bluuebunny/crossref_metadata_2025 huggingface dataset:
Similarity solutions for cylindrical blast waves in magnetogasdynamics
Authors: Ray G. Deb
Published: February 2004

Similarity solutions for strong cylindrical blast waves, under a constant axial current, and valid for small times, are obtained. The medium is of low constant pressure and follows an inverse power law for density.
Electron plasma waves in an unbounded uniform magnetoplasma
Authors: Stenzel R. L.
Published: February 2004

Electron plasma waves propagating perpendicular to B0 in a weakly magnetized uniform plasma are observed above the upper hybrid frequency. Dispersion and damping follow classic laws. Application to high precision plasma diagonstics is pointed out.
Ballistic second-order plasma wave echoes in a Maxwellian plasma
Authors: Ripin B. H. , Pechacek R. E.
Published: February 2004

Ballistic second-order plasma wave echoes are observed in a Maxwellian plasma. In some cases a small resonant coupling is also seen.
Test gas properties behind a decelerating shock wave in a shock tube
Authors: Light G. C.
Published: February 2004

Measurements of electron density behind a shock wave in air are presented. Operating conditions are such that shock-wave deceleration, boundary-layer mass loss, and chemical nonequilibrium are important in the determination of the development of the electron density behind the shock wave. A one-dimensional unsteady analysis is described. Calculated electron density is compared with experimental values. Agreement is within a factor of 2. The difference is probably attributable to expansion waves embedded in the test gas.
Axial distribution for a hot electron plasma
Authors: Haste G. R. , Lazar N. H.
Published: February 2004

Bremsstrahlung measurements have been used to determine the axial distribution of density and temperature in an electron cyclotron heating experiment. The results show two heating mechanisms. Low energy electrons turn at the resonance position and are resonantly heated. High energy electrons turn well inside their resonance position and are nonresonantly heated.
Dynamic stabilization of plasmas by means of a high-frequency-modulated electron beam
Authors: Aghevli R. , Rowe J. E.
Published: February 2004

The stabilizing effects that a beam of longitudinally nonuniform density imposes on beam-plasma instabilities are investigated using a hydrodynamic model adapted for an infinite, one-dimensional beam-plasma system. The electron beam is characterized by either of two types of longitudinal inhomogeneity—square-wave or sinusoidal. The results, for the square-wave type of inhomogeneity, indicate a disappearance of the convective instabilities below a threshold frequency as well as a reduction in the growth rate for the remainder of the spectrum. Similar results are obtained for the case of a high-frequency sinusoidal pulsation of the beam density. Effects resulting from finite temperature plasma electrons are also discussed.
Feedback stabilization of an ion-acoustic instability
Authors: Boswell R. W. , Christiansen P. J.
Published: February 2004

A remote feedback technique has been employed to stabilize an ion-acoustic type of instability in a plasma with a low frequency density modulation. The plasma is unstable for certain values of n and dn/dr which occur during part of the period of the low frequency modulation. Agreement with the Van der Pol approach is good when the instability is allowed to saturate and the cross field diffusion is shown to decrease when the plasma is stabilized.
Thermal creep of rarefied gas in a circular tube
Authors: Kanki Tatsuo , Iuchi Satoru
Published: February 2004

A numerical solution of the Boltzmann-Krook equation for the thermal creep of a rarefied gas in a circular tube is compared with Knudsen's transpiration formula, Maxwell's equation, and the model of Bosanquet.
Source flows in magnetohydrodynamics
Authors: Yu C. P. , Doe A. L.
Published: February 2004

An analysis is presented for the magnetohydrodynamic flow due to a constant mass source expanding into a uniform magnetic field. The shape of the free surface is calculated as a function of time.
Observations of two-stream ion wave instability
Authors: Christoffersen G. B. , Prahm L. P.
Published: February 2004

A double-humped ion velocity distribution function is produced in a Q-machine cesium plasma. When the plasma becomes unstable, a growing wave amplitude and a characteristic change in the phase velocity of a grid-excited ion-acoustic wave are observed.
Ion-ion instability induced by ac electric fields
Authors: Papadopoulos Konstantinos , McBride John B.
Published: February 2004

The presence of flow frequency fields in a plasma substantially modifies the marginal stability condition for a counterstreaming ion-ion instability and allows the system to be unstable even if the electron thermal energy is much smaller than the relative ion streaming energy.
Early-time model of laser plasma expansion
Authors: Book D. L. , Clark R. W.
Published: February 2004

A realistic density profile is used to model the spherical expansion of a plasma into a stationary magnetized plasma. Magnetic compression develops where streaming and ambient densities are comparable. Peak magnetic intensities are typically much lower than predicted by Longmire's model.
Probability distributions and correlations in a turbulent boundary layer
Authors: Frenkiel François N. , Klebanoff Philip S.
Published: February 2004

One-dimensional and joint probability density distributions for longitudinal components of turbulent velocities as well as higher-order correlations are measured in a turbulent boundary layer on a flat plate using hot-wire anemometry and high-speed computing methods. The effect of the nonlinear response of the hot-wire is taken into account. Data pertaining to the general nature of the turbulent boundary layer are presented and comparison is made between the measured correlations and those corresponding to a Gaussian probability distribution of turbulent velocities as well as to non-Gaussian distributions of the Gram-Charlier type. Similar comparisons are made of the measured one-dimensional and joint probability distributions. Probability distributions in the boundary layer are also compared to those measured downstream of a grid. The closure of the tails of the probability distribution and its effect on the accuracy of the measurements of higher-order moments is considered.
Two-point correlation model and the redistribution of Reynolds stresses
Authors: Naot D. , Shavit A. , Wolfshtein M.
Published: February 2004

A quasi-isotropic locally homogeneous model for the two-point double-velocity correlation tensor is developed by the application of a plausible set of symmetry restrictions to this tensor. The two-point correlation is related to the single-point correlation by three independent functions, and reduces to the nonisotropic single-point correlation and the isotropic two-point correlation in the limiting cases. It is shown that the model implies that by the use of three independent microscales (and macroscales) it is possible to describe a matrix of 27 elements of microscales (and macroscales) which describe the nonisotropic field. The model is also used to calculate the dissipation rate of the components of the Reynolds stresses. Finally, a formula which expresses the redistribution of the velocity fluctuations due to pressure fluctuations is developed.
Velocity profiles in steady and unsteady rotating flows for a finite cylndrical geometry. II.
Authors: Jerskey T. , Penner S. S.
Published: February 2004

Measurements have been performed with a laser-Doppler velocimeter of the radial dependence of azimuthal velocity components, using liquid H2O, in cylindrical containers with aspect ratios A (i.e., the ratio of height l to radius b) ranging from 0.212 to 1.64. The reciprocal Ekman number ranged from 980 to 60 000. The radius was fixed at 5.25 cm. The rotating disk was located at the top. Our data are in fair agreement with numerical results of Tomlan and Hudson. Oscillations, observed during steady flow, are inertial waves with frequencies and amplitudes depending on aspect ratio and disk angular velocity. Spin-down parameters fit a theoretical solution given previously. Observed oscillations during spin-down have been accounted for through a heuristic argument involving convection of boundary-layer fluid downward along the axis near the just-stopped disk.
Structure of thixotropic suspensions in shear flow: I. Mechanical properties
Authors: Weymann H. D. , Chuang M. C. , Ross R. A.
Published: February 2004

A theory for the steady state viscosity η of thixotropic clay-water suspensions is given. The numerical results of this analysis can be approximated by u + u2/10 = K/γ̇ where u = (ηr − 1)/C, γ̇ is the shear rate, η∞ is the viscosity for γ̇ → ∞, ηr =η/η∞, and K and C are parameters depending on concentration and temperature. For large shear rates this expression reduces to the Bingham behavior ηr = 1 + τ0/η∞γ̇, where τ0 is the Bingham yield stress. Experiments on a Wyoming bentonite at various concentrations and temperatures give good agreement with the theoretically predicted behavior. The comparison of experimental and analytical results yields the cohesive force per particle and the ratio of the major and minor dimensions of the bentonite particles.
Nonlinear radial wave propagation in low density expanding flows with application to the free jet
Authors: Grundy R. E.
Published: February 2004

The nonlinear wave propagation in a high Mach number, low-density region of a spherically symmetric expanding gas flow is considered. It is well known that classical inviscid gas dynamics is inadequate in describing such flow regimes and consequently the investigation is initiated with Boltzmann's equation. The asymptotic theory describing such a flow has the effect of truncating any order moment equation. This and other simplifications inherent in the approach enable the time dependent moment equations to be integrated and the solutions used in the study of boundary and initial value problems. The theory is applied to the study of a pulse propagating along the centerline of a steady axially symmetric free jet exhausting into vacuum.
Stationary shocks and toroidal diffusion
Authors: Greene J. M. , Winsor N. K.
Published: February 2004

For a resistive plasma of stellarator or low-temperature tokamak type, the quasistationary equilibrium is rotating at the reduced sound speed Bθνth/Bz, and has a slow (acoustic branch) shock fixed in space. Dissipation in the shock can increase plasma loss by an order of magnitude over the Pfirsch-Schlüter rate. For a very weak shock, the loss rate scales with the resistivity as η4/3; for a stronger (but still weak) shock, it scales as η3/2 . On the diffusion time scale, flow along the lines of force must develop.
Ion-acoustic instability in the positive column of a helium discharge
Authors: Fenneman D. B. , Raether M. , Yamada M.
Published: February 2004

The ion-acoustic instability of the helium positive column in the pressure regime 0.05 to 0.25 Torr is studied. Instability of the column is predicted by a kinetic theory which includes the effects of collisions with neutrals, but not by a hydrodynamic theory. In the regime of the experiment the ion-acoustic instability arises from the resonant interaction of those electrons having velocities close to the phase velocities of the ion-acoustic waves (inverse Landau damping) even though the electron-neutral collision frequency exceeds the ion-acoustic frequency. The helium positive column is well suited to the study of this instability mechanism because the important velocity hierarchy ion thermal velocity ≪ ion-acoustic phase velocity ≪ electron drift velocity ≪ electron thermal velocity is naturally well established. The detection of the spontaneously excited waves is found to be crucially dependent on the bias of the detecting probe. The onset characteristics, spectral properties, spatial distribution, and saturation intensity are measured and compared with theoretical predictions.
Energy recovery from energetic plasma streams by traveling waves
Authors: Mirkin M. I. , Briggs R. J.
Published: February 2004

An adiabatic theory of the energy exchange between magnetically confined charged particles and a traveling electrostatic wave with slowly varying phase speed and amplitude is presented. The results are applied to a basic assessment of the usefulness of traveling-wave techniques for efficient energy recovery from energetic plasma streams. Severe constraints on the energy conversion efficiency attainable by this approach are indicated by the model.
Simple universal equilibrium spectrum
Authors: Millsaps Knox
Published: February 2004

A closed form solution of the von Kármán integral equation that describes the turbulent cascade is presented for a universal equilibrium spectrum under the specific assumption that the energy transfer from the macro to the micro components is due to the same mechanical process.
Anomalous impedance of a plasma column
Authors: Storer R. G.
Published: February 2004

Anomalous values of the impedance of a cylindrical plasma column at radio frequencies are illustrated by an exact solution of Maxwell's and Boltzmann's equations. It is shown that resonances occur at frequencies differing from those expected from an analysis of a plane plasma slab.
Energy deposition of a fast deuteron in a hot deuterium plasma
Authors: Evans Foster
Published: February 2004

The spatial and temporal distribution of the energy deposited by a fast deuteron in a hot deuterium plasma is calculated taking into account energy loss to thermal ions by scattering that results from elastic nuclear processes in addition to the usual Coulomb interaction with thermal electrons and ions. The method of calculation and the approximations involved are discussed, and numerical results are given for a deuterium plasma at normal liquid density. For plasma electron temperatures above approximately 10 keV, the effect of including nuclear processes in d -d scattering is to cause the energy of a fast deuteron to be deposited nearer to its point of origin in space and time with relatively more energy going directly to ions.
Tearing mode in the cylindrical tokamak
Authors: Furth H. P. , Rutherford P. H. , Selberg H.
Published: February 2004

Detailed computational results are presented on the stability and radial distribution of linear tearing modes in cylindrical tokamaks of various radial profiles. In the case of a skin-current profile, a “double tearing mode”, with two points of discontinuity in the radial magnetic field perturbation is found. An analytical method is also derived for comparison of the stability of different radial profiles. It is further shown that the tearing mode can be driven by finite electron viscosity, as well as by the usual finite resistivity mechanism.
Quenching of the beam-plasma instability by mode mixing at a density discontinuity
Authors: Böhmer H. , Jackson E. A. , Raether M.
Published: February 2004

Experiments on the spatial instability of a beam-plasma system led to the observation that the instability is quenched when irradiated by high power microwaves. It is conjectured that this effect is due to a local decrease in plasma density in the irradiated region. A theoretical model is detailed that explains the salient features of the observed effect. Auxiliary measurements on a system with a controlled density gradient are presented that give strong support for the proposed mechanism.
Effect of a surrounding gas on magnetohydrodynamic instabilities in Z pinch
Authors: Manheimer Wallace M. , Lampe Martin , Boris Jay P.
Published: February 2004

The effect of an ionized or un-ionized background on magnetohydrodynamic instabilities in a Z pinch is considered. It is shown that the growth rate may be reduced by at least one or two orders of magnitude even though the background pressure is small compared with the pinch pressure. The stabilizing effect of launching shocks in the background gas is considered qualitatively. It is shown that it is theoretically possible to construct equilibria such that confinement for a Lawson time can be attained, but only for backgrounds of roughly liquid density. Also, it is shown that lightning discharges are stabilized by the presence of the background atmosphere.
Effect of Krook model collisions on the two-stream instability
Authors: Gula W. P. , Chu C. K.
Published: February 2004

The effects of Krook model collisions on the electron-electron two-stream instability were investigated by means of a computer code. It was found that a collision frequency small in comparison with the electron plasma frequency delays the onset of saturation of the instability, decreases the total electrostatic field energy at saturation, and lowers the linear growth rates. This last effect is in very good agreement with the growth rates predicted by the linear theory of the Krook equation.
Application of cylindrical Langmuir probes to streaming plasma diagnostics
Authors: Segall Stephen B. , Koopman David W.
Published: February 2004

The current-voltage characteristics of cylindrical probes in a high velocity collisionless plasma flow have been investigated experimentally and theoretically. The plasma was generated by a focused laser pulse incident on a metallic target in vacuum, with an expansion velocity U, such that kTi/Mi ≪ U2 < kTe/me. An analysis, developed from a stationary plasma analog to the flowing case, demonstrated a failure of plasma shielding of probe potential in the electron attracting region, even when λD = (kTe/4πnee2) 1/2 ≪ R, the probe radius. Under these conditions, modifications of relatively simple previous treatments were found to be valid for computing electron current to a probe. The electron characteristics derived from the present analysis agree well with experimental results for a voltage range of typically − 5 kTe /e < V < + 3kTe/e around plasma potential. The ion and electron portions of the characteristics are consistent with each other and with independent diagnostic measurements.
Effect of magnetic field errors on confinement in bumpy tori
Authors: Sprott J. C.
Published: February 2004

Numerical calculations of field line trajectories and drift orbits show that small field perturbations can destroy the single particle confinement in bumpy tori. Criteria are derived for tolerable field errors assuming neoclassical diffusion.
Measurement of nonresonant absorption in a fully ionized plasma
Authors: Weisbach Michael F. , Ahlstrom Harlow G.
Published: February 2004

Measurements have been made of the absorption of CO2 laser light at 10.6 μm by a fully ionized argon plasma. These values are compared with the theoretical values which are calculated from the measured electron densities and temperatures in the plasma.
Power absorption in a nonuniform collisionless magnetoplasma
Authors: Brownell J.
Published: February 2004

It is shown that a nonuniform collisionless magnetoplasma may absorb power from an external source through the excitation of a large number of radially varying electrostatic modes. If a randomizing mechanism is present, irreversible plasma heating can take place.
Potential flow past a sphere tangent to a plane
Authors: Latta G. E. , Hess G. B.
Published: February 2004

Uniform potential flow past two equal spheres in contact, parallel to the common tangent plane, is analyzed. The velocity is found to diverge approaching the point of contact as r −2+√2. Application of this result to critical velocity phenomena in superfluid helium is discussed.
Turbulence description of Couette flow
Authors: Chung Paul M.
Published: February 2004

The simplified statistical theory developed earlier is extended to the wall shear flows. This is accomplished by formulating the contribution of the smaller eddies to the observable properties, which becomes significant very close to the wall, from an available stochastic analysis of the Navier-Stokes equation. Turbulent Couette flow is then analyzed by the use of the theory. Comparison of the Couette flow solutions obtained with the available experimental results shows that the present theory satisfactorily describes the rather detailed turbulence structure of the flow field as well as the mean velocity profile and the surface shear.
Knudsen effects in a Scott effect experiment
Authors: Wells C. W. , Wood L. T. , Hildebrandt A. F.
Published: February 2004

A thermal torque sometimes observed in Scott effect measurements has been studied experimentally and an explanation for the thermal torque proposed. The magnitude of the thermal torque can be comparable to the Scott torque depending on geometrical and thermal anisotropies. The thermal torque is predicted to decrease with application of an axial magnetic field.
Reflection of a shock wave from a thermally accommodating wall: Molecular simulation
Authors: Deiwert George S.
Published: February 2004

Reflection of a plane shock wave from a wall has been simulated on a microscopic scale using a direct simulation Monte Carlo technique of the type developed by Bird. A monatomic gas model representing argon was used to describe the fluid medium and a simple one-parameter accommodation coefficient model was used to describe the gas-surface interaction. The influence of surface accommodation was studied parametrically by varying the accomodation coefficient from zero to one. Results are presented showing the temporal variations of flow field density, and mass, momentum, and energy fluxes to the wall during the shock wave reflection process. The energy flux was used to determine the wall temperature history. Comparisons with experiment are found to be satisfactory where data are available.
Radial particle loss in a highly ionized cylindrical plasma column
Authors: Chung K. , Huang K. C. , Levi E.
Published: February 2004

The statistical properties of the plasma fluctuations in a long plasma column produced by a hollow cathode arc discharge show that different states of weak plasma turbulence exist. The transition between these states occurs as a result of changes in the confining magnetic field, the background gas pressure, and the boundary conditions. Associated with such transitions are radical changes in the plasma confinement. A sudden jump in the radial particle loss rates is manifested by the increase of the current collected by Buchelnikova ring-collectors and by the change in the radial density profiles measured by electrostatic probes.
Decay of poloidal rotation in a tokamak plasma
Authors: Stix Thomas H.
Published: February 2004

Radial electric fields may be built up in a tokamak by several mechanisms such as nonambipolar particle transport or loss, or the inhomogeneous deposition of electric charge which occurs as a result of the injection of fast neutral atoms. The initial effect of the radial fields is to produce a poloidal rotation of the plasma. Such rotation, however, subjects the moving elements of the plasma to energy dissipation by magnetic pumping, which damps the rotation in a period of the order of the ion-ion collision time. The problem is analyzed for the “plateau” and “banana” regimes by applying the drift kinetic equation, with a simple relaxation collision term, to a slab-model low-β plasma. The calculation may be more generally applied to the problem of momentum dissipation for any low-β long-mean-free-path plasma in a periodic or stochastic magnetic field.
Effect of the plasma density profile on ion-cyclotron wave generation
Authors: Hosea J. C. , Sinclair R. M.
Published: February 2004

It is shown that the loading of a Stix coil by ion-cyclotron wave production in plasma, which exhibits a second maximum previously reported to be anomalous, can be explained in detail by taking into account the plasma density profile. Data from a number of experiments show that the efficiency for heating the plasma by wave absorption is a monotonically increasing function of density. The reduced heating efficiency observed at the second loading maximum relative to the first can be attributed to damping of the waves responsible for the second maximum in the lower density surface region of the plasma column.
Steady-state solutions for relativistically strong electromagnetic waves in plasmas
Authors: Max Claire Ellen
Published: February 2004

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. However, nonlinear effects can greatly increase the maximum plasma density at which a relativistically strong wave can propagate. Applications to laser-plasma interactions and to pulsar environments are discussed.
Experimental observations of the thermal expansion of a plasma
Authors: Goldenbaum G. C. , Gerber K. A.
Published: February 2004

A dense argon plasma (n e = 4 × 1018cm − 3, KT = 4 eV) is created and allowed to expand either into a vacuum or into a low density, partially ionized plasma. Expansion into a vacuum is shown to be dominated by electric-field effects which accelerate ions to much higher energies (E ≲ 180 eV) than the original thermal energy. Expansion into a low density (n e = 1 × 1013cm − 3) 10% ionized plasma of the same species was dominated by resonant charge exchange giving the appearance of momentum transfer. Expansion into a hydrogen plasma shows essentially complete momentum transfer as in a blast wave. Expansion of a hydrogen plasma into an ambient argon plasma shows spatially separated regions in which the hydrogen appears to collisionally snowplow the argon plasma.
Simple models of solid and hollow relativistic electron beams with arbitrarily high current
Authors: Lawson J. D.
Published: February 2004

A model of a neutralized electron beam in which the electrons make helical orbits about the axis is described. This differs from previous models in that there is no longitudinal field or azimuthal current. Three particular cases, corresponding to (1) uniform charge density in a solid beam, (2) uniform current density in a solid beam, and (3) uniform charge density in a hollow beam are analyzed. In none of these configurations is there a current limit, and all the electrons move in the forward direction.
Wave packet formulation of nonlinear plasma wave kinetics
Authors: Nishikawa Kyoji , Fried Burton D.
Published: February 2004

A theory of nonlinear plasma wave propagation is presented which contains, as particular cases, both the nonlinear Schrödinger equation for coherent waves and the kinetic wave equation for weak plasma turbulence. Fluctuations are represented as a superposition of “micro” wave packets, with finite spread but negligible overlap in wavenumber and frequency. For the case of coherent wave propagation a nonlinear Schrödinger equation is derived, generalized over precious versions in that linear Landau damping nonlinear frequency shift, nonlinear damping, and three-dimensional effects are all included, as well as the non-local, non-Markovian interaction characteristic of this equation. In the case of weak plasma turbulence, the kinetic wave equation is generalized to include self-interaction of the micro packets, which, just as in the coherent case, results in non-local, non-Markovian terms, not heretofore considered in weak turbulence formulations.
Wave-wave coupling in nonresonant unstable systems
Authors: Jackson E. Atlee , Raether M.
Published: February 2004

The expansion of the dielectric function, employed in deriving the equations for wave-wave coupling, often diverges if the wave-particle interactions are nonresonant. This difficulty can be avoided by expanding about the complex eigenmodes of the linear system. This is illustrated for a cold beam-plasma system.
Self-diffusion coefficient of neon
Authors: Weissman Stanley
Published: February 2004

The self-diffusion coefficient of neon has been measured from 77° to 1400°K. The experimental values of the self-diffusion coefficients are mutually consistent with experimental data for the viscosity and thermal conductivity of pure neon. The self-diffusion data have been used to estimate values of the isotope thermal diffusion factor for neon and these estimated values are generally consistent with recent direct measurements of the thermal diffusion factor.
Theory for momentum transfer to a surface with a high-power laser
Authors: Pirri Anthony N.
Published: February 2004

A model is developed for the momentum transferred to a solid from a laser-supported gaseous detonation wave initiated in air above the surface. One-dimensional gasdynamic analysis is used for the detonation wave moving away from the surface and cylindrical blast-wave theory is employed to partially account for two dimensional effects. Momentum transfer coupling coefficients (impulse/laser energy) are calculated which are functions of the laser energy flux, pulse duration, and the beam and target surface areas. Results are compared with recent experimental data obtained using a high-power CO2 laser.
Wave-wave contribution to the high-frequency resistivity of nonequilibrium plasma
Authors: Hirshfield J. L.
Published: February 2004

A theory is given for that part of the high-frequency plasma resistivity attributable to the pairwise excitation of electrostatic waves. A class of nonequilibrium states is considered with arbitrary values of the electron-to-ion temperature ratio, and of the relative electron-to-ion drift speed (short of instability). Numerical results are presented and compared with earlier work, where various approximations had been used to account for ion dynamics.
Relativistic electron beam neutralization in a dense magnetized plasma
Authors: Chu K. R. , Rostoker N.
Published: February 2004

For the case of a longitudinal magnetic guide field this problem has been treated neglecting ion dynamics [R. Lee and R. N. Sudan, Phys. Fluids 14, 1213 (1971)]. Under the assumptions Ωe ≫ ωpe,Ωi ≫ ωpi, where ωp, Ω are plasma and gyrofrequencies, there is no neutralization because both electrons and ions are tied to field lines. When Ωe ≫ ωpe and Ωi < ωpi, it is essential to consider ion dynamics since the ions play the dominant role in neutralization. In the final state, the beam is essentially neutralized both electrically and magnetically and the energy associated with plasma oscillations is a small fraction of the beam energy except when the radius of the beam is small compared with the plasma skin depth.
Parametric instability of a relativistically strong electromagnetic wave
Authors: Max Claire Ellen
Published: February 2004

The stability of a circularly polarized electromagnetic wave that is strong enough to make plasma electrons, but not ions, relativistic is studied. Small perturbations are considered which propagate parallel to the large-amplitude driver. A relativistically strong wave can be unstable on time scales as short as twice its own oscillation period, and decays into a forward-going plasma oscillation and either one or two electromagnetic waves. Ion motion introduces an additional instability which can be important at short perturbation wavelengths, where the driver would otherwise be stable. The unstable ion and electron modes both have potential for producing anomalously large acceleration of relativistic particles, as well as significant amounts of backscattered light. These effects may be important in two applications: (1) the use of intense lasers to heat or compress plasma, and (2) the plasma surrounding a pulsar, if the pulsar is losing energy by radiation of electromagnetic waves at its rotation frequency. Instability persists in the nonrelativistic regime, reducing to stimulated Raman scattering as a special case.
Structure in the nonlinear saturation spectrum of parametric instabilities
Authors: Fejer J. A. , Kuo Yu-Yun
Published: February 2004

The nonlinear saturation spectrum of the decay instability is obtained in the limit of small spontaneous emission, for comparable ion and electron temperatures, from numerical solutions of a kinetic equation based on an accurate expression for the nonlinearity. The spectral energy occupies several pairs of isolated saucer-shaped regions in wave-vector space. The regions increase in thickness, angular diameter, and number as the pump power is increased. The theory thus predicts the generation of waves propagating in directions which can differ substantially from the direction of the pump field. Ionospheric observations confirm this prediction; they were difficult to reconcile with the predictions of previous theories based on an approximate expression for the nonlinearity. The present work also corrects the results of previous one-dimensional theories that used an accurate expression for the nonlinearity and predicted “spectral lines” in the limit of vanishing spontaneous emission. Excitation of the purely growing instability is predicted for pump powers greater than about 2.5 times the threshold of the decay instability.
Nonlinear theory and angular spectrum of the ion-acoustic instability
Authors: Sleeper Arthur M. , Weinstock Jerome , Bezzerides B.
Published: February 2004

A nonlinear theory of the current-driven ion-acoustic instability is presented. The saturation mechanism is the perturbation of the ion orbits by the turbulent waves, which results in a broadening of the resonant interaction between the ions and the waves. The angular spectrum and rms field fluctuation energy are calculated and compared both with experiment and two-dimensional computer simulations. An approximate expression for the angular spectrum, obtained in three dimensions, predicts a broad angular spectrum as well as a fluctuation level which is in order of magnitude agreement with two recent experiments. More complete numerical results in two dimensions also predict a broad angular spectrum in agreement with the two-dimensional simulations, and a fluctuation level in very good numerical agreement with the simulations.
Study of the propagation of ion acoustic waves in a weakly ionized plasma
Authors: Cussenot J. R. , Fabry M.
Published: February 2004

This study of ion acoustic waves in a low density plasma is based on a theoretical model which takes into consideration ion collisions and ion drift velocity.
Nonlinear saturation of the relativistic beam-plasma instability in the presence of ion density fluctuations
Authors: Toepfer A. J. , Poukey J. W.
Published: February 2004

The effect of finite ion density fluctuations driven by return current instabilities on the nonlinear saturation level of the relativistic beam-plasma instability is calculated for cases of experimental interest. The effect of initial plasma temperature is also discussed.
Heating of underdense plasmas by intense lasers
Authors: Kruer W. L.
Published: February 2004

It is shown that intense lasers with frequencies (ω0) much greater than the electron plasma frequency (ωp e) will drive instabilities even in the electrostatic limit.
Electric field correlations in the guiding-center plasma
Authors: Joyce Glenn , Montgomery David , Emery Mark
Published: February 2004

Electric field autocorrelations for the two-dimensional electrostatic guiding-center plasma are calculated numerically. It is concluded that the autocorrelation, averaged over a thermal equilibrium ensemble, is damped in an approximately exponential fashion, as predicted by Taylor and McNamara. Oscillatory behavior of the type predicted by Taylor and Thompson is not observed.
Transient flow and heating in a pinched plasma column
Authors: York Thomas M. , Stover Elmer K.
Published: February 2004

The axial flow and heating of an argon plasma in a pinched plasma column of a pulsed, linear z-pinch device was experimentally examined with a unique pressure sensing instrument capable of resolving mass flow properties. Transient (∼ 5 μsec) axial pressure profiles identify periods of intense flow (4 × 104m/sec) and heating (Ti ∼ 70 eV); mechanisms generating such effects are considered.
Experimental verification of collisionless electron cyclotron damping
Authors: McVey B. D. , Scharer J. E.
Published: February 2004

Measurements of collisionless spatial cyclotron damping rates and finite minimum wavelengths near resonance (0.7 ≤ ω/ωc ≤ 1.0) are presented for a right-hand circularly polarized wave propagating in a magnetic beach. The magnetic beach is sufficiently weak so that a WKB approximation for the spatial variation of the wave electric field is valid. It is shown that the plasma and waves satisfy conditions for which the collisionless damping process is dominant. A technique is presented which uses the wave data to determine the plasma density and temperature by means of the theoretical hot plasma spatial dispersion relation for the whistler mode. The resulting plasma parameters agree consistently for both the measured wave numbers and damping rates as well as with those obtained from Langmuir probe data.
Excitation of electrostatic modes by mode conversion-numerical method
Authors: Tang Ting-wei , Mani Siva A.
Published: February 2004

The study of mode conversion between the extraordinary mode and the Bernstein mode in a warm inhomogeneous collisionless magnetoplasma is carried out numerically by solving for the Fourier transformed electric fields, using a recently developed integral formulation. Reflection and transmission coefficients for the incident extraordinary wave are obtained as functions of the peak number density for an inverseparabolic electron density profile. In addition to previously reported resonances occurring at the total reflection, antiresonances are also found. The spatial dependence of the electric fields at these resonances is presented.
Current-driven modes in two-dimensional plasma configurations
Authors: Coppi Bruno , Rem Jan
Published: February 2004

A search for current driven modes in two-dimensional (toroidal) plasma configurations is made for regimes where the effective collision frequency of trapped electrons is smaller than their average bounce frequency and the drift velocity of the circulating electron is smaller than the thermal velocity. If the current carrying part of the circulating electron distribution function is represented by a Spitzer-Härm type of model, no significant growth rates of possible current driven modes can be found whether their wavelengths along the magnetic field are long or short in comparison with the field connection length. One reason for this is that in a realistic toroidal configuration, there are very few electrons with longitudinal velocities much smaller than the electron thermal velocity, which are not trapped and carry current. The only significant current driven instability found depends on the assumption that collisions or, possibly, the effects of higher-frequency fluctuations, may induce a sufficiently finite longitudinal thermal conductivity of the circulating electrons.
Ion-acoustic disturbances stimulated by truncated source distributions
Authors: Jacob J. H. , Hirshfield J. L.
Published: February 2004

Plasma disturbances resulting from a modulated non-Maxwellian ion distribution emanating into a half-space plasma are discussed. The non-Maxwellian ion distribution is formed experimentally by truncating the distribution entering an energy analyzer situated at one end of a plasma column. The lower energy ions are modulated and reflected back into the plasma. When all the ions are absorbed by the analyzer, no propagating ion disturbance is observed. On reflecting some low energy ions, an ion-acoustic wave is detected. The wave amplitude initially increases when a larger segment of the ion distribution is reflected. However, when ions with velocities comparable to the phase velocity of the wave are reflected, the wave amplitude decreases. The signal velocity of the wave is also observed to increase as a greater number of ions are reflected. A modified fluid analysis to explain the observations is presented. In the analysis care is taken to include correct nonsymmetric velocity-space source functions derived from a ballistic model.
Formation of ion-acoustic shocks
Authors: White Roscoe B. , Fried Burton D. , Coroniti Ferdinand V.
Published: February 2004

The formation of an ion-acoustic shock in a numerically modeled two chamber double plasma device is investigated for a plasma of cold ions and isothermal Boltzmann electrons. An initial potential ramp applied to the driver chamber launches an ion-acoustic pulse into the target chamber which steepens into a shock. The quasisteady shock structure agrees with observed double plasma shocks. An upper limit of Mach 1.6 is observed independent of the potential ramp magnitude, in agreement with theory.
Some magnetohydrodynamic free boundary equilibria
Authors: Stevens D. C.
Published: February 2004

An iterative computational method of solving certain axially symmetric free boundary problems is presented. At each step of the iteration, the boundary is displaced closer to the equilibrium position by an amount proportional to the unbalanced force acting on the boundary. The method is used to find the behavior of a tokamak plasma in adiabatic compression under a uniform vertical field. Also, the Princeton adiabatic toroidal compressor is simulated and a comparison of the results is given.
Stability of the developing laminar pipe flow
Authors: Huang L. M. , Chen T. S.
Published: February 2004

Linear stability due to axisymmetric disturbances is studied for developing laminar flow in the entrance region of a circular tube. The present study provides much more accurate and reliable neutral stability results than those reported by Tatsumi.
van Hove self-correlation functions in a Maxwell gas
Authors: Deutsch Owen L. , Yip Sidney
Published: February 2004

The eigenvalues of the test-particle collision operator for Maxwell molecules are calculated. The results are used to analyze the spectral distribution of the van Hove self-correlation function.
Gaseous diffusion coefficients for Ar-Ne
Authors: Weissman Stanley
Published: February 2004

Diffusion coefficients for Ar-Ne have been measured from 296 to 1363 °K. The data agree with other measurements and values derived from other properties. The data also agree with a corresponding-states treatment but not with a correlation relation at high temperatures.
Virtual exciter of ion-acoustic waves in an external magnetic field
Authors: Alexeff I. , Hirose A.
Published: February 2004

When a pulse disturbance is applied to a wire in a magnetized plasma, a receiving probe exhibits two ion-acoustic disturbances, one depends only on d⊥, the cross-field distance, and the other on the actual distance, (d‖2 + d⊥2)1/2, between the exciter and the receiver.
Linear threshold of the Buneman-Farley instability
Authors: Abhyankar V.G. , Simon A.
Published: February 2004

The wavelength (k) dependence of the threshold drift velocity (ν) for onset of the Buneman-Farley instability is determined. Inclusion of small terms omitted previously yields a finite k for minimum ν, rather than k = 0 or k = ∞ as in two earlier studies.
Sideband instability in the water bag approximation
Authors: Bloomberg H. W.
Published: February 2004

A self-consistent water bag distribution of trapped particles is used to numerically study the sideband instability of finite amplitude plasma waves. Equilibria including high and low concentrations of particles at the bottom of the wave troughs are considered.
Electrohydrodynamic oscillation and stability of a charged drop
Authors: Saville D. A.
Published: February 2004

Small amplitude oscillations of a charged fluid globule immersed in a viscous dielectric are studied with special regard for the processes of surface charge relaxation and convection. Perfect dielectrics and conductors behave in identical fashion insofar as oscillation frequencies and stability are concerned whenever viscous effects are small. This similarity is due to interfacial charge convection, in the case of a perfect dielectric, and charge conduction, with a perfect conductor. The damping of stable oscillations depends, however, on the rate of interfacial charge relaxation: With instantaneous relaxation the damping rates are the same as those found with uncharged droplets, while with slower relaxation rates the dissipation is concentrated in an electrohydrodynamic boundary layer outside the drop. If viscous effects predominate then the existence of charge relaxation introduces oscillatory behavior in place of the aperiodic damping characteristic of uncharged drops. Several special circumstances are examined in detail.
Dynamic interactions of monomolecular films with imposed electric fields
Authors: Zelazo R. E. , Melcher J. R.
Published: February 2004

The electric surface force density caused by imposed electric fields and their concomitant surface charges is the basis for studying monomolecular films on liquid interfaces. The film is modeled as a compressible viscous two-dimensional fluid characterized by an elasticity ℰ, a surface dilatational viscosity, a surface shear viscosity, surface diffusion, and chemical equilibrium with film molecules diffusing through a liquid substrate. In the first of three configurations considered, the static rise in film surface pressure is experimentally shown to equal the integrated static shear stress. Steady “second-order” film circulations and film rupture under high electric stress, are discussed. In the second configuration, temporally and spatially periodic electric stresses are used to study the dilatational film dynamics in an “imposed ω-k” configuration having angular frequency ω and wavenumber k. Experiments demonstrate the theoretically predicted dilatational resonance at ω = (E0k2/√2ρη)2/3, where ρ and η are, respectively, the mass density and viscosity of the liquid bulk. Effects of surface and bulk diffusion, as well as dilatational viscosity, are shown each to have a characteristic effect on the frequency response. In the third configuration, surface shearing of a film is modeled and sensitivity to surface shearing viscosity predicted.
Formation of vortex rings in a stratified atmosphere
Authors: Simons Girard A. , Larson Richard S.
Published: February 2004

A model for the evolution of an inviscid buoyant thermal into a vortex ring is developed by placing Hill's spherical vortex in a gravitational field. The atmospheric pressure gradient interacts with the density gradient at the edge of the thermal to produce vorticity. This additional effect is treated as an unsteady perturbation to Hill's steady-state solution and causes the spherical vortex to evolve into a torus. Torus formation times are obtained in terms of the thermal radius a, the initial rise velocity V0, and the degree of buoyancy g(Δρ/ρ) (Δρ/ρ) arbitrary). As V0 → 0, the results for a buoyant bubble are recovered. However, when V02 > ag(Δρ/ρ), the internal circulation of the thermal changes the time scale of torus formation. Denoting the thermal density as ρt and that in the atmosphere as ρ∞, the torus formation times are shown to be [3aρt/g(ρ∞ − ρt)]1/2 in the buoyant limit and V0/g[(ρ∞/ρt)1/2 − 1] in the inertial (large V0) limit. The analysis is extended to a density-stratified atmosphere, and it is shown that the expansion of the rising thermal may eliminate the buoyant force before the torus can form. The conditions under which a torus can form are obtained in terms of a, g, V0 , Δρ/ρ and H, the atmospheric scale height.