bluuebunny/crossref_metadata_2025 huggingface dataset:
A hybrid-kinetic model for high-β plasmas
Authors: D’Ippolito Daniel A. , Davidson Ronald C.
Published: March 2003

A hybrid-kinetic model (Vlasov ions and drift-kinetic electrons) is developed to describe the equilibrium and stability properties of collisionless high-beta plasmas in arbitrary magnetic field configurations. No ordering of ion properties (such as ω/Ωi and rLi/L⊥) is assumed, so the ions are described by the exact (unexpanded) Vlasov equation. The electrons are assumed to be strongly magnetized with ω/Ωε ∼rLe/L⊥=ε≪1, and the electron Vlasov equation is expanded in ε to give a drift-kinetic equation for fe. Examples of linear screw-pinch equilibria are constructed to demonstrate the ease with which equilibrium solutions are found within this formalism. Also, it is shown that the hybrid-kinetic model correct to O (ε) includes physical effects which are important during the implosion and immediate post-implosion phases of high-density pinch experiments, where stability behavior is characterized by the fast time scale ω−1LH= (ΩeΩi)−1/2. In particular, a local dispersion relation is derived for the modified-two-stream and lower-hybrid-drift instabilities, which have characteristic growth rates of order (ΩeΩi)1/2 when ω2pe/Ω2e≫1.
Propagation and collisionless absorption of linearly converted lower hybrid plasma waves
Authors: Simonutti Mario D.
Published: March 2003

Mode conversion and collisionless absorption of externally driven waves in the lower hybrid frequency range in an inhomogeneous plasma are described through numerical analysis of the locally evaluated linear dispersion relation for a homogeneous plasma. The effects of finite temperature and inhomogeneity of the plasma are emphasized since, according to the linear theory, these effects are responsible for the eventual absorption of the waves by the plasma. The exact forms of the dispersion relations, derived first from the two-fluid equations with an isotropic pressure law and then from the Vlasov equation, are analyzed for plasma parameters applicable to present day tokamaks. The two-fluid theory predicts that a mode conversion to an acoustic wave takes place near the lower hybrid resonance density layer. The Vlasov theory, in addition, predicts that this may be followed by a second mode conversion at a lower density. The results of the Vlasov theory also include electron Landau damping and ion cyclotron harmonic damping.
Scattering of electromagnetic waves into plasma oscillations via plasma particles
Authors: Lin A. T. , Dawson J. M.
Published: March 2003

A plasma subjected to an intense electromagnetic wave can exhibit a large number of parametric instabilities. An interesting example which has received little attention is the decay of the electromagnetic wave into a plasma oscillation with the excess energy and momentum being carried off by electrons. This process has been simulated on a one−and−two−halves dimensional electromagnetic code. The incident electromagnetic wave had a frequency near the plasma frequency so that decay into a plasma oscillation and a backscattered electromagnetic wave was excluded. As expected, the threshold for this instability was very large , so it is unlikely that this instability is competitive in most laser plasmas. Nevertheless, the physical mechanism involved provides a means for absorption of laser light and acceleration of particles in a plasma containing large amplitude plasma oscillations.
Plasma heating by relativistic electron beams. I. Two-stream instability
Authors: Thode Lester E. , Sudan R. N.
Published: March 2003

A one-dimensional model of the two-stream instability between a relativistic electron beam and a plasma shows that the saturated level of the wave electric field is determined by a single parameter. Due to relativistic effects, the efficiency of energy transfer via the hydrodynamic two-stream instability is a decreasing function of total beam energy in the strongly relativistic regime. The model is supported by numerical simulation experiments. The spectrum of the spatial harmonics generated during the buildup of the primary spectrum obeys a power law dependence. Anomalous heating of the electrons via parametric instability driven by the primary spectrum is observed. For long times the beam energy loss is proportional to the initial beam kinetic energy and most of this energy is picked up by the hot tail of the plasma electron distribution.
Stability of a pair of co-rotating vortices
Authors: Jimenez Javier
Published: March 2003

The linear stability of a pair of co-rotating vortex filaments is studied with a view toward clarifying the behavior of these pairs in the shear layer. The configuration is found to be stable within the long wave approximation.
Effect of Compton scattering on the radiation energy spectrum of a radiative fluid
Authors: Chan K. L. , Yu Kin C.
Published: March 2003

An evolutionary equation of the radiation energy spectrum of an optically thick, viscous, compressible radiative fluid is derived. The stability of the solution of the anisotropic part of the photon distribution is studied.
Excitation and linear mode conversion of low hybrid resonance cones in an inhomogeneous plasma
Authors: Kuehl H. H. , Ko K. K.
Published: March 2003

The field near the resonance cone for frequencies near the lower hybrid frequency is considered. By including higher-order thermal terms, the proper nonsingular fields near the resonance cones due to a localized rf source at the plasma boundary are derived.
Cylindrical ion wave excited by a modulated thin electron beam
Authors: Ohnuma Toshiro , Fujita Takao , Shibata Kan , Adachi Saburo
Published: March 2003

When a circular thin electron beam modulated at a prescribed frequency is injected into a weakly magnetized plasma along the magnetic field, cylindrical ion waves are found to be launched in the direction nearly perpendicular to the electron beam both experimentally and theoretically.
Relativistic electron dynamics in a cusped magnetic field with a downstream drift region
Authors: Destler W. W. , Misra P. K. , Rhee M. J.
Published: March 2003

Studies are reported of the motion of relativistic electrons injected first through a narrow magnetic cusp and then into a downstream region in which the particle motion is assumed to be adiabatic. Experiments performed to check the theory are also presented.
Criteria for acoustic instability in a gas with ambient vibrational and radiative nonequilibrium
Authors: Srinivasan J. , Vincenti W. G.
Published: March 2003

When acoustic waves propagate in a gas, nonequilibrium phenomena can manifest themselves in either (or both) the ambient and perturbed states of the gas. To study the relatively unexamined effects of ambient nonequilibrium, the present paper uses a macroscopic, gas-dynamic approach to investigate the influence of such nonequilibrium, primarily as regards vibration and secondarily as regards associated radiation. In situations where the vibrational temperature exceeds the translational temperature, ambient vibrational nonequilibrium, from whatever source, is shown to cause instability (i.e., wave amplification) provided the vibrational relaxation time is a descreasing function of temperature (or increases at less than a specified rate) and the degree of ambient nonequilibrium is sufficiently high. Ambient radiative nonequilibrium will cause instability, in cases where the external-source temperature exceeds the gas temperature, provided the absorption coefficient is an increasing function of temperature and the rate of radiant energy input is sufficiently large.
Nonlinear behavior of line vortices
Authors: Macagno Matilde , Macagno Enzo
Published: March 2003

A simple model is formulated following classical lines and used to investigate the decay of line vortices in which both self-induced and ambient turbulence may exist. The effect of molecular viscosity is included, since it may be important at certain times and in certain regions of the vortices. Circulation overshoot, predicted for the first time by Saffman, is also predicted by this model when self-induced turbulence is taken into account. This occurs even if no trace of overshoot is present initially. Experimental data of Focke, which exhibit overshoot, are used to test the model. The presence of a logarithmic portion in the circulation profiles of turbulent vortices is discussed critically.
Experimental results for oscillating flow in a curved pipe
Authors: Munson B. R.
Published: March 2003

Experimental results are presented describing the character of the secondary flow developed within a curved pipe for which the primary (axial) flow is driven by an oscillating pressure gradient. The comparison between previous theory and experiment is excellent.
The role of polydispersity in the mechanism of drag reduction
Authors: Huntson Donald L. , Reischman Michael M.
Published: March 2003

The effects of polydispersity in drag reduction were studied by testing two narrow molecular weight distribution polystyrene samples individually and in mixtures. The results indicate that the largest molecules in the distribution determine the value of the onset point and that this value decreases with increasing molecular weight. Above the onset point the magnitude of the drag reduction effect is shown to be a complex function of both molecular weight and polydispersity.
Series solution for the planar asymmetric blunt-body problem
Authors: Schwartz Leonard W.
Published: March 2003

Accurate semi-analytic solutions to the inverse blunt-body problem have been obtained using a method of series expansion. Rational fractions are used for series summation and analytic continuation. Angles of incidence up to 30° and Mach numbers as low as 2 have been considered. The maximum entropy streamline will not wet the body surface in asymmetric flow. It may pass either above or below the stagnation streamline. Limit lines appear in the supersonic portion of the flow field, both in the shock layer and in its upstream analytic continuation.
Solution of Maxwell’s moment equations by the method of rational truncation and coordinate straining
Authors: Baganoff D. , Elliott J.P.
Published: March 2003

A method is developed for truncating and closing any valid system of moment equations of the Boltzmann equation. The method is based on the idea that a rational truncation procedure for any system of moment equations must be developed from an orthonormal expansion for the distribution function, and that the convergence of the expansion can be accelerated if the coordinates in velocity space are scaled in accordance with any asymmetry in the distribution function that may be apparent from the physical situation. The procedure allows the determination of closure relations among any set of moments that may be convenient for a particular problem. Application of the method to the problem of shock-wave structure gives, for the first time, results at only the 13-moment level of approximation that are comparable to the Mott–Smith solution.
Computational study of the first stage of hypersonic ion beam neutralization: The cross neutralization stage
Authors: Pomot C. , Dolique J. M.
Published: March 2003

A study is made of the first stage of evolution of a hypersonic ion beam in which thermoelectrons are emitted by a heated grid, known as the neutralizer. Downstream from the neutralizer there appears successively as a sheath a range of periodic and quasi-stationary electric field and a front where the electric field oscillates with the plasma frequency. The sheath is self-regulated. Some electrons are trapped in the periodic and stationary electric field. The characteristics of the periodic, quasi-stationary range correspond to those of both an experimental study and one-dimensional time-independent macroscopic theory. This quasi-stationary regime builds up in a time smaller than ωpe−1 and is studied for a few periods ωPe−1. The subsequent evolution of this state of nonequilibrium is not investigated. The experimental study has shown that, as for the neutralization of a subsonic ion beam, it leads to a field-free, homogeneous medium: a ’’synthesized plasma.’’ The importance of the first stage described herein, which may be called the gross neutralization stage, is due to the properties of mean neutrality in the current and in the charge insured by the regulating sheath, properties which will be preseved downstream.
Radial density distribution of charged particles in an electronegative discharge plasma with space charges
Authors: Kocian P.
Published: March 2003

The radial distribution of the electrons, as well as the positive and negative ions, respectively, has been determined theoretically in the positive column of the low-pressure discharge in an electronegative gas. The problem has been solved using a system of hydrodynamic equations and Poisson’s equation. This latter equation must be considered because of the volume recombination of the negative and positive ions and because of the space charges produced in the positive column. The method has been applied to the special case of the conical equipotentials often occuring in electronegative gases.
Nonlinear saturation of stimulated diffusion scattering
Authors: Weinstock J. , Rognlien T. D. , Lee Kai Fong
Published: March 2003

A nonlinear instability theory is presented for stimulated scattering of electromagnetic ordinary-mode radiation from electrostatic ’’diffusion modes.’’ These ’’diffusion modes’’ are excited unstable by the incident radiation, and have their linear damping rates proportional to the diffusion tensor. Two diffusion modes are found; one corresponds to thermal diffusion and the other to particle diffusion. The thermal diffusion mode was previously calculated by Berger, Goldman, and DuBois for a two-dimensional model. The present calculation is made for three dimensions to show that the radiation is scattered over a wide angle in the plane perpendicular to a uniform magnetic field. A three-dimensional model is necessary to determine nonlienar effects. The saturated level of the electrostatic diffusion modes is calculated explicitly. For ionospheric modification experiments it is found that the electron density fluctuations are almost 1% of the ambient electron density.
Collisions in multi-dimensional plasma simulations
Authors: Matsuda Y. , Okuda H.
Published: March 2003

Collisions in multi-dimeniosnal plasma simulation models using finite-size particles are studied numerically and analytically. Drag and diffusion of particles in velocity space are measured and are compared with the theoretical predictions for two-, two-and-a-half-, and three-dimensional models. For two- and three-dimensional models, the measurement agrees reasonably well with the Balescu–Lenard theory. For the two-and-a-half-dimensional model, it is shown that the collisions strongly depend on the choice of the angle between magnetic field and wave vector due to the limited phase space available in the model. For a strongly magnetized plasma with Ωe≳ωpe, the effective collisions are significantly reduced for a simulation plasma when a≳ρe (where a is particle size, and ρe is the gyroradius) in contrast to a real plasma where the effective collisions depend weakly on the magnetic field.
Models for quasi-linear equations
Authors: Abraham-Shrauner Barbara
Published: March 2003

The quasi-linear equation for a weakly turbulent plasma is treated by specifying the time dependence of the imaginary part of the frequency of a mode γk(t) for several models. For unstable plasmas an oscillatory diffusion coefficient, D, is found and several methods are discussed for insuring that D is positive. For wave modes that stabilize at high electric field fluctuation levels, it is found that the one-particle distribution function must be treated as an operator if the diffusion time is equal to or greater than growth time. Our results confirm the picture given by Burns and Knorr within the limits of our models.
Comments on ’’Infinite−β limit of the drift instability’’
Authors: Saison R.
Published: March 2003

Stability of the force−free high−β plasma is considered. Comments on the deviation of the dispersion relations obtained for the highly unstable made are presented. (AIP).
Observations of harmonic dispersion and sideband coupling in a plasma
Authors: Jahns Gary , Van Hoven Gerard
Published: March 2003

Experiments with large−amplitude electron−wave signals demonstrate the existence of nonlinear Floquet−Bloch harmonics and of a passive four−wave coupling interaction. Propagation of the first spatial−temporal harmonic is verified by direct dispersion measurements. The parametric process acts to couple test−wave excitations at nearby frequencies symmetric about a high−level pump. Several possible models for this effect are examined, and it is shown that a four−wave mode−coupling process provides the only consistent explanation. The observed passive interaction operates at spatial positions and at pump−wave levels preceding the turn−on of the trapped−electron sideband instability, and also in the presence of detrapping interference. These results indicate the indifference of the four−wave mechanism to particle trapping, and lead to the inference that the unstable electron sidebands must also be coupled by this competing nonlinear process. Implications of this conclusion for studies of the sideband instability are discussed.
Coherent nonlinear theory of a cyclotron instability
Authors: Sprangle P. , Manheimer Wallace M.
Published: March 2003

A general nonlinear theory of coherent instabilities is presented and applied to the generation of microwaves by a relativistic beam. The instability is driven both by ∂f/∂p⊥ ≳ 0 and the relativistic dependence of cyclotron frequency on particle energy. This dependence can cause a bunching in the azimuthal angle in such a way as to cause net particle energy to decrease. The nonlinear evolution of this system is studied by writing the orbit equations for a small number of particles averaged over the fast time scale. The orbit equations are then integrated numerically. The equation for the mode amplitude is found by conserving energy between waves and particles. A simple analytic theory is also presented which successfully predicts the maximum field amplitude and also the behavior of the system for times long after saturation.
Computer experiments on clump formation in plasma
Authors: Hui B. H. , Dupree Thomas H.
Published: March 2003

Phase−space density granulations called clumps are simulated by computer experiments. The experimental results compare well with the theoretical predictions. In particular, we show that these clumps can be as large as the linear response. The criteria for steady−state clump turbulence are also examined numerically.
Nonaxisymmetric equilibria in tokamaks and Ohmically heated stellarators
Authors: Lo Surdo C. , Sestero A.
Published: March 2003

An asymptotic expansion scheme is set up, which is appropriate to deal with the deviations from axisymmetry occurring in tokamaks and Ohmically heated stellarators. Solutions of the magnetohydrostatic equations are sought to all orders in the expansion parameter, which is related both to the magnitude of the deviations from axisymmetry and to the ratio of poloidal vs toroidal components of current and magnetic field. Arguments are presented for the existence of the solution to any finite order, the pressure and current profiles across the plasma column, in general, being determined by the nonaxisymmetric part of the external magnetic field. If the latter, however, has certain symmetries, then a degeneracy occurs, and the pressure and current profiles can again be given with some degree of arbitrariness. It is shown that for tokamaks and stellarators of standard design, viz., including the perturbations associated with the ’’ripples’’ in the toroidal field, the ’’gaps’’ in the copper shell, and the helical windings, the degree of arbitrariness in the pressure and current profiles is the same as in the axisymmetric theory. Thus, in such machines the above profiles are expected to be governed entirely by transport effects, a conclustion which is borne out by the experiments.
Experimental results for low Reynolds number flow between eccentric rotating spheres
Authors: Menguturk M. , Munson B. R.
Published: March 2003

Experimental results concerning secondary flow and torque measurement for low Reynolds number flow in an eccentric spherical annulus are compared with previous theory. The results compare very well, especially for small eccentricities for which the perturbation theory is valid.
Mode−mode coupling theory of the heat convection threshold
Authors: Graham R. , Pleiner H.
Published: March 2003

The fluctuations of a horizontal fluid layer heated from below are analyzed, based on the hydrodynamic equations in the Boussinesq approximation including thermodynamic fluctuating forces. By means of a formalism, recently developed by Martin, Rose, and Siggia, a system of coupled nonlinear integral equations is derived for a set of correlation functions, response functions, and appropriate ’’self−energies.’’ The equations are solved approximately in several steps of simplification. In addition to results of an earlier linear theory, our results cover a narrow region near the convection threshold, where mode−mode coupling provides the only mechanism of energy dissipation. The fluctuation intensities, and the correlation times and correlation lengths, are calculated in that region. These quantities diverge at the convection threshold in the linearized theory, but remain finite, if mode−mode coupling is taken into account.
Period between bursts at high Reynolds number
Authors: Gordon Clifford M.
Published: March 2003

Intermittent periods of high momentum transport have been measured in a tidal boundary layer (Reϑ ≈ 2.6×105). The data have been interpreted in terms of the bursting phenomenon reported in laboratory experiments. The experimental period between bursts is consistent with that predicted by T ≈ kδ*/U∞ where k is the displacement thickness, and U∞ is the stream velocity outside the boundary layer.
Structure of a shock wave in a vibrationally relaxing diatomic gas
Authors: Pai T. G. , Ramachandra S. M.
Published: March 2003

The kinetic theory of axially elastic spherocylinder molecules is used for obtaining the shock structure in a vibrationally relaxing diatomic gas. A trimodal and a quadrimodal ansatz are proposed for the distribution function within a shock, and a moment method is used to determine the unknown weight functions in the ansatz. The collision integrals in the moment equations are 22−fold out of which 16−fold integrations are carried out analytically and the remaining integrations are performed numerically using a Monte Carlo technique. The differential equations in the weight functions are solved numerically and shock profiles in nitrogen are obtained for a range of upstream Mach numbers and pressures.
Two−wavelength holography for measuring plasma electron density
Authors: Radley R. J.
Published: March 2003

The spatial distribution of free electrons in a stationary, cw, laser−produced air plasma has been measured using single−pulse, two−wavelength holographic interferometry. This measuring technique provided a noncontact method of directly measuring electron density uninfluenced by the other plasma constituents. The general theoretical basis for this type of two−wavelength holography and its application to ionized gases are discussed. Also described are the experimental methods used to implement the technique. Interferograms of the plasma were made at two laser input powers: 3500 W and 6200 W. The electron density was measured as a function of radius and axial position in the plasma, which was oriented vertically to insure cylindrical symmetry. The range of measured values was 1016−1017 electrons/cm3 for diameters ranging from 0.2 to 0.8 cm.
Strong field high−frequency plasma response
Authors: Wright Thomas P.
Published: March 2003

The plasma response to a strong high−frequency electric field has been reformulated in a way that shows that the basic nonlinear parameter is α = Λη0 (ωp/ω0)2, where Λ is essentially the number of particles in a Debye sphere and η0 = E0 (4πn0kBT)−1/2 is the usual electric field parameter. Numerical integration has produced results which show such phenomena as locally increased absorption, lower dissipation rates for strong fields, and somewhat deeper penetration of the electromagnetic wave turning point (compared with weak field results).
Parametric decay of intense radiation into a whistler wave
Authors: Klein H. H. , Manheimer Wallace M. , Ott Edward
Published: March 2003

The parametric decay instability of a large amplitude extraordinary pump wave into a whistler wave and a backscattered extraordinary wave is investigated by computer simulation.
Destabilizing effects from a fast−isotropic ion component
Authors: Mai L. P. , Horton Wendell
Published: March 2003

The destabilizing effects of a fast, isotropic ion component are calculated for the principal electrostatic plasma modes. The change to γk = Im (ωk) is given for a class of peaked energy distributions ranging from mono−energetic to near Maxwellian.
Evolution of the ion−acoustic instability in a direct−current discharge plasma
Authors: Yamada M. , Raether M.
Published: March 2003

The nonlinear development of the ion−acoustic instability in a weakly ionized helium plasma has been investigated. Measurements of the magnitude and frequency dependence of the energy spectrum are consistent with the idea that the resultant turbulent state is controlled by competition between trapping of electrons by the waves and untrapping by either electron−neutral or Coulomb collisions. The effect of a dc electric field on the instability is discussed and additional data on the linear spatial growth rate and the unstable frequency range are presented.
Kinetic theory of the heat transfer near a cylinder
Authors: Pomeau Y.
Published: March 2003

The heat flow on a cylinder immersed in an infinite rarefied gas is well defined in the free molecular limit. To first order in the inverse Knudsen number, the correction to this free molecular value diverges logarithmically, for a reason quite similar to that explaining the divergence of the virial expansion of transport coefficients of two−dimensional gases. When one accounts for the most divergent terms of an expansion of this flux in powers of the inverse Knudsen number, this logarithmic divergence does not disappear, due to hydrodynamical phenomena taking place at a distance from the cylinder that is much larger than the mean free path. This situation is somewhat similar to that encountered in studying the divergent transport coefficients of two−dimensional gases. It is discussed from the point of view of a possible experiment.
Numerical calculation of finite amplitude effects in unstable laminar boundary layers
Authors: Antar Basil N. , Collins Frank G.
Published: March 2003

A numerical study of one stage of the transition region from laminar to turbulent flow of the boundary layer over a flat plate was performed. The theoretical development follows that of Benney and Lin in which the interaction of a two−dimensional and a restricted three−dimensional periodic disturbance was considered up to second order terms in a series expansion. Several laminar profiles were studied, all belonging to the Falkner−Skan family. The assumption of equal wave speeds for the two−dimensional and three−dimensional disturbances was relaxed, giving rise to a slow modulation of the mean secondary flow. The resulting mean secondary flow compared favorably with both the existing experimental work and the restricted analytical solution of Benney. The flow depended principally upon the disturbance spanwise wavenumber, β, whose variation resulted, in some instances, in a system of counter−rotating vortices, one on top of the other, for the mean secondary flow.
Improved form of the low Reynolds number k−ε turbulence model
Authors: Hoffman Gilbert H.
Published: March 2003

The behavior of the k−ε turbulence model at a turbulent/nonturbulent interface is examined to determine the turbulent diffusion coefficients σk and σε. The analysis leads to a dilemma caused by the modeling of the generation term in the k and ε equations. Based on limiting values of σk and σε derived from this analysis, a revised form of the low−Reynolds−number incompressible k−ε turbulence model is presented which incorporates a new set of model constants, a linear form of the near wall dissipation term in the k equation, and deletion of a nonphysical term in the ε equation. The revised model is applied to fully developed flow in a channel and found to give better agreement with experiment than the original form of the model developed by Jones and Launder.
Geometric optics in space− and time−varying plasmas
Authors: Bernstein Ira B.
Published: March 2003

The formal theory of geometric optics in a space− and time−varying plasma is developed assuming that there propagates a small amplitude wave, that there is a linear, causal, but, in general, nonlocal relation between current density and electric field, and that the background plasma does not change much in a locally defined wavelength or period. The description reduces to a system of ordinary differential equations along rays everywhere tangent to the group velocity, one such system of rays for each mode. These equations are formally Hamiltonian in character. They permit the introduction of an energy density such that negative energy waves will be unstable in a lossy medium, as seen by an observer moving with the group velocity, providing that the divergence of the bundles of rays is not too great.
Laser heating of a dense plasma pinch
Authors: Chapin David L. , Duderstadt James J.
Published: March 2003

A single fluid, two−temperature, one−dimensional magnetohydrodynamic model has been developed to describe the properties of a linear pinch plasma heated by an axially directed laser beam. The coupling of the laser light energy with the pinch dynamics is studied in detail. The laser light absorption occurs primarily through the inverse bremsstrahlung process, but the effect of enhanced absorption for sufficiently intense lasers has also been studied. Results of the calculations show a strong interaction between the heating by radial compression (pinching) and heating by the laser beam. It was found that the most important considerations in obtaining efficient heating of the plasma are the time profiles of the laser pulse and the electric current. The results of the anomalous absorption studies indicate that the increased absorption can cause the electron and ion temperatures to decouple and may actually be detrimental to the efficient laser heating of dense pinch type plasmas.
Alpha particle energy absorption in a reacting DT sphere
Authors: Cooper Ralph S. , Evans Foster
Published: March 2003

The fraction of the α−particle energy absorbed in a reacting DT sphere by Rutherford interactions with ions and electrons is computed and compared to previous results obtained by neglecting interactions with ions.
Linear theory of a cold relativistic beam propagating along an external magnetic field
Authors: Godfrey Brendan B. , Shanahan William R. , Thode Lester E.
Published: March 2003

The linear theory of a cold relativistic electron beam propagating parallel to an external magnetic field and through a cold, homogeneous plasma is investigated. The electromagnetic dispersion relation is solved numerically and compared with analytical predictions based on the electrostatic approximation. It is found that electromagnetic effects are important for determining the entire unstable spectrum. However, except for the strong magnetic field regime, the maximum growth rates and corresponding frequencies are in agreement with those predicted by the electrostatic approximation. In the strong magnetic field regime the two−stream spectrum is found to be much narrower in angle than predicted by the electrostatic approximation. In the moderate and strong magnetic field regime the growth rate of waves propagating at large angles with respect to the beam are independent of beam energy.
Similarity transformation for flow in a cone
Authors: Vander Werff Terry J.
Published: March 2003

A similarity transformation is presented for radial flow in a cone of a
Experimental observation of internal solitary waves in a stratified fluid
Authors: Hurdis David A. , Pao Hsien−Ping
Published: March 2003

Propagation of internal solitary waves has been experimentally observed within a region of sudden vertical density variation. The propagation speeds compare well with the theoretical predictions of Benjamin and Davis.
Higher−order asymptotic solutions to the Bhatnagar−Gross−Krook equation
Authors: Wen Shih−liang , Chi L. K.
Published: March 2003

The boundary layer equations are the zeroth−order solutions to the BGK equation when the Chapman−Enskog procedure is coupled with the Prandtl analysis. The first− and second−order asymptotic solutions are obtained. They are higher−order corrections to the usual boundary layer equations.
Effect of collisions on an impurity plasma mode
Authors: Wong S. K.
Published: March 2003

Calculations of the effect of collisions on an impurity plasma mode with a Krook model shows that the instability criterion is unaffected by collisionality up to very high collision frequencies.
Estimate of the radial potential jump in a theta−pinch
Authors: Commisso R. J. , Kunze H.−J.
Published: March 2003

A method for estimating the radial jump of the plasma potential associated with the piston in a theta−pinch is described. Small amounts of impurity atoms with different masses are added to the filling gas, and from spectroscopic measurements it is determined if they are picked up by the piston.
Estimation of the influence of turbulence induced scattering on gasdynamic laser characteristics
Authors: Brunné M. , Milewski J. , Stańco J. , Zieliński A.
Published: March 2003

The radiation output power losses due to the scattering induced by spatial nonuniformities of the medium refraction index are analyzed for an active cavity of the gasdynamic laser. The analysis is based upon the nonlinear equations of chemical kinetics. The attenuation of the coherent radiation power caused by the statistically homogeneous and isotropic flow nonuniformities is treated as a passive loss measured by an extinction coefficient related to the integral scale of the turbulence and the mean-square fluctuation of the refractive index. A set of straightforward analytical formulas are given for both the coherent and incoherent radiation power as well as for the laser efficiency.
Simulation of laser beat heating of a plasma
Authors: Cohen Bruce I. , Mostrom Michael A. , Nicholson Dwight R. , Kaufman Allan N. , Max Claire Ellen , Langdon A. Bruce
Published: March 2003

A new relativistic electromagnetic computer simulation code, with one spatial dimension, is described which explicitly follows right- and left-going electromagnetic waves by integrating along the characteristics of Maxwell’s equations. To illustrate its suitability for the study of laser-plasma interactions, simulations are discussed of the heating of plasma by two opposed lasers whose beat frequency drives a local plasma oscillation. Excellent agreement is obtained with analytic theory in the linear-response regime.
Saturation of the relativistic two-stream instability by electron trapping
Authors: Lampe Martin , Sprangle P.
Published: March 2003

The single-wave weak cold relativistic two-stream instability has been studied in one dimension by numerical integration of the equations of motion, energy conservation, and Poisson’s equation. The dynamics is shown to depend only on the single parameter S = β02γ0(nb/2np)1/3. The nondimensionalized wave energy at initial saturation due to beam trapping, W1 = 〈E2〉/8πnbmc2γ0, reaches a maximum W1 = 0.09 at S = 0.4 and then decreases with S, but if S≳0.5 the wave energy is larger at subsequent bounces of the trapped particles, so that Wmax increases roughly monotonically with S, reaching 0.11 at S = 3. The drop-off of W1(S) is due to a relativistic tendency of beam electrons to bunch in the part of the orbit where the beam electron energy is largest. The self-consistent nonlinear shifts in wave frequency and amplitude are shown to play an essential role in extracting energy from the beam.
Flow in the entrance region of noncircular ducts
Authors: Wiginton C. L.
Published: March 2003

A remarkably simple method of solution is given for an eigenvalue problem arising in laminar flow in ducts which uses eigenfunctions of the Helmholtz equation. The only computation involved is the determination of zeros of a series to obtain the eigenvalues.
Nonlinear breakup of a laminar liquid jet
Authors: Lafrance Pierre
Published: March 2003

A perturbation analysis of the capillary instability of an inviscid liquid jet of circular cross section was carried out to third order. The results show that the nonlinear terms are responsible for the presence of satellite drops. The dimensionless cutoff wavenumber, which separates regions of stability and instability, remains unity to third order. The present theory was used in a computer simulation of jet breakup, and it was found that predicted surface wave profiles, disturbance amplification rates and drop sizes are in excellent agreement with the data of previous investigators. New experimental results are presented as additional support of the theory.
Whistler sideband instability
Authors: Denavit J. , Sudan R. N.
Published: March 2003

Resonant electrons in a large-amplitude whistler wave acquire a correlation in phase of their perpendicular velocities with respect to the wave magnetic field, which results in unstable growth of other whistler waves with frequencies near the main wave frequency. This instability is analyzed and the results of the analysis are compared with computer simulations.
Energy loss of a relativistic, finite electron beam in a plasma
Authors: Gerwin Richard A.
Published: March 2003

The rate of energy dissipation by the beam-induced reverse current in a resistive plasma is calculated numerically with emphasis on the effects of finite beam radius and length.
Effect of finite disturbances on axisymmetric Taylor vortex flow
Authors: Koschmieder E. L.
Published: March 2003

Taylor vortices caused by finite axisymmetric disturbances around the inner cylinder in a long apparatus with a resting outer cylinder have been studied. The forced Taylor vortices are unstable if their wavelengths are either too long or too short as compared with the critical wavelength of undisturbed Taylor vortex flow. It has also been found that axisymmetric Taylor vortices are stable to finite azimuthal disturbances over a large range in supercritical Taylor numbers in this apparatus with η=0.727.
Three-dimensional equilibrium of the anisotropic, finite-pressure guiding-center plasma: Theory of the magnetic plasma
Authors: Hall Laurence S. , McNamara Brendan
Published: March 2003

Theoretical and numerical methods now give a complete solution to the problem of finite-β plasma equilibrium in mirror magnetic wells and toroidal devices. The equilibria can be made consistent on all of the progressively longer time scales of the guiding-center fluid model, including the particle magnetic drifts and the Coulomb scattering equilibrium of a neutral injected plasma. The theory of equilibrium in the guiding-center fluid model of a finite-β plasma with an arbitrary, anisotropic pressure tensor can be formulated as a classical magnetostatic system: ∇⋅B = 0, ∇×H = 0, B = H + 4πM(B). The plasma magnetization is found explicitly in terms of three physically distinct components related to the laws of conservation of magnetic moment, of longitudinal invariant, and of the sign of the velocity along B of particles that do not undergo mirror reflection. A condition is derived upon the field geometry whereby a large class of special equilibria can be found in which all particles on a given line drift on the same surface, the omnigenous surface. Such systems allow a specially simple connection between particle and fluid models in the guiding-center fluid theory. The usefulness of the theory is exemplified by application to the problem of a finite-β plasma in a magnetic well. Finally, a brief treatment of stability in terms of the energy principle is given. The omnigenous equilibria have particularly simple stability criteria.
Propagation of an unstable spectrum of plasmons in the presence of random inhomogeneities
Authors: Coste Jean , Reinisch Gilbert , Silevitch Michael B. , Montes Carlos
Published: March 2003

A one-dimensional stochastic kinetic equation for the propagation of unstable plasmons (Langmuir modes) in the presence of large scale random spatial fluctuations is presented, within the frame of the WKB approximation, and then solved. Using probabilistic arguments, an effective growth rate is evaluated, which turns out to be much smaller than the plasmon growth rate in the absence of fluctuations. The theory is then applied to the beam-plasma kinetic instability and to the stimulated photon-plasmon interaction. The former case exhibits a shift of the turbulent plasmon spectrum toward larger wavenumbers. The latter case shows a strong reduction in the efficiency of the stimulated process (i.e., much smaller growth rate) and the removal of the strong asymmetry inherent in this problem.
Collective modes in an inhomogeneous beam injected plasma
Authors: Coppi Bruno , Bhadra Dilip K.
Published: March 2003

The effects of microinstabilities, which are excited in a confined plasma characterized by two ion components, e.g., a high temperature deuterium component and a low temperature tritium component, are investigated. The relevant growth rates depend on the radial temperature and density gradients of the hot ion population as well as on the electron temperature gradient. The main consequences of the excited modes can be the extraction of energy from the hot ion component, the scattering of weakly trapped and weakly circulating orbits for the same component, and the enhancement of the particle and thermal energy transport across the magnetic field for all ion and electron populations.
Anomalous heat conduction along the field lines for turbulently heated plasmas
Authors: Caponi M. Zales , Krall Nicholas A.
Published: March 2003

A quasi-linear model is presented to study the effect of turbulence and finite length on heat loss by conduction along the field lines in a plasma heated by cross-field instabilities. The turbulence contribution to energy confinement along the field lines is calculated self-consistently from the quasi-linear moment equation. The electron temperature is found to be highly dependent on the competition between heat loss to the ends and turbulent heat production due to the instabilities. The results, discussed for a wide range of plasma parameters, may explain the cooling of electrons on the time scale of interest (e.g., implosion time) in several theta-pinch experiments.
Observations of plasma heating in a turbulent torus
Authors: Bengtson Roger D. , Gentle K. W. , Jancarik J. , Medley S. S. , Nielsen P. , Phillips P.
Published: March 2003

The Texas turbulent torus is a device to turbulently heat a plasma and maintain the heating current to confine the plasma in a tokamak configuration. Initial results show penetration of the heating current at densities up to 1013 cm−3, heating of the electrons to temperatures of order 10 keV, and the heating of a fraction of the ions to temperatures of several keV.
Mode conversion and harmonic generation at the upper hybrid layer in toroidal plasmas
Authors: Schuss J. J. , Hosea J. C.
Published: March 2003

The behavior of an extraordinary wave normally incident along a decreasing magnetic field gradient in a warm collisionless toroidal plasma is considered. Full electromagnetic Vlasov theory is used and the density gradient lengths are assumed to be much larger than all wavelengths. In the case for which the upper hybrid layer is accessible, it is shown that the incident wave almost completely converts into a backward Bernstein mode at the layer. The Bernstein mode then propagates until it is absorbed near the cyclotron layer. The second harmonic generated by this pump field is calculated, and its usefulness for poloidal magnetic field measurements in tokamaks is discussed. The theory is found to be in qualitative agreement with previous experimental results.
Laser radiation forces in laser-produced plasmas
Authors: Stamper J. A.
Published: March 2003

There are two contributions to laser radiation forces acting on the electrons. Transfer of momentum from the fields to the electrons results in a field pressure contribution and occurs whenever there is absorption or reflection. The quiver pressure contribution, associated with electron quiver motion, is due to inhomogeneous fields inducing momentum transfer within the electron system. It is shown that the ponderomotive force with force density, [(ε−1)/8π]∇〈 (δE)2〉, does not include the field contribution and does not lead to a general description of macroscopic processes. A theory is discussed which does give a general macroscopic description (absorption, reflection, refraction, and magnetic field generation) and which reduces to the ponderomotive force for purely sinusoidal fields in a neutral, homogeneous, nonabsorbing plasma.
Prediction of the effect of streamline curvature on turbulence
Authors: Irwin H. P. A. H. , Smith P. Arnot
Published: March 2003

It is shown that the observed effects of small amounts of streamline curvature on turbulence are accounted for by the curvature terms which appear in the Reynolds stress equations and in the turbulence model of Launder, Reece, and Rodi. Because of the smallness of these terms, this is a surprising result, but their effect is shown to appear in a magnified form in the effective eddy viscosity. A comparison is made between computed solutions of the modeled Reynolds stress, mean momentum and dissipation rate equations, and experimental data for curved wall jets, a curved free jet, and curved boundary layers. The curvature effects are well predicted when the curvature terms are included. The turbulence model implies that the turbulence shear stress is relatively insensitive to longitudinal accelaration which seems to be in reasonable agreement with experiment.
Comments on ’’Toroidal equilibrium of current carrying plasmas’’
Authors: Infeld Eryk
Published: March 2003

A method for constructing large aspect ratio troidal equilibrium is shown to be more general than relaized by the original author.
Fluid dynamic damping of ion acoustic waves
Authors: Schott L.
Published: March 2003

Expressions are derived for the spatial damping rate of ion acoustic waves traveling through inhomogeneous plasmas enclosed in plane, cylindrical, or spherical surfaces. The waves are assumed to have the same symmetry as the plasma. The solutions are valid for wavelengths small compared with the size of the plasma and negligible Landau damping. Ionization of the gas by beam or plasma electrons and ion-neutral collisions are taken into account. The wave is more heavily damped when it travels from the plasma boundary to the center than vice versa.
Maximization in the damping rate of the ion acoustic wave in a two-ion plasma
Authors: Nakamura Masaharu , Ito Masataka , Nakamura Yoshiharu , Itoh Tomizo
Published: March 2003

The characteristics of dispersion and Landau damping of ion acoustic waves are experimentally investigated in an argon-helium plasma with varying ion composition ratio. The dispersion relations change continuously from the argon mode to the helium mode. The damping rate has a maximum when the ion number density ratio (r = nHe/nA + nHe) is about 0.08. This maximum is attributed to the resonance of helium ions with the argon mode ion acoustic wave and is consistent with theoretical predictions.