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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 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Laboratory studies of the charge neutralization of a rocket payload during electron beam emission

The charge neutralization of an electrically-isolated rocket payload emitting an energetic electron beam has been studied in experiments in the large vacuum chamber at Johnson Space Center. The introduction of an RF-discharge-produced ambient plasma density (10,000 to 50,000 per cu cm) reduces the payload potential to 200 V for low current (1 and 10 ma) beams. The ignition of the beam-plasma discharge provides an efficient neutralization process for higher current beams.

Bernstein, W.↗
NASA NTRS1982

Photochemistry of SO2 in the atmosphere of Io and implications on atmospheric escape

Photochemical models of Io's atmosphere are presented with the assumption that SO2 is the major gas and that the SO2 surface pressure is controlled by vapor-pressure equilibrium at the surface. Photolysis of SO2 leads to efficient production of SO, O2, S, and O. Of these products, O and S are likely to be the dominant constituents in the upper atmosphere, and the atmospheric escape is expected to be in atomic form. Nonthermal escape processes are necessary to populate the plasma torus. SO2 surface densities greater than 100-billion per cu cm are needed on the dayside to supply the required amounts of S and O to maintain the torus. Surface chemistry presents an interesting possibility, namely, the conversion of O to O2, in which case O2 will be the dominant constituent throughout the nightside and over the polar caps with a surface O2 density of 10-billion per cu cm.

Kumar, S.↗
NASA NTRS1982

On the three-dimensional magnetic structure of the plasmoid created in the magnetotail at substorm onset

The magnetic field in the plasmoid which is created by the reconnection of magnetic field lines at a neutral line formed in the near-earth region of the plasma sheet at substorm onset, and which flows out of the magnetotail into the magnetosphere's wake, displays a strong positive or negative Y(SM) component that has been difficult to reconcile with the standard, two-dimensional reconnection geometry. It is shown that this deviation of the magnetic field is a manifestation of the newly-reconnected field line loop's draping toward the tail's central or midnight meridian, and that the draping is a consequence of the three-dimensional plasma flow associated with the reconnection process.

Hones, E. W., Jr.↗
NASA NTRS1982

High-resolution X-ray spectra of solar flares. VI - Impulsive soft X-ray flares

Doschek et al. (1980) and Feldman et al. (1980) have discussed high-resolution soft X-ray spectra of solar flares. The present investigation is concerned with the characteristics of the impulsive events as observed in soft X rays and the cooling of the flare plasma in terms of energy loss processes. A class of intense, short-lived solar flares which appear to be characterized by very high densities at high temperatures is found. For the 1979 November 6 event, the cooling time is so rapid that the density obtained may be a lower limit. The main cooling mechanism for the flares is found to be radiative. Two of the events are associated with strong gamma-ray emission and both of these events are very unusual in their soft X-ray emission. The 1979 November 9 flare shows extremely broad X-ray emission lines during the rise phase, indicative of nonthermal velocities of the order of 300 km/s.

Feldman, U.↗
NASA NTRS1983

The adiabatic motion of charged dust grains in rotating magnetospheres

Adiabatic equations of motion are derived for the micrometer-sized dust grains detected in the Jovian and Saturn magnetospheres by the Pioneer 10 and 11 spacecraft. The adiabatic theory of charged particle motion is extended to the case of variable grain charge. Attention is focused on the innermost and outermost limits to the grain orbit evolution, with all orbits tending to become circular with time. The parameters such as the center equation of motion, the drift velocity, and the parallel equation of motion are obtained for grains in a rotating magnetosphere. Consideration is given to the effects of periodic grain charge-discharge, which are affected by the ambient plasma properties and the grain plasma velocity. The charge-discharge process at the gyrofrequency is determined to eliminate the invariance of the magnetic moment and cause the grain to exhibit radial movement. The magnetic moment increases or decreases as a function of the gyrophase of the charge variation.

Northrop, T. G.↗
NASA NTRS1984

Practical Applications and Uses of Solid Lubricant Films

Practical applications are illustrated with discussions covering the reasons for use of solid lubricants, required performance, lubricant selection, and results obtained for the various examples shown. The applications described cover a broad range of solid lubricants. Included are soft lamellar compounds, organic polymers, soft elemental metals, oxides and compounds for high temperature use. The illustrations selected cover a broad range of lubricant application techniques delineating the reasons for the different processing procedures which include bonded films, plasma spraying, sputtering, ion plating and electrodeposition.

Bernard C Stupp↗
NASA NTRS1983

Microwave signatures from a reconnecting plasma pinch, with application to loop flares

A calculation is made of microwave signature of a cylindrical plasma pinch undergoing magnetic reconnection, a process which occurs in many astrophysical situations, such as solar flares. Depending on the viewing angle and the average energy of the accelerated electrons, the microwaves from this betatron-like source show various amounts of circular polarization. The degree of polarization is shown to be frequency dependent, and the sense of polarization is sometimes reversed. The power spectrum is predicted to have several interesting properties, which can be compared with high-resolution measurements.

Mok, Y.↗
NASA NTRS1983

The structure and emission of a non-radiative shock

Observational data and the capabilities of current models for observed filament and shock features of supernova remnants are considered. The filaments emit Balmer lines originating in nonthermal shocks. Models of the generation mechanisms must account for the shock structure and the possibilities of electron thermal precursors to the shock and plasma turbulence, as well as equilibration processes for electron and ion temperatures. It is not yet known if a Maxwellian velocity distribution fits the electrons and ions. An assumption of Coulombic equilibration of ions and electrons has agreed well with some observed forbidden line intensities in the Cygnus Loop, while other lines require detailed radiative transfer calculations.

Raymond, J. C.↗
NASA NTRS1987

ITO/InP solar cells: A comparison of devices fabricated by ion beam and RF sputtering of the ITO

This work was performed with the view of elucidating the behavior of indium tin oxide/indium phosphide (ITO/InP) solar cells prepared by RF and ion beam sputtering. It was found that using RF sputter deposition of the ITO always leads to more efficient devices than ion beam sputter deposition. An important aspect of the former technique is the exposure of the single crystal p-InP substrates to a very low plasma power prior to deposition. Substrates treated in this manner have also been used for ion beam deposition of ITO. In this case the cells behave very similarly to the RF deposited cells, thus suggesting that the lower power plasma exposure (LPPE) is the crucial process step.

Coutts, T. J.↗
NASA NTRS1989

Hollow-Cathode Source Generates Plasma

Device generates argon, krypton, or xenon plasma via thermionic emission and electrical discharge within hollow cathode and ejects plasma into surrounding vacuum. Goes from cold start up to full operation in less than 5 s after initial application of power. Exposed to moist air between operations without significant degradation of starting and running characteristics. Plasma generated by electrical discharge in cathode barrel sustained and aided by thermionic emission from emitter tube. Emitter tube does not depend on rare-earth oxides, making it vulnerable to contamination by exposure to atmosphere. Device modified for use as source of plasma in laboratory experiments or industrial processes.

Deininger, W. D.↗
NASA NTRS1988

The spherical probe electric field and wave experiment

The experiment is designed to measure the electric field and density fluctuations with sampling rates up to 40,000 samples/sec. The description includes Langmuir sweeps that can be made to determine the electron density and temperature, the study of nonlinear processes that result in acceleration of plasma, and the analysis of large scale phenomena where all four spacecraft are needed.

Gustafsson, G.↗
NASA NTRS1989

Thermodynamic properties of the heliospheric plasma

A global-scale study is conducted of the radial evolution of the solar wind's temperature (T), number density (n), and entropy (s) thermodynamic properties, on the basis of plasma data from such sources as IMP and ISEE 3, in conjunction with an MHD simulation model. The radial evolution of T and s indicates that the heliospheric plasma is subjected to a heating process; this heating is interpreted to be largely due to the cumulative effect of the shock process with increasing distance from the sun. This simulation model is also used to extrapolate the thermodynamic properties of the solar wind from Voyager 2 to the region of the outer heliosphere that is bounded by the termination shock.

Whang, Y. C.↗
NASA NTRS1989

Slow shock characteristics as a function of distance from the X-line in the magnetotail

Both particle and MHD simulations are performed to study the characteristics of slow shocks in the magnetotail. The particle simulations indicate that switch-off shocks exhibit large amplitude rotational wave trains, while magnetotail slow shocks with an intermediate Mach number M(An) less than M(c) of about 0.98 do not display such rotational wave trains. The MHD simulations show that the spontaneous reconnection process in the near-earth plasma sheet leads to the formation of a pair of slow shocks tailward of the reconnection line (X-line). The properties of slow shocks are found to vary as a function of the distance from X-line due to the formation of plasmoid. Slow shocks in most regions of magnetotail are found to be nonswitch-off shocks with M(An) of less than 0.98. The present results are used to discuss the lack of large amplitude rotational wave trains at slow shocks in the deep magnetotail.

Lee, L. C.↗
NASA NTRS1989

Magnetic fields in the central engines of active galactic nuclei

Important physical processes which may occur in the central engines of active galactic nuclei and which rely on the presence of a strong magnetic field are discussed. These processes include those involved in the plasma physics of hot tenuous accretion flows, the production of nonthermal continuum radiation, and the radiative manifestation of hydromagnetic jet production. The main arguments which support the hypothesis that supermassive black holes are the prime movers in the central engines are reviewed, and some major deduction regarding the physical state of the accreting gas are pointed out.

Begelman, Mitchell C.↗
NASA NTRS1990

Observations of thermal ion influxes about the space shuttle

Ion mass spectrometer measurements made as part of the University of Iowa's Plasma Diagnostic Package on the STS-3 and Spacelab 2 Space Shuttle missions sampled a variety of ion composition and collected ion current responses to gas emissions from the vehicle. The only other shuttle ion measurements were made by an Air Force Geophysics Laboratory (AFGL) quadrupole spectrometer flown on STS-4. Gas emissions change the distribution of the incoming plasma through scattering and charge transfer processes. A background flux of contaminant ion species (mostly relating to water) always exists in the near vicinity of the shuttle with a magnitude which is dependent on the look direction of the spectrometer but which varies differently with changes in the angle of attack than that of the ambient ions. There is a near shuttle wake cavity in the contaminant ion distributions which has a different spatial configuration than the wake of the ambient ions. Although water dumps produce the most persistent ion perturbations, the sources for ion current modification were best delineated from measurements made when only one or two of the Reaction Control System thrusters fired for a relatively long duration. Contaminant ion perturbations associated with such firings were observed to persist for the order of a second after the cessation of the firings. The dense thruster plumes are efficient collisional, charge exchange barriers to the passage of ambient ions. Collected ion current perturbations were more evident for firings of the rear verniers, whose plumes scatter off projecting surfaces, than for the nose thrusters. The effect of the Vernier firings was found to depend not only on the location and attitude of the spectrometer with respect to the shuttle and thruster plume direction, but also on the orientation of the local magnetic field with respect to the shuttle velocity.

Grebowsky, Joe M.↗
NASA NTRS1991

Indium gallium arsenide microwave power transistors

Depletion-mode InGaAs microwave power MISFETs with 1-micron gate lengths and up to 1-mm gate widths have been fabricated using an ion-implantation process. The devices employed a plasma-deposited silicon/silicon dioxide gate insulator. The dc I-V characteristics and RF power performance at 9.7 GHz are presented. The output power, power-added efficiency, and power gain as a function of input power are reported. An output power of 1.07 W with a corresponding power gain and power-added efficiency of 4.3 dB and 38 percent, respectively, was obtained. The large-gate-width devices provided over twice the previously reported output power for InGaAs MISFETs at X-band. In addition, output power stability within 1.2 percent over 24 h of continuous operation was achieved. In addition, a drain current drift of 4 percent over 10,000 sec was obtained.

Johnson, Gregory A.↗
NASA NTRS1993

Optical Technologies for UV Remote Sensing Instruments

Over the last decade significant advances in technology have made possible development of instruments with substantially improved efficiency in the UV spectral region. In the area of optical coatings and materials, the importance of recent developments in chemical vapor deposited (CVD) silicon carbide (SiC) mirrors, SiC films, and multilayer coatings in the context of ultraviolet instrumentation design are discussed. For example, the development of chemically vapor deposited (CVD) silicon carbide (SiC) mirrors, with high ultraviolet (UV) reflectance and low scatter surfaces, provides the opportunity to extend higher spectral/spatial resolution capability into the 50-nm region. Optical coatings for normal incidence diffraction gratings are particularly important for the evolution of efficient extreme ultraviolet (EUV) spectrographs. SiC films are important for optimizing the spectrograph performance in the 90 nm spectral region. The performance evaluation of the flight optical components for the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) instrument, a spectroscopic instrument to fly aboard the Solar and Heliospheric Observatory (SOHO) mission, designed to study dynamic processes, temperatures, and densities in the plasma of the upper atmosphere of the Sun in the wavelength range from 50 nm to 160 nm, is discussed. The optical components were evaluated for imaging and scatter in the UV. The performance evaluation of SOHO/CDS (Coronal Diagnostic Spectrometer) flight gratings tested for spectral resolution and scatter in the DGEF is reviewed and preliminary results on resolution and scatter testing of Space Telescope Imaging Spectrograph (STIS) technology development diffraction gratings are presented.

Keski-Kuha, R. A. M.↗