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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Convection

We review the status of theoretical work on magnetospheric convection in the lower auroral zone and at midlatitudes, and compare with various observed features, such as ionospheric electric fields and plasma flows, the form of the plasmasphere, and the distribution of plasma-sheet particles. We present preliminary results from a new series of computerized convection models, which follow the time evolution of the inner magnetosphere (L less than around 10), self-consistently including ionospheric currents and Birkeland currents, as well as the currents generated in a model plasma sheet with a realistic energy spectrum. We find that the model plasma sheet's inner edge quickly becomes rather sharp. Computed electric field distributions resemble those obtained earlier for a simple single-energy plasma sheet.

Harel, M.↗
NASA NTRS1975

ATS-5 observations of plasma sheet particles before the expansion-phase onset, appendix C.

Behavior of the plasma sheet around its earthward edge during substorms was studied by using high resolution (every 2.6 sec) measurements of proton and electron fluxes by ATS-5. In the injection region near midnight the flux increase at the expansion-phase onset is shown to lag behind the onset of the low-latitude positive bay by several minutes. Depending upon the case, before the above increase (1) the flux stays at a constant level, (2) it gradually increases for some tens of minutes, or (3) it briefly drops to a low level. Difference in the position of the satellite relative to the earthward edge and to the high-latitude boundary of the plasma sheet is suggested as a cause of the above difference in flux variations during the growth phase of substorms. Magnetograms and tables (data) are shown.

Fujii, K.↗
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 NTRS1991

The preliminary feasibility of intercalated graphite railgun armatures

Graphite intercalation compounds may provide an excellent material for the fabrication of electromagnetic railgun armatures. As a pulse of power is fed into the armature the intercalate could be excited into the plasma state around the edges of the armature, while the bulk of the current would be carried through the graphite block. Such an armature would have both diffuse plasma armatures and bulk conduction armatures. In addition, the highly anisotropic nature of these materials could enable the electrical and thermal conductivity to be tailored to meet the specific requirements of electromagnetic railgun armatures. Preliminary investigations have been performed in an attempt to determine the feasibility of using graphite intercalation compounds as railgun armatures. Issues of fabrication, resistivity, stability, and electrical current spreading have been addressed for the case of highly oriented pyrolytic graphite.

Gaier, James R.↗
NASA NTRS1994

Evidence for ion transport and molecular ion dominance in the Venus ionotail

We present analyses from the five Pioneer Venus Orbiter plasma experiments and the plasma wave experiment when a patch of plasma with enhanced densities was encountered in the near-Venus ionotail during atmospheric entry at an altitude of approximately 1100 km in the nightside ionosphere. Our analyses of the thermal and superthermal ion measurements in this plasma feature provides the first evidence that at times molecular ions in the 28-32 amu mass range are dominant over atomic mass species thus yielding evidence for a transport mechanism that reaches into the lower ionosphere. Analysis of plasma analyzer (OPA) observations at this time indicates the presence of ions measured in the rest frame of the spacecraft at approximately 27 and 37 volt energy per unit charge steps. In the rest frame of the planet these superthermal ions are flowing from the dawn direction at speeds (assuming they are O2(+)) of approximately 8 km/s and with a flow component downward (perpendicular to the ecliptic plane) at speeds of approximately 2 km/s. OPA analyses also determine the ion number flux, energy, flow angles, and angular distributions. Plasma wave bursts appear to indicate that plasma density decreases within and on the equatorward edge of the patch of enhanced plasma densities are associated with ion acoustic waves and relative ion streaming.

Intriligator, D. S.↗
NASA NTRS1990

Feasibility of intercalated graphite railgun armatures

Graphite intercalation compounds may provide an excellent material for the fabrication of electro-magnetic railgun armatures. As a pulse of power is fed into the armature the intercalate could be excited into the plasma state around the edges of the armature, while the bulk of the current would be carried through the graphite block. Such an armature would have the desirable characteristics of both diffuse plasma armatures and bulk conduction armatures. In addition, the highly anisotropic nature of these materials could enable the electrical and thermal conductivity to be tailored to meet the specific requirements of electromagnetic railgun armatures. Preliminary investigations were performed in an attempt to determine the feasibility of using graphite intercalation compounds as railgun armatures. Issues of fabrication, resistivity, stability, and electrical current spreading are addressed for the case of highly oriented pyrolytic graphite.

Gaier, James R.↗
NASA NTRS1994

Imaging The Leading Edge Of A Weld

Proposed optical system integrated into plasma arc welding torch provides image of leading edge of weld pool and welding-arc-initiation point. Welding torch aligned better with joint. System includes coherent bundle of optical fibers and transparent cup.

Mcgee, William F.↗
NASA NTRS1982

In situ observations of Io torus plasma

The physical properties of the Io plasma formation deduced from in situ observations are described. The torus plasma is characterized by spatially distinct regions with steep gradients in plasma parameters between them. The innermost region has a cool plasma which collapses toward the centrifugal equator and gives rise to a distinctive localized concentration of plasma well inside of Io's orbit. The next region has a warm plasma which includes the L-shell of Io and is the presumed injection region of the plasma. Other regions, known as the plasma ledge and ramp, are described. The changes in plasma characteristics are accounted for by centrifugally driven flux tube interchange diffusion to provide radial mass transport. The ramp is shown to result from impoundment of the plasma by the inner edge of the energetic particle population. It is also shown how the power required to excite the ultraviolet emissions of the torus and the Jovian aurora determines the rate at which new plasma is fed into the torus.

Sullivan, J. D.↗
NASA NTRS1972

Momentum transfer interaction of a laser-produced plasma with a low-pressure background.

The expansion of a laser-produced metallic plasma into a photoionized hydrogen background has been experimentally studied. Langmuir probe and microwave diagnostics have detected an interaction front which decelerates with a dependence on background density and time consistent with a momentum coupling between the laser plasma and the ionized fraction of the background. An ion percursor has also been observed. Calculations of scattering cross sections indicate that multiple-encounter Coulomb scattering will dominate collisional momentum transfer. The leading edge of the laser plasma contains multiply charged ions of charge state z greater than or equal to 5, and collisional effects appear adequate to explain the principal features of the momentum coupling. The ion precursor may have a collisionless origin.

Koopman, D. W.↗
NASA NTRS2007

Use of Plasma Actuators as a Moving-Wake Generator

The work documented in this report tests the concept of using plasma actuators as a simple and easy way to generate a simulated moving-wake and the disturbances associated with it in turbines. This wake is caused by the blades of the upstream stages of the turbine. Two types of devices, one constructed of arrays of NACA 0018 airfoils, and the one constructed of flat plates were studied. The airfoils or plates were equipped with surface mounted dielectric barrier discharge (DBD) plasma actuators, which were used to generate flow disturbances resembling moving-wakes. CTA hot-wire anemometry and flow visualization using a smoke-wire were used to investigate the wake independence at various spacings and downstream locations. The flat plates were found to produce better results than the airfoils in creating large velocity fluctuations in the free-stream flow. Different dielectric materials, plasma actuator locations, leading edge contours, angles of attack and plate spacings were investigated, some with positive results. The magnitudes of the velocity fluctuations were found to be comparable to existing mechanical moving-wake generators, thus proving the feasibility of using plasma actuators as a moving-wake generator.

Corke, Thomas C.↗
NASA NTRS1989

Plasma pressure in the environment of Jupiter, inferred from Voyager 1 magnetometer observations

A model combining the internal magnetic field with a self-consistent model of the Jovian magnetodisc was fitted to the Voyager 1 Jovian magnetic field data by means of a generalized inverse technique. The model parameters included the internal field spherical harmonic coefficients as well as with parameters describing the plasma distribution in the magnetosphere. Assuming that the pressure in the middle and outer magnetosphere is related to the unit flux tube volume V through PV exp gamma = const, the model fit yielded a value of 0.88 for gamma. If the hot (30 keV) plasma is transported adiabatically inward under the interchange instability triggered by centrifugal force of the heavy torus ions, losses are not sufficient to account for such a low value of gamma beyond L = 10. Closer to the planet, as the outer edge of the Io plasma torus is approached, PV exp gamma is found to decrease inward, as expected from the particle measurements, which identified an inner boundary of the particle fluxes in that region. With the present stage of the development of magnetodisc models, secular variations of the internal field still remain difficult to estimate.

Caudal, G.↗
NASA NTRS1976

High-beta effects and anomalous diffusion in plasmas expanding into magnetic fields

A metallic laser-produced plasma is allowed to expand transversely into an applied magnetic field, under conditions where the typical ion cyclotron radius is much larger, and the electron cyclotron radius much smaller, than the experimental dimensions. A stationary background plasma may also be present. Initially, the flow energy density exceeds (B squared/8 times pi), where B is the ambient magnetic field. Magnetic coil probes, Langmuir probes, and microwave diagnostics are used to study the plasma-field interaction. Field compression at the leading edge and field exclusion within the expanding plasma are seen. The diagnostic measurements and comparison with a theoretical model demonstrate plasma turbulence and anomalously high diffusion of field into the expanding plasma.

Koopman, D. W.↗
NASA NTRS1990

Ion precipitation from the inner plasma sheet due to stochastic diffusion

Plasma sheet ions do not conserve their first adiabatic invariant when the magnetic field is appreciably tail-like. They do conserve a different adiabatic invariant but only to linear, rather than exponential, accuracy in the appropriate small parameter. Thus significant stochastic diffusion can occur for particles crossing the separatrix dividing the segments of orbits on which the particles cross and do not cross the tail midplane. Such ions can escape the plasma sheet and precipitate into the atmosphere. Stochastic scattering is strongest from those field lines where the ion's Larmor period in the normal component of the neutral sheet magnetic field approximately equals its bounce period. By comparing the rates of stochastic ion loss and convection in the tail, it is possible to estimate the location and thickness of the inner edge of the ion plasma sheet created by stochastic ion loss. Ions of different masses precipitate into the atmosphere at slightly different locations. Since wave particle interactions are not needed, this precipitation will always occur and should be particularly evident during quiet geomagnetic conditions, when it is less likely to be masked by other precipitation mechanisms.

Zelenyi, L.↗
NASA NTRS1987

Self-similar potential in the near wake

The plasma potential is measured near the edge of an electrically floating obstacle placed in a steady-state, supersonic, unmagnetized, neutral plasma flow. Equipotential contours show the sheath of the upstream side of the obstacle wrapping around the edge of the obstacle and fanning out into the near wake. Both fluid theory and the data find the near-wake plasma potential to be self-similar when ionization, charge exchange, and magnetic field can be neglected. The theory also finds that fluid velocity is self-similar, the near wake is nonneutral, and plasma density is not self-similar. Strong electric fields are found near the obstacle and equipotential contours are found to conform to all boundaries.

Diebold, D.↗
NASA NTRS2002

Plasmaspheric Density Troughs: Global IMAGE EUV Observations and Analysis via Global Core Plasma Modeling

To date, the IMAGE EUV camera has observed several plasmaspheric density trough features inside the plasmapause under a wide range of geomagnetic activity. From the perspective of EUV, a density trough feature appears as a channel of diminished pixel counts which spans a width of L-shell (DELTA L) and magnetic local time (MLT) inside the plasmapause. Plasmaspheric density troughs are found to be morphologically complex possessing considerable spatial and temporal variability. We present an analysis of the evolution of trough DELTA L and MLT extent as functions of associated D (sub ST) and K (sub p) history. Trough features range in size from 0.16 less than or equal to DELTA L less than or equal to 1.2 with azimuthal extent from 1500 less than or equal to MLT less than or equal to 1200. All cases of plasmaspheric density troughs studied to date appear to have evolved as a result of the inner edge of the afternoon/evening plasma drainage plume being wrapped around through the nightside plasmasphere. The structure of plasmaspheric density trough features is further probed by analyzing simulated EUV images produced by forward modeling artificially introduced regions of depleted density into both static and dynamic global core plasmaspheric models. Forward modeling suggests that (1) L-shell refilling of density troughs during storm recovery can be modeled as filling from the ionosphere toward the equator (i.e., bottom-up refilling), and (2) that an erosion process is operating within flux tubes beyond the outer L-shell wall of the observed density troughs.

Adrian, M. L.↗
NASA NTRS1977

Ray trajectories in a torus: An application of MACSYMA to a complex numerical computation

The study of ray trajectories of plasma waves in a torodial geometry using MACSYMA is an example of how symbolic, numerical, and graphical facilities can be used in concert to accomplish a complex computational goal. Computational features of this study which are of particular significance include: the derivation of code (i.e. writing functions to generate program fragments), the use of array functions to simplify the specification of a numerical iteration scheme, and the graphical presentation of the results. Mathematically, this study originates in the solution of a linear inhomogeneous partial differential equation in 3 dimensions by the method of characteristics. While it is possible to describe this equation compactly by using vector notation, and by specifying the spatial variation of the coefficients in terms of intermediate parameters, the transformation of the equation into a form amenable to solution is very tedious. A MACSYMA program is presented for obtaining description of the rf field structure excited by a waveguide located at the edge of a toroidal plasma confinement device.

Kulp, J. L.↗
NASA NTRS1985

Resonance cone structure in a warm inhomogeneous bounded plasma with lower-hybrid resonance layers

The paper presents a theoretical study of the problem of the wave fields excited by a gap source at the edge of an inhomogeneous magnetized plasma with a pair of lower-hybrid resonance layers present and bounded by conducting walls. The approach used is that of a solution as a sum of multiply reflected extraordinary mode and ion-thermal resonance cones as an alternative to the guided-wave mode approach. A diagrammatic scheme for writing the solution is given which can be used to determine in great detail the structure and properties of the resonance cones and the way they transform across the back-to-back hybrid layers. Evanescent resonance cones are shown to exist in the high-density region between the hybrid resonance layers and to tunnel through to the other side, maintaining this general structure if the layer is relatively thin.

Grabbe, C. L.↗