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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Characteristics of nonthermal electrons accelerated during the flash phase of small solar flares

Observations of impulsive hard X-rays and other flash phase emissions from small solar flares are analyzed in order to determine the characteristics of energetic electrons accelerated during the flash phase. The electron spectrum and its time variation are deduced from a model of the X-ray source in which the electron injection is continuous, and the electron energy loss is primarily due to collisions with the ambient plasma and escape into the corona. The instantaneous electron spectrum in the X-ray source, as well as the acceleration spectrum, are found to be nonthermal. The observations are consistent with a flare model having the following properties: (1) the acceleration region is located in the lower corona where the ion density is less than 10 to the 9th power per cubic centimeter, (2) the total kinetic energy of the nonthermal electron is approximately 10 percent of the total flare energy, so that the efficiency of the acceleration process is very high, (3) the nonthermal electrons (and protons) provide energy for all flash phase emissions, (4) the acceleration is a continuous process with a time constant less than 1 second, or a continuous series of impulses each lasting less than 1 second and a total duration of approximately 100 seconds, (5) the electron spectrum continuously hardens during the increasing phase of the X-ray burst and softens during the decreasing phase and, (6) the more energetic flares to not necessarily produce a harder electron spectrum.

Kane, S. R.↗
NASA NTRS1978

On the relation between phase path, group path and attenuation in a cold absorbing plasma

Consideration is given to a cold absorbing plasma in which the collision frequency is zero. Expressions are developed which relate the attenuation and the group and phase refractive indices. It is found that because the expressions for the group and phase refractive indices and the imaginary part of the refractive index are closely related in form, the attenuation is related to the difference between the group and phase paths. Numerical calculations have derived approximations which significantly increase the range of known approximations of this type.

Bennett, J. A.↗
NASA NTRS1983

A deficiency of O III in the Io plasma torus

Evidence for a deficiency of O III ions in the Io plasma torus is reported and implications of this deficiency for the physical processes controlling the plasma are considered. Observations of the O III 5007-A as well as Cl III and S III emissions from the Io plasma torus were made by a ground-based echelle spectrograph and intensified Reticon detector in February and May, 1981. The O III observations allow an upper limit of 4/cu cm to be placed on torus O III abundance, which is inconsistent with expectations for a low density plasma controlled by electron collisions. The inclusion of ion-ion and ion-atom charge exchange reactions and a depleted high energy electron component in the model is found to suppress O III levels, however observed limiting values are only achieved if it is assumed that the O III is kinetically hot. In addition, the charge-exchange model developed is inconsistent with previous observations of the kinetics of the S II-S III system. The present observations also establish upper limits of 2 R on 5518-A and 5538-A Cl III emission, and an emission rate of 58 + or - 40 R for the S III 6312-A line in the hot torus.

Brown, R. A.↗
NASA NTRS1991

Nonlinear penetration of whistler pulses into collisional plasmas via conductivity modifications

A strong electromagnetic impulse (about 0.2 microsec) with central frequency in the whistler-wave regime is applied to a large laboratory plasma dominated by Coulomb collisions. Local electron heating at the antenna and transport along B0 create a channel of high conductivity along which the whistler pulse penetrates with little damping. Because of its rapid temporal evolution, this new form of modulational instability does not involve ducting by density gradients which require ion time scales to develop.

Urrutia, J. M.↗
NASA NTRS1961

The Neutralization of Ion-Rocket Beams

The experimental ion-beam behavior obtained without neutralizers is compared with both simple collision theory and plasma-wave theory. This comparison indicates that plasma waves play an important part in beam behavior, although the present state of plasma-wave theory does not permit more than a qualitative comparison. The theories of immersed-emitter and electron-trap neutralizer operation are discussed; and, to the extent permitted by experimental data, the theory is compared with experimental results. Experimental data are lacking completely at the present time for operation in space. The results that might be expected in space and the means of simulating such operation in Earth-bound facilities, however, are discussed.

Kaufman, Harold R.↗
NASA NTRS1992

A semikinetic model for early stage plasmasphere refilling. I - Effects of Coulomb collisions

A collisionless, time-dependent, kinetic plasma model is applied to the problem of baseline plasmasphere refilling of an initially depleted flux tube, without regard for the effects of wave-particle interactions. Refilling calculations for various flux tubes and for different ionospheric plasma fluxes and temperatures are performed. In each case considered, the same set of events occurs. Initially, two polar wind outflows develop from each hemisphere and set up counterstreaming beams. With time the vacant phase space region between these beams fills, primarily because of collision-induced particle diffusion but also because of lowering ambipolar potential drops from the increasing density in the plasmasphere. In contrast to all previous hydrodynamic approaches, no formation of shocks was found. The plasma first evolves an isotropic, nearly Maxwellian velocity distribution in a region that starts near the ionosphere and moves outward toward the equator. For reasonable topside ionospheric temperatures and fluxes, the thermal plasma all along an L shell is found to become nearly isotropic in 6 to 30 hr, consistent with the observations of Horwitz et al. (1984).

Wilson, G. R.↗
NASA NTRS2010

High-Energy Electron-Ion and Photon-Ion Collisions: Status and Challenges

Non-LTE plasmas are ubiquitous in objects studied in the UV and X-ray energy bands. Collisional and photoionization cross sections for atoms and ions are fundamental to our ability to model such plasmas. Modeling is key in the X-ray band, where detector properties and limited spectral resolution limit the ability to measure model-independent line strengths, or other spectral features. Much of the motivation for studying such collisions and many of the tools, are not new. However, the motivation for such studies and their applications, have been affected by the advent of X-ray spectroscopy with the gratings on Chandra and XMM-Newton. In this talk I will review this motivation and describe the tools currently in use for such studies. I will also describe some current unresolved problems and the likely future needs for such data.

Kallman, Timothy R.↗
NASA NTRS1987

The infrared diagnostic of a dusty plasma with applications to supernova remnants

IRAS observations of infrared emission from supernova remnants constitute the first observational evidence of shock-heated dust in the interstellar medium. These observations can provide valuable information on the morphology of supernova remnants, and on their interaction with the ambient interstellar medium. In particular, they can be used to study the physical condition and the cooling rate of dusty astrophysical plasmas. In this paper, consideration is given to the possibilities and limitations of using the infrared observations as a diagnostic for the shocked gas, and as a means of determining remnant parameters. The paper presents improved calculations for the cooling rate of a dusty plasma by means of gas-grain collisions, and the equilibrium temperature of the dust for a variety of plasma conditions. These results are then used to define the density-temperature parameter space of the plasma, which, given its infrared spectrum, should be occupied by the observed remnant. This constraint can be used to estimate distances to supernova remnants and to set limits on various parameters that determine their evolution. The analysis is applied to the remnants Cas A and the Cygnus Loop.

Dwek, Eli↗
NASA NTRS1987

Generation of plasma waves by thick-target electron beams, and the expected radiation signature

The production of plasma waves by a nonthermal beam of high-energy electrons injected into a background thermal plasma was investigated. The coupled kinetic equations for nonthermal electrons were solved, and the level of the plasma waves produced by the bump-on-tail instability arising as a result of the Coulomb collisions of nonthermal electrons with background plasma was estimated. In addition, the radiation signatures of these waves were examined. It is shown that the wave-particle interactions have a significant effect on the overall distribution of the electrons and that it is unlikely that such effects can be discerned in the observed bremsstrahlung or synchrotron radiation of the nonthermal electrons. However, a significant fraction of the energy lost by the beam is transferred to plasma waves and is then dissipated by the thermal plasma.

Hamilton, Russell J.↗
NASA NTRS1967

Gaseous electronics

Electron collisional effects on wave propagation in nonmagnetized plasma

ELECTRONICS↗
NASA NTRS1993

Micro- to macroscale perspectives on space plasmas

The Earth's magnetosphere is the most accessible of natural collisionless plasma environments; an astrophysical plasma 'laboratory'. Magnetospheric physics has been in an exploration phase since its origin 35 years ago but new coordinated, multipoint observations, theory, modeling, and simulations are moving this highly interdisciplinary field of plasma science into a new phase of synthesis and understanding. Plasma systems are ones in which binary collisions are relatively negligible and collective behavior beyond the microscale emerges. Most readily accessible natural plasma systems are collisional and nearest-neighbor classical interactions compete with longer-range plasma effects. Except for stars, most space plasmas are collisionless, however, and the effects of electrodynamic coupling dominate. Basic physical processes in such collisionless plasmas occur at micro-, meso-, and macroscales that are not merely reducible to each other in certain crucial ways as illustrated for the global coupling of the Earth's magnetosphere and for the nonlinear dynamics of charged particle motion in the magnetotail. Such global coupling and coherence makes the geospace environment, the domain of solar-terrestrial science, the most highly coupled of all physical geospheres.

Eastman, Timothy E.↗