bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolution of finite disturbances in dissipative gasdynamics
Authors: Halabisky Lorne , Sirovich Lawrence
Published: February 2004

The initial-value problem for small amplitude disturbances governed by the Navier-Stokes equations is considered. This is shown to be governed by a system of Burgers and diffusion equations. The asymptotic solution of the finite amplitude initial-value problem is obtained by the introduction of asymptotic initial data. The analysis is also applied to the solution of a semi-infinite shock tube problem.
Shock waves structured by nonequilibrium ionizing and thermal phenomena
Authors: Foley William H. , Clarke Joseph H.
Published: February 2004

Ionizing shock waves in helium and argon are structured by nonequilibrium radiative and inelastic collisional transitions. The model atom of the monatomic gas has three electronic energy levels. The monatomic gas is not in local equilibrium with respect to population, and local translational equilibrium between the heavy species present and the electron gas is not assumed either. For the flow conditions studied, the physics and morphology of the shock is further developed on a continuum basis from previous work, and the shock is found to consist of a far precursor due to radiative excitation, a near precursor due to radiative ionization, an embedded transport shock, an inelastic and thermal collisional relaxation zone, and an equilibrium radiating tail. Of particular interest in the results are (i) the heating of the electron gas in the precursor by the said radiative and the associated de-exciting collisional mechanisms and (ii) the subsequent, electron-triggered collisional relaxation zone which is optically transparent to radiation; thus, nonequilibrium radiative and collisional processes are locally uncoupled throughout the shock. A family of numerical examples is displayed diagrammatically for an upstream temperature of 300°K and an upstream pressure of 10−4. atm. Selected were those accompanying downstream temperatures giving nominal equilibrium degrees of ionization of either 0.8 or 0.95.
Magnetohydrodynamic shock structure in strong transverse magnetic fields
Authors: Taussig Robert T.
Published: February 2004

Collision-dominated transverse magnetohydrodynamic shock structure is examined for the case where the magnetic fields are strong enough to make the plasma transport properties anisotropic. Different electron and ion temperatures are assumed. A singular perturbation approach is taken to obtain an analytic description of the steady shock structure. For very high Mach numbers (i.e., us≫ai, upstream sound speed) the shock width is given by Δs≅2×10−2 us4n1 [ 1 − 32 (γ+1γ−1) bs2us2] (m) in hydrogen where us, n1, b1, and γ are the shock speed, upstream number density, Alfvén speed, and ratio of specific heats, respectively, and where (us/b1)2≳ 12 has been assumed. This shock width is at least an order of magnitude less than shock widths calculated at the same shock speeds with isotropic dissipation coefficients. The results agree reasonably well with previous computer simulations and experimental data.
Dynamics of electromechanical flow structures
Authors: Jones Thomas B. , Melcher James R.
Published: February 2004

Free-surface gravity flows and capillary wicking provide examples of flow structures with fluid partially ducted at “free” surfaces by external forces. “Wall-less” electromechanical flow structures are developed which have a similar nature, but with polarization forces providing the orientation at free surfaces. Like their mechanical counterparts, these have the ability to ingest liquid or expel vapor through their walls. The structures consist of electrodes running in the flow direction z with slowly varying cross sections in a plane transverse to the flow. A formulation is given of the long-wave nonlinear (principal mode) dynamics, with use made of energy functions to represent a broad class of possible mechanical and electrical structure geometries. Based on the considerable analogy shown between electromechanical and gravity flows, conservative flow transitions and shock conditions are described. The role played by gravity waves in conventional free-surface flows is taken by polarization waves. Three types of experiments illustrate the significance of the model: (i) standing and traveling wave resonances, (ii) critical flow transition, and (iii) fluid pendulum oscillations. Quantitative checks on the small-amplitude wave dynamics, and on the nonlinear steady dynamics as well as qualitative observations on the behavior of an electrohydraulic jump, are reported.
Anomalous plasma heating induced by a very strong high-frequency electric field
Authors: DeGroot J. S. , Katz J. I.
Published: February 2004

Simulation calculations and theory which show that a very strong electric field with a frequency near the plasma frequency parametrically excites electrostatic turbulence are presented. The plasma is strongly heated with the electrons receiving most of the energy. A simple electron trapping theory accounts for the saturation electric field. After the plasma becomes turbulent, the real part of the frequency of the ion mode is drastically changed from the linear value.
Saturation of kinetic plasma instabilities by particle trapping
Authors: Dewar R. L.
Published: February 2004

The amplitude at which a single unstable Langmuir or ion-acoustic wave in a collisionless plasma saturates due to electron trapping is estimated using both the adiabatic and sudden approximations, and is shown to obey the approximate relation ωb∼3γlin. This is found from momentum conservation. It is found that energy conservation implies a nonlinear dispersion relation that is linearly independent of that derived from Poisson's equation, but that a reasonable distribution of resonant particles can be found that satisfies both relations.
Behavior of relativistic beams undergoing hose motion in a plasma channel
Authors: Moses K. G. , Bauer R. W. , Winter S. D.
Published: February 2004

A 6-MeV electron beam with current of 100-200 A was used to study the hose instability of a relativistic electron stream. The growth rates of the instability were experimentally determined, and measured values displayed the trends predicted by theoretical analyses. The magnitude and position of the maximum growth rate as related to the perturbing frequency and plasma-current decay times agreed well with the predictions of both the rigid and nonrigid beam models. The general dependence of growth rate on the ratio of channel radius to beam radius was observed.
Thin E-layer equilibria
Authors: Rensink Marvin E.
Published: February 2004

The equilibrium of an infinitely long, thin E layer under the influence of external and self-fields is studied. The canonical angular momentum and the total energy per particle are constant in this analysis. The results can be summarized as follows: (1) with complete charge neutralization, as the number of particles N increases, the E-layer radius R e tends toward the value Re = (RwRc)1/2, where R w and R c are the radii of the outer and inner conducting walls, respectively, (2) the total kinetic energy per particle initially decreases as N increases; (3) the axial temperature increases with N so as to maintain stability with respect to the tearing mode; and (4) the current per unit length saturates at a value well beyond that required for field reversal.
Effect of free-stream vorticity on boundary-layer stability
Authors: Werle M. J. , Mook D. T. , Tang H.
Published: February 2004

The Orr-Sommerfeld equation was used to estimate the influence of free-stream vorticity on the stability of incompressible boundary-layer flow. The primary flow velocity profiles were obtained using second-order boundary-layer theory. Self-similar flows with positive and negative pressure gradients and free-stream vorticities were considered. The results show that positive vorticity at the edge of the boundary layer is stabilizing. The free-stream vorticity influences the critical Reynolds numbers significantly when the pressure gradient is small, and influences the range of unstable wave lengths when the pressure gradient is large. The present results indicate that small amounts of vorticity in the free stream might have a large influence on transition.
Further investigations on the nonlinear behavior of a system of parallel line vortices
Authors: Rao K. Sankara
Published: February 2004

The dynamical behavior of a system of parallel line vortices with the vorticity vector of some of the vortices being parallel to the Z axis while that of the rest of the vortices is antiparallel, is investigated numerically. It has been shown that a vortex system where some of the vortices are antiparallel to the rest evolves to a state of low vortex density. Therefore, it is unlikely to be produced in the experiments involving rotation of liquid helium II.
Shock-wave propagation in inhomogeneous atmospheres
Authors: Nunziato J. W. , Walsh E. K.
Published: February 2004

The propagation of shock waves in atmospheres with spatially dependent density and temperature fields is considered. Assuming the medium to be an ideal polytropic gas, and representing the shock wave as a propagating singular surface, an expression is given for the variation in the shock strength in terms of the density gradient behind the wave and a critical density gradient. An example of shock wave propagation in the near-earth atmosphere is presented.
Magnetohydrodynamic streaming flow past a sphere at low Hartmann numbers
Authors: Mathon Rudolf , Ranger K. B.
Published: February 2004

The streaming flow of a weakly conducting viscous fluid past a nonconducting sphere in the presence of an aligned uniform magnetic field is investigated for low Hartmann numbers using a Galerkin method. If convection effects are neglected, it is found that eddies occur symmetrically fore and aft of the sphere when the Hartmann number exceeds 2.9.
Transport properties of two-temperature partially ionized argon
Authors: Miller E. J. , Sandler S. I.
Published: February 2004

Calculations are presented for the transport properties of a two-temperature argon plasma based on the Chapman-Enskog and perturbed-Lorentzian solutions of the Boltzmann equations. The convergence problems known to exist in the Chapman-Enskog solution for the properties of a one-temperature argon plasma also occur here; this difficulty is removed by using the perturbed Lorentzian solution at low and moderate degrees of ionization. Also, it is found that the lowest order perturbed Lorentzian and Chapman-Enskog approximate solutions provide upper and lower bounds to the actual solution at low and moderate degrees of ionization. Finally, owing to the Ramsauer minimum in the electron-atom cross section, the electrical conductivity of the two-temperature argon plasma is found to decrease with increasing electron temperature (at fixed heavy particle temperature and electron density) at low degrees of ionization, and increase with increasing electron temperature at higher degrees of ionization.
Direct nonlinear coupling of electromagnetic waves and electrostatic waves in a plasma: Theory
Authors: Van Hoven Gerard , Phelps David A.
Published: February 2004

Nonlinear coupling among small amplitude electromagnetic and electrostatic waves in a cylindrical plasma-column waveguide is analyzed theoretically. The warm plasma equations of motion, in the displacement/polarization format, are combined with the wave equation for guided transverse magnetic waves to derive the system dispersion relation and the coupled-mode equations for this configuration. The coupling coefficients predict the strength of a given multiwave interaction from the intrinsic properties of the plasma waveguide. When the frequency selection rule is satisfied, for wave numbers consistent with the system dispersion relation, off-resonance excitation will occur if the interaction is confined to a finite length of the waveguide. Typical interaction resonances are illustrated on the system dispersion diagram by an experimentally useful graphical construction. Numerical estimates of the coupling strengths of selected three-wave “scattering” and “radiation” interactions are made from data obtained with the aid of this diagram. The analytical results are then illustrated and interpreted.
Comparison of the hot-electron plasmas produced using two different plasma sources in a magnetic mirror compression experiment
Authors: DeNeef C. P. , Pechacek R. E. , Trivelpiece A. W.
Published: February 2004

The hot-electron plasma produced in a single-stage magnetic mirror compression experiment using a deuterated titanium washer stack source is compared with the nonneutral hot-electron plasma produced using a thermionic electron gun source. Both plasmas contain approximately 5 × 1011 electrons with 0.3-MeV mean energy and 0.3-MeV temperature at the peak magnetic field of 18.5 kG, and both remain trapped for more than 20 msec. These plasmas are similar because deuterated titanium washer stack sources are electron sources during the first few μsec of operation and because the electron dynamics during compression is not strongly affected by the ion dynamics. The effect of the plasma self fields upon synchrotron radiation is investigated. The properties of these plasmas are compared with three other pulse compression hot electron plasmas obtained using a washer stack source.
Bifurcation and stability of long-wavelength helical hydromagnetic equilibria
Authors: Yeh Tyan
Published: February 2004

When a plasma is confined by magnetic fields inside a cylindrical conducting wall, the configuration of equilibrium can have either circular symmetry or helical symmetry. Thus, a sharp-boundary screw pinch can have a circular or helical interface between the plasma and the vacuum. Each possesses the same amounts of total plasma mass, axial magnetic flux in plasma, axial magnetic flux in vacuum, and total azimuthal magnetic flux. It is shown that in the neighborhood of a point of bifurcation there are stable long-wavelength helical equilibria. The equivalent circular equilibria with the same plasma mass and magnetic fluxes are unstable.
Cone focusing of intense relativistic electron beams
Authors: Olson Craig L.
Published: February 2004

An analytic theory, embodying an axially-dependent breakdown model, is presented to explain the focusing experienced by an intense relativistic electron beam upon its injection into a gently-tapered, metallic guide tube (cone) filled with a neutral gas. The mechanism of cone focusing is thereby believed to be identified for the first time. The theory predicts the relative efficiency, relative fluence gain, energy loss along the cone, pressure variation, and cutoffs, with full dependence on the beam, cone, and neutral gas parameters. The theory is in good agreement with experiment. It is emphasized that the axially-dependent nature of the breakdown must be considered to explain the focusing; in addition, it is shown why image charges, image currents, or specular reflections can not explain the focusing.
Adiabatic envelope conservation in cone focus trajectories
Authors: Olson Craig L.
Published: February 2004

The envelope of the adiabatic trajectory solution for particle motion that occurs in cone focusing of intense relativistic electron beams is investigated. Comparisons with exact trajectory envelopes (obtained numerically) show that the adiabatic envelope is an excellent approximation under a wide variety of circumstances. Consequently, several important effects are disclosed: (1) The axial dependence of the breakdown (and not the radial dependence) is explicitly shown to determine the focusing, (2) increasing the cone angle rapidly leads to increased losses, (3) angular momentum created by scatter in the anode foil typically should not cause significant losses, and (4) increase of the beam temperature along the cone axis is demonstrated. A novel explanation of “adiabatic envelope conservation” is included.
Electron temperatures and thermal conduction in high-energy θ pinches
Authors: Morse Richard L.
Published: February 2004

The common occurrence of electron temperatures of a few hundred electron volts in θ-pinch experiments is shown by simple analytic arguments to be rather tightly determined by a balance between energy gained from collisions with the much higher-temperature ions and thermal conduction to material walls. It is also shown that electron thermal conduction should not cause a greater loss of energy from straight θ pinches of any length than ion end loss unless rather large magnetic mirror ratios can be obtained. This applies in particular to straight θ-pinch fusion feasibility experiments and fusion reactors. Also several suggestions are presented for reducing end losses and heating plasma columns.
Observations of collisionless drift waves
Authors: LaQuey Robert E.
Published: February 2004

Velocity distribution functions of both the electron and the proton component of the magnetospheric plasma are measured in 62 logarithmically spaced steps from 50 eV to 50 keV by an instrument carried upon the ATS-5 spacecraft in circular synchronous orbit (6.6 earth radii). Oscillations which appear to be collisionless drift waves having periods of several minutes or longer are found in this data. Linearized wave theory can be use to predict the theoretical perturbation distribution function fT in terms of the perturbing fields and the equilibrium distribution function F. The functional dependence of the theoretical perturbation distribution function fT upon particle energy can then be compared with that of the measured perturbation fM. The linear wave theory is found to predict correctly a change in the sign of fM which occurs at a critical particle energy E* and the relative magnitude of fM over the entire energy range.
Limiting Mach number of an embedded ion shock
Authors: Grewal Mahesh S.
Published: February 2004

The ion Mach number seen by the ion shock embedded in a collisional shock propagating in an electron proton gas is found to reach a limiting value of 2.66 as the free stream Mach number goes to infinity.
Current-driven ion acoustic instability in a collisional plasma
Authors: Sundaram A. K. , Kaw P. K.
Published: February 2004

An analytical investigation of the current driven ion wave instability in a collisional plasma, taking account of the background temperature variations, has been carried out.
Phase effects in nonlinear wave-wave interactions
Authors: Fisher R. K. , Hirshfield J. L.
Published: February 2004

An attempt is made to clarify the differences in the nonlinear plasma interaction of two fixed-phase wavepackets from that of two random-phase packets, and present a simple interpretation which is in agreement with the available experimental results.
Effect of induced axial electric field on a relativistic electron beam pulse propagating through a plasma
Authors: Swain David W.
Published: February 2004

If a plasma exhibits anomalous conductivity, the shape of a high-current beam pulse injected into the plasma may be strongly affected after propagating less than one-pulse length.
Stability of a viscous fluid between rotating cylinders with axial flow and pressure gradient round the cylinders
Authors: Elliott L.
Published: February 2004

The stability of a viscous fluid between two concentric cylinders with an axial flow is investigated for the case in which the azimuthal velocity is the sum of a velocity distribution due to the rotation of the cylinders and a “pumping” velocity distribution due to the pressure gradient acting round the cylinders. The outer cylinder is stationary and the spacing between the cylinders is assumed small. For various small Reynolds numbers associated with the axial flow the Taylor number is computed for a large range of values of the ratio of the average pumping velocity to the average velocity of the rotation.
Thermal stability of radiating fluids: The Bénard problem
Authors: Arpaci Vedat S. , Go′zu″m Doğan
Published: February 2004

The Bénard problem of the radiating nongray fluids is examined in terms of the Eddington approximation. The nongrayness of radiation is prescribed by the ratio and product of the Planck and Rosseland means of the absorption coefficient, η = (αP/αR)1/2 and αM = (αPαR)1/2, respectively. Effects of radiation on the classical problem are then characterized by four parameters: the Planck number, P0 (the ratio of conduction to radiation), optical thickness, τ = αMd (d being the distance between the plates) nongrayness of the fluid η and the emissivity of boundaries ε0 and ε1, respectively. The radiation in general has a stabilizing effect; decreasing P0, increasing degree of nongrayness for η > 1, changing color of boundaries from black to mirror all delay the onset of instability. The boundary color and nongrayness of gas are responsible for the extrema observed in stability curves. Accuracy of the Eddington approximation is checked with the exact solution and the convergence of the approximate solution is studied in terms of the first and second approximations. Results are given for black-black, mirror-mirror, and black-mirror boundaries.
Thermal stability of radiating fluids: Asymmetric slot problem
Authors: Arpaci V. S. , Bayazitoğlu Y.
Published: February 2004

The buoyancy driven thermal stability of a radiating nongray gas between two infinitely long vertical plates is studied analytically. The Squire theorem is shown to hold, and two-dimensional disturbances are more dangerous than the corresponding three-dimensional ones. A combination of the Galerkin and Chandrasekhar methods are used to solve the eigenvalue problem associated with two-dimensional disturbances. In contrast to the Benard problem, the effect of radiation on the onset of stationary cells diminishes as the optical thickness of the gas increases indefinitely.
Poiseuille flow and thermal creep of a rarefied gas between parallel plates
Authors: Kanki Tatsuo , Iuchi Satoru
Published: February 2004

A numerical solution of the Boltzmann equation with the Bhatnagar-Gross-Krook model is obtained for Poiseuille flow and thermal creep of a rarefied gas between two parallel plates. The numerical results of Poiseuille flow are in fair agreement wth the experimental data of Dong and predict the Knudsen minimum in volume flow rate. The present results of the thermal creep approach a thermal transpiration formula analyzed on the basis of the elementary kinetic theory of gases as the density of the gas decreases and agree well with Maxwell's equation continuum theory in the range of low Knudsen number. The effect of the thermal creep on the velocity profile of Poiseuille flow is very large, especially at the Knudsen layer near the plate.
Method for the interpretation of surface pressure measurements under rarefied hypersonic conditions
Authors: Harbour Peter J. , Bienkowski George K.
Published: February 2004

A method to interpret properly surface measurements near the leading edge of sharp slender bodies in hypersonic flow is described. The results, using a two-sided Maxwellian distribution function at the surface, are used to relate: (a) the surface molecular flux, Φ, to pc, the pressure in a cavity connected through a sharp lipped orifice to the surface, and (b) the surface normal stress, pyy, to pc and either (method 1) the surface number density or (method 2) the surface heat transfer and shear stress. Attention is drawn to the importance of the correct treatment of normal momentum accommodation coefficient, angle of attack, and orifice geometry. The present method is compared with others in which py y is obtained from pc and while it agrees with them in the continuum and slip regimes, it is the only method to agree with the correct free-molecular flow limit. Flat plate pressure measurements, although made through tubes rather than sharp lipped orifices, are reviewed. Despite the attendant errors, which have been confirmed by very recent work, the following conclusions are drawn. (i) Results from methods (1) and (2) are consistent. (ii) Previous calculations of py y are in error by up to a factor of three when the shear stress is finite. (iii) py y near the leading edge approaches somewhere near the free molecular limit.
Exact solutions for the problem of power-law recompression of a fully developed centered expansion
Authors: Lee T. S.
Published: February 2004

The problem of power-law recompression of a fully developed centered one-dimensional expansion is examined for the case of γ = 3. Two closed-form integrals based on the similarity theory are derived. A physical picture based on finite-amplitude traveling waves is developed. Explicit formulas for the flow distributions in the recompression layer are obtained for the power exponent values of 4/3, 3/2, 2, 3, and 4. Applications to problems in one-dimensional unsteady release and two-dimensional steady escape of detonation products are noted.
Transport coefficients of ionized argon
Authors: Devoto R. S.
Published: February 2004

The electrical conductivity, translational and reactive thermal conductivity and viscosity have been computed for ionized argon in thermodynamic equilibrium at pressues from 0.001-1000 atm and temperatures to 35 000°K. Comparison of the values with experiments shows reasonable agreement.
Probe design for orbit-limited current collection
Authors: Laframboise J. G. , Parker L. W.
Published: February 2004

A new type of electrostatic probe design is proposed, which should permit temperature and density measurements for both ions and electrons from the accelerated current regions of the probe characteristics. Ion temperature measurements, in particular, have been difficult to obtain using standard probe techniques. The method is based on the use of one of a family of nonspherical probe geometries which can be operated as if they were spheres collecting orbit-limited current. One such probe is a proposed multi-electrode system having the advantage that the collector can be made much smaller than the usual spherical probe. The simultaneous use of this probe with a standard orbit-limited cylindrical probe would then enable the above measurements to be made. The multi-electrode probe may itself function as an orbit-limited collector of both the spherical and cylindrical types, with different bias strategies on its electrodes for the two cases. The proposed probe operation is theoretically justified by rederiving the usual orbit-limited current expressions for spheres and circular cylinders, without making any assumption regarding particle angular momentum conservation. The expressions are thereby shown to apply to a wider variety of probe shapes, including: (a) any convex cylinder, (b) any “sufficiently convex” three-dimensional collector (for example prolate and oblate spheroids having major to minor axis ratios up to 1.653 and 2.537, respectively), and (c) the proposed multi-electrode design. Some aspects of probe use in flowing plasmas and in magnetic fields are also discussed.
Continuum analysis of the photoionization chamber in the transition from low to high rates of ionization
Authors: Wardlaw Andrew B. , Cohen Ira M.
Published: February 2004

The photoionization chamber consists of a test gas which is bounded by parallel plates and ionized to a small extent by incident radiation. The charged particles formed by the ionization process diffuse to the walls of the chamber where they recombine. The particle densities and electric field distributions as well as the current-voltage characteristic are studied. At low levels of ionization the electron density is neglected with respect to the ion density. By coupling this simplification with correct scaling, it is possible to obtain analytic solutions. The resulting current-voltage characteristic reflects the rate of ionization as well as the ratio of the ion to the electron temperature. When this ratio is equal to unity, the ion and electron current fluxes saturate at the same rate. If this ratio is less than unity, the electron current flux saturates more slowly than the ion current flux. At higher levels of ionization the electron density can no longer be neglected with respect to the ion density and the problem is solved numerically. The current-voltage characteristic obtained in this case can be approximated analytically at small and large voltages. The expression which applies to small voltages agrees with the results of other double probe studies.
Lagrangian description of phase space flow: Turbulent heating
Authors: Koch Paul
Published: February 2004

Anomalous electrostatic dissipation in a collisionless plasma is caused by an induced charge separation which, in the homogeneous case, is particularly large when high local concentrations of the two species occur close together. If a turbulent plasma state has evolved from an unstable initial state which is only slightly perturbed, particle bunching (with maximum number density proportional to T0−1/4 at low initial temperature T0) takes place at points of overtaking - reversal of the ordering of particles with the same initial velocity. Overtaking is governed by a differential equation which involves the applied field only implicitly. Use of this equation in a simple case shows that a bunch of particles of one species causes bunching in the other species, and that the sense of the resulting turbulent electric field is such as to oppose the laminar motion. The characteristic time of formation of an ion bunch by an electron bunch of incremental number density Δn is (4πe2Δn/mi)−1/2. When the charge separation is expressed in terms of Lagrangian coordinates, a possible example of this phenomenon is revealed by the appearance of islands in the relevant curve. The islands represent adjacent bunches of electrons and ions, and preliminary investigation indicates that they might provide a major portion of the dissipation. A computer study to amplify these findings is proposed.
Theory of light scattering from dense plasmas
Authors: Linnebur E. J. , Duderstadt J. J.
Published: February 2004

Projection operator techniques have been applied to derive a coupled set of exact kinetic equations describing microscopic density fluctuations in an infinite, fully-ionized, classical plasma in thermal equilibrium. The time dependence of the nonlocal collision terms in these equations is then approximated in such a way as to yield the correct short and long time behavior of density fluctuations, while allowing the explicit calculation of the dynamic structure factor S (k ,ω) characterizing electron density fluctuations in classical plasmas of arbitrary density. This theory is then applied to analyze light scattering from dense, collision-dominated plasmas, and the results of these calculations are found to compare favorably with both experimental data as well as with earlier theories (at least in the regimes in which these earlier theories are valid).
Nonlinear evolution of the decay instability in a plasma with comparable electron and ion temperatures
Authors: Kruer W. L. , Valeo E. J.
Published: February 2004

The nonlinear evolution of the decay instability in a plasma driven by an externally imposed pump field oscillating near the electron plasma frequency is considered. For a plasma with comparable electron and ion temperatures and for weak pump fields, nonlinear Landau damping of electron plasma waves on the ions is the dominant nonlinearity. It is demonstrated that a one-dimensional wave kinetic equation describes the dominant interactions for spectral intensities whose characteristic angular width is small. This equation is solved numerically with the exact form for the matrix element which describes the coupling. An analytical solution is found for the spectral intensity in the limit in which the (small) spontaneous emission term is neglected. The plasma wave energies obtained both numerically and analytically are in good agreement. General characteristics of the plasma wave spectrum agree with observations in the ionosphere. The enhanced dissipation rate of the pump due to the presence of the fluctuations agrees with that observed in a laboratory experiment.
Effect of a sheath on the fields of a probe in a hot magnetized plasma
Authors: Singh N.
Published: February 2004

A probe excites two waves, a slow and a fast wave in a hot magnetized plasma when ω<ωp and ωc≫ωp. These waves propagate only within a cone of half-cone angle sin−1(ω/ωp). It is found that the sheath around the probe effectively attenuates the two waves and the slow wave is attenuated more than the fast one.
Transient current overshoot to electrostatic probes in continuum, slightly ionized plasmas
Authors: Cohen Ira M.
Published: February 2004

A spherical probe is subjected to a potential ramp with rise time of the order of the electron diffusion time, after which, the final potential is maintained constant. The electron current overshoots its final value by an amount proportional to the electron conductivity.
Application of the Kubo-Mori theory to the line shape of plasma oscillations
Authors: Walsh J. E.
Published: February 2004

The Kubo-Mori modified theory of Brownian motion is applied to the longitudinal oscillation problem. It is found that the dispersion and friction determined by this theory are equivalent to ordinary plasma dispersion.
Crossover frequencies in multicomponent plasma
Authors: Uberoi C.
Published: February 2004

A method for finding the roots of the equation D = O in a multicomponent plasma with positive and negative ion species is given. The use of dispersion diagrams (ω-k diagrams) for right- and left-circularly polarized waves is made to locate these roots in pass or stop bands.
Effect of satellite waves on the resonant three-wave coupling
Authors: Chang J. , Chang J. S.
Published: February 2004

Resonant wave-wave coupling of a wave-triplet and its satellites are considered. The results show that by including the satellite waves the dynamic behavior of the coupled waves differs significantly from that of an isolated wave-triplet in both the explosive and the decay instabilities.
Axial compression of the astron E-layer during neutralization
Authors: Christofilos N. C. , Fowler T. K.
Published: February 2004

It is shown that, despite processes that tend to elongate the astron E-layer as it is built up by injecting successive pulses of electrons, in a good vacuum this tendency is overcome by the slow turn-on of focusing forces that compress the E layer as it slowly neutralizes.
Lineshape of stable electrostatic fluctuations in a beam plasma system
Authors: Walsh J. E. , Conrad J. R. , Diaz C. J.
Published: February 2004

The stable electrostatic fluctuations in a cylindrical magnetized beam plasma system show a triplet structure. The position and relative height of the peaks are directly related to the linearized dispersion relation.
Saturation in cyclotron resonance heating of plasma
Authors: Arunasalam V.
Published: February 2004

It is shown that a nonlinear change in the distribution function may limit the maximum power that can be dumped into a plasma near cyclotron resonance if a finite k‖ exists.
Correct values for high-frequency power absorption by inverse bremsstrahlung in plasmas
Authors: Johnston Tudor Wyatt , Dawson John M.
Published: February 2004

Numerical corrections are made to previous values for the power absorption coefficient and some common errors noted.
Motion of a turbulent buoyant thermal in a calm stably stratified atmosphere
Authors: Wang C. P.
Published: February 2004

A simple model for the motion of a turbulent buoyant thermal in a calm, stably stratified atmosphere is proposed. Using this model, the average motion of the thermal can be described in terms of its initial density difference, velocity and effective radius, and the three nondimensional gross parameters: mass entrainment constant, effective drag coefficient, and turbulence dissipation rate. Relations between the local turbulence field and the three gross parameters are discussed. Also, the maximum height a thermal can reach in a stable atmosphere for various initial conditions and gross parameters can be approximated by a simple power law relation.
Wave height and wave resistance in the presence of a viscous wake
Authors: Lurye Jerome R.
Published: February 2004

The wave disturbance set up by the uniform motion of a Lagerstrom “singular needle” on or below the free surface of an incompressible viscous fluid is analyzed. Since the motion of this singularity generates a viscous wake, the interaction of the latter with the free surface is automatically included in the analysis. Based on formal expressions derived in earlier work, asymptotic representations for the wave height are derived which are valid for large Reynolds number relative to wavelength and for large distances downstream of the singularity. These representations explicitly show the effect of the viscous wake on the amplitude and phase of the surface waves. A definition of wave resistance is formulated appropriate to the large Reynolds number case, and curves of the wave resistance of the singularity versus speed are calculated.
Trailing vortex-pair instability
Authors: Narain Jai Prakash , Uberoi Mahinder S.
Published: February 2004

The instability of a vortex-pair to infinitesimal disturbances is studied in the inviscid and incompressible fluid approximations. The cores of the vortices contain uniform axial-velocity jets of fluid density different from that of the surrounding medium. In one model a nonrotating core with surrounding potential vortex is assumed, and in the other a uniformly rotating core. In the lowest order of a perturbation parameter, denoting the ratio of vortex core radius to the distance between the vortices, the long-wavelength symmetric amplification factor of a vortex-pair decreases with increasing jet axial-velocity in either model, with decreasing core density in a rotating core model, and with increasing core density in nonrotating core model. The vortex-pair is more unstable to negative mode of deformation than to the positive mode in the presence of an axial jet in both models considered. The surface tension has a destabilizing effect on the vortex pair in the long-wavelength approximations. The effect of core density and jet axial velocity on long-wavelength symmetric amplification factors of the vortex pair in higher orders of perturbation parameters have also been outlined.
Structure of thixotropic suspensions in shear flow: II. Optical properties
Authors: Ross R. A. , Weymann H. D. , Chuang M. C.
Published: February 2004

A theory of the opacity of bentonite-water suspensions as a function of the shear rate is given. The experimental opacity behavior confirms previous theoretical predictions of the aggregate size distribution. The extinction coefficient of bentonite was determined at two wavelengths.
Stability of a plane Poiseuille flow of a finite linear viscoelastic fluid
Authors: Tackels G. , Crochet M. J.
Published: February 2004

The stability of the plane Poiseuille flow of a finite linear viscoelastic fluid is studied without restriction on the magnitude of the natural time. It is assumed that the relaxation function decays exponentially. Curves of neutral stability show the important destabilizing influence of the memory of the fluid.
Stresses on a raindrop falling at terminal velocity in a vertical electric field—A numerical method
Authors: Richards C. N. , Dawson G. A.
Published: February 2004

A technique is presented for calculating all the forces, with the exception of aerodynamic forces, acting on a raindrop falling at terminal velocity in air and subjected to a vertical electrical field such as might occur in the base of a thundercloud. The ultimate aim is a prediction of the onset of hydrodynamic instability of the drop under electric stress. Since as yet no model of aerodynamic flow around the drops is available, this method of calculating the forces and the deduced aerodynamic pressure profiles is presented. These profiles are compared to previous work and are shown to be reasonable. The assumption of a model of aerodynamic flow would allow the prediction of raindrop instability and corona, believed to be responsible for the initiation of lightning strokes.
Heat conduction in binary gas mixtures between concentric cylinders
Authors: Yeh Bao-Tzang , Frohn Arnold
Published: February 2004

The heat conduction in binary gas mixtures of monatomic gases between concentric cylinders is investigated theoretically using Maxwell's moment method. By using Maxwell's force law, analytical results are obtained for small temperature differences. The heat conduction coefficient obtained in the present analysis for the continuum region agrees with the Chapman-Enskog well known result for binary mixtures. In order to check the theoretical results, the heat loss from a fine wire in investigated experimentally for different He-Ar and He-Kr mixtures. The measured heat conduction agrees well with the results of the present analysis.
High-speed leading edge problem
Authors: Huang A. B. , Hwang P. F. , Giddens D. P. , Srinivasan R.
Published: February 2004

The sharp leading edge problem has been studied for both monatomic and diatomic gases using the Boltzmann equation with the Bhatnagar-Gross-Krook type models as the governing equation and the discrete ordinate method with a closed-boundary value approach as a tool. Plate length relative to the freestream mean free path is taken to be 52. The gas-surface interaction law is assumed to be diffuse reflection. The local distribution functions of molecular velocities and internal energies (for the diatomic gas) for the entire flow field have been calculated for M ∞ = 6.1; thus, the complete flow field has been determined for Tw/T0 = 0.11 and 0.18. Comparisons are made between the calculated results and experimental data. It should be pointed out that the present theory provides a technique to calculate not only gasdynamic variables such as density, flow velocity, pressure, and temperature, but also the nonequilibrium distributions of molecular velocities and internal energies that are very useful in the determination of nonequilibrium radiation intensities.
Relativistic gasdynamics
Authors: Chiu H. H.
Published: February 2004

A method is developed to reduce the problem of steady relativistic gasdynamics to an equivalent Newtonian flow. The basic theorems, and laws of the steady relativistic gases are established. Numerical studies of the flow fields of a relativistic shock wave, nozzle flow, and Prandtl-Meyer flow are also presented. The aspects of photon gasdynamics and the basic experiments for the justification of the relativistic photon gas theory are suggested.
Effective collision frequency of electrons in gases
Authors: Itikawa Yukikazu
Published: February 2004

Two kinds of effective collision frequencies are considered for electrons in a gas. They are shown to be useful in the study of various transport properties of electrons. From the best available data on the momentum-transfer cross section, those effective collision frequencies are calculated and tabulated as functions of the electron temperature for H, He, O, Ne, Ar, Kr, Xe, Cs, Hg, H2, N2, O2, CO, NO, H2O, CO2, N2O, NH3, and CH4. Mobilities and diffusion coefficients obtained from the resulting effective collision frequencies are compared with experimental data.
Transport properties of a toroidal plasma at low-to-intermediate collision frequencies
Authors: Hinton F. L. , Rosenbluth Marshall N.
Published: February 2004

The neoclassical plasma transport coefficients for axisymmetric toroidal magnetic confinement systems are calculated in the regime of low-to-intermediate collision frequency. The problem of solving the linearized drift kinetic equations, and calculating the transport coefficients, is formulated as a variational principle. A maximal form of the variational principle, which is valid in the low-to-intermediate collision frequency regime, is used in a numerical solution of the finite dfiference equations, to obtain the distribution function at points on a mesh in phase space. A new analytical result is used to check the accuracy of the numerical calculation for small collision frequencies; this is a correction to the asymptotic banana regime result, obtained from a Wiener-Hopf analysis of the boundary layer in phase space between the trapped and untrapped particle regions. An analytical correction to the plateau regime analtyical result is also obtained. The transport coefficients are found to be monotonic functions of collision frequency, with a gradual transition from the banana regime to the plateau regime. Analytical formulas have been fitted to the numerically computed results.
Model equations for mode coupling saturation in unstable plasmas
Authors: Ott Edward , Manheimer Wallace M. , Book David L. , Boris Jay P.
Published: February 2004

Some simple one-dimensional model equations for instability saturation by resonant mode coupling which are of the general form ∂u/∂t; + σ1 u ∂u/∂x + M[u] = O, where M[u] = i/2π∫ d k ω(k)∫ d x ′ u(x ) exp [k(x − x′)] are examined theoretically and numerically. For nondispersive ω(k), it is found the temporal evolution is characterized by the formation and merging of shocks. Also, the level of saturation can depend on the physical size of the unstable system. If disperisive effects are strong, the solution is characterized by the formation of solitons.
Critical shear and growth rates for drift waves in a nonuniform current-carrying plasma
Authors: Gladd Nevel T. , Horton Wendell
Published: February 2004

From numerical and analytical solutions of the normal mode equation for drift waves in a sheared magnetic field, the critical shear S c for the onset of instability and the normal mode growth rates at subcritical shear are obtained. At low beta and without a parallel current it is shown that approximately twice the previously indicated shear is required for stability and the (m e / m i)1/3 scaling of S c is confirmed. The addition of a parallel plasma current is shown to increase initially the critical shear quadratically with current and then linearly at larger currents. The effect of electron and ion temperature gradients is studied with equal density and temperature gradients resulting in aproximately a 50% reduction in S c. Finally, the effect of finite beta on the critical shear is studied.
Asymptotic behavior of the two-stream instability
Authors: Biskamp D. , Chodura R.
Published: February 2004

The asymptotic or self-similar behavior of the one-dimensional two-stream instability previously observed in numerical simulations is investigated theoretically. The main result, the relation νd = νe, implies a principle of maximum dissipation. On the microscopic level it is shown that the quasilinear solution is inconsistent with νd = ν, and the assumption of an adiabatically growing Bernstein-Greene-Kruskal wave cannot explain the observed similarity law. It is proposed that the observed behavior is due to the instability of a Bernstein-Greene-Kruskal wave. Suitably chosen simulation computations are performed to demonstrate this concept.
Collisionless dissipation of a cross-field electric current
Authors: Biskamp D. , Chodura R.
Published: February 2004

A detailed analysis is given of the development of the electrostatic turbulence excited by a cross-field current in a high density (ωp e ≫ Ωe ) collisionless plasma, as obtained from one- and two-dimensional computer simulations. The drift velocity required for instability is found to be only slightly smaller than the critical drift for the unmagnetic two-stream instability in contrast to the electron cyclotron drift instability. In one dimension the system remains self-similar in the turbulent phase, < Ẽ2 > /8πnTe ≃ const, while the electron thermal velocity and the effective collision frequency increase linearly with time, ν* ∝ Ωet, in agreement with the theory of coherent trapped-electron heating by Forslund, Morse, and Nielson. The switch-off drift velocity, however, is νd ≈ 2cs, and hence the thickness of a magnetic sheath would be Δ ∼ c/ωpi instead of Δ ∼ c/Ωe. In two dimensions two projections are investigated, the j-B plane and the plane perpendicular to B, the latter being the more relevant. The heating is much less efficient than in one dimension, ν * ≲ 5 × 10−3 ωpe. It is found that ν* ∝ 〈Ẽ2〉/8πnT, indicating stochastic dissipation. The gross features of the two-dimensional behavior correspond to the picture of ion-sound instability with electron runaway prevented by gyration.