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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 NTRS1972

Thermal positive ions in the outer ionosphere and magnetosphere from Ogo 1.

Study of the positive thermal ion densities measured with a spherical electrostatic analyzer aboard OGO 1 between September and October, 1964. A high variability of charged-particle distributions is established within and beyond the plasmapause boundary. The density gradient was in an inverse relation to the plasmapause L position and was consistently about one order of magnitude higher for the afternoon sector orbits than for the nightside orbits. Irregularities of different types were observed in the positive thermal ion densities within the plasmasphere and outside it, showing no correlation with the magnetic activity level. A delay of 3 to 9 hr was observed in the movement of the plasmapause following an increase in the magnetic activity level on the nightside.

Ahmed, M.↗
NASA NTRS1984

Dynamics of the Venus ionosphere - A two-dimensional model study

A two-dimensional model of the ionosphere of Venus which simulates ionospheric dynamics by self-consistently solving the plasma equations of motion, including the inertial term, in finite difference form has been constructed. The model, which is applied over the solar zenith angle range extending from 60 to 140 deg and the altitude range 100 to 480 km, simulates the measured horizontal velocity field quite satisfactorily. The ion density field is somewhat overestimated on the dayside, because of the choice model neutral atmosphere, and underestimated on the nightside, because of setting the ionopause height at too low an altitude. It is concluded that solar photoionization on the dayside and ion recombination on the nightside are the processes mainly responsible for accelerating the plasma to the observed velocities. The plasma flow appears to be sufficient to maintain the nightside ionosphere at or near the observed median level of ion densities.

Whitten, R. C.↗
NASA NTRS1987

Proton and oxygen plasmas at Uranus

Despite the presence of several large, ice moons within the Uranian magnetosphere, the Voyager 2 spacecraft did not detect any heavy ion plasma. This paper estimates the heavy ion density that would be consistent with a heavy neutral torus formed by photosputtering, charged particle sputtering, and micrometeoroid impact vaporization of icy surfaces on the moons, taking into account the large 60 deg angle between the satellite orbit plane and the magnetic equator. The expected heavy ion density is unobservably small. The observed proton plasma of the inner magnetosphere can be maintained by ionization of the atomic hydrogen corona and by the ionospheric proton source driven by photoelectron escape, for a plasma residence time of about 30 days. These two proton sources are comparable near L = 5. The same 30-day residence time for energetic protons implies an upper limit of 0.00001 on the fraction of incident solar wind protons that enter the magnetosphere and penetrate to within L less than 6 while conserving their first adiabatic invariants.

Cheng, Andrew F.↗
NASA NTRS1976

Diurnal variation of thermal plasma in the plasmasphere

All of the OGO-5 light ion density measurements were used to determine the average global topology of the equatorial plasmasphere density distribution. The variation of the light ion equatorial density at L less than or equal to 3.2 with local time was deduced by determining the average density observed within one hour of a specific local time and within 0.1 of a given L coordinate. The average H(+) density showed a semidiurnal variation with peaks near noon and midnight. The He(+) observations also revealed multiple peaks throughout the day but with smaller amplitudes than those of H(+). At L above 3.2 plasma trough conditions increase the scatter of densities. The average variation of the H(+) density with L within the plasmasphere is found to be steepest near midnight and can be least-squares fitted equally well to either an exponential variation or to a power law.

Chen, A. J.↗
NASA NTRS1981

Bodies in flowing plasmas - Laboratory studies

A brief review of early rudimentary laboratory studies of bodies in flowing, rarefied plasmas is presented (e.g., Birkeland, 1908), along with a discussion of more recent parametric studies conducted in steady plasma wind tunnels, which includes the study by Hall et al. (1964), in which a strong ion density enhancement in the center of the ion void created downstream from the body was observed. Good agreement was found between the experimental results and theoretical calculations which omit ion thermal motion. Examples in which in situ data on the interaction between satellites and the ionospheric plasma have been elucidated by the laboratory results are presented, and include evidence for a midwake axial ion peak, and ion current density in the near-wake region. The application of the ionospheric laboratory to basic space plasma physics is discussed, and its application to some types of solar system plasma phenomena is illustrated.

Stone, N. H.↗
NASA NTRS1977

Time-resolved double-probe study in a He-Hg afterglow plasma

An experimental double-probe technique is described which allows the He(+) ion density to be measured directly as a function of time in the afterglow of a helium-metal-vapor discharge. As an application example, two CW laser transitions of the He-Hg(+) laser at 6150 and 7944 A are considered which both arise from excited 7p (2) P terms of Hg II. The time-resolved double-probe technique is used to measure the destruction rate of the He(+) ion density, which is then compared with the spontaneous-emission decay rate for 7p (2) P terms of Hg II. The results obtained show unambiguously and directly that the dominant excitation process for the two transitions considered is a charge-transfer collisional reaction of the form He(+) plus Hg yields He plus metastable Hg(+) plus the energy defect for this reaction. It is noted that the time-resolved double-probe technique may provide a simple method for measuring ion mobilities in a multi-ion plasma.

Shay, T.↗
NASA NTRS1988

Excitations of low-frequency hydromagnetic waves by freshly created ions in the solar wind

Low-frequency hydromagnetic waves excited by newborn ions in the solar wind plasma are studied. The freshly created ions appear in the solar wind frame with a ring beam distribution. Both Alfven and fast magnetosonic waves are made unstable by the presence of the newborn ions. The dependence of the growth rate of both waves on the newborn ion density, the angle between the interplanetary magnetic field (IMF) and solar wind flow, and the angle of wave propagation relative to the IMF is investigated. Analytic approximations for the growth rates are presented, and numerical solutions of the dispersion equation are shown. The approximations are quite close to the numerically determined growth rates. It is found that the waves grow preferentially in the direction parallel to the IMF, and that the growth rates increase with both newborn ion density and the angle between the IMF and the solar wind flow.

Price, C. P.↗
NASA NTRS1992

Energetic ion phase space densities in Neptune's magnetosphere

Ion phase densities of Neptune are presently ascertained at the first and second adiabatic invariants of charged-particle motion on the basis of an analysis of Voyager 2 measurements. The profiles thus obtained are interpreted as indicative of generally inward radial diffusion, with an energetic ion source near L = 10. Excellent agreement is obtained between inbound and outbound phase-space density profiles at the values of the invariants; this suggests approximately axisymmetric, quasi-stationary radiation belts. The inward diffusing power carried by energetic ions appears adequate for powering Neptune's aurora, if enough of the ions are lost to the Neptune atmosphere.

Cheng, Andrew F.↗
NASA NTRS1997

Gravity Wave Seeding of Equatorial Plasma Bubbles

Some examples from the Atmosphere Explorer E data showing plasma bubble development from wavy ion density structures in the bottomside F layer are described. The wavy structures mostly had east-west wavelengths of 150-800 km, in one example it was about 3000 km. The ionization troughs in the wavy structures later broke up into either a multiple-bubble patch or a single bubble, depending upon whether, in the precursor wavy structure, shorter wavelengths were superimposed on the larger scale wavelengths. In the multiple bubble patches, intrabubble spacings vaned from 55 km to 140 km. In a fully developed equatorial spread F case, east-west wavelengths from 690 km down to about 0.5 km were present simultaneously. The spacings between bubble patches or between bubbles in a patch appear to be determined by the wavelengths present in the precursor wave structure. In some cases, deeper bubbles developed on the western edge of a bubble patch, suggesting an east-west asymmetry. Simultaneous horizontal neutral wind measurements showed wavelike perturbations that were closely associated with perturbations in the plasma horizontal drift velocity. We argue that the wave structures observed here that served as the initial seed ion density perturbations were caused by gravity waves, strengthening the view that gravity waves seed equatorial spread F irregularities.

Singh, Sardul↗
NASA NTRS1986

Viscous pumping and the spin-down of thermospheric gyres and jets

Strong gyres and jets can be generated at auroral latitudes in the thermosphere by enhanced electric fields during geomagnetic substorms. Typical height profiles of ion density suggest that the ion drag force should generate large curvature in the vertical profile of the winds in the highly viscous region of the thermosphere above about 200 km. It is proposed that the poststorm spin-down of these gyres and jets proceeds via Ekman circulations driven by the curvatures in the height profiles of the winds. Analytic and numerical calculations of the ageostrophic winds forced by curvature in model geostrophic wind profiles show that the ageostrophic wind speeds and directions depend mainly on the kinematic viscosity in the region of curvature and the total change in shear in the geostrophic wind. Ageostrophic wind speeds for typical thermospheric jets can exceed 200 m/s (about 50 percent of the jet winds). Spin-down times of thermospheric jets and cyclonic gyres by the Ekman pumping mechanism are estimated at less than about 6 hours.

Walterscheid, R. L.↗
NASA NTRS1988

Corotation lag of Saturn's magnetosphere - Global ionospheric conductivities revisited

In view of the recent publication of Eviatar and Richardson (1986), who have calculated the Pedersen conductance of Saturn's ionosphere to be much smaller than previous estimates, the Pedersen conductance is recalculated using the same neutral atmosphere model as these authors. The results confirm the earlier estimates that the ionospheric Pedersen conductance of Saturn's ionosphere ranges from 0.3 to 17 mho near the terminator as a function of latitude. The source of discrepancy appears to be the inclusion by Eviatar and Richardson of ion density into the ion-neutral collision frequency term, which is incorrect. Contrary to the conclusion of Eviatar and Richardson, Saturn's ionospheric Pedersen conductance is high enough to impose nearly perfect corotation between the ionosphere and the magnetosphere.

Cheng, Andrew F.↗
NASA NTRS1999

Bond Dissociation Energies of the Tungsten Fluorides and Their Singly-Charged Ions: A Density Functional Survey

The dissociation of WF6 and the related singly-charged cations and anions into the lower fluorides and fluorine atoms has been investigated theoretically using density functional theory (B3LYP) and relativistic effective core potentials, with estimates of spin-orbit effects included using a simple model. The inclusion of spin-orbit is essential for a correct description of the thermochemistry. The total atomization energy of the neutral and anionic WF6 is reproduced to within 25 kcal/mol, but comparison of individual bond dissociation energies with available experimental data shows discrepancies of up to 10 kcal/mol. The results are nevertheless useful to help resolve discrepancies in experimental data and provide estimates of missing data.

Dyall, Kenneth G.↗
NASA NTRS2012

Farfield Ion Current Density Measurements before and after the NASA HiVHAc EDU2 Vibration Test

There is an increasing need to characterize the plasma plume of the NASA HiVHAc thruster in order to better understand the plasma physics and to obtain data for spacecraft interaction studies. To address this need, the HiVHAc research team is in the process of developing a number of plume diagnostic systems. This paper presents the initial results of the farfield current density probe diagnostic system. Farfield current density measurements were carried out before and after a vibration test of the HiVHAc engineering development unit 2 that simulate typical launch conditions. The main purposes of the current density measurements were to evaluate the thruster plume divergence and to investigate any changes in the plasma plume that may occur as a result of the vibration test. Radial sweeps, as opposed to the traditional polar sweeps, were performed during these tests. The charged-weighted divergence angles were found to vary from 16 to 28 degrees. Charge density profiles measured pre- and post-vibration-test were found to be in excellent agreement. This result, alongside thrust measurements reported in a companion paper, confirm that the operation of the HiVHAc engineering development unit 2 were not altered by full-level/random vibration testing.

Huang, Wensheng↗
NASA NTRS1980

Model calculations of the dayside ionosphere of Venus - Ionic composition

Comprehensive model calculations of the dayside ion density distributions were carried out and compared with results from the Pioneer Venus ion mass spectrometer. The coupled continuity and momentum equations were solved for O2(+), O(+), CO2(+), C(+), N(+), He(+), and H(+) densities for altitudes well away from the ionopause, where the horizontal transport terms are negligible. Chemical equilibrium solutions, describing conditions below about 200 km, were also obtained for N2(+), NO(+), and CO(+). The agreement between the model calculations of ion density and the measurements is good for some species, such as O(+), and rather poor for others, such as CO(+), indicating that while a basic understanding of the major chemical and physical processes controlling the composition and vertical distribution of the dayside Venus ionosphere, well below the ionopause, has been achieved, there are many important details requiring further investigations.

Nagy, A. F.↗
NASA NTRS1972

The magnetospheric plasma tail

The structural nature of the earth's plasmasphere at onset and immediately following an intense magnetic storm is examined. Thermal proton density measurements by the RF ion mass spectrometer on the low altitude polar orbiting satellite OGO-4 were compared on five consecutive nightside passes during the early recovery stage of an intense storm occuring in September 1967. Observational results revealed (1) characteristic termination of the dense plasmapause, (2) secondary enhancement of the ion density poleward of the first abrupt plasmapause, and (3) an elongated plasma tail during the recovery phase of the storm.

Grebowsky, J. M.↗