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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 NTRS1997

Coordinated XTE/EUVE Observations of Algol

We performed a coordinated RXTE observation of the prototypical eclipsing binary Algol in conjunction with EUVE and ASCA observations. Observing the x-ray spectrum of Algol with ASCA, EUVE, and RXTE provides critical, near-simultaneous constraints on the distribution of the hottest temperature plasma in the Agol system: this is required to unambiguously determine the coronal Fe abundance. After some initial shuffling of observatory schedules with the help of mission planners, the coordinated multiwavelength observation was successfully performed in February, 1996. Analysis of the data, including development of new, IDL-based global model fitting routines, was accomplished from mid-1996 to mid-1997. The results indicate that the initial estimates of [Fe/H] approximately 0.3 dex (Stern et al.) are confirmed, and the Algol high temperature plasma thus has an Fe deficiency relative to the (Anders and Grevesse) solar abundance.

Stern, Robert A.↗
NASA NTRS2008

A Hot Microflare Observed with RHESSI and HINODE

RHESSI and Hinode observations of a GOES B-class flare are combined to investigate the origin of 15 MK plasma. The absence of any detectable hard X-ray emission coupled with weak blueshifted emission lines (indicating upward velocities averaging only 14 km/s) suggests that this was a result of direct heating in the corona, as opposed to nonthermal electron precipitation causing chromospheric evaporation. These findings are in agreement with a recent hydrodynamical simulation of microflare plasmas that found that higher temperatures can be attained when less energy is used to accelerate electrons out of the thermal distribution. In addition, unusual redshifts in the 2 MK Fe xv line (indicating downward velocities of approx.14 km/s) were observed cospatial with one of the flare ribbons during the event. Downflows of such high-temperature plasma are not predicted by any common flare model.

Milligan, Ryan O.↗
NASA NTRS1976

Investigation of forbidden transitions in argon ions

An attempt has been made to observe the visible forbidden argon coronal lines at 553.6 nm (Ar X), 691.7 nm (Ar XI), 847.6 nm (Ar XIII), and 441.2 nm (Ar XIV) in a deuterium-argon plasma produced in a large theta pinch. The electron temperature (250 eV) and the electron density (5 by 10 to the 16th power per cu cm) were measured by Thomson scattering of ruby laser radiation. This temperature is adequate to produce ionization stages up to Ar XIV, as was verified by photographic observation of Ar XIV lines. No line corresponding to the coronal lines was observed from the high-temperature plasma, but lines with wavelengths very nearly identical to those of two of the forbidden transitions were observed; these lines were due to allowed transitions of Ar II in a cooler portion of the plasma. Calculation of rate coefficients in the Coulomb-Born approximation shows that for laboratory experiments, electron collisions are much more important than radiative decay in depopulating the upper state of the forbidden lines.

Jalufka, N. W.↗
NASA NTRS2016

Correlation of Coronal Plasma Properties and Solar Magnetic Field in a Decaying Active Region

We present the analysis of a decaying active region observed by the EUV Imaging Spectrometer on Hinode during 2009 December 7-11. We investigated the temporal evolution of its structure exhibited by plasma at temperatures from 300,000 to 2.8 million degrees, and derived the electron density, differential emission measure, effective electron temperature, and elemental abundance ratios of Si/S and Fe/S (as a measure of the First Ionization Potential (FIP) Effect). We compared these coronal properties to the temporal evolution of the photospheric magnetic field strength obtained from the Solar and Heliospheric Observatory Michelson Doppler Imager magnetograms. We find that, while these coronal properties all decreased with time during this decay phase, the largest change was at plasma above 1.5 million degrees. The photospheric magnetic field strength also decreased with time but mainly for field strengths lower than about 70 Gauss. The effective electron temperature and the FIP bias seem to reach a basal state (at 1.5 x 10(exp 6) K and 1.5, respectively) into the quiet Sun when the mean photospheric magnetic field (excluding all areas <10 G) weakened to below 35 G, while the electron density continued to decrease with the weakening field. These physical properties are all positively correlated with each other and the correlation is the strongest in the high-temperature plasma. Such correlation properties should be considered in the quest for our understanding of how the corona is heated. The variations in the elemental abundance should especially be considered together with the electron temperature and density.

Sun: abundances↗
NASA NTRS2002

Magnetized Target Fusion

Magnetized target fusion (MTF) is under consideration as a means of building a low mass, high specific impulse, and high thrust propulsion system for interplanetary travel. This unique combination is the result of the generation of a high temperature plasma by the nuclear fusion process. This plasma can then be deflected by magnetic fields to provide thrust. Fusion is initiated by a small traction of the energy generated in the magnetic coils due to the plasma's compression of the magnetic field. The power gain from a fusion reaction is such that inefficiencies due to thermal neutrons and coil losses can be overcome. Since the fusion reaction products are directly used for propulsion and the power to initiate the reaction is directly obtained from the thrust generation, no massive power supply for energy conversion is required. The result should be a low engine mass, high specific impulse and high thrust system. The key is to successfully initiate fusion as a proof-of-principle for this application. Currently MSFC is implementing MTF proof-of-principle experiments. This involves many technical details and ancillary investigations. Of these, selected pertinent issues include the properties, orientation and timing of the plasma guns and the convergence and interface development of the "pusher" plasma. Computer simulations of the target plasma's behavior under compression and the convergence and mixing of the gun plasma are under investigation. This work is to focus on the gun characterization and development as it relates to plasma initiation and repeatability.

Steven T. Griffin↗
NASA NTRS2018

Multi-Scale Modeling of Low-Density Carbon-Phenolic Ablators

Protecting a spacecraft during atmospheric entry is one of highest risk factors that needs to be mitigated during design of a space exploration mission. At entry speeds from space, air turns into high-temperature plasma, and spacecraft Thermal Protection Systems (TPS) are needed to protect the vehicle payload. Modern successful material architectures of spacecraft shields use a porous carbon fiber substrate impregnated with phenolic as an ablator material. In the lecture, efforts to build a Predictive Material Modeling framework for porous ablators from micro-scale to macro-scale will be presented. Several numerical methods and techniques will be summarized that use voxelized images to compute geometrical properties of the porous substrate. These computed properties include porosity, specific surface area and tortuosity that are otherwise indirectly measured through experimental techniques. Direct simulation Monte Carlo (DSMC), a particle-based method for approximating the Boltzmann equation, is used to compute the permeability coefficient of the porous substrate based on its digitized representation. The method computes the flow within the microstructure, where the size of the pores may approach the mean-free-path of the flow. Finally, a high-fidelity model implemented in PATO (Porous-material Analysis Toolbox) is discussed, and some examples of ablative material response are presented, including for the first time 3D simulations of the full tiled heat shield for the Mars Science Laboratory (MSL) capsule.

Ablators↗
NASA NTRS1973

Soft X-ray flare spectra

Large solar flares produce intense soft X-ray emission, indicating the existence of high temperature plasmas that coexist in time with the plasmas responsible for the normally observed brightenings in H-alpha. The time behavior of the X-ray flux, as revealed, for example, by ion chamber detectors on the series of Solrad monitoring satellites, appears to roughly mimic the intensity-time behavior of the H-alpha flare, insofar as start times, times of maximum flux, and approximate decay times are concerned. In recent years, soft X-ray spectra of both active regions and solar flares have been obtained by instruments flown on spacecraft such as the Orbiting Solar Observatory (OSO) series. The disbursing elements used were Bragg crystals, and in the 8 Angstrom region the resolution is typically approximately 1200. This paper discusses the observed characteristics of X-ray flare spectra and spectroscopic diagnostics for determining electron temperatures, electron densities, and departures from ionization equilibrium within the soft X-ray emitting plasma.

Doschek, G. A.↗
NASA NTRS1975

Slow X-ray bursts and flares with filament disruption

The data from OGO-5 and OSO-7 X-ray experiments have been compared with optical data from six chromospheric flares with filament disruption associated with slow thermal X-ray bursts. Filament activation accompanied by a slight X-ray enhancement precedes the first evidence of H-alpha flare by a few minutes. Rapid increase of the soft X-ray flux accompanies the phase of fastest expansion of the filament. Plateau or slow decay phases in the X-ray flux are associated with slowing and termination of filament expansion. The soft X-ray flux increases as F approaches (A + Bh)h, where h is the height of the disrupted prominence at any given time and A and B are constants. We suggest that the soft X-ray emission originates from a growing shell of roughly constant thickness of high-temperature plasma due to the compression of the coronal gas by the expanding prominence.

Roy, J.-R.↗
NASA NTRS1976

Performance and heat transfer characteristics of the laser-heated rocket - A future space transportation system

The application of advanced liquid-bipropellant rocket engine analysis techniques has been utilized for prediction of the potential delivered performance and the design of thruster wall cooling schemes for laser-heated rocket thrusters. Delivered specific impulse values greater than 1000 lbf-sec/lbm are potentially achievable based on calculations for thrusters designed for 10-kW and 5000-kW laser beam power levels. A thruster wall-cooling technique utilizing a combination of regenerative cooling and a carbon-seeded hydrogen boundary layer is presented. The flowing carbon-seeded hydrogen boundary layer provides radiation absorption of the heat radiated from the high-temperature plasma. Also described is a forced convection thruster wall cooling design for an experimental test thruster.

Shoji, J. M.↗
NASA NTRS1977

The influence of autoionization accompanied by excitation on dielectronic recombination and ionization equilibrium

In the process of dielectronic recombination, the doubly excited state formed by radiationless capture may autoionize preferentially into an excited state of the recombining ion. This additional autoionization process has not been discussed in previous treatments of dielectronic recombination. The dielectronic recombination rates for certain nonhydrogenic Fe ions, although still larger than the direct radiative recombination rates, are found to be substantially reduced by the inclusion of the additional autoionization rate in the branching ratio for the stabilizing radiative transition. Consequently, the temperatures of maximum equilibrium abundance are significantly lower than those predicted by recent calculations. Finally, the radiative energy loss rate coefficients are calculated for radiation processes involving electron Fe-ion collisions in high-temperature plasmas. Electron impact excitation of resonance line radiation is the dominant radiative cooling mechanism in steady-state plasmas at temperatures where ions with bound electrons are abundant. However, it is found that the radiation emitted during dielectronic recombination can be more important than direct recombination radiation and bremsstrahlung.

Jacobs, V. L.↗
NASA NTRS1977

Multiple loop activations and continuous energy release in the solar flare of June 15, 1973

The spatial and temporal evolution of the high-temperature plasma in the solar flare of June 15, 1973, is studied using XUV spectroheliograms and X-ray filtergrams obtained from Skylab. The analysis focuses on the changing forms and brightness of Fe XXIII 263-A and Fe XXIV 255-A images. Temperatures and emission measures computed for different times during the flare are compared with those derived from Solrad-9 flux data, the electron temperature in the bright compact core of the Fe XXIV image is determined, and a coronal origin is suggested for this bright core. The observational evidence shows that the overall flare event involved a number of different preexisting loops and arches which were activated in succession. The activation and heating are found to have persisted well past the end of the burst phase, implying that the energy release did not end when the impulsive phase was over. The overall development of the flare is summarized on the basis of the observed order of appearance of the loops.

Widing, K. G.↗
NASA NTRS1978

Emission-line spectra of two active regions on the solar limb - 1175-1940 A

Skylab emission-line spectra (1175 to 1940 A) of two active regions on the solar limb are examined. Electron densities for the active regions are derived using the intensity ratios of selected intersystem and allowed lines. The intensity ratios in the active regions are compared with those observed previously in quiet-sun and coronal-hole regions. The behavior of coronal forbidden lines relative to transition-zone lines is discussed along with the solar continuum intensities near and above the limb. These continuum intensities are then compared with those at similar slit positions for the quiet sun and the previously studied coronal hole. The active-region data are found to be consistent with either (1) multithermal loops with the high-temperature plasma occupying the tops of the loops or (2) nearly isothermal loops with the hotter loops extending to higher altitudes.

Feldman, U.↗
NASA NTRS1979

Radiation energy conversion in space

Topics discussed at the third NASA conference on radiant energy conversion are reviewed. The unconcentrated-photovoltaic-generation version of a solar power satellite is described, noting that it will consist of a 21.3 x 5.3-sq-km silicon-solar-cell array expected to provide 17 Gw of electrical power, with 1 km in diam transmitters oriented to beam 2.45 GHz microwave power to two receiving/rectifying 'rectennas' on earth. The Solares space-energy-system concept, designed for providing a large fraction of the world's energy needs at costs comparable to those of future coal/nuclear alternative, is considered, as are subsystems for improving the economics of the solar power satellite. A concept proposing the use of relativistic-electron-storage rings for electron-beam energy transmission and storage, and a report on the production of a high temperature plasma with concentrated solar radiation are taken into account. Laser-conversion systems, including the direct-solar-pumped space laser, and the telec-powered spacecraft, are discussed.

Billman, K. W.↗
NASA NTRS1980

Effects of angular-momentum-changing collisions on dielectronic satellite spectra

A generalization of the low-density corona-model theory of the intensities of satellite lines of the resonance lines emitted by multiply charged helium-like ions in the X-ray spectra of high-temperature plasmas is developed in order to take account of electron collisional transitions between close autoionizing levels. A formalism for determining the population densities of the autoionizing levels and the satellite line intensities is presented, and the quantum mechanical calculation of autoionization, radiative decay and electron-induced collisional transitions is discussed. Generalized emission rate coefficients corresponding to dielectronic recombination and inner-shell-electron collisional excitation are tabulated as functions of electron density and temperature. The procedure is then used to illustrate the effects of angular-momentum-changing electron collisions on the intensities of the satellites of the 1s2p 1P to 1s2 1S resonance line of the ions Al XII and Si XIII. It is concluded that the collisional transitions have their most significant effect on the intensities of satellite transitions from metastable autoionizing states, which may be useful in determining plasma densities.

Jacobs, V. L.↗
NASA NTRS1980

New advances in thermal plasma research

Recent measurements obtained of the cold or thermal plasma of the earth's magnetosphere, which is believed to originate in the ionosphere, are reviewed. Consideration is given to the results of ATS 6 measurements which indicated unexpectedly high plasma temperatures and varied pitch-angle distributions, and the data from the low-energy plasma experiments on board GEOS 1 and 2 and ISEE 1, which were intended to clarify the ATS 6 results. These later measurements of ion composition, plasma energy and plasma distribution are noted to have confirmed earlier data and discovered new plasma components (D(+) or He(+2)), an intermixing of cold ionospheric plasma and hot magnetospheric plasma, the ordering of the plasma by the magnetic field rather than the ram direction in the outer magnetosphere, and wave phenomena. Questions remaining concerning the temperature and composition distributions of the plasmasphere and plasma trough, the relative densities of the cold and warmer components of the magnetosphere, plasma energization mechanisms, and the relative mix of the various plasma distributions are indicated.

Chappell, C. R.↗
NASA NTRS1982

On the reality of a boundary in the H-R diagram between late-type stars with and without high temperature outer atmospheres

The Linsky-Haisch hypothesis (1979) that a boundary exists in the H-R diagram separating yellow giants from red giants and supergiants is tested. IUE 1150-2000 A low-resolution spectra of 10 stars chosen to constitute a reverse bias sample are presented and discussed. Despite the bias, weak C IV emission indicative of high-temperature plasma was observed in four of the six stars chosen to be probable red stars, while no C IV emission was detected in the four stars chosen to be yellows. In a second test using the entire sample of 39 stars, nearly all of the yellow giants and supergiants were found to have an emission feature at 1549 A, which is attributed to C IV. The large magnitude dispersion could be attributed to temporal or spatial variability, differing magnetic field strengths and geometries, or age-related effects during post-main-sequence evolution. It is concluded that the Linsky-Haisch transition region boundary is a real phenomenon.

Simon, T.↗