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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 145 records · Page 8
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NASA NTRS1974

Effect of Faraday rotation on the circular polarization of the Crab Nebula

The effect of Faraday rotation on the circular polarization of an electromagnetic wave propagating through a magnetized plasma is calculated for various limits of the plasma and wave parameters appropriate to a 30-Hz wave in the Crab Nebula. It is shown that a static magnetic field of the proper geometry and only a few times stronger than the wave field can reduce the circular polarization of the nonlinear inverse Compton radiation to a value below the observed upper limit.-

Gerver, M. J.↗
NASA NTRS1978

Operational modes for a wave injection facility aboard spacelab and a sub-satellite

Various modes of operation are described for an orbiting wave injection facility planned to measure the properties of waves propagating in space plasma. Such a facility would cover a wide frequency range including MF and HF. Phase shift and Doppler shift measurements will yield more accurate measurements of echo time delay and the angle of arrival. Because Spacelab will involve some sub-satellites, some consideration is given to propagation between two vehicles both at HF and VHF.

Dyson, P. L.↗
NASA NTRS1980

The low-frequency continuum as observed in the solar wind from ISEE 3 - Thermal electrostatic noise

The low frequency continuum (LFC) noise between 30 and 200 kHz has been investigated from the ISEE 3 spacecraft in the solar wind by means of a radio astronomy experiment more sensitive than previously available. It is demonstrated that the LFC radiation observed in the solar wind is in the form of longitudinal plasma waves rather than transverse electromagnetic waves. The observed spectral characteristics are found to be a function of antenna length. In addition, both the absence of antenna spin modulation and the fact that these plasma waves do not propagate to large distances imply a local origin for the LFC.

Hoang, S.↗
NASA NTRS1991

Solidification processing superalloys in an electric field

The phase morphology of a given superalloy's microstructure is established during solidification. Solidification-processing in an applied electric field is a technique currently undergoing experimental characterization at NASA-Marshall. The method is predicated on the simplest model of a metallic solid, in which ions are arranged in basic space lattices that are permeated by an 'electron gas' whose valence electrons are free to move in the solid. When in a superheated liquid state, the metal is seen as a dense 'cold plasma' of electrons and ions. The application of an electric field during solidification establishes a steady, continuous current flow; the direction of propagation of the plasma waves coincides with the direction of the electric field. Such an alignment introduces an ordered arrangement of the electric vectors and introduces an additional degree of order in an already highly ordered alloy.

Ahmed, Shaffiq↗
NASA NTRS2008

The International Heliophysical Year

It is now widely recognized that evolution in the solar system proceeds through a set of Universal Processes, i.e. reconnection, particle acceleration, plasma wave generation and propagation, etc. By studying these Universal Processes together, in diverse environments, and in a comparative way, new scientific insights will be gained. This is perhaps best understood by citing a few examples: (I) Shocks are observed in situ in the interplanetary medium, shocks are believed to play a role in the acceleration of particles in the solar corona, and standing bow shocks and termination shocks separate the major regions in the heliosphere. Shock formation, and particle acceleration are universal processes. (2) Aurorae are observed on Earth, Saturn, and Jupiter, and Jovian auroral "footprints" have been observed on 10, Ganymede and Europa. The formation of aurorae is observed to be the universal response of a magnetized body in the solar wind. The International Heliophysical Year (IHY) specifically highlights the cross-disciplinary study of universal physical processes in the solar system, observed in a variety of settings. The study of these processes will provide new insights that will lead to a better understanding of the universal processes in the solar system that affect the interplanetary and planetary environments, and pave the way for safe human space travel to the Moon and planets in the future, and it will serve to inspire the next generation of space physicists.

Davila, Joseph M.↗
NASA NTRS1993

Stability of an inhomogeneous two-component plasma with magnetic viscosity

The stability of a semiinfinite quasi-neutral inhomogeneous plasma with magnetic viscosity has been discussed by using JWKB approximation in which the parameters are regarded slowing varying. Dispersion relation is obtained and discussed. It is found that the inhomogeneous system is unstable for all perturbations with k(y) = 0. A dispersion relation for homogeneous plasma is also obtained and discussed. It is shown that fast and slow-MHD waves propagate in the homogeneous plasma in the limit of almost perpendicular propagation under certain conditions.

Kumar, Nagendra↗
NASA NTRS1994

Plasma and radio waves from Neptune: Source mechanisms and propagation

This report summarizes results obtained through the support of NASA Grant NAGW-2412. The objective of this project is to conduct a comprehensive investigation of the radio wave emission observed by the planetary radio astronomy (PRA) instrument on board Voyager 2 as if flew by Neptune. This study has included data analysis, theoretical and numerical calculations, ray tracing, and modeling to determine the possible source mechanism(s) and locations of the Neptune radio emissions. We have completed four papers, which are included in the appendix. The paper 'Modeling of Whistler Ray Paths in the Magnetosphere of Neptune' investigated the propagation and dispersion of lighting-generated whistler in the magnetosphere of Neptune by using three dimensional ray tracing. The two papers 'Numerical Simulations of Bursty Radio Emissions from Planetary Magnetospheres' and 'Numerical Simulations of Bursty Planetary Radio Emissions' employed numerical simulations to investigate an alternate source mechanism of bursty radio emissions in addition to the cyclotron maser instability. We have also studied the possible generation of Z and whistler mode waves by the temperature anisotropic beam instability and the result was published in 'Electron Cyclotron Wave Generation by Relativistic Electrons.' Besides the aforementioned studies, we have also collaborated with members of the PRA team to investigate various aspects of the radio wave data. Two papers have been submitted for publication and the abstracts of these papers are also listed in the appendix.

Wong, H. K.↗
NASA NTRS1994

Plasma and radio waves from Neptune: Source mechamisms and propagation

The purpose of this project was to conduct a comprehensive investigation of the radio wave emission observed by the planetary radio astronomy (PRA) instrument on board Voyager 2 as it flew by Neptune. The study has included data analysis, theoretical and numerical calculations, and ray tracing to determine the possible source mechanisms and locations of the radiation, including the narrowband bursty and smooth components of the Neptune radio emission.

Menietti, J. Douglas↗
NASA NTRS1979

Magnetospheric plasma waves

Space measurements have provided a wealth of data on wave phenomena, plasma parameters, and energetic particle characteristics within the earth's magnetosphere. In the present paper, the generation, propagation, and interaction of plasma waves are discussed, along with the interpretation of the observations. Data on plasma waves from other planetary magnetospheres and cosmic plasma systems are examined and interpreted by analogy to the earth's magnetosphere. Areas requiring continued plasma wave research are indicated.

Shawhan, S. D.↗
NASA NTRS1983

Self-modulational formation of pulsar microstructures

A nonlinear plasma theory for self-modulation of pulsar radio pulses is discussed. A nonlinear Schroedinger equation is derived for strong electromagnetic waves propagating in an electron-positron plasma. The nonlinearities arising from wave-intensity-induced particle-mass variation may excite the modulational instability of circularly and linearly polarized pulsar radiation. The resulting wave envelopes can take the form of periodic wave trains or solitons. These nonlinear stationary waveforms may account for the formation of pulsar microstructures.

Chian, A. C.-L.↗
NASA NTRS1973

Steady-state solutions for relativistically strong electromagnetic waves in plasmas.

New steady-state solutions are derived which describe electromagnetic waves strong enough to make plasma ions and electrons relativistic. A two-fluid model is used throughout. The following solutions are studied: (1) linearly polarized waves with phase velocity much greater than c; (2) arbitrarily polarized waves with phase velocity near c, in a cold uniform plasma; (3) circularly polarized waves in a uniform plasma characterized by a scalar pressure tensor. All of these waves are capable of propagating in normally overdense plasmas, due to nonlinearities introduced by relativistic effects. The propagation of relativistically strong waves in a density gradient is examined, for the example of a circularly polarized wave strong enough to make electrons but not ions relativistic. It is shown that such a wave propagates at constant energy flux despite the nonlinearity of the system.

Max, C. E.↗
NASA NTRS1993

Studies of classical radiation emission from plasma wave undulators

We examine the characteristics of the classical radiation emitted by a relativistic electron beam that propagates perpendicularly through a large amplitude relativistic plasma wave. Such a study is useful for evaluating the feasibility of using relativistic plasma waves as extremely short wavelength undulators for generating short wavelength radiation. The electron trajectories in a plasma wave undulator are obtained using perturbation techniques and are then compared to numerical simulation results. The frequency spectrum and angular distribution of the spontaneous radiation emitted by a single electron and the stimulated radiation gain are obtained analytically, and are then compared to 3-D numerical simulations. The characteristics of the plasma wave undulator are compared to the ac FEL undulator and the conventional FEL.

Williams, Ronald L.↗
NASA NTRS1976

Whistler wave propagation in a large magnetoplasma

A large collisionless quiescent plasma source is developed for investigating the phase and amplitude distribution of antenna-launched whistler waves in a specified parameter regime relating wave frequency to electron cyclotron frequency. Wave dispersion is studied both by interferometer techniques with monochromatic waves and by propagation of short phase-coherent wave bursts. The wave damping mechanism is examined by propagating perfectly ducted whistler waves. The dispersion of single frequency waves and wave packets is demonstrated. Trough ducting for wave frequency to electron cyclotron frequency ratio greater than 1/2 is verified, and new eigenmodes in nonuniform plasmas at ratio values less than 1/2 are observed. It is shown that geometric effects due to ray divergence and wave refraction dominate over collisional damping.

Stenzel, R. L.↗
NASA NTRS2011

Space-Time Localization of Plasma Turbulence Using Multiple Spacecraft Radio Links

Space weather is described as the variability of solar wind plasma that can disturb satellites and systems and affect human space exploration. Accurate prediction requires information of the heliosphere inside the orbit of the Earth. However, for predictions using remote sensing, one needs not only plane-of-sky position but also range information the third spatial dimension to show the distance to the plasma disturbances and thus when they might propagate or co-rotate to create disturbances at the orbit of the Earth. Appropriately processed radio signals from spacecraft having communications lines-of-sight passing through the inner heliosphere can be used for this spacetime localization of plasma disturbances. The solar plasma has an electron density- and radio-wavelength-dependent index of refraction. An approximately monochromatic wave propagating through a thin layer of plasma turbulence causes a geometrical-optics phase shift proportional to the electron density at the point of passage, the radio wavelength, and the thickness of the layer. This phase shift is the same for a wave propagating either up or down through the layer at the point of passage. This attribute can be used for space-time localization of plasma irregularities. The transfer function of plasma irregularities to the observed time series depends on the Doppler tracking mode. When spacecraft observations are in the two-way mode (downlink radio signal phase-locked to an uplink radio transmission), plasma fluctuations have a two-pulse response in the Doppler. In the two-way mode, the Doppler time series y2(t) is the difference between the frequency of the downlink signal received and the frequency of a ground reference oscillator. A plasma blob localized at a distance x along the line of sight perturbs the phase on both the up and down link, giving rise to two events in the two-way tracking time series separated by a time lag depending the blob s distance from the Earth: T2-2x/c, where T2 is the two-way time-of-flight of radio waves to/from the spacecraft and c is the speed of light. In some tracking situations, more information is available. For example, with the 5-link Cassini radio system, the plasma contribution to the up and down links, y(sub up)(t) and y(sub dn)(t), can be computed separately. The times series y(sub up)(t) and y(sub dn)(t) respond to a localized plasma blob with one event in each time series. These events are also separated in time by T2-2x/c. By cross-correlating the up and down link Doppler time series, the time separation of the plasma events can be measured and hence the plasma blob s distance from the Earth determined. Since the plane-of-sky position is known, this technique allows localization of plasma events in time and three space dimensions.

Armstrong, John W.↗