SEARCH · Engineering Papers

Results for “Plasma optics”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7

All sources NASA NTRS DOE OSTI

NASA NTRS1982

Starprobe - The mission and system options

The current science, mission and system concepts of a Starprobe mission to the sun are summarized for a launch in the late 1980s, arriving at the sun in the early 1990s. Gravitational, optical, and plasma scientific experiments have been studied for this mission to 4 solar radii. The necessarily high energy trajectories rely on Jupiter gravity assist as a means to send sufficient payloads to the sun. New spacecraft subsystem technologies are required to support the scientific data acquisition and return from 4 solar radii and are summarized here. A set of mission and system options to reduce mission cost were investigated and are discussed.

Randolph, J. E.↗

NASA NTRS1980

X-ray spectroscopy of supernova remnants

The information which can be obtained from X-ray spectroscopy of supernova remnants is considerd. The fitting of X-ray detector counts to models of the incident spectrum is discussed, and the types of thermal emission models generally employed are presented, including the power law, black body, and thermal bremsstrahlung models of the continua and models of the emission of a hot, optically thin plasma in collisional equilibrium. Observations of 12 supernova remnants made with the Solid State Spectrometer on board the Einstein Observatory are reported, and metal abundances inferred from the lines of the eight remnants showing thermal spectra are summarized. Questions raised by the failure to observe the overabundance of Fe predicted by stellar evolution and hydrodynamic modeling are discussed, and the need to develop more detailed models of the conditions in a supernova remnant in order to interpret the X-ray spectra is noted.

Szymkowiak, A. E.↗

NASA NTRS1981

Numerical studies of the energy balance in coronal loops

A numerical method is applied to treat the energy balance of quasi-static solar coronal loops, which have been observed to persist for periods much greater than the radiative cooling time. The quasi-static loop model employed takes into account gravity, density-, temperature- or position-dependent energy input, an accurate form of the radiative losses and variable loop cross-sectional area, under assumptions of energy input by coronal heating balanced by radiative and conductive losses, an optically thin plasma, energy conduction along the field lines only and hydrostatic equilibrium. Computations of an emission measure function for various distributions of the energy input and loop geometries are then presented which show that little information on the location of the energy input may be gained from spectral line intensity measurements integrated over a single loop.

Underwood, J. H.↗

NASA NTRS1982

X-ray spectrum of Capella and its relation to coronal structure and ultraviolet emission

The binary system Capella has been observed on 1979 March 15 and on 1980 March 15-17, with the objective grating spectrometer on board the Einstein Observatory. The spectrum measured with the 1000 1/mm grating covers the range 5-30 A with a resolution less than 1 A. The spectra show evidence for a bimodal temperature distribution of emission measure in an optically thin plasma with one component about 5,000,000 K and the other one about 10,000,000 K. Spectral features can be identified with line emissions from O VIII, Fe XVII, Fe XVIII, Fe XXIV, and Ne X ions. Good spectral fits have been obtained assuming standard cosmic abundances. The data are interpreted in terms of emission from hot static coronal loops rather similar to the magnetic arch structures found on the sun. It is shown that the conditions for such a model can exist on Capella. Typical values of loop base pressure and half-length are derived for both temperature components and discussed in relation to UV observations.

Mewe, R.↗

NASA NTRS1984

Optically-thick, highly-variable plasma in interacting binaries

The interacting binaries HD 207739 and R Arae were observed by IUE. The ultraviolet spectrum of HD 207739 undergoes complex variations in both the lines and the continuum. Considerable circumstellar matter is present; R Arae (B9p + ?) exhibits SiIV, CIV and even NV absorption features. Both the lines and continuum are variable. An unusual secondary eclipse which is deeper in the ultraviolet than in the visible is present near phase 0.6. The CII line has a P cygni profile with emission present at all observed phases. These systems are probably in a relatively short-lived phase of evolution which is not often observed.

Kondo, Y.↗

NASA NTRS1988

Contamination of the space station environment by vented chemicals

Gaseous materials vented from materials and life science experiments on the Space Station may have noticeable effects on the optical or plasma environment. The magnitude of the effects depends on: (1) rarefied gas dynamics; (2) photochemical reactions; and (3) airglow excitation mechanisms. In general, the effects from atomic species can be mitigated, but the disturbances resulting from venting of molecules like SF6, CO2 and C2H2 can be significant. The interaction of molecules with ambient plasma at orbital velocities should be studied with laboratory or space experiments.

Bernhardt, Paul A.↗

NASA NTRS1989

Effect of coronal elemental abundances on the radiative loss function

The solar photosphere and corona abundances tabulated by Meyer (1985) and the chromospheric abundances given by Murphy (1985) are used here to recalculate radiative loss functions for equilibrium, low-density, optically thin plasmas. Results from a representative standard photospheric abundance set and from coronal and chromospheric abundance sets showing depletions of up to a factor of four in certain elemental abundances are compared. A significant difference is found for both the coronal and chromospheric abundance sets, with the peak of the radiative loss curve shifted closer to 10 to the 6th K than to the standard 2 x 10 to the 5th K found from photospheric abundances. Consequences of these new calculations, in particular for the cool loop model of Antiochos and Noci (1986), are discussed.

Cook, J. W.↗

NASA NTRS1989

Mass flow in interacting binaries observed in the ultraviolet

Recent satellite observations of close binary systems show that practically all binaries exhibit evidence of mass flow and that, where the observations are sufficiently detailed, a fraction of the matter flowing out of the mass-losing component is accreted by the companion and the remainder is lost from the binary system. The mass flow is not conservative. During the phase of dynamic mass flow, the companion star becomes immersed in optically-thick plasma and the physical properties of that star elude close scrutiny.

Kondo, Yoji↗

NASA NTRS1989

Soft X-ray emission lines from low-mass X-ray binaries. I - Collision-dominated models

The soft X-ray line emission from five low-mass X-ray binaries observed by the Einstein Observatory (HEAO 2) Objective Grating Spectrometer is examined. Observed spectra are fitted to model spectra consisting of emission from an optically thin plasma. Fits are performed using a variety of different assumptions for elemental abundances, heating and ionization mechanisms, and the distribution of gas temperature and ionization parameter. The results are discussed in the context of current models for the accretion flow in low-mass X-ray binaries.

Kallman, T. R.↗

NASA NTRS1990

Ginga observations of a long-duration X-ray flare in the Algol system

Algol was observed by the Ginga X-ray satellite for about 2 days in January 1989, including both the primary and most of the secondary optical eclipses. No evidence for X-ray eclipses was seen. A large flare lasting over 12 h was detected prior to and during secondary eclipse. The flare began with a peak temperature of about 69 MK, gradually decaying to about 36 MK. Variable Fe line emission at 6.7 keV ws observed. The Fe line equivalent width is in clear disagreement with theoretical predictions for an optically thin plasma.

Stern, R. A.↗

NASA NTRS1991

A numerical simulation of magnetic reconnection and radiative cooling in line-tied current sheets

Radiative MHD equations are used for an optically thin plasma to carry out a numerical experiment related to the formation of 'postflare' loops. The numerical experiment starts with a current sheet that is in mechanical and thermal equilibrium but is unstable to both tearing-mode and thermal-condensation instabilities. The current sheet is line-tied at one end to a photospheric-like boundary and evolves asymmetrically. The effects of thermal conduction, resistivity variation, and gravity are ignored. In general, reconnection in the nonlinear stage of the tearing-mode instability can strongly affect the onset of condensations unless the radiative-cooling time scale is much smaller than the tearing-mode time scale. When the ambient plasma is less than 0.2, the reconnection enters a regime where the outflow from the reconnection region is supermagnetosonic with respect to the fast-mode wave speed. In the supermagnetosonic regime the most rapidly condensing regions occur downstream of a fast-mode shock that forms where the outflow impinges on closed loops attached to the photospheric-like boundary. A similar shock-induced condensation might occur during the formation of 'postflare' loops.

Forbes, T. G.↗

NASA NTRS1992

Downward-deployed tethered satellite systems, measurement techniques, and instrumentation - A review

This paper describes a number of scheduled and proposed Shuttle-based downward-deployed tethered satellite systems (TSSs) the purpose of which is to determine the structure of the lower thermosphere and to measure the atmospheric and aerodynamic effects in the vicinity of the satellite, the aerothermodynamic effects on the satellite's surface, and the dynamics of the tether and its endmass, the satellite. The instruments for the downward-deployed tethered missions will include mass spectrometers and other density sensors, plasma instrumentation, optical spectrophotometers, magnetometers, and instrumentation to measure the effects on satellite surface (such as the surface temperature, heat transfer, and pressure; gas adsorption on surfaces, chemistry with other gas molecules and surface material, and desorption from the surface; and surface charging).

Brown, Kenneth G.↗

NASA NTRS1992

Ginga observations of X-ray flares on Algol

The Ginga X-ray satellite observed Algol (Beta Per) for 2 days in 1989 January, including both the primary optical eclipse and most of the secondary eclipse. We derive upper limits of about 20 and 10 percent, respectively, for the eclipsed flux fraction during the two eclipses. A large flare lasting over 12 hr was seen prior to and during secondary eclipse. High-temperature Fe line emission is clearly detected in the proportional counter data. The Fe line equivalent width is variable during the flare, ranging from 0.4-1.0 keV. Except for two intervals during the flare rise, the observed equivalent width is lower than predicted using solar abundances and an optically thin plasma model. Similar behavior has also been observed by Ginga in a large flare on UX Ari: in both events, opacity effects at line center may be playing a significant role. Loop model analysis of the large flare suggests that it involves a substantially longer loop or loops than a shorter duration Algol flare seen with Exosat.

Stern, R. A.↗

NASA NTRS1993

X-ray spectra of 12 distant clusters of galaxies

An X-ray spectral analysis of 12 distant clusters of galaxies observed on-axis with the Einstein Observatory imaging proportional counter is presented. Statistically, X-ray spectral data of the highest red shift clusters in the sample are inconsistent with an optically thin plasma emission model plus absorptions only in the Milky Way. Inclusions of excess absorptions in the clusters significantly improve the spectral fits to the data, indicating the possible presence of large amounts of X-ray absorbing cool gas in some of the distant clusters. By using X-ray luminosities determined from observed fluxes only in the 0.8-3.5 keV band and the temperature-to-luminosity correlation for nearby clusters, the estimated temperatures of the hot intracluster medium in these distant clusters constrain the absorption columns in the clusters. The data also show possible positive temperature evolution of the hot ICM with time which, if present, would further increase the absorptions required in fitting the spectra.

Wang, Qingde↗

NASA NTRS1994

Hard X-rays from NGC 4151: A thermal origin?

We present a model for explaining the recent combined X-ray and low-energy gamma-ray observations of the Seyfert galaxy NGC 4151. According to this model, soft photons become Comptonized in a hot spot producing simultaneously the low-energy power law as observed by Ginga and the high-energy cutoff observed by the Oriented Scintillation Spectrometer Experiment (OSSE). Implementing recently developed theoretical calculations toward a generalized theory of Comptonization, we were able to find fits to the observations using only two parameters which characterize the physical quantities of the emission region: the plasma cloud optical depth and its temperature. We find that there is no need for additional nonthermal, reflection, or higher temperature thermal components to fit the aforementioned OSSE and Ginga observations. We derive in addition the size of the photon region and the temperature of the upscattered soft photons. We should emphasize, also, that any attempt at fitting only the high-energy parts of the spectrum (photon energies greater than 60 keV) by the Sunyaev & Titarchuk (1980) nonrelativistic Comptonization model leads to an underestimate of the Comptonization parameter y (or, equivalently, to an overestimation of the X-ray power-law spectral slope) and leads, as a result, to incorrect proportions between the low-energy and high-energy parts of the spectrum.

Titarchuk, Lev↗

NASA NTRS1993

The spectrum of the planetary nebula NGC 6567

Because of the similarity of its spectrum to that of NGC 6572 particularly in the UV we have made a detailed study of NGC 6567 using both the IUE for the UV region and the Hamilton Echelle at Lick Observatory for the optical region. Plasma diagnostics suggest an electron temperature of about 11,500 K an electron density near 9000/cu cm. The chemical composition of this Population Type II high-velocity planetary nebula is found from ionic concentrations and a theoretical model. The 'metal'/H ratio is lower than in the sun, except for C whose abundance is enhanced to about 30% over the solar value and for He which may be slightly enhanced. There is no evidence of any spectral variability.

Hyung, Siek↗

NASA NTRS1998

A Search for X-Ray Evidence of a Compact Companion to the Unusual Wolf-Rayet Star HD 50896 (EZ CMa)

We analyze results of a approx.25 ksec ASCA X-ray observation of the unusual Wolf-Rayet star HD 50896 (= EZ CMa). This WN5 star shows optical and ultraviolet variability at a 3.766 day period, which has been interpreted as a possible signature of a compact companion. Our objective was to search for evidence of hard X-rays (greater than or equal to 5 keV) which could be present if the WN5 wind is accreting onto a compact object. The ASCA spectra are dominated by emission below 5 keV and show no significant emission in the harder 5-10 keV range. Weak emission lines are present, and the X-rays arise in an optically thin plasma which spans a range of temperatures from less than or equal to 0.4 keV up to at least approx. 2 keV. Excess X-ray absorption above the interstellar value is present, but the column density is no larger than N(sub H) approx. 10(exp 22)/sq cm. The absorption-corrected X-ray luminosity L(sub x)(0.5 - 10 keV) = 10(exp 32.85) erg/s gives L(sub x)/ L(sub bol) approx. 10(exp -6), a value that is typical of WN stars. No X-ray variability was detected. Our main conclusion is that the X-ray properties of HD 50896 are inconsistent with the behavior expected for wind accretion onto a neutron star or black hole companion. Alternative models based on wind shocks can explain most aspects of the X-ray behavior, and we argue that the hotter plasma near approx. 2 keV could be due to the WR wind shocking onto a normal (nondegenerate) companion.

Skinner, Stephen L.↗

NASA NTRS2000

Ion Thruster Used to Propel the Deep Space 1 Spacecraft to Comet Encounters

The NASA Solar Electric Propulsion Technology Applications Readiness (NSTAR) Project provided a xenon ion propulsion system to the Deep Space 1 (DS1) spacecraft to validate the propulsion system as well as perform primary propulsion for asteroid and comet encounters. The On-Board Propulsion Branch of the NASA Glenn Research Center at Lewis Field developed engineering model versions of the 30-cm-diameter ion thruster and the 2.5-kW power processor unit (PPU). Glenn then transferred the thruster and PPU technologies to Hughes Electron Dynamics and managed the contract, which supplied two flight sets of thrusters and PPU s to the Deep Space 1 spacecraft and to a ground-based life verification test at the Jet Propulsion Laboratory (JPL). In addition to managing the DS1 spacecraft development, JPL was responsible for the NSTAR Project management, thruster life tests, the feed system, diagnostics, and propulsion subsystem integration. The ion propulsion development team included NASA Glenn, JPL, Hughes Electronics, Moog Inc., and Spectrum Astro Inc. The overall NSTAR subsystem dry mass, including thruster, PPU, controller, cables, and the xenon storage and feed system, is 48 kg. The mass of the xenon stored onboard DS1 was about 81 kg, and the spacecraft wet mass was approximately 500 kg.The DS1 spacecraft was launched on October 24, 1998, and on July 29, 1999, it flew within 16 miles of the small asteroid Braille (formerly 1992KD) at a relative speed of 35,000 mph. As of November 1999, the ion propulsion system had performed flawlessly for nearly 149 days of thrusting. NASA has approved an extension to the mission, which will allow DS1 to continue thrusting to encounters with two comets in 2001. The DS1 optical and plasma diagnostic instruments will be used to investigate the comet and space environments. The spacecraft is scheduled to fly past the dormant comet Wilson- Harrington in January 2001 and the very active comet Borrelly in September 2001, at which time approximately 500 days of ion engine thrusting will have been completed.

Sovey, James S.↗