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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Stationary Plasma Thruster Plume Emissions

The emission spectrum from a xenon plasma produced by a Stationary Plasma Thruster provided by the Ballistic Missile Defense Organization (BMDO) was measured. Approximately 270 individual Xe I, Xe II, and XE III transitions were identified. A total of 250 mW of radiated optical emission was estimated from measurements taken at the thruster exit plane. There was no evidence of erosion products in the emission signature. Ingestion and ionization of background gas at elevated background pressure was detected. The distribution of excited states could be described by temperatures ranging from fractions of 1 eV to 4 eV with a high degree of uncertainty due to the nonequilibrium nature of this plasma. The plasma was over 95 percent ionized at the thruster exit plane. Between 10 and 20 percent of the ions were doubly charged. Two modes of operation were identified. The intensity of plasma emission increased by a factor of two during operation in an oscillatory mode. The transfer between the two modes of operation was likely related to unidentified phenomena occurring on a time scale of minutes.

Manzella, David H.↗
NASA NTRS1977

The Viking solar corona experiment

The 1976 Mars solar conjunction resulted in complete occultations of the Viking spacecraft by the sun at solar minimum. During the conjunction period, coherent 3.5- and 13-cm wavelength radio waves from the orbiters passed through the solar corona and were received with the 64-m antennas of the NASA Deep Space Network. Data were obtained within at least 0.3 and 0.8 R sub s of the photosphere at the 3.5- and 13-cm wavelengths, respectively. The data can be used to determine the plasma density integrated along the radio path, the velocity of density irregularities in the coronal plasma, and the spectrum of the density fluctuations in the plasma. Observations of integrated plasma density near the south pole of the sun generally agree with a model of the corona which has an 8:1 decrease in plasma density from the equator to the pole. Power spectra of the 3.5- and 13-cm signals at a heliocentric radial distance of about 2 R sub s have a 1/2 power width of several hundred hertz and vary sharply with proximate geometric miss distance. Spectral broadening indicates a marked progressive increase in plasma irregularities with decreasing ray altitude at scales between about 1 and 100 km.

Tyler, G. L.↗
NASA NTRS1999

Effectiveness of Near-Grazing Incidence Reflection in Creating the Rotationally Modulated Lanes in the Jovian Hectometric Radio Emission Spectrum

The Galileo plasma wave instrument has identified a narrow (in frequency) attenuation band in the hectometric emission that varies in frequency with system 3 longitude. It is possible to model this emission band assuming a high-latitude cyclotron source region with emission that is efficiently attenuated when the ray path is nearly tangent to an L shell that is close to the Io flux tube. The data suggest that the mechanism for attenuating the emission is very efficient, with the ratio of attenuated to unattenuated emission I/I(sub o) < 0.02, and not a strong function of frequency. In this paper we demonstrate that incoherent scattering alone cannot explain the attenuation lane, which does not preclude coherent scattering by uncertain processes. We find rather that the source of attenuation is consistent with near-grazing incidence reflection of emission from an L shell that is near the Io flux tube (a caustic surface).

Menietti, J. D.↗
NASA NTRS1991

The O VII soft X-ray spectrum and its application to hot plasmas in astrophysics

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.

Gabriel, A. H.↗
NASA NTRS1975

Requirements for space shuttle scatter radar experiments

The feasibility of carrying out scatter radar experiments on the space shuttle was analyzed. Design criteria considered were the required average transmitter power, frequency resolution, spatial resolution, and statistical accuracy. Experiments analyzed were measurement of the naturally enhanced plasma line and the ion component of the incoherent scatter spectrum, and the plasma line artificially enhanced by an intense HF radio wave. The ion component measurement does not appear feasible, while the other two appear reasonable for short ranges only.

Harker, K. J.↗
NASA NTRS1977

Magnetosheath electrostatic turbulence

The spectrum of electrostatic plasma waves in the terrestrial magnetosheath was studied using the plasma wave experiment on the IMP-6 satellite. Electrostatic plasma wave turbulence is almost continuously present throughout the magnetosheath with broadband (20 Hz- 70 kHz) r.m.s. field intensities typically 0.01 - 1.0 millivolts/m. Peak intensities of about 1.0 millivolts/m near the electron plasma frequency (30 - 60 kHz) were detected occasionally. The components usually identified in the spectrum of magnetosheath electrostatic turbulence include a high frequency ( or = 30 kHz) component peaking at the electron plasma frequency f sub pe, a low frequency component with a broad intensity maximum below the nominal ion plasma frequency f sub pi (approximately f sub pe/43), and a less well defined intermediate component in the range f sub pi f f sub pe. The intensity distribution of magnetosheath electrostatic turbulence clearly shows that the low frequency component is associated with the bow shock, suggesting that the ion heating begun at the shock continues into the downstream magnetosheath.

Rodriquez, P.↗
NASA NTRS1990

Identification of hydrogenlike and heliumlike transitions in the spectrum of laser-produced magnesium plasmas

Nonresonance spectral lines of Mg XII and Mg XI emitted by magnesium laser-produced plasmas have been observed in the extreme-vacuum-ultraviolet region and their transitions classified. As many as eight beams of the Omega laser system of the Laboratory for Laser Energetics at the University of Rochester were linearly focused onto magnesium-coated flat targets to produce linear plasma radiation sources from 3 to 6 mm long. The spectra were photographed end-on with a grazing-incidence spectrograph. The identified Mg XII lines are classified as 2s-3p, 2p-3d, 2s-4p, 2p-4d, and 3d-4f transitions. The identified Mg XI lines are classified as 1s2s-1s3p, 1s2p-1s3d, 1s2p-1s4d, 1s3p-1s4d, and 1s3d-1s4f.

Moreno, J. C.↗
NASA NTRS1978

Fluctuation spectra in the NASA Lewis bumpy-torus plasma

The electrostatic potential fluctuation spectrum in the NASA Lewis bumpy-torus plasma was studied with capacitive probes in the low pressure (high impedance) mode and in the high pressure (low impedance) mode. Under different operating conditions, the plasma exhibited electrostatic potential fluctuations (1) at a set of discrete frequencies, (2) at a continuum of frequencies, and (3) as incoherent high-frequency turbulence. The frequencies and azimuthal wave numbers were determined from digitally implemented autopower and cross-power spectra. The azimuthal dispersion characteristics of the unstable waves were examined by varying the electrode voltage, the polarity of the voltage, and the neutral background density at a constant magnetic field strength.

Singh, C. M.↗
NASA NTRS1972

Modulational instability of whistlers in cold plasmas

The paper obtains the modulational stability spectrum of whistlers in cold plasmas taking into consideration both ion motion and relativistic effects. The unstable band is contiguous to Omega sub e/4 and, depending on the plasma density, lies above or below that frequency Omega sub e is the electron cyclotron frequency of the static magnetic field. The relevance of the instability to whistlers in the magnetosphere is discussed.

Brinca, A. L.↗
NASA NTRS1988

Spectral signature of the beam plasma discharge

The effect of the beam current on the spectrum of a beam plasma discharge (BPD) in N2 at 50, 100, or 400 microtorr is investigated experimentally in the 2.6-m chamber described by Bernstein et al. (1983). The results are presented graphically and discussed in detail. An increase in the ratio of first positive N2 emissions to first negative N2(+) emissions at BPD onset is shown to disappear at currents above the BPD threshold and is attributed to a large population of suprathermal electrons.

Hallinan, T. J.↗
NASA NTRS1981

Annihilation radiation from a hot e(+)-e(-) plasma

Pair annihilation in hot e(+)-e(-) plasmas is studied. The annihilation rate, luminosity and spectrum of optically thin plasmas of temperatures above 10 to the 8th power K are calculated by means of a Monte Carlo simulation. For a given temperature, the spectrum is peaked at an energy equal to 0.511 MeV plus a positive definite quantity of order kT. In high temperature sources, such as gamma ray bursts, this blue shift can amount to a significant fraction of 0.511 MeV. The annihilation line is also temperature broadened. The width varies as T to the 1/2 power for kT much less than 0.511 MeV, and as T for kT much greater than 0.511 MeV. The widths of the 400 to 460 keV emission lines observed from several gamma ray bursts set limits on the temperatures of the pair annihilation region in burst sources. The burst emission is either nonthermal or the pair annihilation region is spatially distinct from the site of the outburst itself.

Ramaty, R.↗
NASA NTRS1984

Interferometric phase velocity measurements

Phase velocities of plasma waves near the lower hybrid frequency were measured with an interferometer composed of two spatially separated electron-density probes. The plasma waves were produced in the F-region ionosphere by an argon ion beam. By calculating the normalized cross spectrum of the plasma waves a coherency of .98 was estimated along with a maximum phase difference of pi/3 radians between the two probes. This implies that the wavelength was 6 meters compared to an O(+) gyroradius of 3.8 meters, and that the phase velocity was 45 km/sec compared to an ion-beam velocity of 12.4 km/sec. These numbers compare favorably with recent predictions of a nonresonant mode produced by a dense ion beam.

Kintner, P. M.↗
NASA NTRS1978

Comparative characteristics of electron energy spectrum in PIG and arc type discharge plasmas

The electron distribution functions relative to the velocity component directed along the magnetic field are compared for PIG and arc type discharges. The identity of these functions for the plasma region pierced by the primary electron beam and their difference in the peripheral part of the discharge are shown. It is concluded that the electron distribution function in the PIG type discharge is formed during one transit of the primary electron through the discharge gap. The mechanisms of electron energy spectrum formation in both the axis region and the peripheral region of the discharge are discussed.

Romanyuk, L. I.↗
NASA NTRS1993

Cyclotron harmonic lines in magnetic fluctuations of spiralling electrons in plasmas

The magnetic fluctuation spectrum in a magnetoplasma containing energetic electrons is observed to exhibit many lines at the cyclotron harmonics. It is shown that these fluctuations are neither due to cyclotron radiation nor due to velocity-space instabilities but due to coherent solenoidal fields produced by electron cyclotron orbits and excited by thermal fluctuations. Such line spectra, observed in discharges and beam-plasma systems, may be useful for precise magnetic field diagnostics in plasmas.

Golubiatnikov, G.↗
DOE OSTI2025

Data for "Plasma shape effects on the Alfvén eigenmode spectrum through Alfvén slow-magnetosonic wave coupling"

electron density profile as a function of normalized poloidal flux: psinorm ne(10^20/m^3) dne/dpsiN Pressure profile as a function of normalized poloidal flux: psinorm ptot(KPa) dptot/dpsiN scaled to oftain beta=5% at magnetic axis Magnetic safety factor profile as a function of normalized poloidal flux: psinorm q_profile All needed to perform the NOVA calculations.

Alfven waves↗
DOE OSTI2024

Time-of-flight vs time-of-arrival in neutron spectroscopic measurements for high energy density plasmas

The neutron time-of-flight (nToF) diagnostic technique has a lengthy history in Inertial Confinement Fusion (ICF) and High Energy Density (HED) Science experiments. Its initial utility resulted from the simple relationship between the full width half maximum of the fusion peak signal in a distant detector and the burn averaged conditions of an ideal plasma producing the flux [Lehner and Pohl, Z. Phys. 207, 83–104 (1967)]. More recent precision measurements [Gatu-Johnson et al., Phys. Rev. E 94(8), 021202 (2016)] and theoretical studies [Munro, Nucl. Fusion 56, 035001 (2016)] have shown the spectrum to be more subtle and complicated, driving the desire for an absolute calibration of the spectrum to disambiguate plasma dynamics from the conditions producing thermonuclear reactions. In experiments where the neutron production history is not well measured, but the neutron signal is preceded by a concomitant flux of photons, the spectrum can be in situ calibrated using a set of collinear detectors to obtain a true “time-of-flight” measurement. This article presents the motivation and overview of this technique along with estimates of the experimental precision needed to make useful measurements in existing and future nToF systems such as the pulsed power Z-machine located in Albuquerque, NM, at Sandia National Laboratories.

Fusion experiments↗
NASA NTRS1983

Jupiter Data Analysis Program: Analysis of Voyager wideband plasma wave observations

Voyager plasma wave wideband frames from the Jovian encounters are analyzed. The 511 frames which were analyzed were chosen on the basis of low-rate spectrum analyzer data from the plasma wave receiver. These frames were obtained in regions and during times of various types of plasma or radio wave activity as determined by the low-rate, low-resolution data and were processed in order to provide high resolution measurements of the plasma wave spectrum for use in the study of a number of outstanding problems. Chorus emissions at Jupiter were analyzed. The detailed temporal and spectral form of the very complex chorus emissions near L = 8 on the Voyager 1 inbound passage was compared to both terrestrial chorus emissions as well as to the theory which was developed to explain the terrestrial waves.

Kurth, W. S.↗