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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Polarization-separated double-imaging spectroscopy for weakly-ionized plasma diagnostics

Laser Thomson scattering, which provides thermal properties of electrons, has been extensively utilized in plasma diagnostics. However, being a non-resonant linear light scattering technique, it often encounters several challenges in weakly-ionized plasma diagnostics due to spectral overlap with different scatterings induced from other existing species, including Mie, Rayleigh, and rotational Raman scatterings. To address this challenge, we propose an imaging spectroscopy technique, polarization-separated double-imaging spectroscopy (PoDIS), which selectively separates specific scatterings based on their polarization characteristics. Using an atmospheric plasma jet as a plasma source for demonstration, we show that PoDIS can effectively separate rotational Raman and Thomson scatterings from a superimposed spectrum without prior knowledge or assumptions about the thermal properties of neutrals or electrons. This separation enables independent fitting of the rotational Raman and Thomson scattering spectra, allowing for precise determination of the thermal properties of neutral particles and electrons separately.

Bak, Junhwi [Texas A&M University, College Station↗
DOE OSTI2026

Ring Asymmetry and Spin in M87*

Event Horizon Telescope (EHT) images of the supermassive black hole M87* depict an asymmetric ring of emission. General relativistic magnetohydrodynamic (GRMHD) models of M87* and its accretion disk predict that the amplitude and location of the ring’s peak brightness asymmetry should fluctuate due to turbulence in the source plasma. We compare the observed distribution of brightness asymmetry amplitudes to the simulated distribution in GRMHD models, across varying black hole spin a * . We show that, for strongly magnetized (MAD) models, three epochs of EHT data marginally disfavor ∣a * ∣ ≲ 0.2. This is consistent with the Blandford–Znajek model for M87’s jet, which predicts that M87* should have nonzero spin. We show quantitatively how future observations could improve spin constraints and discuss how improved spin constraints could distinguish between differing jet-launching mechanisms and black hole growth scenarios.

Bernshteyn, Vadim [Univ. of Illinois at Urbana-Cha↗
NASA NTRS1971

Development and initial operating characteristics of the 20 megawatt linear plasma accelerator facility

A 20-megawatt linear plasma accelerator facility, a steady flow, Faraday-type plasma accelerator facility for high velocity aerodynamic testing, was constructed, developed, and brought to an operational status. The accelerator has a 63.5-mm-square and 0.5-meter-long channel and utilizes nitrogen-seeded with 2 % mole fraction of cesium vapor. Modification of the original accelerator design characteristics and the improvements necessary to make the arc heater a suitable plasma source are described. The measured accelerator electrode current distribution and the electrode-wall potential distributions are given. The computed and the measured values are in good agreement. Measured pitot pressure indicates that an accelerator exit velocity of 9.2 km/sec, is obtained with 30 of the 36 electrode pairs powered and corresponds to a velocity increase to about 2 1/4 times the computed entrance velocity. The computed stagnation enthalpy at the accelerator exit is 92 MJ/kg, and the mass density corresponds to an altitude of about 58 km. The 92 MJ/kg stagnation enthalpy corresponds to a kinetic energy content at low temperature equivalent to a velocity of 13.6 km/sec.

Carter, A. F.↗
NASA NTRS1972

Pulsed metallic-plasma generators.

A pulsed metallic-plasma generator is described which utilizes a vacuum arc as the plasma source. The arc is initiated on the surface of a consumable cathode which can be any electrically conductive material. Ignition is accomplished by using a current pulse to vaporize a portion of a conductive film on the surface of an insulator separating the cathode from the ignition electrode. The film is regenerated during the ensuing arc. Over 100 million ignition cycles have been accomplished by using four 0.125-in. diameter zinc cathodes operating in parallel and high-density aluminum-oxide insulators. Among the applications being investigated for the generator are metal deposition, vacuum pumping, electric propulsion, and high-power dc arc interruption.

Gilmour, A. S., Jr.↗
NASA NTRS1973

Multiring probe in a flowing ionospheric plasma.

Description of a multiring probe placed in an ionospheric flow simulation chamber utilizing a modified Kaufman ion engine for its plasma source. The pertinent details of the probe design, instrumentation, and operating procedures are discussed, and the preliminary results obtained are presented.

Sheldon, J. W.↗
NASA NTRS1974

Extreme ultraviolet spectra of highly ionized oxygen and fluorine

The foil-excitation method has been used to study the extreme ultraviolet spectra of highly ionized oxygen and fluorine. Several previously unreported lines in heliumlike fluorine are reported and other newly reported lines in heliumlike oxygen have been measured to higher accuracy. Included in the measurements are certain heliumlike oxygen transitions of significance in interpretation of solar-flare spectral observations. The wavelength determinations are usually in good agreement with calculated results which includes relativistic corrections, but discrepancies arise when nonrelativistic calculations are used. A comparison of the present results and those recently obtained by theta-pinch and laser-induced plasma sources is made for both heliumlike and lithiumlike ions; a few discrepancies occur, with results in most cases in better agreement with relativistically corrected calculations. Certain unidentified lines in the spectra may be attributable to radiative transitions between quartet states of lithiumlike ions.

Pegg, D. J.↗
NASA NTRS1974

Periodic escape of relativistic electrons from the Jovian magnetosphere

We adopt a model in which the Jovian magnetospheric tail is forced open by plasma that is accelerated out of the ionosphere by the centrifugal force of corotation. Any longitudinal asymmetry that exists in the ionospheric plasma source and/or the planetary magnetic field will cause a diurnal variation in the radial extent of the trapping region for energetic electrons. This diurnal variation in the extent of the particle trapping region can result in a time-dependent loss of relativistic electrons from the Jovian magnetosphere, modulated at the planetary rotation period. The diurnal trapping process may be relevant to the observation of electron pulses in interplanetary space during the Pioneer 10 approach to Jupiter.

Hill, T. W.↗
NASA NTRS1975

Central structure of low-n Balmer lines in dense plasmas

The investigation reported is concerned with disagreements between the computations of Kepple and Griem (1968) and the results of calculations based upon the 'unified theory' proposed by Vidal et al. (1973). Experiments were conducted with a high-pressure electromagnetically driven shock tube as the plasma source. The diagnostic methods used are discussed along with the experimental results and their significance.

Hey, J. D.↗
NASA NTRS1976

Sample preparation of metal alloys by electric discharge machining

Electric discharge machining was investigated as a noncontaminating method of comminuting alloys for subsequent chemical analysis. Particulate dispersions in water were produced from bulk alloys at a rate of about 5 mg/min by using a commercially available machining instrument. The utility of this approach was demonstrated by results obtained when acidified dispersions were substituted for true acid solutions in an established spectrochemical method. The analysis results were not significantly different for the two sample forms. Particle size measurements and preliminary results from other spectrochemical methods which require direct aspiration of liquid into flame or plasma sources are reported.

Chapman, G. B., II↗
NASA NTRS1976

Longitudinal asymmetry of the Jovian magnetosphere and the periodic escape of energetic particles

An earlier model of the Jovian magnetosphere is utilized in which the centrifugal stress of corotating plasma distends the outer magnetosphere and opens the tail field. Because of a longitudinal asymmetry in the ionospheric plasma source strength, caused principally by the nonaxisymmetric surface field, the closed-field region in the tail expands and contracts with the rotation period, resulting in a 10-hour modulation of the flux of energetic particles escaping from the magnetosphere into interplanetary space.

Hill, T. W.↗
NASA NTRS1978

Thirty-centimeter-diameter ion milling source

A 30-cm beam diameter ion source has been designed and fabricated for micromachining and sputtering applications. An argon ion current density of 1 mA/cu cm at 500 eV ion energy was selected as a design operating condition. The completed ion source met the design criteria at this operating condition with a uniform and well-collimated beam having an average variation in current density of + or - 5% over the center of 20 cm of the beam. This ion source has a multipole magnetic field that employs permanent magnets between permeable pole pieces. Langmuir probe surveys of the source plasma support the design concepts of a multipole field and a circumferential cathode to enhance plasma uniformity.

Robinson, R. S.↗
NASA NTRS1980

Ion heating by strong electrostatic ion cyclotron turbulence

A theory of the ion heating due to electrostatic ion cyclotron (EIC) waves in the auroral zone is presented. Due to the slowly convecting nature of the EIC mode, quasi-linear plateau formation cannot stabilize the waves, and growth occurs until the nonlinear mechanisms of ion resonance broadening and electron trapping provide saturation. The large amplitude and coherent nature of the resulting wave imply that quasi-linear theory provides only a lower limit to the ion heating. An upper bound on the heating rate is derived using a time-average model of ion dynamics in the coherent waves. The effects of ion heating in the presence of the magnetic gradient force and parallel electric fields are considered, with the result that perpendicular energies over 100 eV are easily attainable from a 1 eV source plasma. Perpendicular heating in the absence of a parallel electric field yields conical ion distributions, which in the presence of an electric field become field-aligned beams.

Lysak, R. L.↗
NASA NTRS1980

Some possible effects of Jupiter's rings on the Jovian inner plasmasphere

The ionospheric plasma density on magnetic field lines threading the Jovian rings which are located inside approximately 1.8 Jupiter radii on the jovigraphic equatorial plane is calculated by using a rotating ion exosphere model. It is found that the bulk of the ionospheric particles on these field lines are on ballistic trajectories. On field lines approximately symmetric with respect to the jovigraphic equator, the ring, which to a first approximation would absorb the population of trapped particles, consequently has little effect. On field lines which are made asymmetric by the higher-order multipoles of Jupiter's field and the tilt of the dipole axis, the rings may have a significant effect. It is suggested that better definition of the rings' atmospheric and ionospheric properties is required to model these localized effects. If the rings are found to be an important plasma source for the inner magnetosphere, the present exospheric model will have to be revised.

Luhmann, J. G.↗
NASA NTRS1981

X-ray line emission from the Puppis A supernova remnant - Oxygen lines

Six prominent X-ray emission lines of O VII and O VIII have been detected from a portion of the Puppis A supernova remnant in observations with the Einstein Observatory Focal Plane Crystal Spectrometer. The lines are sufficiently well resolved to serve as diagnostics of the emitting plasma. From the relative intensities of the lines, it is inferred that the population of O VIII is about 1.5 times that of O VII, and that electron collisions are the dominant excitation mechanism in the plasma. A locus of allowed electron temperatures and interstellar-absorption column densities is derived: 1.5 x 10 to the 6th K, and (2-6) x 10 to the 21st per sq cm. The data are consistent with either a thin plasma source in equilibrium at a temperature of 2.2 x 10 to the 6th K with a column density of 4 x 10 to the 21st per sq cm, or with a nonequilibrium source in which the electrons have been shock-heated to a higher temperature and oxygen is underionized.

Winkler, P. F.↗
NASA NTRS1980

Importance of differential charging for controlling both natural and induced vehicle potentials on ATS-5 and ATS-6

Three techniques of discharging satellites used on the P78-2 satellite were the ejection of a beam of electrons from an electron gun; the emission of electrons from a heated, biased filament; and the ejection of a plasma containing energetic positive xenon ions and low energy electrons. When the P78-2 satellite ground to plasma potential difference reached several hundred volts, each of the three techniques was able to completely discharge the satellite. The comparative effctiveness of the techniques were clearly shown. Two days later, the satellite charged to -8 keV upon entering eclipse. The electron gun, emitting 1 mA of electrons with 150 eV energy, reduced the difference in potential between satellite ground and the ambient plasma to -1 kV, but could not completely discharge the satellite. The plasma source completely discharged the satellite.

Whipple, E. C.↗
NASA NTRS1983

Longitudinal asymmetry of the Io plasma torus

Remote observations of the Io plasma torus have revealed a persistent longitudinal asymmetry in the brightness of optical S(+) emission lines but not of ultraviolet S(2+) emission lines. The S(+) asymmetry (with respect to the corotating System III coordinates) has been attributed to an asymmetric plasma source; the question then arises, why do the higher ionization states of sulfur not reflect a similar asymmetry? The explanation proposed here is based on the fact that torus ions do not quite corotate at the System III rate because of mass loading. If the resulting System III drift period of the ions is intermediate between the ionization lifetimes of S(+) and S(2+), then the asymmetry of the source will be obscured by longitudinal drift for the relatively long-lived multiply-ionized sulfur ions, but not for short-lived S(+).

Hill, T. W.↗