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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

E and F region study of the evening sector auroral oval - A Chatanika/Dynamics Explorer 2/NOAA 6 comparison

Simultaneous data from the Chatanika radar and the DE 2 and NOAA 6 satellites are used to study the typical behavior of the winter evening-sector auroral plasma during moderate and steady magnetic activity. The equatorward edge of the auroral E layer, of the region 2 field-aligned currents, and of the region of intense convection are colocated. The auroral E layer extends several degrees south of the equatorward edge of the keV electron precipitation from the CPS. Although the main trough and ionization channel are embedded in a region of intense electric field where the plasma flows sunward at high speed, the flux tubes associated with these two features have different time histories. The midlatitude trough is located south of the region of electron precipitation, above a proton aurora. The ionization channel marks the poleward edge of the main trough and is colocated with the equatorward boundary of the electron precipitation from the central plasma sheet.

Senior, C.↗
NASA NTRS1979

The screen hole plasma sheath of an ion accelerator system

Results of the first probing of the screen hole sheath of an ion accelerator system are presented. The screen hole sheath, represented as a set of equipotential contours, extends over a large distance within the discharge plasma. Under no conditions examined does the sheath enter the screen hole. Edge hole defocusing of multiaperture accelerator systems is due primarily to local plasma density variations rather than adjacent screen hole sheath interactions. The sheath boundary is independent of screen-to-accelerator grid spacing when the grid set is operated at the minimum ion beam divergence condition. Significant ion focusing effects occur in the sheath adjacent to the screen grid webbing leading to increased ion source beam current efficiency with decreasing screen-to-accelerator grid separation and/or screen grid thickness.

Aston, G.↗
NASA NTRS1982

A high-resolution X-ray image of Puppis A - Inhomogeneities in the interstellar medium

Eleven HRI exposures from the Einstein Observatory are assembled into an 0.1-4 keV image of the Puppis A supernova remnant which displays a complex morphology that may reflect the structure of the shocked interstellar medium. In addition to showing a density gradient of a factor greater than four across the approximately 30 pc diameter of the remnant perpendicular to the galactic plane, a shell of X-ray emission is seen surrounding the northern half of Puppis A, coincident with the radio shell, whose edge brightness profile indicates direct hot plasma heating by the blast wave rather than evaporation from clouds. The interior structure of the supernova remnant suggests inhomogeneities whose sizes range over 0.1-5 pc, but with moderate density contrast. Although isolated clouds of 10-30/cu cm density are responsible for the two brightest X-ray features, they represent only a small fraction of the Puppis A mass.

Petre, R.↗
NASA NTRS1990

The temporal development of hollow cathode discharges

The temporal development of hollow cathode discharges was studied by means of electrical and optical diagnostic techniques. The results indicate that the discharge develops in two stages. The initial breakdown occurs along the longest straight path of the system, i.e., from the anode to the bottom of the cathode hole. This predischarge is confined to a narrow filament along the axis and carries a current of up to hundreds of milliamperes. The resulting distortion of the electric field in the cathode hole is assumed to cause a radial breakdown from the filamentary plasma on the axis to the edge of the cathode hole. After this second breakdown, an increase in current by more than three orders of magnitude is observed. Measurements with axial magnetic fields support the two-stage model.

Ngo, Mai T.↗
NASA NTRS1995

Four large-scale field-aligned current systmes in the dayside high-latitude region

A system of four current sheets of large-scale field-aligned currents (FACs) was discovered in the data set of simultaneous Viking and Defense Meteorological Satellire Program-F7 (DMSP-F7) crossing of the dayside high-latitude region. This paper reports four examples of this system that were observed in the prenoon sector. The flow polarities of FACs are upward, downward, upward, and downward, from equatorward to poleward. The lowest-latitude upward current is flowing mostly in the central plasma sheet (CPS) precipitation region, often overlapping with the boundary plasma sheet (BPS) at its poleward edge, andis interpreted as a region 2 current. The pair of downward and upward FACs in the middle of te structure are collocated with structured electron precipitation. The precipitation of high-energy (greater than 1 keV) electrons is more intense in the lower-latitude downward current sheet. The highest-latitude downward flowing current sheet is located in a weak, low-energy particle precipitation region, suggesting that this current is flowing on open field lines. Simulaneous observations in the postnoon local time sector reveal the standard three-sheet structure of FACs, sometimes described as region 2, region 1, and mantle (referred to the midday region O) currents. A high correlation was found between the occurrence of the four FAC sheet structure and negative interplanetary magnetic field (IMF) B(sub Y). We discuss the FAC structurein terms of three types of convection cells: the merging, viscous, andlobe cells. During strongly negative IMF B(sub Y), two convection reversals exist in the prenoon sector; one is inside the viscous cell, and the other is between the viscous cell and the lobe cell. This structure of convection flow is supported by the Viking electric field and auroral UV image data. Based on the convection pattern, the four FAC sheet structure is interpreted as the latitude overlap of midday and morning FAC systems. We suggest that the for-current sheet structure is common in a certain prenoon localtime sector during strongly negative IMF B(sub Y).

Ohtani, S.↗
NASA NTRS1995

Geometry of interplanetary magnetic clouds

Two dimensional magnetohydrodynamic simulations are presented of the distortion of a magnetic flux rope that is being accelerated through ambient solar wind plasma. The flux rope magnetic field has an axial component parallel to the solar wind field and an azimuthal component, which lies in the simulation plane. As the flux rope moves through the solar wind plasma, vortices form on its trailing edge and couple strongly to its interior. If the flux rope azimuthal field is weak, it deforms into an elongated banana-like shape a few Alfven transit times. A strong azimuthal field component tends to inhibit this distortion. If the flux rope is taken to model a magnetic cloud, it is suggested that the shape of the cloud at 1 AU is determined by its distortion in the inner solar wind. Distortion timescales beyond 1 AU are estimated as many days. It is estimated that effective drag coefficients somewhat greater than unity are appropriate for modelling flux rope propagation.

Cargill, P. J.↗
NASA NTRS1985

High-resolution studies of the HF ionospheric modification interaction region

The use of the pulse edge analysis technique to explain ionospheric modifications caused by high-power HF radio waves is discussed. The technique, implemented at the Arecibo Observatory, uses long radar pulses and very rapid data sampling. A comparison of the pulse leading and trailing edge characteristics is obtained and the comparison is used to estimate the relative changes in the interaction region height and layer width; an example utilizing this technique is provided. Main plasma line overshoot and miniovershoot were studied from the pulse edge observations; the observations at various HF pulsings and radar resolutions are graphically presented. From the pulse edge data the development and the occurrence of main plasma line overshoot and miniovershoot are explained. The theories of soliton formation and collapse, wave ducting, profile modification, and parametric instabilities are examined as a means of explaining main plasma line overshoots and miniovershoots.

Duncan, L. M.↗
NASA NTRS1993

Magnetosheath-ionspheric plasma interactions in the cusp/cleft. 2: Mesoscale particle simulations

Ionospheric plasma flowing out from the cusp can be an important source of plasma to the magnetosphere. One source of free energy that can drive this outflow is the injection of magnetosheath plasma into the cusp. Two-dimensional (three velocity) mesoscale particle simulations are used to investigate the particle dynamics in the cusp during southward interplanetary magnetic field. This mesoscale model self-consistently incorporates (1) global influences such as the convection of plasma across the cusp, the action of the mirror force, and the injection of the magnetosheath plasma, and (2) wave-particle interactions which produce the actual coupling between the magnetosheath and ionospheric plasmas. It is shown that, because the thermal speed of the electrons is higher than the bulk motion of the magnetosheath plasma, an upward current is formed on the equatorward edge of the injection region with return currents on either side. However, the poleward return currents are the stronger due to the convection and mirroring of many of the magnetosheath electrons. The electron distribution in this latter region evolves from upward directed streams to single-sided loss cones or possibly electron conics. The ion distribution also shows a variety of distinct features that are produced by spatial and/or temporal effects associated with varying convection patterns and wave-particle interactions. On the equatorward edge the distribution has a downflowing magnetosheath component and an upflowing cold ionospheric component due to continuous convection of ionospheric plasma into the region. In the center of the magnetosheath region, heating from the development of an ion-ion streaming instability causes the suppression of the cold ionospheric component and the formation of downward ionospheric streams. Further poleward there is velocity filtering of ions with low pitch angles, so that the magnetosheath ions develop a ring-beam distribution and the ensuing wave instabilities generate downward ionospheric conics. These downward ionospheric components are eventually turned by the mirror force, leading to the production of upward conics at elevated energies throughout the region.

Winglee, R. M.↗
NASA NTRS1997

Guided Plasmaspheric Hiss Interactions with Superthermal Electrons: Resonance Curves and Timescales - Part 1

Under the proper conditions, guided plasmaspheric hiss is shown to be more efficient than Coulomb collisions at scattering electrons in the superthermal energy range of 50 to 500 eV. Broadband, whistler mode hiss becomes guided by plasma density gradients, intensifying the wave energy densities and focusing the wave normal angles. These waves are shown to interact through Cherenkov (Landau) resonance with electrons below 500 eV, and the presented equatorial plane timescales for pitch angle, energy, and mixed diffusion are shown to be faster than Coulomb collision timescales for typical values at the inner edge of the plasmapause and in detached plasma regions. In the latter case, energy diffusion timescales of less than 100 s for small pitch angle electrons between 250 and 500 eV indicate that these waves have the potential to dramatically change the distribution function.

Liemohn, M. W.↗
NASA NTRS1999

Guided Plasmaspheric Hiss Interactions with Superthermal Electrons: Resonance Curves and Timescales - 1

Under the proper conditions, guided plasmaspheric hiss is shown to be more efficient than Coulomb collisions at scattering electrons in the superthermal energy range of 50 to 500 eV. Broadband, whistler mode hiss becomes guided by plasma density gradients, intensifying the wave energy densities and focusing the wave normal angles. These waves are shown to interact through Cherenkov (Landau) resonance with electrons below 500 eV, and the presented equatorial plane timescales for pitch angle, energy, and mixed diffusion are shown to be faster than Coulomb collision timescales for typical values at the inner edge of the plasmapause and in detached plasma regions. In the latter case, energy diffusion timescales of less than 100 s for small pitch angle electrons between 250 and 500 eV indicate that these waves have the potential to dramatically change the distribution function.

Liemohn, M. W.↗
NASA NTRS1992

Equatorial bubbles updrafting at supersonic speeds

Plasma and electric field observations from two satellite encounters with equatorial plasma bubbles updrafting at velocities of about 2 km/s are presented. These large, upward velocities are consistent with an adaptation of Chandrasekhar's model for the motion of plasma blobs supported against gravity by a magnetic field. Vector magnetic field measurements, available during one of the bubble encounters show a perturbation of about 150 nT, directed radially outward from the earth, near the western wall of deepest plasma depletion. This magnetic variation is too large to be caused by simple shunting of the g x B current along the bubble's edge. Rather, it is Alfvenic in nature, radiating from a generator located near the magnetic equator, in the plasma outside the bubble's leading edge. A heuristic model of a depleted flux tube with constant circular cross section moving upward through a background plasma predicts most of the measurements' qualitative features.

Aggson, Thomas L.↗
NASA NTRS1990

The interaction of active comets with the solar wind

The interaction of the solar wind with active comets is investigated based on observations of cometary plasma processes and studies of comets using telescopes and photographic plates. Data were also collected when a spacecraft flew through the tail of Comet Giacobini-Zinner in 1985 and five spacecraft encountered Comet Halley in 1986. The solar wind is considered to be supersonic (thermal Mach number 2-10) and to carry a magnetic field twisted into an Archimedean spiral by the rotation of the sun. Since the wind can change its properties during the time a spacecraft is inside the ionosphere or magnetosphere of the body being studied, it is difficult to separate spatial from temporal effects. Photoionization results in addition of plasma to the solar wind. Between the outer and inner edges of the cometosheath, the increasing rate of ion pickup causes the flow to slow down until it stagnates, while the plasma density and the magnetic field strength increase.

Neugebauer, Marcia↗
NASA NTRS2020

Plasma-environment effects on K lines of astrophysical interest III. IPs, K thresholds, radiative rates, and Auger widths in Fe ix – Fe xvi

Aims. In the context of black-hole accretion disks, we aim to compute the plasma-environment e ects on the atomic parameters used to model the decay of K-vacancy states in moderately charged iron ions, namely Fe ix – Fe xvi. Methods. We used the fully relativistic multiconfiguration Dirac–Fock method approximating the plasma electron–nucleus and electron–electron screenings with a time-averaged Debye–Hückel potential. Results. We report modified ionization potentials, K-threshold energies, wavelengths, radiative emission rates, and Auger widths for plasmas characterized by electron temperatures and densities in the ranges 10^(5)-10^(7) K and 10^(18)-10^(22)/cu. cm. Conclusions. This study confirms that the high-resolution X-ray spectrometers onboard the future XRISM and Athena space missions will be capable of detecting the lowering of the K edges of these ions due to the extreme plasma conditions occurring in accretion disks around compact objects.

J. Deprince↗
NASA NTRS1978

Friction and wear of several compressor gas-path seal movements

Rub interaction experiments were conducted on a series of sintered and plasma sprayed compressor gas path seal materials in contact with Ti-6Al-4V blade tip and knife edge rotors. The most rub tolerant materials investigated were sintered Nichrome and plasma sprayed nickel 25 percent graphite. The effectiveness of providing a compliant substrate for dense seal material coatings was also demonstrated. In general, it was observed that rotor wear and high frictional energy generation rates accompanied smearing or surface densification of the materials investigated. The onset of smearing was sensitive to rub interaction parameters and seal geometry. Two complementary models were proposed to account for the smearing trends. One is based on thermal effects, the other on particulate escape effects. They were shown to be consistent with the experimental evidence at hand, and together they predict that smearing, with the onset of high energy rub conditions, is favored when incursion rates (radial motion) are low, incursion depths are high, the seal geometry is of a knife-edge character, and the seal particle size is small.

Bill, R. C.↗
NASA NTRS1991

Micrometeorite erosion of the man rings as a source of plasma in the inner Saturnian plasma torus

Micrometeorite bombardment is presently suggested to be a source of water molecules and molecular ions in the region between the outer edge of the main rings of Saturn and Encedalus, adding to those neutrals and plasma that are generated by the sputtering of icy satellites. In view of uncertainties concerning the magnitude and distribution of the ring source, an examination is conducted of limiting cases. The implications of such cases for the Cassini division are calculated, and a discussion of their possible relevance to the region's neutral and plasma cloud is presented.

Pospieszalska, M. K.↗
NASA NTRS1992

A case study of plasma structure in the dusk sector associated with enhanced magnetospheric convection

Consideration is given to a case study based on a combination of ground whistler and satellite measurements of thermal plasma density which provides additional evidence that the abrupt western edge of the bulge region of the magnetosphere, reported earlier from whistlers, is a real phenomenon. The present data and previous MHD modeling work suggest that this distinctive feature develops during periods of steady or declining substorm activity, when dense plasma previously carried sunward under the influence of enhanced convection activity begins to rotate with the earth at angular velocities that decrease with increasing L value and becomes spirallike in form. Whistler data are used to identify a narrow dense plasma feature, separated from the main plasmasphere and extending sunward into the late afternoon sector at L values near the outer observed limits of the main plasmasphere and extending sunward into the edge of the main bulge, found by both whistler stations to be at about 1800 MLT, appeared to be quasi-stationary in sun-earth coordinates during the prevailing conditions of gradually declining geomagnetic agitation.

Carpenter, D. L.↗
NASA NTRS1980

Ion temperature troughs induced by a meridional neutral air wind in the night-time equatorial topside ionosphere

A mathematical model was constructed to calculate O(+) and H(+) concentrations, field-aligned velocities, and electron temperatures in the night-time equatorial topside ionosphere. The model is used to establish the ability of F-region neutral air winds to produce observed ion temperature distributions, and to study the properties of ion temperature troughs as functions of altitude, latitude, and ionospheric composition. The O(+) - H (+) transition height represents an altitude limit above which the ion cooling from adiabatic expansion of the plasma is very small; the northern and southern edges of the ion temperature troughs are restricted to the limiting dip altitudes determined by magnetic field line geometry and by the functional form of the F-region neutral wind velocity.

Bailey, G. J.↗
NASA NTRS1994

The deformation of flux tubes in the solar wind with applications to the structure of magnetic clouds and CMEs

Two dimensional magnetohydrodynamic simulations of the distortion of a magnetic flux tube, accelerated through ambient solar wind plasma, are presented. Vortices form on the trailing edge of the flux tube, and couple strongly to its interior. If the flux tube azimuthal field is weak, it deforms into an elongated banana-like shape after a few Alfven transit times. A significant azimuthal field component inhibits this distortion. In the case of magnetic clouds in the solar wind, it is suggested that the shape observed at 1 AU was determined by distortion of the cloud in the inner heliosphere. Distortion of the cloud beyond 1 AU takes many days. It is estimated that effective drag coefficients slightly greater than unity are appropriate for modeling flux tube propagation. Synthetic magnetic field profiles as would be seen by a spacecraft traversing the cloud are presented.

Cargill, Peter J.↗