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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Collisional processes in cometary plasmas

The interaction of the solar wind with comets is initiated at large distances from the nucleus by the ionization of cometary neutrals. The resulting contamination of the solar wind with cometary ions mass-loads the solar wind flow, causing it to slow down. The plasma-comet interaction is largely collisionless at large cometocentric distances. However, collisional processes become important in the inner coma (within the cometopause). Collisional processes include charge-transfer between solar wind protons and neutrals, ion-neutral friction, electron and ion thermal cooling, and ion-neutral chemistry. For example, the magnetometer on the Giotto spacecraft observed a diamagnetic cavity near closest approach. This cavity is a consequence of the balance between an inward-directed magnetic pressure gradient force and an outward ion-netural frictional force. Thermalization of the cometary ion distribution function by Coulomb collisions is another important process in the inner coma of an active comet.

Cravens, T. E.↗
NASA NTRS1999

The Magnetospheric Multiscale Mission...Resolving Fundamental Processes in Space Plasmas

The Magnetospheric Multiscale (MMS) mission is a multiple-spacecraft Solar-Terrestrial Probe designed to study the microphysics of magnetic reconnection, charged particle acceleration, and turbulence in key boundary regions of Earth's magnetosphere. These three processes, which control the flow of energy, mass, and momentum within and across plasma boundaries, occur throughout the universe and are fundamental to our understanding of astrophysical and solar system plasmas. Only in Earth's magnetosphere, however, are they readily accessible for sustained study through in-situ measurement. MMS will employ five co-orbiting spacecraft identically instrumented to measure electric and magnetic fields, plasmas, and energetic particles. The initial parameters of the individual spacecraft orbits will be designed so that the spacecraft formation will evolve into a three-dimensional configuration near apogee, allowing MMS to differentiate between spatial and temporal effects and to determine the three dimensional geometry of plasma, field, and current structures. In order to sample all of the magnetospheric boundary regions, MMS will employ a unique four-phase orbital strategy involving carefully sequenced changes in the local time and radial distance of apogee and, in the third phase, a change in orbit inclination from 10 degrees to 90 degrees. The nominal mission operational lifetime is two years. Launch is currently scheduled for 2006.

Curtis, S.↗
NASA NTRS1991

Physical processes in the plasma mantle of Venus

The results are presented of a study, which analyzed data from 10 Pioneer Venus orbits in order to see whether similar wave particle interaction processes also exist in the corresponding region around Venus. The first conclusion is that the apparent physical processes in the mantle are indeed similar around Venus and Mars. The planetary thermal O(+) ions outside the ionopause interact with the shocked solar wind and excite electrostatic waves close to the lower hybrid frequency. These waves propagate inwards, heating first the electron and deeper down in the ionosphere the thermal ion population. The observed superthermal ions are believed to be the product of this wave particle interaction process. It is also concluded that the wave energy transferred to the thermal electrons is of the right magnitude (about 4 x 10 exp 9 eV/sq cm s) to provide the supplemental heat source necessary to reconcile observed and calculated electron temperatures in the ionosphere.

Szego, K.↗
NASA NTRS1982

Processes in relativistic plasmas

The establishment and maintenance of a Boltzmann distribution in particle kinetic energies is investigated for a plasma with theta = KTe/mc-squared much greater than unity, where m is the electron mass. It is shown that thermalization of the electron gas by binary collisions is not sufficiently effective to maintain the equilibrium distribution when other processes that perturb the equilibrium are taken into account. Electron-positron pair production in electron-electron and electron-ion collisions, and perturbations of a Boltzmann distribution by nonthermal processes are evaluated. Thermalization by means of other mechanisms, such as interaction with plasma waves is discussed, and the opacity of a relativistic plasma is computed for Compton scattering, pair production in the fields of electrons and ions, inverse bremsstrahlung, and synchrotron self-absorption.

Gould, R. J.↗
NASA NTRS1992

Plasma-neutral interaction processes in the magnetosphere of Saturn

Models of Saturnian magnetospheric processes are reviewed emphasizing the interaction of charged and neutral particles in the gaseous phase and mentioning the role of solid matter. It is found that interpretations of different Voyager datasets regarding the Saturnian magnetosphere can vary. Specific interactions examined to resolve these discrepancies include charge exchange, ion-atom interchange, isotropizing and thermalizing collisions, and interactions between magnetospheric charged particles and surface layers of the icy satellites. The latter interactions result in sputtering of the surface or atmosphere as well as neutral injections into the magnetosphere. Constraints based on known reaction rates are shown to be useful in analyzing the abundances of the water-group molecules. The composition of the magnetospheric plasma is shown to be related to the differences between the interactions of atomic and molecular plasmas with neutral matter.

Eviatar, Aharon↗
NASA NTRS1973

Physics of planetary ionospheres

The fundamental physical and chemical processes in an idealized planetary ionosphere are considered as a general abstraction, with actual planetary ionospheres representing special cases. After describing the structure of the neutral atmospheres (the barosphere, the thermosphere, and the exosphere) and noting the principal ionizing radiations responsible for the formation of planetary ionospheres, a detailed study is made of the thermal structure of these ionospheres and of the chemical processes and plasma-transport processes occurring in them. The features of equilibrium and realistic models of planetary ionospheres are discussed, and an attempt is made to determine the extent of these ionospheres. Considering the ionosphere as a plasma, a plasma kinetic approach is developed for determining the effects of interactions between individual particles and waves in this plasma. The use of remote-sensing radio techniques and direct measurement or in situ techniques is discussed. Finally, the observed properties of the ionospheres of the Earth, Mars, Venus, and Jupiter are reviewed.

Bauer, S. J.↗
NASA NTRS1990

Linear and non-linear studies of Alfven waves in space. Stationary and dynamic processes in magnetospheric plasmas

The Final Technical Report on linear and non-linear studies of Alfven waves in space is presented. Areas of research included relaxation of magnetotail plasmas with field-aligned currents; the equilibrium dayside magnetosphere; macroscale particle simulation of kinetic Alfven wave physics; ballooning stability of plasmas with sheared equilibrium flows; theory of the drift-mirror instability; collisionless tearing instability in magnetotail plasmas; and nonadiabatic behavior of the magnetic moment of a charged particle in a dipole magnetic field and the development of stochastic webs.

Bhattacharjee, A.↗
NASA NTRS1992

The coalescence instability in collisionless plasmas

The process whereby magnetic island structures tend to merge into larger units is known as magnetic island coalescence. This coalescence process is investigated for the case of a collisionless plasma by means of 2D particle simulations. The pairwise merging of a preformed island chain leads to a gentle redistribution of the density and current density profiles. The nonlinear evolution of the collisionless tearing instability in a long system is found to lead to a much more violent coalescence process resulting in the formation of a vacuum X region. This stage is characterized by enhanced growth rates for the long-wavelength modes that exceed the maximum linear tearing growth rate, super-Alfvenic flows away from the reconnection X line, substantial bulk heating in the parallel direction, and the formation of energetic particle tails in the direction of the inductive electric field.

Pritchett, P. L.↗
NASA NTRS1986

Ion acceleration - A phenomenon characteristic of the 'expansion of plasma into a vacuum'

The physics of the complex process by which plasma expands across a strong density gradient is briefly discussed with particular emphasis on the resulting ion acceleration. The results from a laboratory experiment that addresses the steady-state expansion of a collisionless, streaming plasma into the wake of a body are presented. The experimental results are in good qualitative agreement with theoretical predictions, thereby demonstrating the equivalence of expansion with distance in the flow direction to time in the one-dimensional theory. On this basis, the potential application of the plasma process in space plasma physics is mentioned.

Samir, Uri↗
NASA NTRS1976

X-ray emission from high temperature plasmas

The physical processes occurring in plasma focus devices were studied. These devices produce dense high temperature plasmas, which emit X rays of hundreds of KeV energy and one to ten billion neutrons per pulse. The processes in the devices seem related to solar flare phenomena, and would also be of interest for controlled thermonuclear fusion applications. The high intensity, short duration bursts of X rays and neutrons could also possibly be used for pumping nuclear lasers.

Harries, W. L.↗
NASA NTRS1986

Plasma assisted surface coating/modification processes: An emerging technology

A broad understanding of the numerous ion or plasma assisted surface coating/modification processes is sought. An awareness of the principles of these processes is needed before discussing in detail the ion nitriding technology. On the basis of surface modifications arising from ion or plasma energizing and interactions, it can be broadly classified as deposition of distinct overlay coatings (sputtering-dc, radio frequency, magnetron, reactive; ion plating-diode, triode) and surface property modification without forming a discrete coating (ion implantation, ion beam mixing, laser beam irradiation, ion nitriding, ion carburizing, plasma oxidation). These techniques offer a great flexibility and are capable in tailoring desirable chemical and structural surface properties independent of the bulk properties.

Spalvins, T.↗
NASA NTRS1987

Plasma assisted surface coating/modification processes - An emerging technology

A broad understanding of the numerous ion or plasma assisted surface coating/modification processes is sought. An awareness of the principles of these processes is needed before discussing in detail the ion nitriding technology. On the basis of surface modifications arising from ion or plasma energizing and interactions, it can be broadly classified as deposition of distinct overlay coatings (sputtering-dc, radio frequency, magnetron, reactive; ion plating-diode, triode) and surface property modification without forming a discrete coating (ion implantation, ion beam mixing, laser beam irradiation, ion nitriding, ion carburizing, plasma oxidation. These techniques offer a great flexibility and are capable in tailoring desirable chemical and structural surface properties independent of the bulk properties.

Spalvins, T.↗
NASA NTRS1986

Advanced electric propulsion and space plasma contactor research

A series of experiments performed on an 8 cm dia. ring cusp magnetic field ion thruster are described. The results show the effects of anode and cathode position and size, ring cusp axial location and discharge chamber length on plasma ion energy cost and extracted ion fraction. Thruster performance is shown to be improved substantially when optimum values of these parameters are used. Investigations into the basic plasma phenomena associated with the process of plasma contacting are described. The results show the process of electron collection from a background plasma to a hollow cathode plasma contactor exhibits a higher impedance than the process of electron emission from the hollow cathode. The importance of having cold ions present to facilitate the plasma contacting process is shown. Results of experiments into the behavior of hollow cathodes operating at high interelectrode pressures (up to approx. 100 Torr) on nitrogen and ammonia are presented. They suggest that diffuse emission from the insert of a hollow cathode can be sustained at high interelectrode pressures if the cathode is made of non-conducting material and the cathode internal pressure is reduced by evacuating the cathode interior. A theoretical model of discharge chamber operation developed for inert gas thrusters is extended so it can be used to evaluste the performance of mercury ion thrusters. Predictions of the model are compared to experimental results obtained on two 30 cm dia. thrusters.

Wilbur, P. J.↗
NASA NTRS1982

A phenomenological model for orificed hollow cathodes

A quartz hollow tube cathode was used to determine the operating conditions within a mercury orificed hollow cathode. Insert temperature profiles, cathode current distributions, plasma properties profile, and internal pressure-mass flow rate results are summarized and used in a phenomenological model which qualitatively describes electron emission and plasma production processes taking place within the cathode. By defining an idealized ion production region within which most of the plasma processes are concentrated, this model is expressed analytically as a simple set of equations which relate cathode dimensions and specifiable operating conditions, such as mass flow rate and discharge current, to such important parameters as emission surface temperature and internal plasma properties. Key aspects of the model are examined.

Siegfried, D. E.↗
NASA NTRS1977

X-ray emission from high temperature plasmas

The physical processes occurring in plasma focus devices were investigated with particular emphasis on X-ray emission. Topics discussed include: trajectories of high energy electrons; detection of ion trajectories; spatial distribution of neutron emission; space and time resolved emission of hard X-rays from a plasma focus; the staged plasma focus as a variation of the hypocloidal pinch; formation of current sheets in a staged plasma focus; and X-ray and neutron emission from a staged plasma focus. The possibility of operating dense plasma-focus type devices in multiple arrays beyond the scaling law for a single gun is discussed.

Harries, W. L.↗