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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Jovian decametric arcs - An estimate of the required wave normal angles from three-dimensional ray tracing.

Three-dimensional ray tracing is applied to an analysis of variable radio wave normal angle effects on the associated decametric (DAM) arc structures in the Jovian magnetosphere. The analysis is bed on 1-40 MHz radio signature recorded during Voyage 1 and 2 passages. The frequencies considered are above the R-X cut-off, and several ratios of the emission frequency/source frequency. The ray tracing code is based on a cold plasma formula and integration of the Hasselgrove (1955) equations. It is assumed that the emission is in the R-X mode, the source lies at the foot of an Io flux tube, and the emission cone is hollow. Attention is focused on data for two intense, vertex-late, high curvature DAM arc. A possible source for the arcs is found to be doppler-shifted gyroemission from a beam of electrons with an energy of 10 keV. A value of 1.1 is set as the limit of the doppler shift of the DAM emissions.

Menietti, J. D.↗
NASA NTRS1985

Lightning-induced electron precipitation from the magnetosphere

Precipitation of radiation belt particles induced by whistlers that are generated by atmospheric lightning discharges and propagate over L shells of 2-4.5 is considered. Using a test particle model of the whistler-particle interaction, the energy spectra and temporal profile of whistler-induced fluxes as a function of L shell are quantitatively determined for a representative plasmaspheric cold plasma distribution. Results indicate that for higher energy electron precipitation (E greater than 40 keV) there exists an inner magnetospheric region (L between 2 and 3) where the level of whistler-induced precipitation can be expected to be comparatively high. Implications of this finding in terms of observational results are discussed.

Chang, H. C.↗
NASA NTRS1985

The hidden ion population - Revisited

In an investigation conducted by Olsen (1982) on the basis of particle data taken with an electrostatic analyzer, it was found that a cold plasma population with a density between 10 and 100 per cu cm appeared suddenly when the satellite was eclipsed, but was hidden in sunlight. The present paper has the objective to show further measurements of ordinarily 'hidden' ion populations, in order to resolve some of the questions raised in connection with the Scatha satellite data reported by Olsen. It is found that the retarding ion mass spectrometer (RIMS) detector is capable of measuring the core of the plasma distribution in sunlight and eclipse, though the task is more easily done in eclipse. There are, however, limitations concerning the ability of the detector to measure all the plasma, all the time. It is, therefore, pointed out that continuous effective measurements of the 'hidden' ion population of the magnetosphere still awaits satellites with effective means of potential control.

Olsen, R. C.↗
NASA NTRS1986

Field-aligned electron precipitation at the edge of an arc

Measurements of field-aligned electrons at the edge of an arc are presented from a sounding rocket flight through a quiet afternoon auroral arc. High time resolution measurements show the evolution of the electron distribution function over the 2.3-km width of field-aligned precipitation. A nearly constant 1.2-eV perpendicular temperature was found for these field-aligned fluxes over a broad range of parallel energies (100 - 900 eV). The small perpendicular temperature indicates that the acceleration region is located at a low altitude. Two models of cold plasma convection into the edge of a V-shaped potential structure are examined and found to be consistent with both the observed fluxes and spatial width of the edge precipitation. Both models predict an average source plasma density less than 130/cu cm to account for the observed field-aligned fluxes and thus an acceleration region well above 1000 km.

Mcfadden, J. P.↗
NASA NTRS1985

Observations of ion cyclotron waves near synchronous orbit and on the ground

Ion cyclotron waves (ICWs) generated in the magnetosphere by the ion cyclotron instability of 10-100 keV protons are now known to be the origin of short-period (0.1-5 Hz) electromagnetic field oscillations observed by synchronous spacecraft and on the earth's surface. Observations of the various wave characteristics, including spectral and polarization properties, that lead to the identification of generation and propagation mechaniisms, and regions in the magnetosphere are described with reference to ATS-6, GEOS, and ground-based wave data and interpreted using cold plasma propagation theory. The presence of heavy ions (O/+/, He/+/) dramatically modifies ICW magnetospheric propagation characteristics giving rise to spectral slots and polarization reversals. These properties may be used in plasma diagnostics. Finally satellite-ground correlations and techniques for determining the magnetospheric source position of ICWs not seen at synchronous orbit but observed on the ground as structured Pc1 pulsations are considered.

Fraser, B. J.↗
NASA NTRS1986

Ion cyclotron waves observed near the plasmapause

Pc2 electromagnetic ion cyclotron waves at 0.1 Hz, near the oxygen cyclotron frequency, have been observed by ISEE-1 and -2 between L = 7.6 - 5.8 on an inbound near equatorial pass in the dusk sector. The waves occurred in a thick plasmapause of width about 1 earth radius and penetrated about 1 earth radius into the plasmasphere. Wave onset was accompanied by significant increases in the thermal (0-100 eV) He(+) and the warm (0.1-16 keV/e) O(+) and He(+) heavy ion populations. Wave polarization is predominantly left-handed with propagation almost parallel to the ambient magnetic field, and the spectral slot and polarization reversal predicted by multicomponent cold plasma propagation theory are identified in the wave data. The results are considered as an example of wave-particle interactions occurring during the outer plasmasphere refilling process at the time of the substorm recovery phase.

Fraser, B. J.↗
NASA NTRS1987

Whistler mode emissions in the Uranian radiation belts

Voyager 2 detected intense whistler mode emissions and fluxes of energetic electrons during the outbound pass through the region of auroral L shells. The observed energetic (E greater than 22 keV) electron distribution, a model warm (E less than 27.5 keV) electron distribution, and the cold plasma density profile deduced by Kurth et al. (1987) are used to calculate the ray path-integrated spatial amplification of whistlers which arrive at Voyager 2 from the magnetic equator. By matching the calculated amplification and the relative gains at different frequencies deduced from the observed whistler power spectrum, the pitch angle anisotropy parameters of the electron distributions are determined to within a fairly narrow range of values. The estimated bounce average pitch angle diffusion coefficient indicates that electrons are on strong diffusion over a wide range in energies. The electron precipitation energy flux is sufficient to produce the observed auroral light emissions.

Coroniti, F. V.↗
NASA NTRS1988

Cyclotron line resonant transfer through neutron star atmospheres

Monte Carlo methods are used to study in detail the resonant radiative transfer of cyclotron line photons with recoil through a purely scattering neutron star atmosphere for both the polarized and unpolarized cases. For each case, the number of scatters, the path length traveled, the escape frequency shift, the escape direction cosine, the emergent frequency spectra, and the angular distribution of escaping photons are investigated. In the polarized case, transfer is calculated using both the cold plasma e- and o-modes and the magnetic vacuum perpendicular and parallel modes.

Wang, John C. L.↗
NASA NTRS1989

Rocket observations of the precipitation of electrons by ground VLF transmitters

Recent results obtained with electric and magnetic receivers aboard a NASA sounding rocket launched on July 31, 1987 are presented which relate multiple electron spectral peaks observed in the bounce loss cone fluxes to the resonant interaction of electrons with VLF waves from ground transmitters. The correlation of transmitter signals passing through the ionosphere with the precipitated electrons was investigated. The analysis of these in situ wave and particle data addresses the propagation of waves through the ionosphere, and, through an application of the resonant theory, enables an estimation of the cold plasma density in the interaction region.

Arnoldy, Roger L.↗
NASA NTRS1989

Organic solids produced from simple C/H/O/N ices by charged particles - Applications to the outer solar system

The effects of charged particle irradiation by cold plasma discharge on surfaces of H2O:CH4 clathrate with a 200:1 ratio and on ices composed of H2O and C2H6 or C2H2 are examined. The molecules studies are found in Comet Halley and are plausible constituents in icy outer solar system objects. The IR transmission spectra of four ice-tholin residues obtained in the laboratory are compared with spectra produced by irradiation of gases and ices containing simple hydrocarbons. The similarities between CH4 clathrate residue and Halley organic grains, and the surface transport or atmospheric replenishment activity on Triton and Pluto are discussed.

Khare, B. N.↗
NASA NTRS1990

Resonant decay of global MHD modes at 'thick' interfaces

A global surface mode can exist on a 'surface' which is not a true discontinuity, but without sufficient dissipation it is not a normal mode and it decays in time via resonance absorption. The decay rate can be calculated analytically when the 'surface' is thin. The goal of this paper is to numerically estimate the decay rate when the surface is not thin. A cold plasma in a uniform magnetic field is considered in which density varies linearly across the 'surface'. In this linearized calculation, the global surface mode is driven in steady state by an antenna located in one of the uniform regions external to the surface. The frequency is a free parameter, and resonance curves are computed numerically without approximations. The widths of the resonance curves are used to estimate the free decay times of undriven surface modes, via the uncertainty principle. When applied to the active solar corona, the decay rates are large enough to account for the coronal heating, but it should be kept in mind that the role of nonlinearity in resonance absorption is still undetermined.

Hollweg, Joseph V.↗
NASA NTRS1990

A statistical characterization of plasmasphere density structure and boundary locations

Plasmaspheric density profiles and their cold plasma boundaries observed by the retarding ion mass spectrometer aboard the DE-1 satellite were classified using the results of a statistical study. Six different categories of the plasmasphere density profiles were identified: 'featureless', featureless with enhancement near left, multiple-plateau, featureless with trough, multiple-plateau with trough, and other complex structure profiles. An explanation for the occurrence of these different profiles is presented.

Horwitz, J. L.↗
NASA NTRS1990

Innovative techniques for the production of energetic radicals for lunar materials processing including photogeneration via concentrated solar energy

The Department of Materials Science and Engineering (MSE) is investigating the use of monatomic chlorine produced in a cold plasma to recover oxygen and metallurgically significant metals from lunar materials. Development of techniques for the production of the chlorine radical (and other energetic radicals for these processes) using local planetary resources is a key step for a successful approach. It was demonstrated terrestrially that the use of UV light to energize the photogeneration of OH radicals from ozone or hydrogen peroxide in aqueous solutions can lead to rapid reaction rates for the breakdown of toxic organic compounds in water. A key question is how to use the expanded solar resource at the lunar surface to generate process-useful radicals. This project is aimed at investigating that question.

Osborn, D. E.↗
NASA NTRS1990

Relaxation of the loss-cone by quasi-linear diffusion of the electron-cyclotron maser instability in the solar corona

A self-consistent numeric two-dimensional code using kinetic-wave particle equations has been developed and applied to the maser dynamics of the solar corona. Time histories generated by the code reveal details of the evolution of the linear phase, the saturation and subsequent relaxation of the loss cone. Quantitative values are obtained for the saturation time, the amount of the converted free energy, the critical wave energy level for onset of maser diffusion, the velocity and pitch angle range of the resonant particles, and the relative importance of the different magnetoionic modes and harmonics. A wide range of initial conditions is covered by varying the loss-cone distribution and the ambient cold plasma parameters.

Aschwanden, Markus J.↗
NASA NTRS1990

Theory of electromagnetic cyclotron wave growth in a time-varying magnetoplasma

The effect of a time-dependent perturbation in the magnetoplasma on the wave and particle populations is investigated using the Kennel-Petchek (1966) approach. Perturbations in the cold plasma density, energetic particle distribution, and resonance condition are calculated on the basis of the ideal MHD assumption given an arbitrary compressional magnetic field perturbation. An equation is derived describing the time-dependent growth rate for parallel propagating electromagnetic cyclotron waves in a time-varying magnetoplasma with perturbations superimposed on an equilibrium configuration.

Gail, William B.↗
NASA NTRS1990

Auroral kilometric radiation - An example of relativistic wave-particle interaction in geoplasma

The earth's auroral kilometric radiation (AKR) is believed to be produced by the electron-cyclotron maser instability. This instability is the result of a wave-particle interaction in which relativistic effects are crucial. An explanation is given as to how these relativistic effects alter the shape of the resonance curve in velocity space and modify the R - X mode wave dispersion near the electron cyclotron frequency compared to the results obtained in the nonrelativistic limit and from cold-plasma theory. The properties of the cyclotron maser instability in a driven system are illustrated using two-dimensional electromagnetic particle simulations which incorporate a continual flow of primary energetic electrons along the magnetic field.

Pritchett, P. L.↗
NASA NTRS1991

ULF waves upstream of the Venus bow shock - Properties of one-hertz waves

Pioneer Venus Orbiter data are used here to study the properties of a class of ULF upstream waves with relatively high observed frequencies. These waves show significant similarity to 'one-Hz' waves identified at earth in the ISEE 1 and 2 observations and the whistler waves identified earlier by IMP 6 observations. The waves appear almost immediately after the spacecraft crosses the magnetic field tangent line to the bow shock surface into the region of connected field lines. The wave amplitude decreases with distance from the shock measured along the magnetic field line. Group velocities calculated using the cold plasma dispersion relation indicate that the waves have sufficient upstream velocities to propagate form the shock into the solar wind. The totality of observations seem best explained by a source of right-handed whistler mode waves at the bow shock.

Orlowski, D. S.↗
NASA NTRS1991

Evolution to nonequilibrium in simple models of prominence filaments

The support of cold plasma against gravity by a line-tied magnetic field is considered. The normal component of the field at the boundaries, the mass/unit flux, and the magnetic shear are all specified. Fixing the first two of these quantities, and varying the third leads to evolutionary sequences. When the magnetic shear is less than a critical value, an infinite number of solutions exist. When the magnetic shear is sufficiently large, there are no solutions with the desired topology. These results support the idea that prominences erupt as a result of evolution to magnetic nonequilibrium.

Zweibel, Ellen G.↗