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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Propagation of charge-exchange plasma produced by an ion thruster

A charge-exchange plasma is produced downstream of ion thrusters by collisions between energetic ions and neutrals escaping through the ion optics. The charge-exchange ions flow radially from the thruster beam due to electric fields produced by its density gradient. The propagation of the charge-exchange plasma after it leaves the thruster beam is the subject of this paper. Under the proper conditions there is an 'end-effect' of a long, cylindrical Langmuir probe which allows a significant increase in collected ion current when the probe is aligned with a flowing plasma. This effect is used to determine the charge-exchange plasma flow direction at various locations relative to the ion thruster. A portion of the charge-exchange plasma flows upstream of the ion thruster and can represent a contamination source to electrically propelled spacecraft. The ion current collected by the probe as a function of its angle with respect to the plasma flow allows determination of the plasma density and plasma flow velocity at the probe's location upstream of the ion thruster optics. The density value obtained from the ion current agree to within a factor of two of density values obtained by typical voltage-current Langmuir probe characteristics.

Carruth, M. R., Jr.↗
NASA NTRS1994

Magnetospheric space plasma investigations

A time dependent semi-kinetic model that includes self collisions and ion-neutral collisions and chemistry was developed. Light ion outflow in the polar cap transition region was modeled and compared with data results. A model study of wave heating of O+ ions in the topside transition region was carried out using a code which does local calculations that include ion-neutral and Coulomb self collisions as well as production and loss of O+. Another project is a statistical study of hydrogen spin curve characteristics in the polar cap. A statistical study of the latitudinal distribution of core plasmas along the L=4.6 field line using DE-1/RIMS data was completed. A short paper on dual spacecraft estimates of ion temperature profiles and heat flows in the plasmasphere ionosphere system was prepared. An automated processing code was used to process RIMS data from 1981 to 1984.

Comfort, Richard H.↗
NASA NTRS2008

Experimental Plans for Subsystems of a Shock Wave Driven Gas Core Reactor

This Contractor Report proposes a number of plans for experiments on subsystems of a shock wave driven pulsed magnetic induction gas core reactor (PMI-GCR, or PMD-GCR pulsed magnet driven gas core reactor). Computer models of shock generation and collision in a large-scale PMI-GCR shock tube have been performed. Based upon the simulation results a number of issues arose that can only be addressed adequately by capturing experimental data on high pressure (approx.1 atmosphere or greater) partial plasma shock wave effects in large bore shock tubes ( 10 cm radius). There are three main subsystems that are of immediate interest (for appraisal of the concept viability). These are (1) the shock generation in a high pressure gas using either a plasma thruster or pulsed high magnetic field, (2) collision of MHD or gas dynamic shocks, their interaction time, and collision pile-up region thickness, and (3) magnetic flux compression power generation (not included here).

Kazeminezhad, F.↗
NASA NTRS1976

Some modifications of the theory of colloidal plasmas

Two effects leading to significant modifications of the theory of colloidal plasmas are discussed. The first concerns the fact that depending on the sign of the electric potential on a droplet in a colloidal plasma, the electrons or the ions impact on the droplet with a much higher effective temperature than their background plasma temperature. The analytical expression for this temperature is derived in the first part of the paper. In the second part, it is shown that the electron-droplet collision rate in a wet alkali-metal vapor plasma may be substantially modified by the effect of the attractive potential between a droplet and an electron because of the image of the electron in the droplet. This effect is found to be important when the droplet sizes are in the submicron range.

De, B. R.↗
NASA NTRS2019

NIAC Phase I Final Report: On-Orbit, Collision-Free Mapping of Small Orbital Debris

Sub-centimeter orbital debris is currently undetectable using ground-based radar and optical methods. However, the pits in Space Shuttle windows produced by paint chips (e.g. the 3.8mm diameter pit produced by a 0.2mm paint chip on STS-7) demonstrate that small debris can cause serious damage to spacecraft. Recent analytical, computational and experimental work has shown that charged objects moving quickly through a plasma will cause the formation of solitons in the plasma density. Due to their exposure to the solar wind plasma environment, even the smallest space debris will be charged. Depending on the debris size, charge and velocity, the plasma signature of the solitons may be detected by simple instrumentation on spacecraft. We will describe the amplitude and velocity of solitons that may be produced by mm-cm scale orbital debris in LEO. We will discuss the feasibility of mapping sub-cm orbital debris using a fleet of CubeSats equipped with Langmuir probes. The time and fleet size required to map the debris will also be described. Plasma soliton detection would be the first collision-free method of mapping the small debris population.

Orbital Debris↗
NASA NTRS1973

On the cause of equatorial spread F.

It is suggested that convective electric fields in the equatorial ionosphere are generated by neutral winds (zonal or meridional) which act on regions having structure in their field aligned Pedersen conductivity integrals. The conductivity structure is presumably caused by long-lived metallic ions concentrated irregularly below the F layer at altitudes where their collision and gyrofrequencies are comparable. The resulting plasma convection leads to large-scale irregularities and sets up gradients in the electric field that drive other instability mechanisms to produce small-scale irregularities. The mechanism proposed requires a different velocity above and below 200 km for winds in the magnetic east-west direction, but for winds in the magnetic meridian direction, an altitude gradient is not required.

Hanson, W. B.↗
NASA NTRS1998

Modeling Electric Field Influences on Plasmaspheric Refilling

We have a new model of ion transport that we have applied to the problem of plasmaspheric flux tube refilling after a geomagnetic disturbance. This model solves the Fokker-Planck kinetic equation by applying discrete difference numerical schemes to the various operators. Features of the model include a time-varying ionospheric source, self-consistent Coulomb collisions, field-aligned electric field, hot plasma interactions, and ion cyclotron wave heating. We see refilling rates similar to those of earlier observations and models, except when the electric field is included. In this case, the refilling rates can be quite different that previously predicted. Depending on the populations included and the values of relevant parameters, trap zone densities can increase or decrease. In particular, the inclusion of hot populations near the equatorial region (specifically warm pancake distributions and ring current ions) can dramatically alter the refilling rate. Results are compared with observations as well as previous hydrodynamic and kinetic particle model simulations.

Liemohn, M. W.↗
NASA NTRS2011

Heliospheric Observations of Energetic Particles

Heliospheric observations of energetic particles have shown that, on long time averages, a consistent v^-5 power-law index arises even in the absence of transient events. This implies an ubiquitous acceleration process present in the solar wind that is required to generate these power-law tails and maintain them against adiabatic losses and coulomb-collisions which will cool and thermalize the plasma respectively. Though the details of this acceleration process are being debated within the community, most agree that the energy required for these tails comes from fluctuations in the magnetic field which are damped as the energy is transferred to particles. Given this source for the tail, is it then reasonable to assume that the turbulent LISM should give rise to such a power-law tail as well? IBEX observations clearly show a power-law tail of index approximately -5 in energetic neutral atoms. The simplest explanation for the origins of these ENAs are that they are energetic ions which have charge-exchanged with a neutral atom. However, this would imply that energetic ions possess a v^-5 power-law distribution at keV energies at the source of these ENAs. If the source is presumed to be the LISM, it provides additional options for explaining the, so called, IBEX ribbon. This presentation will discuss some of these options as well as potential mechanisms for the generation of a power-law spectrum in the LISM.

Summerlin, Errol J.↗
NASA NTRS2012

Simulations of Magnetic Reconnection - Kinetic Mechanisms Underlying the Fluid Description of Ions

Because of its ability to transfer the energy stored in magnetic field together with the breaking of the flux freezing constraint, magnetic reconnection is considered as one of the most important phenomena in plasma physics. When it happens in a collision less environment such as the terrestrial magnetosphere, it should a priori be modelled with in the framework of kinetic physics. The evidence of kinetic features has incidentally for a long time, been shown by researchers with the help of both numerical simulations and satellite observations. However, most of our understanding of the process comes from the more intuitive fluid interpretation with simple closure hypothesis which do not include kinetic effects. To what extent are these two separate descriptions of the same phenomenon related? What is the role of kinetic effects in the averaged/fluid dynamics of reconnection? This thesis addresses these questions for the proton population in the particular case of anti parallel merging with the help of 2D Hybrid simulations. We show that one can not assume, as is usually done, that the acceleration of the proton flow is only due to the Laplace force. Our results show, for symmetric and asymmetric connection, the importance of the pressure force, opposed to the electric one on the separatrices, in the decoupling region. In the symmetric case, we emphasize the kinetic origin of this force by analyzing the proton distribution functions and explain their structure by studying the underlying particle dynamics. Protons, as individual particles, are shown to bounce in the electric potential well created by the Hall effect. The spatial divergence of this well results in a mixing in phase space responsible for the observed structure of the pressure tensor. A detailed energy budget analysis confirms the role of the pressure force for the acceleration; but, contrary to what is sometimes assumed, it also reveals that the major part of the incoming Poynting flux is transferred to the thermal energy flux rather than to the convective kinetic energy flux, although the latter is generally supposed dominant. In the symmetric case, we propose the pressure tensor to be an additional proxy of the ion decoupling region in satellite data and verify this suggestion by studying a reconnection event encountered by the Cluster spacecrafts. Finally, the last part of this thesis is devoted to the study of the kinetic structure of asymmetric tangential current sheets where connection can develop. This theoretical part consists in finding a steady state solution to the Vlasov-Maxwell system for the protons in such a configuration. We present the theory and its first confrontation to numerical tests.

Aunai, icolas↗
NASA NTRS1982

Transport of energetic electrons in a fully ionized hydrogen plasma

A Monte Carlo method for calculating energetic electron transport in a plasma is presented. The energy loss and angular deflection due to Coulomb collisions as a function of travel distance and energy are derived for energetic electrons in a fully ionized plasma with a uniform magnetic field. Formulas which include the effect of nonuniform B fields on the angular deflection are derived. The Monte Carlo method is applied to the thick-target beam model in which the energetic electrons are injected vertically downward.

Bai, T.↗
NASA NTRS1972

Kinetic theory of a two-dimensional magnetized plasma. II - Balescu-Lenard limit.

The kinetic theory of a two-dimensional one-species plasma in a uniform dc magnetic field is investigated in the small plasma parameter limit. The plasma consists of charged rods interacting through the logarithmic Coulomb potential. Vahala and Montgomery earlier (1971) derived a Fokker-Planck equation for this system, but it contained a divergent integral, which had to be cut off on physical grounds. This cutoff is compared to the standard cutoff introduced in the two-dimensional unmagnetized Fokker-Planck equation. In the small plasma parameter limit, it is shown that the Balescu-Lenard collision term is zero in the long time average limit if only two-body interactions are considered. The energy transfer from a test particle to an equilibrium plasma is discussed and is also shown to be zero in the long time average limit. This supports the unexpected result of zero Balescu-Lenard collision term.

Vahala, G.↗
NASA NTRS1977

Discontinuous transitions in a current-carrying plasma

The properties of 'discontinuous' transitions in a current-carrying plasma are investigated by adopting an approach based on the two-fluid equations for a plasma. Braginskii's (1965) transport equations for a two-fluid plasma carrying a current are presented, and allowance is made for collisions with a background neutral gas as well as for effects of reflected particles. The speed of sound in a current-carrying plasma is derived so that the Mach number can be defined correctly as the ratio of the flow speed to the wave phase velocity in such a plasma. The various types of discontinuities permitted by the relevant jump relations in the absence of reflected particles are classified, the effect of reflected particles on such discontinuities is examined, and it is shown that the degree of indeterminacy of a discontinuity can be changed by the presence of reflected particles. Consideration of shocks containing a population of reflected particles and adiabatic transitions indicates that the pressure of reflected particles alone can give rise to both weak and strong transitions. The construction of discontinuous periodic flow solutions is also discussed.

Lee, H.-J.↗
NASA NTRS1974

Collisional coupling in counterstreaming laser-produced plasmas

The collisional processes which transfer momentum between counterstreaming plasmas are reviewed and applied to the example of a laser-produced plasma expanding into a partially ionized background. Experimental measurements of the dependence of the ion flow field on collisional momentum transfer demonstrate the validity of the simplified treatment of collision processes which have been adopted. A numerical model which simulates the laser-plasma interaction with the background confirms the importance of collisions in previous experimental studies of momentum coupling, and provides some insight into the distinction between collisional and collisionless flow regimes.

Koopman, D. W.↗
NASA NTRS1995

Surface conversion techniques for low energy neutral atom imagers

This investigation has focused on development of key technology elements for low energy neutral atom imaging. More specifically, we have investigated the conversion of low energy neutral atoms to negatively charged ions upon reflection from specially prepared surfaces. This 'surface conversion' technique appears to offer a unique capability of detecting, and thus imaging, neutral atoms at energies of 0.01 - 1 keV with high enough efficiencies to make practical its application to low energy neutral atom imaging in space. Such imaging offers the opportunity to obtain the first instantaneous global maps of macroscopic plasma features and their temporal variation. Through previous in situ plasma measurements, we have a statistical picture of large scale morphology and local measurements of dynamic processes. However, with in situ techniques it is impossible to characterize or understand many of the global plasma transport and energization processes. A series of global plasma images would greatly advance our understanding of these processes and would provide the context for interpreting previous and future in situ measurements. Fast neutral atoms, created from ions that are neutralized in collisions with exospheric neutrals, offer the means for remotely imaging plasma populations. Energy and mass analysis of these neutrals provides critical information about the source plasma distribution. The flux of neutral atoms available for imaging depends upon a convolution of the ambient plasma distribution with the charge exchange cross section for the background neutral population. Some of the highest signals are at relatively low energies (well below 1 keV). This energy range also includes some of the most important plasma populations to be imaged, for example the base of the cleft ion fountain.

Quinn, J. M.↗
NASA NTRS1987

Spectral line shapes. Volume 4 - Proceedings of the Eighth International Conference, College of William and Mary, Williamsburg, VA, June 9-13, 1986

The present conference discusses topics in line broadening and shift phenomena in low-to-moderately dense plasmas, resonances in the continuum, hot and dense laser-produced plasmas, collisional broadening and intermolecular potentials, molecular broadening and collision-induced spectroscopy, collisional redistribution and laser-assisted collision processes, coherent and nonlinear spectroscopy, astrophysical line-shapes, and short-wavelength lasers. Attention is given to the widths and shifts of Be ion lines, the Stark broadening of Xe II and Fe I lines, perturbed and unperturbed series in the line-shapes of autoionizing Rydberg series, the line-broadening of hydrogenic ions in dense plasmas, Doppler-free line-shapes, the Franck-Condon principle, the dynamics of laser-assisted reactive collisions, the gas-kinetic effects of light, collision-induced processes in nonlinear optics, and line-shaping phenomena in cool stars.

Exton, Reginald J.↗
NASA NTRS1996

3-D Simulations of NSTAR Ion Thruster Plasma Interactions

Described is a Particle-in-Cell with Monte Carlo Collision code developed to perform detailed three-dimensional ion thruster simulations. To capture the full kinetic behavior of ion thruster plumes, both the electrons and ions are treated as test particles. Simulation results are given of the NSTAR ion thruster under ground test and in space conditions. Numerical results are compared.

NSTAR Ion Thruster Plasma Ionization Particles↗
NASA NTRS1974

The collisional drift mode in a partially ionized plasma

The structure of the drift instability was examined in several density regimes. Let sub e be the total electron mean free path, k sub z the wave-vector component along the magnetic field, and the ratio of perpendicular ion diffusion to parallel electron streaming rates. At low densities (k sub z lambda 1) the drift mode is isothermal and should be treated kineticly. In the finite heat conduction regime square root of m/M k sub z Lambda sub 1) the drift instability threshold is reduced at low densities and increased at high densities as compared to the isothermal threshold. Finally, in the energy transfer limit (k sub z kambda sub e square root of m/M) the drift instability behaves adiabatically in a fully ionized plasma and isothermally in a partially ionized plasma for an ion-neutral to Coulomb collision frequency ratio.

Hudson, M. K.↗