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NASA NTRS1986

Kinetic theory based new upwind methods for inviscid compressible flows

Two new upwind methods called the Kinetic Numerical Method (KNM) and the Kinetic Flux Vector Splitting (KFVS) method for the solution of the Euler equations have been presented. Both of these methods can be regarded as some suitable moments of an upwind scheme for the solution of the Boltzmann equation provided the distribution function is Maxwellian. This moment-method strategy leads to a unification of the Riemann approach and the pseudo-particle approach used earlier in the development of upwind methods for the Euler equations. A very important aspect of the moment-method strategy is that the new upwind methods satisfy the entropy condition because of the Boltzmann H-Theorem and suggest a possible way of extending the Total Variation Diminishing (TVD) principle within the framework of the H-Theorem. The ability of these methods in obtaining accurate wiggle-free solution is demonstrated by applying them to two test problems.

Deshpande, S. M.↗

NASA NTRS1985

Kinetic cyclotron and synchrotron maser instabilities - Radio emission processes by direct amplification of radiation

This article reviews the theory of the kinetic (cyclotron and synchroton) mase instabilities. The subject has been extensively developed in recent years by many authors, who have been incited by the research of the auroral kilometric radiation and other applications. The maser mechanism is appealing because it is simple and efficient, and can lead to direct amplification of radiation. Two types of electron distribution functions have been investigated so far. These are the loss-cone and hollow-beam disributions which may exist pervasively in many regions within and beyond the solar system. It is likely that the maser instabilities can have many potentially important applications to numerous radio emission processes observed in astrophysical research.

Wu, C. S.↗

NASA NTRS1985

Linear analysis of an axially grooved rectangular gyrotron for harmonic operation

In an axially grooved rectangular waveguide the linearized Vlasov equation is solved to find the perturbed distribution function resulting from the electromagnetic forces on the electrons. The resulting beam current and the propagating electromagnetic waves of the cold tube are used in the inhomogeneous Maxwell's equation to derive the general dispersion equation. This equation is then transformed into the electron beam frame and the resulting linear growth rate of amplification is calculated. By maximizing the linear growth rate, the operational parameters of the gyrotron are then optimized.

Ferendeci, A. M.↗

NASA NTRS1986

The role of nonclassical electron transport in the lower solar transition region

One problem in solar physics is concerned with an understanding of the observed brightness of the quiet solar atmosphere in spectral lines which are formed in the lower solar transition region. The present paper has the objective to examine the possibility that the observed line emission results from nonclassical electron transport effects which are associated with the inherently steep temperature gradients in the solar transition region. The height variation of the electron temperature is parameterized to enable correspondence with a variety of one-dimensional constant pressure transition region models. The models include empirical models, theoretical models, and the constant classical heat fluxx model used by Shoub (1983). The electron velocity distribution function is considered along with the effect on collisional excitation and ionization rates, and effects on heat transport.

Owocki, S. P.↗

NASA NTRS1986

Chaos and nonlinear dynamics of single-particle orbits in a magnetotaillike magnetic field

The properties of charged-particle motion in Hamiltonian dynamics are studied in a magnetotaillike magnetic field configuration. It is shown by numerical integration of the equation of motion that the system is generally nonintegrable and that the particle motion can be classified into three distinct types of orbits: bounded integrable orbits, unbounded stochastic orbits, and unbounded transient orbits. It is also shown that different regions of the phase space exhibit qualitatively different responses to external influences. The concept of 'differential memory' in single-particle distributions is proposed. Physical implications for the dynamical properties of the magnetotail plasmas and the possible generation of non-Maxwellian features in the distribution functions are discussed.

Chen, J.↗

NASA NTRS1986

Field-aligned electron precipitation at the edge of an arc

Measurements of field-aligned electrons at the edge of an arc are presented from a sounding rocket flight through a quiet afternoon auroral arc. High time resolution measurements show the evolution of the electron distribution function over the 2.3-km width of field-aligned precipitation. A nearly constant 1.2-eV perpendicular temperature was found for these field-aligned fluxes over a broad range of parallel energies (100 - 900 eV). The small perpendicular temperature indicates that the acceleration region is located at a low altitude. Two models of cold plasma convection into the edge of a V-shaped potential structure are examined and found to be consistent with both the observed fluxes and spatial width of the edge precipitation. Both models predict an average source plasma density less than 130/cu cm to account for the observed field-aligned fluxes and thus an acceleration region well above 1000 km.

Mcfadden, J. P.↗

NASA NTRS1985

The menagerie of geospace plasma waves

The sounding rocket and satellite observations of space plasma waves within geospace in the frequency range from millihertz to megahertz are studied. Characteristic frequencies and source mechanisms of the plasma waves are described. The use of the Dynamic Explorer-1 Plasma Wave Instrument spectrograms to represent the plasma wave antenna and receiver system of geospace is examined. The ray tracing technique calculates the path of energy flow; the equations required for the analysis are presented. Cross-correlation of the wave electric and magnetic components provide data used to calculate the wave polarization, the direction of propagation, and the wave distribution function.

Shawhan, S. D.↗

NASA NTRS1986

An information measure for class discrimination

This article describes a separability measure for class discrimination. This measure is based on the Fisher information measure for estimating the mixing proportion of two classes. The Fisher information measure not only provides a means to assess quantitatively the information content in the features for separating classes, but also gives the lower bound for the variance of any unbiased estimate of the mixing proportion based on observations of the features. Unlike most commonly used separability measures, this measure is not dependent on the form of the probability distribution of the features and does not imply a specific estimation procedure. This is important because the probability distribution function that describes the data for a given class does not have simple analytic forms, such as a Gaussian. Results of applying this measure to compare the information content provided by three Landsat-derived feature vectors for the purpose of separating small grains from other crops are presented.

Shen, S. S.↗

NASA NTRS1985

A unified n-body and statistical treatment of stellar dynamics

The methods of a new 'hybrid' computed code for stellar dynamics are summarized. All particles in the inner spatial region are followed exactly via a direct N-body code and all particles in the outer spatial region are treated statistically via a distribution function and Fokker-Planck type methods. An intermediate region, with features of both, allows exchange of particles and energy between the outer and inner regions. The code is applied to the period just before core collapse and just after and the results are summarized.

Lightman, A. P.↗

NASA NTRS1986

The effect of heavy ions on the formation and structure of cometary bow shocks

A hybrid simulation model is used to investigate the effects of heavy cometary ions on the formation and structure of a cometary bow shock. The calculations are carried out over various Mach numbers and heavy ion velocity distribution functions. The model is based on previous formulations for phenomena in the solar wind and at the earth's bow shock. The generation of the shock is described in terms of particles injected from one side of the simulation field and reflected from the other end of the field, i.e., a solid wall boundary model. This technique permits the steep buildup of the ion density near the cometary nucleus, followed by coupling of the incident and reflected ion streams to produce a shock. It is shown that at low Mach numbers (up to Mach 2) the shock is transitory and periodically formed by protons, then destroyed by heavy ions (O+). Slightly higher Mach numbers lead to a true stationary shock. An examination of coupling effects between the solar wind and the heavy ions at low Mach numbers by using the Rankine-Hugoniot relations reveals that the ions and the solar wind protons cannot be treated as a single fluid calculating the shock characteristics.

Omidi, N.↗

NASA NTRS1986

Medium-energy electrons and heavy ions in Jupiter's magnetosphere - Effects of lower hybrid wave-particle interactions

A theory of medium-energy (about keV) electrons and heavy ions in Jupiter's magnetosphere is presented. Lower hybrid waves are generated by the combined effects of a ring instability of neutral wind pickup ions and the modified two-stream instability associated with transport of cool Iogenic plasma. The quasi-linear energy diffusion coefficient for lower hybrid wave-particle interactions is evaluated, and several solutions to the diffusion equation are given. Calculations based on measured wave properties show that the noise substantially modifies the particle distribution functions. The effects are to accelerate superthermal ions and electrons to keV energies and to thermalize the pickup ions on time scales comparable to the particle residence time. The S(2+)/S(+) ratio at medium energies is a measure of the relative contribution from Iogenic thermal plasma and neutral wind ions, and this important quantity should be determined from future measurements. The theory also predicts a preferential acceleration of heavy ions with an accleration time that scales inversely with the root of the ion mass. Electrons accelerated by the process contribute to further reionization of the neutral wind by electron impact, thus providing a possible confirmation of Alfven's critical velocity effect in the Jovian magnetosphere.

Barbosa, D. D.↗

NASA NTRS1986

Upwelling O(+) ion source characteristics

The characteristics of an upwelling ion source are discussed. A typical upwelling event is analyzed using Dynamic Explorer 1 satellite retarding ion mass spectrometer (RIMS) observations of the low-energy plasma, and energetic ion and local electromagnetic field observations. The RIMS spectrograms of the O(+) ion species, radial and axial head data for O(+), and spin plan O(+) distribution functions are examined. The features of the upwelling observed include: (1) transverse ion heating to temperature of 100,000 K, (2) large outward flows of O(+), (3) enhanced flow of H(+) and He (+), (4) moderately strong field-aligned current sheets, (5) an associated intense eastward convection channel, and (6) strong wave emissions in the range near and below the proton gyrofrequency. The association between the upwelling O(+) signature and auroral current is investigated. Plasma wave and electric field environments are studied and plasma flows and densities are derived. It is noted that the mechanism for ion heating which defines the source region for these polar ion outflows is related to field-aligned currents and an associated auroral convection channel or jet.

Moore, T. E.↗

NASA NTRS1986

Kinematic evidence of satellite galaxy populations in the potential wells of first-ranked cluster galaxies

The velocities of 38 centrally positioned galaxies (r much less than 100 kpc) were measured relative to the velocity of the first-ranked galaxy in 14 rich clusters. Analysis of the velocity distribution function of this sample and of previous data shows that the population cannot be fit by a single Gaussian. An adequate fit is obtained if 60 percent of the objects lie in a Gaussian with sigma = 250 km/s and the remainder in a population with sigma = 1400 km/s. All previous data sets are individually consistent with this conclusion. This suggests that there is a bound population of galaxies in the potential well of the central galaxy in addition to the normal population of the cluster core. This is taken as supporting evidence for the galactic cannibalism model of cD galaxy formation.

Cowie, L. L.↗

NASA NTRS1986

Theory of Ostwald ripening in a two-component system

When a two-component system is cooled below the minimum temperature for its stability, it separates into two or more immiscible phases. The initial nucleation produces grains (if solid) or droplets (if liquid) of one of the phases dispersed in the other. The dynamics by which these nuclei proceed toward equilibrium is called Ostwald ripening. The dynamics of growth of the droplets depends upon the following factors: (1) The solubility of the droplet depends upon its radius and the interfacial energy between it and the surrounding (continuous) phase. There is a critical radius determined by the supersaturation in the continuous phase. Droplets with radii smaller than critical dissolve, while droplets with radii larger grow. (2) The droplets concentrate one component and reject the other. The rate at which this occurs is assumed to be determined by the interdiffusion of the two components in the continuous phase. (3) The Ostwald ripening is constrained by conservation of mass; e.g., the amount of materials in the droplet phase plus the remaining supersaturation in the continuous phase must equal the supersaturation available at the start. (4) There is a distribution of droplet sizes associated with a mean droplet radius, which grows continuously with time. This distribution function satisfies a continuity equation, which is solved asymptotically by a similarity transformation method.

Baird, J. K.↗

NASA NTRS1986

Plasma waves and continuum radiation in planetary magnetospheres

Voyager data on whistler mode waves and electron cyclotron harmonic emissions are analyzed to understand the interaction of the waves with the dynamics of the electrons. The occurrence and characteristics of Jovian whistler mode chorus and the interactions with the plasma in and near the Io torus are emphasized. Bernstein waves, especially those near the upper hybrid or plasma frequency are discussed to provide insight into an important plasma diagnostic tool and to compare the relevant portions of the electron distribution function at Earth, Jupiter, and Saturn. The nonthermal continuum radiation common to the magnetospheres of Earth, Jupiter, and Saturn is considered. Because of the very low frequency of these radio waves and their close association with upper hybrid resonance emissions, continuum radiation is often associated more closely with the plasma wave spectrum of a planetary magnetosphere than with the planet's radio spectrum.

Kurth, W. S.↗

NASA NTRS1986

Working group report on beam plasmas, electronic propulsion, and active experiments using beams

The JPL Workshop addressed a number of plasma issues that bear on advanced spaceborne technology for the years 2000 and beyond. Primary interest was on the permanently manned space station with a focus on identifying environmentally related issues requiring early clarification by spaceborne plasma experimentation. The Beams Working Group focused on environmentally related threats that platform operations could have on the conduct and integrity of spaceborne beam experiments and vice versa. Considerations were to include particle beams and plumes. For purposes of definition it was agreed that the term particle beams described a directed flow of charged or neutral particles allowing single-particle trajectories to represent the characteristics of the beam and its propagation. On the other hand, the word plume was adopted to describe a multidimensional flow (or expansion) of a plasma or neutral gas cloud. Within the framework of these definitions, experiment categories included: (1) Neutral- and charged-particle beam propagation, with considerations extending to high powers and currents. (2) Evolution and dynamics of naturally occurring and man-made plasma and neutral gas clouds. In both categories, scientific interest focused on interactions with the ambient geoplasma and the evolution of particle densities, energy distribution functions, waves, and fields.

Dawson, J. M.↗

NASA NTRS1987

Some aspects of double layer formation in a plasma constrained by a magnetic mirror

The shift from wave-generated anomalous resistivity toward the more large-scale effects of magnetic confinement of current carrying plasmas was inspired by the more extensive data on auroral particle distribution functions that were made available, data that may often seem consistent with a dissipation-free acceleration of auroral electrons over an extended altitude range. Efforts to interpret these data have brought new vigor to the concept that a smooth and static electric field can be self-consistently generated by suitable pitch angle anisotropies among the high altitude particle populations, different for electrons and ions, and that such an electric field is both necessary and sufficient to maintain the plasma in a quasi-neutral steady state. Certain aspects of this concept are reviewed and criticized, both from a general theoretical standpoint and from the standpoint of what is known about the magnetospheric environment. It is argued that this concept has flaws and that the actual physical problem is considerably more complicated, requiring a more complex electric field, possibly including double layer structures.

Lennartsson, W.↗

NASA NTRS1987

Particle simulation of plasmas on the massively parallel processor

Particle simulations, in which collective phenomena in plasmas are studied by following the self consistent motions of many discrete particles, involve several highly repetitive sets of calculations that are readily adaptable to SIMD parallel processing. A fully electromagnetic, relativistic plasma simulation for the massively parallel processor is described. The particle motions are followed in 2 1/2 dimensions on a 128 x 128 grid, with periodic boundary conditions. The two dimensional simulation space is mapped directly onto the processor network; a Fast Fourier Transform is used to solve the field equations. Particle data are stored according to an Eulerian scheme, i.e., the information associated with each particle is moved from one local memory to another as the particle moves across the spatial grid. The method is applied to the study of the nonlinear development of the whistler instability in a magnetospheric plasma model, with an anisotropic electron temperature. The wave distribution function is included as a new diagnostic to allow simulation results to be compared with satellite observations.

Gledhill, I. M. A.↗