II resonance lines, and the fluorescent lines. The physical properties of the M giants' chromospheres are considered, including the formation of Fe II, the electron density, the degree of ionization of iron, magnesium, silicon, and carbon, the hydrogen ionization and energy balance, and the creation and destruction of photons.

Eaton, Joel A.↗