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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

The structure, energy balance, and winds of cool stars

The phenomena associated with magnetic fields in the Sun are summarized and it is shown that similar phenomena occur in cool stars. High dispersion spectra are providing unique information concerning densities, atmospheric extension, and emission line widths. A recent unanticipated discovery is that the transition lines are redshifted (an antiwind) in beta Dra (G2 Ib) and perhaps other stars. This is interpreted as indicating downflows in closed magnetic flux tubes as are seen in the solar flux tubes above sunspots. The G and K giants and supergiants are classified as active stars, quiet stars, or hybrid stars depending on whether their atmospheres are dominated by closed magnetic flux tubes, open field geometries, or a predominately open geometry with a few closed flux tubes embedded.

Linsky, J. L.↗
NASA NTRS1987

On the polarization, compression and nonoscillatory behavior of hydromagnetic waves associated with pickup ions

Solution of the kinetic dispersion equation shows that heavy pickup ions with large perpendicular energies excite a new hydromagnetic wave mode with maximum growth, high (magnetic field and mass density) compression ratios, and almost linear polarization coexisting slightly away 6-15 deg from parallel propagation. The mode arises from the coupling of the heavy ion beam to the modified left-hand wave dispersion caused by the multiion nature of the medium. The ion beam can also bring about nonoscillatory, purely growing structures distinct from the mirror wave through the coupling of a counter-streaming left-hand mode to a costreaming right-hand wave. The free energy source parameters are varied to determine their relative influence and define the domain of existence of the instability. Its characteristics may prove helpful in the interpretation of recent cometary (Halley and Giacobini-Zinner) and artificial release (AMPTE) observations.

Brinca, Armando L.↗
NASA NTRS1979

A kinetic approach to magnetospheric modeling

The earth's magnetosphere is caused by the interaction between the flowing solar wind and the earth's magnetic dipole, with the distorted magnetic field in the outer parts of the magnetosphere due to the current systems resulting from this interaction. It is surprising that even the conceptually simple problem of the collisionless interaction of a flowing plasma with a dipole magnetic field has not been solved. A kinetic approach is essential if one is to take into account the dispersion of particles with different energies and pitch angles and the fact that particles on different trajectories have different histories and may come from different sources. Solving the interaction problem involves finding the various types of possible trajectories, populating them with particles appropriately, and then treating the electric and magnetic fields self-consistently with the resulting particle densities and currents. This approach is illustrated by formulating a procedure for solving the collisionless interaction problem on open field lines in the case of a slowly flowing magnetized plasma interacting with a magnetic dipole.

Whipple, E. C., Jr.↗
NASA NTRS1973

Molecular attenuation and phase dispersion between 40 and 140-GHz for path models from different altitudes

Radio wave propagation in the 40 to 140 GHz band through the first hundred kilometers of the atmosphere is strongly influenced by the microwave spectrum of oxygen (O2-MS). A unified treatment of molecular attenuation and phase dispersion is formulated. Results of molecular physics are translated into frequency, temperature, pressure, and magnetic field dependencies of a complex refractive index. The intensity distribution of the O2-MS undergoes several changes with increasing altitude. The influence of water vapor is discussed. Examples of computer plots are given as a function of altitude for homogeneous, zenith, and tangential path geometries. Molecular resonances of minor atmospheric gases are discussed briefly.

Liebe, H. J.↗
NASA NTRS1984

Magnetic record support

The magnetic layer of a magnetic record support is coated with a thin film of a polymer with a siloxane bond. The magnetic layer consists of a thin film obtained by vacuum metallization, cathode sputtering or dispersion of a ferromagnetic metal powder in a binder. The polymer with a siloxane bond is produced by the polymerization of an organic silicon compound which inherently contains or is able to form this bond. Polymerization is preferably performed by plasma polymerization.

Nakayama, M.↗
NASA NTRS1994

Nonlinear evolution of a large-amplitude circularly polarized Alfven wave: Low beta

The nature of turbulent cascades arising from the parametric instabilities of a monochromatic field-aligned large-amplitude circularly polarized Alfven wave is investigated via direct numerical simulation for the case of low plasma Beta and no wave dispersion. The magnetohydrodynamic code permits nonlinear couplings in the parallel direction to the ambient magnetic field and one perpendicular direction. Compressibility is included in the form of a polytropic equation of state. Anisotropic turbulent cascades, similar to those found in early incompressible two-dimensional simulations, occur after nonlinear saturation of the parallel propagating decay instability. The turbulent spectrum can be divided into three regimes: the lowest wave numbers are dominated by lower sideband remnants of the parametric process, intermediate wave numbers display nearly incompressible dynamics, and the highest wave numbers are dominated by acoustic turbulence.

Ghosh, S.↗
NASA NTRS2001

Membership and Coronal Activity in the NGC 2232 and Cr 140 Open Clusters

This is the second annual performance report for our grant "Membership and Coronal Activity in the NGC 2232 and Cr 140 Open Clusters." We propose to identify X-ray sources and extract net source counts in 8 archival ROSAT HRI images in the regions of the NGC 2232 and Cr 140 open clusters. These X-ray data will be combined with ground-based photometry and spectroscopy in order to identify G, K, and early-M type cluster members. At present, no members later than approximately F5 are currently known for either cluster. With ages of approximately 25 Myr and at a distance of just 320 - 360 pc, the combined late-type membership of the NGC 2232 and Cr 140 clusters will yield an almost unique sample of solar-type stars in the post-T Tauri/pre-main sequence phase of evolution. These stars will be used to assess the level and dispersion in coronal activity levels, as part of a probe of the importance of magnetic braking and the level of magnetic dynamo activity, for solar-type stars just before they reach the ZAMS. Over the past year we have successfully acquired all of the ground-based data necessary to support the analysis of the archival ROSAT X-ray data in the regions around both of these clusters. By the end of 2001 we expect to have completed the reduction and analysis of the ground-based photometry and spectroscopy and will begin the integration of these data with the ROSAT X-ray data. A certain amount of pressure to complete the work on NGC 2232 is coming from the SIRTF project, as this cluster may be a key component to a circumstellar disk evolution GTO program. We are only too happy to try to help and have worked to speed the analysis as much as possible. The primary activity to be undertaken in the next few months is the integration of the groundbased photometry and spectroscopy with the archival ROSAT X-ray data and then writing the paper summarizing our results. The most time consuming portion of this next phase is, of course, seeing the paper through publication in a peer-reviewed journal. Therefore, we have requested a no-cost extension to the grant to allow us to bring this project to a conclusion.

Patten, Brian M.↗
NASA NTRS2003

Helicon Wave Physics Impacts on Electrodeless Thruster Design

Effective generation of helicon waves for high density plasma sources is determined by the dispersion relation and plasma power balance. Helicon wave plasma sources inherently require an applied magnetic field of .01-0.1 T, an antenna properly designed to couple to the helicon wave in the plasma, and an rf power source in the 10-100 s of MHz, depending on propellant choice. For a plasma thruster, particularly one with a high specific impulse (>2000 s), the physics of the discharge would also have to address the use of electron cyclotron resonance (ECR) heating and magnetic expansion. In all cases the system design includes an optimized magnetic field coil, plasma source chamber, and antenna. A preliminary analysis of such a system, calling on experimental data where applicable and calculations where required, has been initiated at Glenn Research Center. Analysis results showing the mass scaling of various components as well as thruster performance projections and their impact on thruster size are discussed.

Gilland, James↗
NASA NTRS2007

Helicon Wave Physics Impacts on Electrodeless Thruster Design

Effective generation of helicon waves for high density plasma sources is determined by the dispersion relation and plasma power balance. Helicon wave plasma sources inherently require an applied magnetic field of .01-0.1 T, an antenna properly designed to couple to the helicon wave in the plasma, and an rf power source in the 10-100 s of MHz, depending on propellant choice. For a plasma thruster, particularly one with a high specific impulse (>2000 s), the physics of the discharge would also have to address the use of electron cyclotron resonance (ECR) heating and magnetic expansion. In all cases the system design includes an optimized magnetic field coil, plasma source chamber, and antenna. A preliminary analysis of such a system, calling on experimental data where applicable and calculations where required, has been initiated at Glenn Research Center. Analysis results showing the mass scaling of various components as well as thruster performance projections and their impact on thruster size are discussed.

Gilland, James H.↗
NASA NTRS1974

Ultrasonic dispersion (delta V/V) determined from mechanical resonance frequency shifts

With standing wave ultrasonic techniques, small changes in phase velocity which result from changes in some external parameter (e.g., temperature or magnetic field) have traditionally been determined by observing shifts in the mechanical resonance frequency of a composite resonator. Some previous investigators have assumed that the fractional change in velocity is equal to the fractional change in frequency. Substantially improved formulas for determining the dispersion are presented and one of these is shown to be much more accurate than all previous approximations. The results of simulated and actual experiments over wide ranges of dispersion, transducer loading parameter, and frequency are analyzed in order to compare the errors inherent in the various approximations.

Moerner, W. E.↗
NASA NTRS1980

On self-consistent waves and their stability in warm plasmas. II - Instability of circularly polarized waves both in the presence and the absence of an ambient magnetic field

The stability of a self-consistent, large-amplitude, circularly polarized wave in a warm plasma is investigated. For perturbations to the system propagating normal to the plane of circular polarization, a dispersion relation is derived employing an expansion in the nonlinear wave amplitude and the momentum of the plasma particles in the plane of polarization. Instability results both in the absence and presence of a large-scale magnetic field with a growth rate of the order of the nonlinear wave amplitude.

Lee, M. A.↗
NASA NTRS1972

A resonant instability of model proton radiation belts in the Jovian magnetosphere

The ion cyclotron instability and characteristics of the ion cyclotron wave are discussed. A mathematical perturbation technique is applied to the dispersion relations, and the results are applied to the case of propagation parallel to the magnetic field. The ion cyclotron wave is determined in its damping and growth characteristics by resonant protons and electrons, found in momentum space on resonant surfaces. In the relativistic case the resonant surfaces are hyperbolas of revolution around the magnetic field, and protons can have a stabilizing effect. Instability rates are calculated for the region in the equatorial plane with the Ioannidis and Brice density model. The upper limit of proton flux which gives an energy density of the same order of magnitude as the magnetic field energy density is obtained. The upper limit is plotted with respect to distance from Jupiter and the minimum resonant energy contributing to the instability is also plotted.

Neubauer, F. M.↗
NASA NTRS1972

Linear and nonlinear stability characteristics of whistlers

Linear and nonlinear propagating characteristics of right-hand polarized, slow electromagnetic, magnetoplasma waves (whistlers) are discussed in terms of stability and dispersion. An analysis of the stability of whistlers propagating at an angle to the static magnetic field is presented. A new mechanism is derived for the onset of stimulated emissions, and modulational instability for nonlinear whistlers are discussed.

Brinca, A. L.↗
NASA NTRS1976

Space Processing Applications Rocket project, SPAR 1

The experiment objectives, design/operational concepts, and final results of each of nine scientific experiments conducted during the first Space Processing Applications Rocket (SPAR) flight are summarized. The nine individual SPAR experiments, covering a wide and varied range of scientific materials processing objectives, were entitled: solidification of Pb-Sb eutectic, feasibility of producing closed-cell metal foams, characterization of rocket vibration environment by measurement of mixing of two liquids, uniform dispersions of crystallization processing, direct observation of solidification as a function of gravity levels, casting thoria dispersion-strengthened interfaces, contained polycrystalline solidification, and preparation of a special alloy for manufacturing of magnetic hard superconductor under zero-g environment.

Reeves, F.↗
NASA NTRS1978

Small amplitude waves in a hot relativistic two-fluid plasma

The dispersion relation for small amplitude waves in a hot relativistic plasma embedded in a uniform magnetic field is derived. Four plasma modes exist for propagation oblique to the magnetic field, and the mode properties are summarized in a hot relativistic generalization of the cold plasma pond diagram of Stix (1962). The two-fluid approximation is considered, and two-fluid equations are applied in this procedure which summarizes properties of linear waves in an unbounded magnetized relativistic plasma by means of a parameter-space diagram of wave phase velocity.

Hyun, S.↗
NASA NTRS1984

Propagation of axisymmetric disturbances on a twisted magnetic flux tube

The propagation of axisymmetric disturbances on a twisted magnetic flux tube in an inviscid, incompressible, unstratified atmosphere of infinite electrical conductivity is considered. Dispersion effects due to twist appear quickly only on highly twisted flux tubes for a superposition of the lowest radial eigenmodes and wavelengths comparable to the flux tube radius. These radial profiles become distorted and show focusing effects after propagating on the order of ten flux tube radii. This suggests twist effects on hydromagnetic wave propagation may be important where the flux tubes come up through the surface and expand into the tenuous atmosphere.

Bogdan, T. J.↗
NASA NTRS1985

The GOES-G and -H spacecraft design

The design of the Geostationary Operational Environmental Satellites (GOES) uses newer technology and has expanded capability relative to the predecessor GOES series of satellites. The satellite directly transmits day and night observations of hemispheric-scale weather, hurricanes, and other more localized severe storms and relays processed high-resolution observation data along with weather facsimile (WEFAX) data. Weather observations are generated in the visible and infrared spin scan radiometer (VISSR) atmospheric sounder (VAS). The VAS performs visible and infrared imaging as well as multispectral imaging (MSI) and temperature sounding of the atmosphere. The satellite provides direct interrogation and simultaneous relay transmission between the command data acquisition station (CDAS) and the multiple, widely dispersed data collection platforms (DCP). The satellites also monitor the condition of the earth's magnetic field, energetic particle flux, and X-ray emissions from the sun. The satellite performs all communications functions by means of a multifunction communications system that operates on S-band and uhf frequencies at rates varying from 100 bit/s to 28 megabit/s. An experimental capability for the detection of the emergency locator transmitter beacons is included in the GOES-GH design as a part of the international satellite-aided search and rescue system.

Fermelia, L. R.↗
NASA NTRS1985

Lower-hybrid instabilities driven by an ion velocity ring

The lower-hybrid instabilities in high-beta (ratio of plasma to magnetic pressure) plasmas driven by ring-ion distributions in velocity space are investigated. A dispersion equation including electromagnetic effects is derived. In the low-beta limit, analytic expressions are obtained which illuminate the physical nature of the instabilities. The complete dispersion equation is solved numerically as a function of ring speed and plasma beta for several types of ring distribution. Electromagnetic effects are important for relatively energetic rings even in the low-beta regime, suppressing growth rates and shifting the angle of propagation to more oblique angles. Stabilization by thermal effects is also discussed. Application of these results to the earth's bow shock, AMPTE, comets and solar flares is suggested.

Akimoto, K.↗