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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Nonlinear wave particle interaction in the Earth's foreshock

The possibility that ion beams could provide a free energy source for driving an ion/ion instability responsible for the ULF wave occurrence is investigated. For this, the wave dispersion relation with the observed parameters is solved. Secondly, it is shown that the ring-like distributions could then be produced by a coherent nonlinear wave-particle interaction. It tends to trap the ions into narrow cells in velocity space centered around a well-defined pitch-angle, directly related to the saturation wave amplitude in the analytical theory. The theoretical predictions with the observations are compared.

Mazelle, C.↗
NASA NTRS1981

Energetic heavy ions with nuclear charge Z greater than or equal to 4 in the equatorial radiation belts of the earth - Magnetic storms

Direct in situ observations of trapped energetic heavy ions with nuclear charge Z greater than or equal to 4 at energies in the lower MeV range made with Explorer 45 during the period June-December 1972 are presented. It is noted that all measurements were carried out in the vicinity of the geomagnetic equatorial plane and that the data show the varying effects of four major magnetic storm periods. Orders of magnitude increases in the trapped heavy ion population are seen deep within the radiation belts following the August 1972 solar flare and magnetic storm events. Fluxes of the Z greater than or equal to 4 ions are found to decay faster than those of helium ions of comparable energies; typical decay times for these ions are found to be 24-40 days at L less than or equal to 4 and shorter at higher L shells. The observations are compared with the expected post-injection long-term behavior of atomic oxygen ions deduced from charge exhange, radial diffusive transport, and Coulomb collisions. Good agreement is found between theory and observations.

Spjeldvik, W. N.↗
NASA NTRS2003

Facile Generation and Storage of Polycyclic Aromatic Hydrocarbon Ions in Astrophysical Ices

In situ ultraviolet-visible absorption and emission studies of vacuum ultraviolet (VUV) irradiated water-rich, cosmic ice analogs containing polycyclic aromatic hydrocarbons (PAHs) are described. W V irradiation of 12 K water ices containing the PAHs naphthalene (H2O/C10H8 = 200) and 4-methylpyrene (H2O/C17H12 > 500) readily converts the PAHs into their cation form (PAH(+)). Under these conditions, PAH photoionization is the predominant reaction. These ions are trapped and stored in the ices at temperatures between 10 and 50 K, a temperature domain common to ices throughout interstellar clouds and the solar system. Unlike the approx.15% ionization typical after W V irradiation of PAHs isolated in rare-gas matrices, in water ice, PAH photoionization and storage proceed efficiently and almost quantitatively with a greater than 70% ionization yield. As the temperature is increased from 50 to 150 K, the PAH ion bands slowly diminish as the PAH ions ultimately react to form more complex organic species involving the water host. The chemical, spectroscopic, and physical properties of these ion-rich ices can be important in icy objects such as molecular clouds, comets, and planets. Several astrophysical applications are presented.

Gudipati, Murthy S.↗
NASA NTRS1994

Simulations of phase space distributions of storm time proton ring current

We use results of guiding-center simulations of ion transport to map phase space densities of the stormtime proton ring current. We model a storm as a sequence of substorm-associated enhancements in the convection electric field. Our pre-storm phase space distribution is an analytical solution to a steady-state transport model in which quiet-time radial diffusion balances charge exchange. This pre-storm phase space spectra at L approximately 2 to 4 reproduce many of the features found in observed quiet-time spectra. Using results from simulations of ion transport during model storms having main phases of 3, 6, and 12 hr, we map phase space distributions from the pre-storm distribution in accordance with Liouville's theorem. We find stormtime enhancements in the phase space densities at energies E approximately 30-160 keV for L approximately 2.5 to 4. These enhancements agree well with the observed stormtime ring current. For storms with shorter main phases (approximately 3 hr), the enhancements are caused mainly by the trapping of ions injected from open night side trajectories, and diffusive transport of higher-energy (greater than or approximately 160 keV) ions contributes little to the stormtime ring current. However, the stormtime ring current is augmented also by the diffusive transport of higher-energy ions (E greater than or approximately 160 keV) durinng stroms having longer main phases (greater than or approximately 6 hr). In order to account for the increase in Dst associated with the formation of the stormtime ring current, we estimate the enhancement in particle-energy content that results from stormtime ion transport in the equatorial magnetosphere. We find that transport alone cannot account for the entire increase in absolute value of Dst typical of a major storm. However, we can account for the entire increase in absolute value of Dst by realistically increasing the stormtime outer boundary value of the phase space density relative to the quiet-time value. We compute the magnetic field produced by the ring current itself and find that radial profiles of the magnetic field depression resemble those obtained from observational data.

Chen, Margaret W.↗
NASA NTRS1994

Efficient Quenching of Population Trapping in Excited Yb superscript +

The efficiency of various buffer gases in quenching the population trapping states of laser excited ytterbium ions is described. Highly efficient in quenching the population of the trapping states, N subscript 2 has been identified as the most suitable buffer gas to use with ytterbium for the development i=of a trapped ion microwave frequency standard.

Buffer gases↗
NASA NTRS1995

Efficient Quenching of Population Trapping in Excited Yb(+)

We report on a study to determine the efficiency of various buffer gases in quenching the population trapping states of laser-excited ytterbium ions. The ions were confined in an rf-dc hybrid trap, and their (2)S(.5) left and right arrow (2)P(3/2) transition was excited with 329-nm laser light. Buffer gases used include H2, N2, CO2, Ar, and He at several different pressure regimes. We have identified N2 to be highly efficient in quenching the population of the trapping states and thus be the most suitable buffer gas to use with ytterbium for the development of a trapped-ion microwave frequency standard.

Seidel, D. J.↗
NASA NTRS1972

Electron spin resonance of ultraviolet radiation induced defects in ZnO thermal control coating pigment.

Electron spin resonance measurements on variously treated zinc oxide powders reveal that the resonance signal at g = 1.956 is due to one electron trapped oxygen ion vacancy level, at a depth of (0.31 plus or minus 0.02) eV below the conduction band. The electrons at this level are delocalized. Schottky barrier influences nearly the entire bulk of the powder sample, and the bending of the bands caused by chemisorbed oxygen puts the vacancy level above the Fermi level almost through the entire bulk.

Mookherji, T.↗
NASA NTRS1973

Lunar ion flux and energy

The dynamics of the lunar ionosphere and resulting flux of lunar ions to the lunar surface are reviewed. In the Lunar rest frame, ions formed from the neutral lunar atmosphere are accelerated by the interplanetary electric and magnetic fields. The trajectories of heavier ions are primarily along the electric field; the ion flux is in a direction perpendicular to the solar wind flow, correlated to the orientation of the interplanetary magnetic field, and impacts the surface with energies of tens of electron volts to a few keV. Thus we predict a relatively energetic (compared to thermal energies), highly directional, lunar ion flux but with the possibility that light ions such as hydrogen can execute orbits that return them to portions of the lunar surface not directly exposed to the solar wind. The effects of surface electric and magnetic fields are discussed, as is the ion energy spectrum. We calculate the trapping of atmospheric ions which impact the surface and from this the density of neutral Ar 40 in the lunar atmosphere. We show that using the acceleration model, the lunar atmosphere total neutral number density can be calculated from ion detector data.

Manka, R. H.↗
NASA NTRS1977

Direct measurement of the ionization states of energetic carbon and oxygen emitted by the sun

The ionization states of carbon and oxygen accelerated in nine solar-flare particle events have been measured for energies between 15 keV per nucleon and 600 keV per nucleon, using the electrostatic energy-charge analyzer aboard the IMP 8 earth-orbiting spacecraft. The ionization states are found to be remarkably constant from flare to flare, despite great variations in other event parameters. The mean ionic charge for carbon is 5.7, and that for oxygen is 6.2; these values show no statistically significant variation with energy over the range of measurements. The observed states are similar to the respective ionization states in the solar wind. The measured ionization charge states of C and O are shown to be consistent with charge equilibrium established with an electron gas at a temperature of about 1.5 million K, the temperature of the quiet corona. This implies either that the charge states are 'frozen-in' and are not changed by subsequent acceleration and propagation, or that the ions are trapped in the quiet corona after acceleration.

Sciambi, R. K.↗
NASA NTRS1982

The dependence of single event upset on proton energy /15-590 MeV/

Low earth orbit satellite and Jupiter orbiter probe semiconductor devices may incur soft errors or single event upsets, manifested as bit flips, during exposure to such nuclear particles or heavy ions as trapped protons with energies ranging up to 1000 MeV. Experimental data is given on the average proton fluence needed to cause a bit flip as a function of proton energy for isoplanar bipolar TTL RAMs. Error dependence data shape and threshold energy can be related to the existing body of theoretical data on energy deposition following proton nuclear reactions. Experimental data also show that the relative cross sectional amplitude for functionally identical devices can be related to the device's power consumption.

Nichols, D. K.↗
NASA NTRS1987

MHD wave breaking in the outer plasmasphere

Empirical models of the average magnetospheric magnetic field, plasma density, and temperature distributions are used to construct a model of the distribution of MHD wave mode speeds within the magnetosphere. A persistent feature of the derived optical structure is a pronounced minimum of the wave speeds in the outer plasmasphere, i.e., a magnetospheric 'shoal'. This feature does not map along magnetic field lines, but is confined to the equatorial region, leading to a positive radial gradient of wave speeds near synchronous orbit. The breaking of earthward propagating disturbances in this region may play an essential role in the formation of the substorm injection boundary and in the creation of equatorially trapped warm ion distributions.

Moore, T. E.↗
NASA NTRS1988

The virtual cathode as a transient double sheath

The two-dimensional plasma potential measurements are given of a space-charge dominated double sheath near a hot cathode. Laboratory data show that a virtual cathode is a self-consistent solution only for a transient cathode-plasma system. Slow charge exchange ions get trapped in the potential dip that forms the virtual cathode and eventually destroy it.

Intrator, T.↗
NASA NTRS1988

The terrestrial ring current - From in situ measurements to global images using energetic neutral atoms

Electrical currents flowing in the equatorial magnetosphere, first inferred from ground-based magnetic disturbances, are carried by trapped energetic ions. Spacecraft measurements have determined the spectrum and composition of those currents, and the newly developed technique of energetic-neutral-atom imaging allows the global dynamics of that entire ion population to be viewed from a single spacecraft.

Roelof, Edmond C.↗
NASA NTRS1988

Observations of intense ULF pulsation activity near the geomagnetic equator during quiet times

This paper analyzes observations, made by particle and field instruments on the AMPTE CCE satellite, of intense ULF pulsations in the earth's magnetosphere near the geomagnetic equator. These pulsations were observed during magnetically quiet periods in regions characterized by intense fluxes of warm strongly trapped light ions, predominantly H(+), and often with streaming low-energy plasma. The strong latitudinal localization of these pulsations is interpreted to be due to equatorial mass loading or to partial reflection of Alfven wave energy by latitudinal gradients in plasma density. Possible sources of wave energy for these events are discussed.

Engebretson, M. J.↗
NASA NTRS1993

Polar wind ion dynamics in the magnetotail

The circulation of polar wind ions from the high-latitude ionosphere to the plasma sheet is investigated. Single-particle trajectory simulations for the geomagnetic tail show, in addition to the breaking of adiabaticity, the possible creation of new high-altitude mirror points. This trajectory feature results from an intense parallel deceleration imparted by the magnetic field rotation during fast ExB transport. This centrifugal deceleration yields a critical parallel velocity which depends on the magnitude of the convection electric field and below which ions remain trapped inside the neutral sheet.

Delcourt, D. C.↗