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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Measurement realities of current collection in dynamic space plasma environments

Theories which describe currents collected by conducting and non-conducting bodies immersed in plasmas have many of their concepts based upon the fundamentals of sheath-potential distributions and charged-particle behavior in superimposed electric and magnetic fields. Those current-collecting bodies (or electrodes) may be Langmuir probes, electric field detectors, aperture plates on ion mass spectrometers and retarding potential analyzers, or spacecraft and their rigid and tethered appendages. Often the models are incomplete in representing the conditions under which the current-voltage characteristics of the electrode and its system are to be measured. In such cases, the experimenter must carefully take into account magnetic field effects and particle anisotropies, perturbations caused by the current collection process itself and contamination on electrode surfaces, the complexities of non-Maxwellian plasma distributions, and the temporal variability of the local plasma density, temperature, composition and fields. This set of variables is by no means all-inclusive, but it represents a collection of circumstances guaranteed to accompany experiments involving energetic particle beams, plasma discharges, chemical releases, wave injection and various events of controlled and uncontrolled spacecraft charging. Here, an attempt is made to synopsize these diagnostic challenges and frame them within a perspective that focuses on the physics under investigation and the requirements on the parameters to be measured. Examples include laboratory and spaceborne applications, with specific interest in dynamic and unstable plasma environments.

Szuszczewicz, Edward P.↗
NASA NTRS1970

Optical mixing in a magnetoactive plasma

Homogeneous plasma electrostatic oscillations excitation by electromagnetic waves nonlinear interaction in magnetic field, deriving expression for density perturbation

Weyl, G.↗
NASA NTRS1984

Limitation of electrostatic charging of dust particles in a plasma

It is shown that in a dusty plasma consisting of a plasma (density n and temperature T) and dust grains (density N and radius a) the charge on a grain is not given by its free-space value. Instead, the charge is reduced by a factor 1 + x. Except for the optically thin E and G rings, this factor is large. Usually electromagnetic forces on dust particles in Saturn's ring system are too small to produce observable effects. The current carried by dust particles moving relative to the plasma with a speed w is to a good approximation given by j = NQw. Thus, magnetic perturbations by the F ring should be much smaller than previously estimated.

Goertz, C. K.↗
NASA NTRS1987

A cyclotron-maser instability associated with a nongyrotropic distribution

A stability analysis for the cyclotron-maser instability in the presence of a nongyrotropic electron distribution is presented. The model configuration describes a uniformly magnetized cold ambient plasma that contains a relatively diffuse suprathermal electron component coherently bunched in gyrophase. The stability of perturbations propagating parallel to the ambient magnetic field is considered, and substantial growth rates are found to occur. The results are contrasted with those found for a comparable gyrotropic loss-cone distribution, and it is found that the nongyrotropic instability is characterized by substantially higher growth rates.

Freund, H. P.↗
NASA NTRS1990

Observations of flux transfer events - Are FTEs flux ropes, islands, or surface waves?

A reexamination is conducted of evidence for the suggestion that flux-transfer events (FTEs) are related to a nontime-stationary reconnection process, giving attention to the ways in which combined field and plasma variations imply that FTEs are magnetic flux ropes. Both time-varying single x-line and multiple x-line reconnection are able to disturb the surrounding plasma, generating a signature that mimics the flux rope while lacking its topology. While any localized perturbation of the magnetopause surface can produce such a signature, evidence can be adduced against a surface-wave explanation of FTEs.

Elphic, R. C.↗
NASA NTRS2000

Polar Spacecraft Based Comparisons of Intense Electric Fields and Poynting Flux Near and Within the Plasma Sheet-Tail Lobe Boundary to UVI Images: An Energy Source for the Aurora

In this paper, we present measurements from two passes of the Polar spacecraft of intense electric and magnetic field structures associated with Alfven waves at and within the outer boundary of the plasma sheet at geocentric distances of 4-6 R(sub E), near local midnight. The electric field variations have maximum values exceeding 100 mV/m and are typically polarized approximately normal to the plasma sheet boundary. The electric field structures investigated vary over timescales (in the spacecraft frame.) ranging front 1 to 30 s. They are associated with strong magnetic field fluctuations with amplitudes of 10-40 nT which lie predominantly ill the plane of the plasma sheet and are perpendicular to the local magnetic field. The Poynting flux associated with the perturbation fields measured at these altitudes is about 1-2 ergs per square centimeters per second and is directed along the average magnetic field direction toward the ionosphere. If the measured Poynting flux is mapped to ionospheric altitudes along converging magnetic field lines. the resulting energy flux ranges up to 100 ergs per centimeter squared per second. These strongly enhanced Poynting fluxes appear to occur in layers which are observed when the spacecraft is magnetically conjugate (to within a 1 degree mapping accuracy) to intense auroral structures as detected by the Polar UV Imager (UVI). The electron energy flux (averaged over a spatial resolution of 0.5 degrees) deposited in the ionosphere due to auroral electron beams as estimated from the intensity in the UVI Lyman-Birge-Hopfield-long filters is 15-30 ergs per centimeter squared per second. Thus there is evidence that these electric field structures provide sufficient Poynting flux to power the acceleration of auroral electrons (as well as the energization of upflowing ions and Joule heating of the ionosphere). During some events the phasing and ratio of the transverse electric and magnetic field variations are consistent with earthward propagation of Alfven surface waves with phase velocities of 4000-10000 kilometers per second. During other events the phase shifts between electric and magnetic fields suggest interference between upward and downward propagating Alfven waves. The E/B ratios are about an order of magnitude larger than typical values of C/SIGMA(sub p), where SIGMA(sub p), is the height integrated Pedersen conductivity. The contribution to the total energy flux at these altitudes from Poynting flux associated with Alfven waves is comparable to or larger than the contribution from the particle energy flux and 1-2 orders of magnitude larger than that estimated from the large-scale steady state convection electric field and field-aligned current system.

Wygant, J. R.↗
NASA NTRS1977

Plasma oscillations and Landau damping

The Fourier-Hermite expansion is used to follow the time development of a non-analytic initial perturbation of the linearized Vlasov-Poisson system. The calculations differ from some previous applications of the Fourier-Hermite expansion in that they relax certain symmetry conditions on the distribution functions and in that many coefficients are required to describe the initial conditions. The results confirm Weitzner's prediction of the asymptotic t to the -3rd time dependence for this problem, and exhibit the way in which this behavior develops. An appendix outlines the way in which the initial conditions are expanded in Hermite functions.

Crownfield, F. R., Jr.↗
NASA NTRS2007

The Trails of Superluminal Jet Components in 3C 111

The parsec-scale radio jet of the broad-line radio galaxy 3C 111 has been monitored since 1995 as part of the 2cm Survey and MOJAVE monitoring observations conducted with the VLBA. Here, we present results from 18 epochs of VLBA observations of 3C 111 and from 18 years of radio flux density monitoring observations conducted at the University of Michigan. A major radio flux-density outburst of 3C 111 occurred in 1996 and was followed by a particularly bright plasma ejection associated with a superluminal jet component. This major event allows us to study a variety of processes associated with outbursts of radio-loud AGN in much greater detail than possible in other cases: the primary perturbation gives rise to the formation of a forward and a backward-shock, which both evolve in characteristically different ways and allow us to draw conclusions about the workflow of jet-production events; the expansion, acceleration and recollimation of the ejected jet plasma in an environment with steep pressure and density gradients are revealed; trailing components are formed in the wake of the primary perturbation as a result of Kelvin- Helmholtz instabilities from the interaction of the jet with the external medium. The jet-medium interaction is further scrutinized by the linear-polarization signature of jet components traveling along the jet and passing a region of steep pressure/density gradients.

Kadler, M.↗
NASA NTRS1977

Thermodynamics of Thomas-Fermi screened Coulomb systems

We obtain in closed analytic form, estimates for the thermodynamic properties of classical fluids with pair potentials of Yukawa type, with special reference to dense fully ionized plasmas with Thomas-Fermi or Debye-Hueckel screening. We further generalize the hard-sphere perturbative approach used for similarly screened two-component mixtures, and demonstrate phase separation in this simple model of a liquid mixture of metallic helium and hydrogen.

Firey, B.↗
NASA NTRS1979

Ion beam probing of electrostatic fields

The determination of a cylindrically symmetric, time-independent electrostatic potential V in a magnetic field B with the same symmetry by measurements of the deflection of a primary beam of ions is analyzed and substantiated by examples. Special attention is given to the requirements on canonical angular momentum and total energy set by an arbitrary, nonmonotone V, to scaling laws obtained by normalization, and to the analogy with ionospheric sounding. The inversion procedure with the Abel analysis of an equivalent problem with a one-dimensional fictitious potential is used in a numerical experiment with application to the NASA Lewis Modified Penning Discharge. The determination of V from a study of secondary beams of ions with increased charge produced by hot plasma electrons is also analyzed, both from a general point of view and with application to the NASA Lewis SUMMA experiment. Simple formulas and geometrical constructions are given for the minimum energy necessary to reach the axis, the whole plasma, and any point in the magnetic field. The common, simplifying assumption that V is a small perturbation is critically and constructively analyzed; an iteration scheme for successively correcting the orbits and points of ionization for the electrostatic potential is suggested.

Persson, H.↗
NASA NTRS1983

Experimental modelling of satellite wakes in auroral arcs

Preliminary measurements have been made in a large laboratory discharge device configured to simulate plasma wake phenomena. A large relative electron drift impinging on a nonconducting disc gives rise to a perturbed density struture downstream, as well as a reflected beam of electrons upstream. Velocity distribution measurements were made using a novel energy analyzer with angular resolution.

Wild, N.↗
NASA NTRS1983

Plasma jet effects on the ionospheric plasma

Heavy ion beams were injected into the ionospheric plasma (experiments ARCS 1 and ARCS 2). In ARCS 1, operation of a 25eV argon ion source, mounted on a plasma diagnostic payload, produced an accelerated electron population; broadband electric field turbulence; large, spin synchronized electric field perturbations; and depletions of thermal ions. In ARCS 2, the ion source was deployed upward along the local magnetic field direction away from the diagnostic payload, and observed effects are contained within several meters of the ion source. However, enhanced wave levels near the LHR frequency are observed at distances up to 1 km, as are the injected ions themselves. A measurement of the dominant wavelength of the enhanced waves is consistent with an inference based upon the accelerated electron population seen in ARCS 1. This electron population is not evident during ARCS 2.

Moore, T. E.↗
NASA NTRS1984

Comments on the MHD stability of coronal plasmas with line-tying

Reasonable boundary conditions and test functions for photospheric line-tying are discussed, and their effects on the ideal MHD stability of coronal loops are considered. It is concluded that the plasma at the footpoints of a loop may safely be assumed to be stationary. When a simple perturbed test function is used for the energy principle, the function should be helical in form. Constraints on the test function should be discarded because they overestimate stability.

An, C.-H.↗
NASA NTRS1984

A dual-satellite study of the spatial properties of FTEs

Reconnection at the earth's dayside magnetopause may manifest itself primarily as a localized and transient process called a flux-transfer event (FTE). The spatial properties of FTEs are investigated directly by examining data from the ISEE satellite pair when the satellites were separated by more than 1000 km in the vicinity of the magnetopause. Examples of magnetosheath and boundary layer FTEs, each having a dimension normal to the magnetopause of order an earth radius, R(E), are shown, and this scale-size result is substantiated statistically for magnetosheath FTEs. When combined with other information, a 1-R(E) normal dimension implies that the voltage associated with the FTE process at one magnetopause location is at least 10 kV. These findings strengthen the view that the magnetic field comprising an FTE is twisted, this twisting appearing to be continuous in sense across the magnetopause and corresponding to a core field-aligned current of magnitude a few hundred kA. Changes in plasma flow speed and direction are found to be associated with FTEs. The transverse field and flow perturbations accompanying the three magnetosheath FTEs studied here satisfy approximately the Walen relation, the relation which describes a propagating Alfven wave.

Saunders, M. A.↗
NASA NTRS1986

On the thermal durability of solar prominences, or how to evaporate a prominence

The thermal disappearance of solar prominences under strong perturbations due to wave heating, Ohmic heating, viscous heating or conduction was investigated. Specifically, how large a thermal perturbation is needed to destroy a stable thermal equilibrium was calculated. It was found that the prominence plasma appears to be thermally very rugged. Its cold equilibrium may most likely be destroyed by either strong magnetic heating or conduction in a range of parameters which is relevant to flares.

Malherbe, J. M.↗
NASA NTRS1992

Numerical simulations of bursty radio emissions from planetary magnetospheres

One-dimensional electromagnetic particle simulations are used to investigate the characteristics of radiation from electron beams with a large temperature anisotropy, in order to identify the origin of the smooth and bursty radio emissions from Uranus and Neptune observed by the Voyager spacecraft. It is shown that these electron beams, which would typically originate from the sporadic or impulsive injections of energetic electrons, can generate electromagnetic radiation which should be able to escape into the solar wind despite the growth of the electrostatic instability. The amount of radiation with frequencies above the local x mode cutoff increases with the beam speed. It is also proposed that some of the radiation generated below the local x mode cutoff may also be able to escape the plasma and be detected remotely via mode conversion between regions where field-aligned currents produce local perturbations in the magnetic field.

Winglee, R. M.↗
NASA NTRS1999

Singular Plasma Disturbance in the Low-Latitude F Region

We describe here a new phenomenon characterized by unusual patterns of ion drifts inside ion density depletion regions observed by the AE-E satellite in the low-latitude F region. In about 30 depletions, vertical ion drift relative to the background was upward on the western sides, downward on the eastern sides, and zero near the middle where the density depletion was greatest. These drift characteristics are distinct from those observed in plasma bubble depletions. The structures reported here were observed on circular orbits below 300 km altitude and had density depletions of up to 2 orders of magnitude or more below the ambient ion density. The upward and downward drift excursions were up to 200 m/s relative to the background. Almost all these structures were observed over oceans or near coasts and largely between +/- 10 deg and +/- 30 deg clip latitude. The structures were observed mostly as isolated, single depletion regions with the majority of them about 250 km wide in the east-west direction. They occurred during quiet magnetic conditions with near-equal occurrence frequencies in the premidnight and postmidnight periods. The characteristic density and drift signatures indicate westward propagating disturbances in which the bottomside F layer is first lifted and then returned back to its original position, leaving the ionosphere undisturbed after the disturbance passes by. The estimated speed of these disturbances is of the order of 200 m/s. These unique solitary plasma disturbances, which we designate as singular plasma disturbances, are associated with a propagating source of E x B drift, not driven by neutral perturbations at the altitude of observation.

Singh, Sardul↗
NASA NTRS1972

Quantum statistical mechanics of dense partially ionized hydrogen

The theory of dense hydrogen plasmas beginning with the two component quantum grand partition function is reviewed. It is shown that ionization equilibrium and molecular dissociation equilibrium can be treated in the same manner with proper consideration of all two-body states. A quantum perturbation expansion is used to give an accurate calculation of the equation of state of the gas for any degree of dissociation and ionization. The statistical mechanical calculation of the plasma equation of state is intended for stellar interiors. The general approach is extended to the calculation of the equation of state of the outer layers of large planets.

Dewitt, H. E.↗