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At least 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Observations of the magnetospheric boundary layers

Results on magnetospheric boundary layers are reviewed, emphasizing their dynamical importance based on hot plasma observations, energetic particle signatures, heavy ion contributions and the effects of wave-particle interactions. Satellite plasma observations show that 1% to 2% of the oncoming solar wind plasma enters the magnetosphere and is initially transported within the magnetospheric boundary layer. Some of this boundary layer plasma is entrained within the Earth's magnetotail where it can be accelerated. Tests are needed to determine the relative contributions of the primary acceleration processes whose effects are especially evident in the plasma sheet boundary layer.

Eastman, T. E.↗
NASA NTRS1987

Plasma depletions in the Jovian magnetosphere - Evidence of transport and solar wind interaction

A series of plasma voids ('dropouts') was observed by the Plasma Science (PLS) experiment in Jupiter's magnetosphere during the Voyager 2 encounter with that planet. A reexamination of Voyager 2 data has led to the conclusion that the dropout phenomenon cannot be a manifestation of a plasma wake produced by Ganymede. Rather, the appearance of the dropouts is attributed to changes in the upstream solar wind conditions and the global state of the magnetosphere; the proximity of Voyager 2 to Ganymede at the time is considered to be coincidental. It is suggested that these dropouts are evidence of a state of 'bubbling' of the magnetosphere that alternates with 'laminar' states in which, as in the case of the Voyager 1 encounter with Jupiter, voids are not present and that these states correspond to different processes by which plasma is transported out of the system. The nature of these states is related to changes in the magnitude of the upstream solar wind ram pressure. In the bubbling state, this pressure is higher than in the laminar state and drives an intermittent instability. The analysis presented is one of the first attempts to introduce, in space physics, recently acquired theoretical notions of the physics of the finite-beta plasmas of which the Jovian magnetospheric plasma is an important example.

Mcnutt, Ralph L., Jr.↗
NASA NTRS1981

Plasma waves near Saturn: Initial results from Voyager 1

The Voyager 1 encounter with Saturn provided the first opportunity to investigate plasma wave interactions in the magnetosphere of Saturn. An overview of the principal results from the Voyager 1 plasma wave instrument is presented starting with the initial detection of Saturn and ending about four weeks after closest approach. A survey plot of the electric field intensities detected during the Saturn encounter is shown starting shortly before the inbound shock crossing and ending shortly after the outbound magnetopause crossing. Many intense waves were observed in the vicinity of Saturn. To provide a framework for presenting the observations, the results are discussed more or less according to the sequence in which the data were obtained.

Gurnett, D. A.↗
NASA NTRS2001

Detection of Chamber Conditioning by CF4 in the GEC Cell

During oxide etch processes, buildup of fluorocarbon residues on reactor sidewalks can cause to drift and will necessitate time for conditioning and cleaning of the reactor. Various measurements in CF4 and Ar plasmas are made in an attempt to identify a metric able to indicate the chamber condition. Mass spectrometry and a Langmuir probe shows that the buildup of fluorocarbon films on the reactor surface causes a decrease in plasma floating potential, plasma potential, and ion energy in argon plasmas. This change in floating potential is also observed in CF4 plasma operation, and occurs primarily during the first hour and a half of plasma operation. A slight rise in electron density is also observed in the argon plasmas. Because the change is seen in an argon plasma, it is indicative of altered physical, not chemical, plasma-surface interactions. Specifically, the insulating films deposited on metal surfaces alter the electromagnetic fields seen by the plasma, affecting various parameters including the floating potential and electron density. An impedance probe placed on the inductive coil shows a slight reduction in plasma impedance due to this rising electron density. The optical emission of several species, including CF, C2, atomic Si and atomic C, is also monitored for changes in density resulting from the buildup of film on the chamber wall. Changes in the optical emission spectrum are comparable to the noise levels in their measurement.

Cruden, Brett A.↗
NASA NTRS1994

Effect of Rehydration Fluid Osmolality on Plasma Volume and Vasopressin in Resting Dehydrated Men

Elevated plasma vasopressin concentration [PVP], which may act as a dipsogen, decreases promptly following the ingestion of fluids in many mammals including humans. The purpose for this study was to determine whether fluids of varied electrolyte and carbohydrate composition and osmolality (Osm] would modify post-drinking decreases in [PVP] which could be attributed to interaction with plasma volume (PV)- or fluid-electrolyte interactive hormones. Five men (23-41 yr, 78.0 +/- SD 8.2 kg), water deprived for 24 h, drank six fluids (12 ml/kg, at 16.5C in 4.0-6.2 min): water (30 m0sm/kg), NaCl (70 mOsm/kg), NaCl + NaCitrate (270 mOsm/kg), NaCl + 9.7% glucose (650 mOsm/kg), and two commercial drinks containing various ionic and carbohydrate contents (380 and 390 mOsm/kg). Blood (20 ml/sample) was drawn at -5 min before and at +3, +9, +15, +30, and +70 min after drinking. Heart rate, blood pressures, and plasma renin activity, {Na+], [K+], [Osm], aldosterone, atrial natriuretic peptide, and epinephrine concentrations were unchanged after drinking. Post-drinking [PVP] decreased from 1.7 - 3.7 pg/ml within 3 min with all fluids independently of their composition, [Osm], or delta PV; with maximal depression to 0.1-0.7 pg/ml (p<0.05) by 15 min. The continued [PVP] depression with all fluids from 15 to 70 min was accompanied by unchanged plasma (Osm] but 1.8-7.6% increases (p<0.05) in PV with 3) fluids (2 commercial and NaCitrate) and no change with the others. Percent changes in mean [PVP] and plasma norepinephrine concentrations [PNE] at 15 min correlated -0.70 (P<0.10) suggesting that about half the variability in [PVP I I depression was associated with [PNE]. Thus, part of the mechanism for post-drinking [PVP] depression may involve a drinking stimulated norepinephrine (neural) factor.

Geelen, Ghislaine↗
NASA NTRS1995

Measurements of electric fields in the solar wind: Interpretation difficulties

The traditionally measured electric fields in the solar wind plasma (about 1-10 mV/m) are not the natural, primordial ones but are the result of plasma-vehicle interaction. The theory of this interaction is not complete now and current interpretation of the measurements can fail. The state of fully ionized plasma depends on the entropy of the creating source and on the process in which plasma is involved. The increasing twofold of a moving volume in the solar wind (with energy transfer across its surface which is comparable with its whole internal energy) is a more rapid process than the relaxation for the pressure. The presumptive source of the solar wind creation - the induction electric field of the solar origin - has very low entropy. The state of plasma must be very far from the state of thermodynamic equilibrium. The internal energy of plasma can be contained mainly in plasma waves, resonant plasma oscillations, and electric currents. The primordial microscopic oscillating electric fields could be about 1 V/m. It can be checked by special measurements, not ruining the natural plasma state. The tool should be a dielectrical microelectroscope outside the distortion zone of the spacecraft, having been observed from the latter.

Chertkov, A. D.↗
NASA NTRS1979

Magnetospheric plasma waves

Space measurements have provided a wealth of data on wave phenomena, plasma parameters, and energetic particle characteristics within the earth's magnetosphere. In the present paper, the generation, propagation, and interaction of plasma waves are discussed, along with the interpretation of the observations. Data on plasma waves from other planetary magnetospheres and cosmic plasma systems are examined and interpreted by analogy to the earth's magnetosphere. Areas requiring continued plasma wave research are indicated.

Shawhan, S. D.↗
NASA NTRS1989

Report from space plasma science

Space plasma science, especially plasma experiments in space, is discussed. Computational simulations, wave generation and propagation, wave-particle interactions, charged particle acceleration, particle-particle interactions, radiation transport in dense plasmas, macroscopic plasma flow, plasma-magnetic field interactions, plasma-surface interactions, prospects for near-term plasma science experiments in space and three-dimensional plasma experiments are among the topics discussed.

Hastings, D. E.↗
NASA NTRS2004

Complexity and Intermittent Turbulence in Space Plasmas

Sporadic and localized interactions of coherent structures arising from plasma resonances can be the origin of "complexity" of the coexistence of non- propagating spatiotemporal fluctuations and propagating modes in space plasmas. Numerical simulation results are presented to demonstrate the intermittent character of the non-propagating fluctuations. The technique of the dynamic renormalization-group is introduced and applied to the study of scale invariance of such type of multiscale fluctuations. We also demonstrate that the particle interactions with the intermittent turbulence can lead to the efficient energization of the plasma populations. An example related to the ion acceleration processes in the auroral zone is provided.

Chang, Tom↗
NASA NTRS1980

Pioneer Venus plasma observations of the solar wind-Venus interaction

Collection of data from the Ames plasma analyzer on the Pioneer Venus orbiter has permitted long-term measurements of the interaction of the solar wind with Venus. The paper presents a mapping of the ionosheath flow field, plasma measurements in the distant ionosheath and near the distant plasma cavity, and a summary of observations of jumps in the solar wind proton parameters across Venus' bow shock. Also, the apparent detection of ionospheric O(+) accelerated up to solar wind speeds downstream in Venus' ionosheath is discussed.

Mihalov, J. D.↗
NASA NTRS1992

Observations of plasma waves in the solar wind interaction region of Comet Giacobini-Zinner at high time resolution

High-time-resolution spectra of plasma wave emissions detected in the interaction region of Comet Giacobini-Zinner with the solar wind reveal a wave phenomenology much more complicated than first reported. Spectra often exhibit three or more independent peaks, which become more prominent the deeper into the interaction region the spacecraft traversed. The main peaks correspond to whistler emissions below the electron cyclotron frequency, a midfrequency peak near the maximum Doppler shift frequency for waves with k lambda(D) = 1, a high-frequency peak above the Doppler shift maximum frequency, and electron plasma oscillations at the plasma frequency. Similar multipeaked spectra are also observed downstream from weak shocks at Earth, which suggests that the plasma wave generation mechanisms responsible need not require particle populations created by photoionization.

Moses, S. L.↗
NASA NTRS1998

Measurements of the Plasma Parameters and Low Frequency Oscillations in the Fisk Plasma Source

A new plasma device, the Fisk Plasma Source (FPS), has been developed at Fisk University. This plasma device is used to study the physics of low temperature plasmas and plasma-material interactions. The FPS device is a stainless steel vacuum 6-way cross vacuum vessel with at 10-inch inner diameter. Low temperature argon plasmas are generated using DC glow discharge and thermionic filament techniques. Spatial profiles of the plasma density, plasma potential, and electron temperature are measured using Langmuir probes. We present initial experimental measurements of density and temperature profiles in the FPS device. Experimental and theoretical studies of low frequency oscillations observed in the FPS device are also presented.

Thomas, Edward, Jr.↗
NASA NTRS1977

Microscopic Lagrangian description of warm plasmas. III - Nonlinear wave-particle interaction

The averaged-Lagrangian method is applied to nonlinear wave-particle interactions in an infinite, homogeneous, magnetic-field-free plasma. The specific example of Langmuir waves is considered, and the combined effects of four-wave interactions and wave-particle interactions are treated. It is demonstrated how the latter lead to diffusion in velocity space, and the quasilinear diffusion equation is derived. The analysis is generalized to the random phase approximation. The paper concludes with a summary of the method as applied in Parts 1-3 of the paper.

Galloway, J. J.↗
NASA NTRS1967

Dynamical friction.

Chandrasekhar dynamical friction theory for star in cluster adapted to Fokker-Plank electron in two-component plasma theory and including multiple encounters

STAR CLUSTER↗
NASA NTRS2003

Magnetic Flux Compression Experiments Using Plasma Armatures

Magnetic flux compression reaction chambers offer considerable promise for controlling the plasma flow associated with various micronuclear/chemical pulse propulsion and power schemes, primarily because they avoid thermalization with wall structures and permit multicycle operation modes. The major physical effects of concern are the diffusion of magnetic flux into the rapidly expanding plasma cloud and the development of Rayleigh-Taylor instabilities at the plasma surface, both of which can severely degrade reactor efficiency and lead to plasma-wall impact. A physical parameter of critical importance to these underlying magnetohydrodynamic (MHD) processes is the magnetic Reynolds number (R(sub m), the value of which depends upon the product of plasma electrical conductivity and velocity. Efficient flux compression requires R(sub m) less than 1, and a thorough understanding of MHD phenomena at high magnetic Reynolds numbers is essential to the reliable design and operation of practical reactors. As a means of improving this understanding, a simplified laboratory experiment has been constructed in which the plasma jet ejected from an ablative pulse plasma gun is used to investigate plasma armature interaction with magnetic fields. As a prelude to intensive study, exploratory experiments were carried out to quantify the magnetic Reynolds number characteristics of the plasma jet source. Jet velocity was deduced from time-of-flight measurements using optical probes, and electrical conductivity was measured using an inductive probing technique. Using air at 27-inHg vacuum, measured velocities approached 4.5 km/s and measured conductivities were in the range of 30 to 40 kS/m.

Turner, M. W.↗