SEARCH · Engineering Papers
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Summaries are presented of research in basic plasma physics. Nonlinear waves and shock-like phenomena were studied which are pertinent to space physics applications, and include specific problems of magnetospheric and solar wind plasma physics.
Several recent findings from observational researches of various facets of magnetospheric plasmas are summarized. These new results encompass entry of solar wind plasmas into the dayside magnetosphere, the acceleration of plasmas both at great distances from the earth in the magnetotail and at low altitudes over auroral luminosities, and the substantial contributions of the upper ionosphere to the plasma compositions of the distant magnetosphere.
The detection of the optical emission /O I/ 6300 A (8 + or - 4 R) and /S III/ 6312 A (48 + or - 5 R) is reported. It is noted that these emissions are indicators of the ion source morphology and the plasma physical state and that the S III emitters have a kinetic temperature of approximately 10 to the 6th K. When combined with observations of UV lines from the same species, the optical measurements separately imply effective electron temperatures for radiative processes that are mutually consistent (approximately 50,000 K).
Geostationary satellite and ground measurements of dynamic variations of the outer radiation belts and their relations with the development of auroral structures during magnetospheric substorms are analyzed. A comparison of measurements of the H or X geomagnetic field components made by seven auroral stations with ATS-6 low-energy and high-energy particle measurements during the multiple-onset substorm of Aug. 16, 1974 is presented which demonstrates that while the decrease in energetic particle fluxed ends only at the time of a strong substorm onset, rapid motions of the outer radiation belts may occur during the flux decrease. All-sky photographs of auroral phenomena taken at Fort Yukon and College, Alaska are then compared with ATS-1 energetic particle flux measurements in order to demonstrate the relation between flux decreases and increases and distinct substorm phases. Results support the hypothesis of a magnetospheric substorm precursor which appears to be an instability growing at the inner boundary of the plasma layer and approaching the earth, and underline the importance of current and magnetic field variations in charged particle dynamics.
Measurements of the intensities, energy spectra, angular variations, and composition characteristics of the low-energy ion populations (approximately 30 keV to 4 MeV) obtained by both Voyager spacecraft in the outer (more than about 10 Jupiter radii) Jovian magnetosphere are reported and interpreted. Also shown are some of the energetic electron measurements. Using the spectral and angular ion measurements, density and pressure profiles in the magnetosphere are constructed and then compared with results reported by the plasma wave and plasma science investigations (density) and the magnetic field investigation (pressure).
Under the simple postulate that multiple large scale detachable magnetospheric convection eddies can exist in the vicinity of the convection reversal boundary and in the polar cap, by Kelvin-Helmholtz instability or otherwise, it is shown that a number of seemingly disconnected plasma and electric field observations in the polar cap can be organized into a theory of magnetosheath and plasmasheet plasma intrusion into the polar cap. Current theory of inverted V structures then predicts existence of similar, but weaker, structures at the eddy convection reversal boundaries in the polar cap. A possible consequence is that the polar cap auroras are natural offshoots from discrete oval arcs and evidently are formed by similar processes. The two arc systems can occassionally produce an optical image in the form of the theta aurora.
Plasma and electric field signatures of polar cap arcs in their formation region above 5000 km are examined. Signatures for active and for quiet magnetic conditions are presented, both indicating a virtual equivalence of plasma and electric field signatures between the polar and evening discrete arcs, although their optical configurations can be very different. It is proposed that the two types of arcs are indeed the same at active times except that the polar cap arcs occur at multiple convection reversal boundaries of plasmasheet plasmas which intrude into the normal polar cap in the form of multiple cellular eddies. A far-reaching consequence of this hypothesis is the unification of arc formation theory clarifying the distinct roles of arc formation parallel electric fields and of arc configuration and location. Optical and particle data which support this hypothesis are discussed.
Explore the source record for details and available documents.
The S3-3 satellite discovered the principal auroral acceleration region at altitudes of about 1 R(E) over the auroral zone. Intense fluxes of upward flowing O(+) and H(+) ions with keV energies were commonly observed in this region of the magnetosphere. The detailed morphology of these upflowing ions is described, including their latitude, local time, altitude, and magnetic activity dependences and their relationship to the trapped keV electron population. The first measurements of the composition of the trapped keV ions in the radiation belts are also described, showing the importance of the ionospheric source term to the storm time population of ions with energies equal to or less than 16 keV/e.
The International Sun Earth Explorer (ISEE-1) was launched on Oct. 22, 1977 into a geocentric elliptical orbit. The energetic ion mass spectrometer on the satellite is employed in a study of the plasmas encountered by ISEE-1 in its orbits. The experiment is operating successfully and research is progressing in a number of areas. A review in the nature of a progress report on the energetic magnetospheric plasma results is provided. Attention is given to the plasma sheet and ion streams in the magnetotail, the inner magnetosphere, and magnetospheric boundary regions.
Initial observations from the energetic ion composition spectrometer on the DE-1 spacecraft have found mass or charge dependent processes to be operating in the vicinity of an inverted-V event in the auroral acceleration region, above the polar cap ionosphere, and in the mid-altitude dayside cusp. Separate color spectrograms for the different ion species provide a synoptic picture of these processes that can contribute significantly to our understanding of both the solar wind and the ionosphere as sources of energetic magnetospheric ions.
Radial profiles of the ion density and flux-tube content in the Io torus have peak values inside Io's orbit, even though Io is the effective source of these ions. Formation of an inward peak constrains either the velocity distributions or source regions of sputtered neutrals. A further constraint is that the ionization of neutrals on trapped trajectories that return to Io's surface must be limited. A dominant sulphur source is most easily reconciled with these constraints.
Inferences are drawn on the morphology and composition of the Uranus magnetosphere based on low-energy charged particle data collected by Voyager 2. Proton and electron energies in the magnetosphere attained energies of 4 and 1.2 MeV, respectively, although electron intensities surpassed the proton intensities at most energy levels. Protons dominated in the ion energy regime 0.6-1.0 MeV. The ion and electron spectra were Maxwellian below about 200 keV and had a power law distribution at energies over 590 keV. The power law was reduced by a factor of nearly three inside the orbit of Miranda. The proton population is dense enough to polymerize CO and CH4 ice surfaces within 10,000-100,000 yr. The data indicated that the particles are swept out at least to the orbit of Titania by the satellites. The morphology of the magnetosphere closely resembles that around Jupiter, except that plasma sheet distorsion from particle loading is negligible in regions within 15 Uranus radii.
A detailed account is given of the results of the Voyager 2 low-energy charged particle investigation of the Uranian magnetosphere. Data show that the encounter of the inbound bow shock was immediately preceded by intense upstream proton events characterized by bulk streaming pointing approximately tangentially to the magnetospheric boundaries. Observations are presented which suggest that substorm processes analogous to those occurring within the earth's magnetotail are occurring within the Uranian magnetotail.
Voyager 2's low energy charged particle instrument employed an array of solid-state detectors in various configurations to measure energetic electrons and ions within the Neptune magnetosphere in several energy channels. Various features of the intensity, spectral, and anisotropic data obtained suggest that the Triton satellite exerts an important controlling influence over the outer regions of the Neptunian magnetosphere. Composition measurements have indicated the presence of H, H2, and He-4 at 1300:1:0.1 relative abundances, respectively, suggesting a Neptunian ionospheric source for the trapped particle population.
This paper presents values of particle spectral parameters and estimates of plasma densities, temperatures, and beta parameters, obtained with the Low Energy Charged Particle instrument during the Voyager 2 encounter with Neptune on August 24-25, 1989. In addition, trapped electron intensities are compared with the whistler mode stably trapped limits. The results revealed a very good inbound-outbound symmetry for both the proton and the electron profiles, suggesting that there was little dynamical activity in Neptune's magnetosphere during the Voyager encounter. The similarities and differences observed between Neptune and Uranus in the values of plasma density, pressure, and beta are discussed.
Analysis of Voyager 2 low-energy charged particle and magnetic field data in the Uranian magnetotail show that this system has many features similar to those seen at earth. Isotropization of core magnetosphere 28-43 keV ions has been observed at the trapping boundary upon entry into the magnetotail near L = 17, an effect seen in ion populations at earth and attributed to neutral sheet scattering. An extensive and persistent plasma sheet boundary layer is found to contain field-aligned ion streams with a variety of angular and energetically dispersive effects. Streaming distributions in the magnetotail horn region map to the auroral emission region observed by the Voyager ultraviolet spectrometer. A quiet-time near-tail region is distinguished from a distant disturbed region, where evidence of a substorm is observed. There is evidence suggesting that the distant plasma sheet is not corotating with the planet.
The paper presents a revised theory and atomic model for the line intensities emitted by O VII, taking into account all of the processes responsible for the emission. This is used to provide a revision of the density measurements made for solar active regions and during flares, as well as an attempt to understand the spectrum of the Puppis A supernova remnant. In order to explain the strange intensity ratios observed from Puppis A, previous authors have proposed an interpretation based upon a high-temperature thermal plasma in a nonequilibrium ionization state. An alternative model is presented here, based upon the assumed presence of a proportion of fast, nonthermal electrons imbedded in an otherwise thermal plasma at a temperature below 10 to the 6th K. This can adequately explain the observations without the necessity of invoking departures from the ionization balance.