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NASA NTRS1984

The Soft X-ray Diffuse Background: Implications for the Nature of the Local Interstellar Medium

Observations of the diffuse X-ray background in the B and C bands (130-188 eV and 160-284 eV, respectively) provide convincing evidence for the existence of high-temperature interstellar gas. Since the opacity of normal interstellar material is very high, it is assumed that the soft X-ray flux observed in the galactic plane originates within a few hundred parsecs of the Sun. The intensity and B/C ratio of this low-latitude flux can be provided by emission from an equilibrium plasma with normal abundances, T =10 to the 6th power K, and 0.0019 cm(-6) pc emission measure. More sophisticated nonequilibrium models of material heated by a supernova blast wave would reduce the required emission measure somewhat, but not by so much as a factor of two. Arbitrarily limiting the pressure to 10 to the 4th power cm(-3) K gives a maximum density of 0.005 cm(-3) and a minimum radius for the emitting region of 75 pc. This fits in well with ultraviolet interstellar absorption measurements which indicate that the interstellar medium is very deficient in neutral hydrogen out to approx. 100 pc from the Sun.

Mccammon, D.↗
NASA NTRS1992

The hot plasma environment at Jupiter - Ulysses results

Initial results obtained from measurements made by the HI-SCALE (heliosphere instrument for spectra, composition, and anisotropy at low energies) experiment are reported. Data revealed that the Jovian magnetosphere is very extended, with the day-side magnetopause located at about 105 Jupiter radii. The relative abundances of sulfur, oxygen, and sodium to helium decreased with the decreasing radial distance from the planet on the day-side, which suggests that the abundances of Jupiter-derived species are dependent on latitude. Intense fluxes of counter-streaming ions and electrons were discovered in the dusk-side, high-latitude region from the edge of the plasma sheet to the dusk-side magnetopause. These beams of ions and electrons appeared to be very tightly aligned with the magnetic field and to be superimposed on a time- and space variable isotropic hot plasma background. The current carried by measured hot plasma particles are about 1.6 x 10 exp -4 microamps per sq m.

Lanzerotti, L. J.↗
NASA NTRS1974

Plasma and energetic particles in the magnetotail at 60 earth radii

Particle measurements made by the lunar-orbiting Apollo subsatellites have shown that electron energy spectra in the range 0.55-320 keV in the high-latitude magnetotail often fit a power law with an exponent of -3 and a flux at .5 keV of 200,000 to 700,000 el/sq cm s sr keV. In the magnetosheath, electron energy spectra are similar to the high-latitude magnetotail spectra. In the plasma sheet, electron energy spectra often fit the high-energy tail of a Maxwellian distribution with Eo of about 200-500 eV. During times of substorms a number of cases where the plasma sheet appears to thin at onset have been observed. In addition, cases of plasma sheet expansion at onset have also been observed.

Chase, L. M.↗
NASA NTRS1994

Ground and satellite observations of postdawn aurorae near the time of a sudden storm commencement

Meridian scanning photometer measurements taken in the magnetic postdawn sector at Longyearbyen, Svalbard, between 0300 and 0630 UT on December 29, 1981, are analyzed in conjunction with particle and field data retrieved during two near passes of the Dynamics Explorer 2 (DE 2) satellite. The interval included a sudden storm commencement (SSC) at 0455 UT. Pre-SSC optical and particle measurements showed a system of arcs that are spaced at approximately 1.1 deg intervals in magnetic latitude, embedded within the region 1 current system and span the convection reversal. The softer particle precipitation appears to have a source near the flanks of the magnetotail while the harder, more equatorward precipitation originates closer to Earth. During the SSC period the entire sky brightened, with enhanced 630.0-nm emissions extending from the northern horizon to south of magnetic zenith; intense but spatially separated 557.7-nm emissions dominated the southern horizon. DE 2 detected more than an order of magnitude increase and near isotropization of ring current electron fluxes, enhanced precipitation from the plasma sheet and significantly decreases auroral zone convection. Region 1/region 2 currents remained, with wavelike structures superposed. A dual timescale response to the SSC is consistent with ground and satellite measurements. On few minute travel timescales for hydromagnetic waves to pass through the system, magnetospheric particles accelerate and precipitate to increase the ionospheric conductivity. Global, field-aligned currents change more slowly. To maintain similar field-aligned currents with higher ionospheric conductances requires reduced electric fields. After 0520 UT the optical emissions settled into stable, but latitudinally separated bands of 630.0- and 557.7-nm emissions characteristic of cleft and plasma sheet precipitation, respectively.

Egeland, A.↗
NASA NTRS1973

Active cleaning technique for removing contamination from optical surfaces in space

An active cleaning technique for removing contaminants from optical surfaces in space was investigated with emphasis on the feasibility of using plasma exposure as a means of in-situ cleaning. The major work accomplished includes: (1) development of an in-situ reflectometer for use in conjunction with the contaminant film deposition/cleaning facility; (2) completion of Apollo Telescope Mount (ATM) filter treatment experiments to assess the effects of plasma exposure on the UV transmittance; (3) attempts to correlate the atomic oxygen flux with cleaning rate; (4) completion of in-situ butadien contamination/plasma cleaning/UV reflectance measurement experiments; (5) carbon cleaning experiments using various gases; (6) completion of silicone contamination/cleaning experiments; and (7) experiments conducted at low chamber pressures to determine cleaning rate distribution and contamination of surfaces adjacent to those being cleaned.

Shannon, R. L.↗
NASA NTRS1976

Io's atmosphere and ionosphere - New limits on surface pressure from plasma models

The paper studies charge particle impact as a mechanism for the production of Io's ionosphere. Pioneer 10 thermal plasma measurements and magnetospheric plasma models which explain the observed spatial distribution of neutral hydrogen and sodium atoms in the vicinity of Jupiter's satellite Io imply electron fluxes of about 10 to the 10th/sq cm/s. The fluxes and the temperature (about 100 eV) of this plasma suggest that electron impact ionization is the dominant process in forming the ionosphere of Io. It is found that the surface number density of the neutral species required to match the observed electron density profiles is about 10 to the 9th/cu cm or less. This value is two orders of magnitude lower than previous estimates.

Johnson, T. V.↗
NASA NTRS1978

Collisionless effects on the spectrum of secondary auroral electrons at low altitudes

A common feature of all rocket measurements of the differential flux of primary and secondary electrons under auroral activity is that between 30 and 85 eV, where the measurements overlap in energy, the electron flux data can be fitted by a certain power law. In the present paper, it is shown that the existence of plasma waves even in a region where they are nonresonant with the ambient particles can significantly modify the observed flux power law.

Papadopoulos, K.↗
NASA NTRS1984

On the dispersion in brightness of far-ultraviolet emission lines of cool giant stars

Low-resolution spectra have been obtained with the short-wavelength camera of IUE for late-type giant stars of spectral type F5 III-G8 III. These stars are believed to be in their first crossing of the H-R diagram, as inferred from their location along the blue edge of the Hertzsprung gap or their high abundance of lithium. From the earliest spectral type observed along the blue edge of the gap, the normalized C IV flux, which is indicative of 100,000 K plasma, increases to a maximum at G0 and then falls with advancing spectral type. The total range in emission measure of 100,000 K gas is an order of magnitude or more among stars making their first appearance as yellow giants and averages about 25 times higher in these stars than in other G8-K0 yellow giants, the majority of which are probably He-burning post-red giants. The observations tentatively show that transition region emission, and by inference coronal emission, increases in intensity with the growth of convection zones in late-type giants and then declines at lower surface temperatures, perhaps because of rotational spin-down and a weakening of dynamo action.

Simon, T.↗
NASA NTRS1986

High-resolution X-ray spectroscopic evidence of nonequilibrium conditions in the Cygnus Loop

High-resolution spectroscopic X-ray observations of a portion of the Cygnus Loop made with the Focal Plane Crystal Spectrometer aboard the Einstein Observatory are reported. Emission lines for O VII, O VIII, and Ne IX are measured, and upper limits are set to other transitions in O VII and O VIII. The detected emission line fluxes are consistent with emission from an equilibrium plasma with an electron temperature of about 3 x 10 to the 6th K, a value similar to that obtained by numerous previous observers. The absence of any O VII forbidden line emission strongly suggests that the emitting plasma is not in collisional ionization equilibrium. This is shown to be the case using several line diagnostics formed from the observed emission lines and a simple model describing the X-ray emission from an ionizing nonequilibrium plasma.

Vedder, P. W.↗
NASA NTRS1995

First spectral observations of the diffuse background with the Extreme Ultraviolet Explorer

We present the first results from the analysis of the spectroscopic observations of diffuse extreme ultraviolet (EUV) emission taken with the Extreme Ultraviolet Explorer (EUVE) spectrometers in the wavelength range 160-740 A. Although not designed or optimized for diffuse observation, the EUVE spectrometers are the most sensitive diffuse EUV spectrometer in orbit. The spectral resolution for diffuse emission of the medium and long-wavelength spectrometers are 17 and 34 A FWHM, respectively. During the period from 1992 July 25 to 1992 August 19, the spectrometers surveyed a 2 x 20 deg field scanned from (l, b) = (24 deg, -28 deg) to (44 deg, -74 deg) with a total effective exposure time of 575,232 s. The only emission lines detected were those of He I and He II (584, 537, 304 A) with intensities consistent with local geocoronal and/or interplanetary scattering of solar radiation (584 A = 1.30 rayleighs; 537 A = 0.040 R; and 304 A = 0.029 R). Models of the soft X-ray background, which results from a 10(exp 6) K plasma (Local Bubble) surrounding the neutral gas near the Sun (Local Cloud), predict that most of the flux from the hot plasma appears as emission lines in the EUV. We have compared these spectral predictions with our observations to place limits on the emission measure versus temperature of the proposed hot plasma. Using the same plasma model, we derived emissions measures for our data and the C and B soft X-ray bands of the Wisconsin rocket survey. We find that our limits for the plasma emission measure are a factor of 5-10 below the C- and B-band emission measures over the temperature range from 10(exp 5.7) to 10(exp 6.4) K. We explore possible scenarios that could reconcile our results with the X-ray surveys and conclude that depletion or a nonequilibrium plasma state rather than absorption are the more likely explanations of the discrepancy. We also show that our spectrum is inconsistent with the spectrum from the approximately 10(exp 5) K gas at the conductive interface between the hot Local Bubble and the cooler Local Cloud given by Slavin (1989). In addition, we place new limits on the helium ionization parameter in the Sun's vicinity caused by the 10(exp 6) K plasma in the Local Bubble.

Jelinksy, P.↗
NASA NTRS1981

The diffuse extreme-ultraviolet background - Constraints on hot coronal plasma

The Apollo-Soyuz data and data reported by Cash et al. (1976) have been reanalyzed in terms of both isothermal models and temperature distribution models. In the latter case, a power-law form is assumed for the relation between emission measure and temperature. A new upper limit on diffuse flux in the 20-73 eV band derived from Apollo-Soyuz observations made in the earth's shadow has been incorporated in the calculation. In the considered investigation the results of the new analysis are presented and the implications for the physical properties of the hot component of the interstellar medium are discussed. The analysis of the Berkeley extreme ultraviolet (EUV) diffuse background measurements using either isothermal or power law temperature distribution models for the emitting plasma indicates excellent qualitative agreement with hard X-ray data that suggest the sun to be immersed in a hot plasma that pervades most of space out to approximately 100 pc.

Paresce, F.↗
NASA NTRS1974

Low-energy auroral electrons

A measurement of the low-energy auroral electron flux distribution between 0.5 and 80 eV reveals structure between 0.5 and 10.0 eV. The structure is due to the thermal electron Maxwellian distribution and electron energy loss to thermal electrons, molecular nitrogen, and atomic oxygen. Some physical process in the auroral plasma causes the deduced loss function to differ from theory. Reasonable agreement is obtained between calculated and measured N2 second positive emission.

Sharp, W. E.↗
NASA NTRS1973

The angular distribution of ion flux around an ionospheric satellite.

Ion measurements from the Explorer 31 satellite were used to determine the angular distribution of ions around the satellite. The ion distributions were compared with the electron distributions measured on the same satellite. It is shown that the electron currents (fluxes) in the wake are always larger than the ion currents for a wide domain of plasma parameters. A quantitative comparison of the ion fluxes with a neutral approximation model for the angular distribution is considered. It is found that the ion fluxes become progressively larger than the corresponding computed neutral fluxes as the angle of attack increases from 0 to 180 deg.

Samir, U.↗
NASA NTRS2021

Magnetic Structure and Propagation of Two Interacting CMEs from the Sun to Saturn

One of the grand challenges in heliophysics is the characterization of coronal mass ejection (CME) magnetic structure and evolution from eruption at the Sun through heliospheric propagation. At present, the main difficulties are related to the lack of direct measurements of the coronal magnetic fi elds and the lack of 3D in-situ measurements of the CME body in interplanetary space. Nevertheless, the evolution of a CME magnetic structure can be followed using a combination of multi-point remote-sensing observations and multi-spacecraft in-situ measurements as well as modelling. Accordingly, we present in this work the analysis of two CMEs that erupted from the Sun on 28 April 2012. We follow their eruption and early evolution using remote-sensing data, fi nding indications of CME{CME interaction, and then analyse their interplanetary counterpart(s) using in-situ measurements at Venus, Earth, and Saturn. We observe a seemingly single flux rope at all locations, but find possible signatures of interaction at Earth, where high-cadence plasma data are available. Reconstructions of the in-situ flux ropes provide almost identical results at Venus and Earth but show greater discrepancies at Saturn, suggesting that the CME was highly distorted and/or that further interaction with nearby solar wind structures took place before 10 AU. This work highlights the difficulties in connecting structures from the Sun to the outer heliosphere and demonstrates the importance of multi-spacecraft studies to achieve a deeper understanding of the magnetic confi guration of CMEs.

Erika Palmerio↗
NASA NTRS1987

Voids in Jovian magnetosphere revisited - Evidence of spacecraft charging

The Voyager 2 Plasma Science Instrument (PLS) measuring cold plasma number density observed about a dozen 'voids', lasting from a few minutes to 20 min, in the vicinity of the Ganymede-orbit crossing, when the low-energy ion and electron fluxes recorded fell to very low levels. Original interpretations associated these 'voids' with Ganymede wake effects. In the present study, the PLS data are reexamined, in conjunction with data from the magnetic field experiment and the low-energy charged particle (LECP) experiment. The LECP data showed that the PLS voids were accompanied by large enhancements of the flux of energetic electrons and ions, while the magnetic data exhibited no systematic signatures. It is suggested that increased energetic electron fluxes in the void regions intermittently charged the spacecraft negatively to values between a few kV and a few tens of kV, and that spacecraft charging could have produce dropouts in the measured cold ion and electron fluxes and enhancements in the measured fluxes of hot particles consistent with the observations.

Khurana, K. K.↗
NASA NTRSDate not supplied

Simulated Ball Lightning on A Submarine

Silberg (1962) discusses the observation of a ball-shaped glowing plasma (labeled a “plasmoid”) that occurred aboard a diesel-electric submarine when the switchgear opened a circuit carrying a current of 156,000 amps. In 1968 joint NASA/Navy experiments were conducted for an analogous situation aboard a similar submarine to characterize the plasmoids and to determine if they were reproducible with more modest electrical currents. Movies and spectra were obtained for approximately 40 arc events. Several events showed the presence of clouds of glowing gas as well as small plasmoids. The plasmoids had diameters of several mm that lasted approximately 0.2 seconds. Spectra of the initiating arcs showed the presence of emission lines from atomic copper and silver from the electrodes as well as those from singly excited oxygen and nitrogen atoms. Peak currents of several kiloamps were measured. Graphs of the time-histories of plasmoid motion, size, relative color ratios, and relative optical flux will be shown for two plasmoids.

plasma↗
NASA NTRS1962

Landau Damping of Transverse Waves in the Exosphere by Fast Particle Fluxes

We have investigated the Landau damping of transverse waves propagating in the thermal exospheric plasma, by fast particle fluxes which also exist in these regions. The most intense non-thermal fluxes so far detected are those of the auroral producing electrons and protons measured by McIlwain. We find that these fluxes may considerably damp the propagation of whistler modes through some regions. The damping of hydromagnetic waves in the exosphere by this mechanism is negligible.

LANDAU DAMPING↗
NASA NTRS1972

Magnetogasdynamic heat transfer to a hemispherical body in a supersonic argon plasma.

Measurements of the heat transfer to a hemispherical body in a Mach 4.6, low density, argon plasma are reported. The experiments demonstrated that local wall currents affected the heat flux to the electrically conducting surface, both without and with internally applied magnetic fields. Such currents were induced by a nonuniform shock-layer plasma potential; but with applied fields, Hall currents dominated. Magnetic fields significantly increased the stagnation-region heat flux while causing a reduction over the remainder of the hemisphere. For an electrically nonconducting surface, the local heat flux was reduced, and magnetic fields insignificantly affected the heat flux. Analytical treatments indicate that joule and radiation heating were negligible.

Nowak, R. J.↗