bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Ion Motion on the Collisional Conductivity of a Magnetoplasma
Authors: Pytte Agnar
Published: February 2004

The collisional contribution to the electrical conductivity is obtained for a magnetoplasma consisting of an arbitrary mixture of charged particle species. The calculation is based on the Landau collision term and is carried out to second order in the wavenumber. Full account is taken of the ion motion.
Early Behavior of Electrode Vapor Jets in a Pulsed Discharge
Authors: Butter D. A.
Published: February 2004

High-speed photographs have been taken of the early stages of a 10-kV pulsed discharge across the tips of two parallel electrodes in background air at a pressure of 40 μ. Two sharply defined, rapidly moving ( ≈ 100 km/sec) luminous fronts are shown to emanate from both electrodes and the front from the anode lags that from the cathode by about 10 nsec. It is suggested that these luminous fronts are the pulsed analogy of the Tanberg vapor jets and a mechanism of their formation, and an explanation of the “anode lag” is hypothesized in terms of brief intensive energy transfer to evaporated electrode vapor by ion-atom collisions in the early stages of the discharge.
Grid Excitation of Ion Waves at Frequencies above the Ion Plasma Frequency
Authors: Doucet H. J. , Gresillon D.
Published: February 2004

The excitation of ion waves is discussed on the basis of a classical model and experimentally studied in a cesium plasma produced in a single-ended Q machine, when a small voltage is applied on a grid immersed in the plasma. For frequencies smaller than the ion plasma frequency fpi, an ion acoustic wave is observed which is consistent with the predictions of the classical linear kinetic theory for a Maxwellian plasma. For higher frequencies (f ≳ fpi) two components are observed. The ion acoustic wave, which propagates for frequencies higher than the ion plasma frequency and a faster signal, called a “psuedowave” which is in satisfactory agreement with the ballistic linear contribution of ions to the voltage perturbation in the plasma.
Solution of Fokker-Planck Equation for Mirror-Confined, Hot-Electron Plasmas
Authors: Lieberman M. A.
Published: February 2004

The Fokker-Planck equation describing the scattering and energy loss of hot electrons in a mirror-confined, hot-electron plasma is solved, neglecting the effect of hot-electron self-scattering, but including the effect of hot-electron scattering against neutrals, ions, and cold electrons. For a class of initial-value problems (no source), expressions for the time-asymptotic form of the distribution function f, the density n, and the mean-square velocity per contained particle 〈υ2〉 are obtained. For a distribution function with an initial Maxwellian or Druyvestian tail scattering against constant density neutrals, f ∼ υβ for small velocity υ and large time t. For a Maxwellian tail, ln n ∼ t2/3 and 〈υ2〉 ∼ t2/9; for a Druyvestian tail, ln n ∼ t4/3 and 〈υ2〉 ∼ t−2/9. Numerical calculations showing the transition to the asymptotic form of the decay are presented. For the case of steady-state injection of hot electrons, expressions for f, n, and 〈υ2〉 are obtained in terms of the given source distribution function.
Fluctuations and Particle Loss in the Spherator
Authors: Goeler S. von , Sadowski M. , Pacher H. , Yoshikawa S.
Published: February 2004

The relation between particle loss and fluctuation level is studied. Stable discharges are found in hydrogen under conditions of long mean free path and high shear, and with gases of high mass under almost all conditions. A comparison is made of the plasma loss in stable and unstable regions. Wave diffusion is estimated from correlation measurements. Particle loss rate and fluctuation level are found to be essentially uncorrelated.
Effect of Trapped Particles on Nonaxially Symmetric Toroidal Equilibria
Authors: Dobrott D. R. , Greene J. M. , Johnson J. L.
Published: February 2004

The effect of trapped particles on nonaxially symmetric toroidal plasma equilibria in the guiding-center limit is treated by means of the stellarator expansion. A few particles, trapped in the mirrors associated with the small-amplitude helical field, can induce an electrostatic field in a manner analogous to that which appears in the familiar treatment of nonlinear electrostatic oscillations in a one-dimensional plasma. These trapped particles directly affect the component of the current along the field and hence the final magnetic field configuration. Thus, they modify the diffusion across magnetic flux surfaces when small resistivity is introduced.
Equilibrium Diffusion Rate in a Toroidal Plasma at Intermediate Collision Frequencies
Authors: Stringer T. E.
Published: February 2004

It is shown that a consistent equilibrium must include an azimuthal electric field. The ambipolar diffusion rate differs in several respects from earlier estimates, although these differences are not primarily due to the azimuthal field. The new rate tends to be lower. In a stellarator field an ambipolar condition may occur in which the electron diffusion due to the toroidal field variation balances the ion diffusion in the helical variation.
Direct Measurement of the Ion Distribution Function in a Toroidal Octupole
Authors: Erickson C. W.
Published: February 2004

The distribution function was found to be a function only of energy and canonical angular momentum Pθ thus automatically satisfying the Vlasov equation, and being consistent with the assumption of a collisionless plasma. The lifetime of the plasma was inversely proportional to ion velocity and directly proportional to accessible phase space volume. The lifetime of 40 eV ions confined in the field was about 500 μsec which is consistent with the interpretation that the plasma is gradually lost to the supports of the current-carrying hoops although it is known that other losses to walls also occur. Density and current were calculated from the appropriate moments of the measured distribution. Plasma is confined primarily in the low-field central region of the octupole, and the density drops rather sharply in the outer regions of higher field, in the horizontal midplane of the device. The only component of ion current was the azimuthal one, which had a maximum value of about 10−4 A cm−2 and indicated a net mass flow in the positive θ direction.
Stability of Asymmetric Hydrodynamically Developing Channel Flows
Authors: Chen T. S. , Sparrow E. M.
Published: February 2004

Linear stability is studied for developing channel flows induced by asymmetric velocity profiles at the inlet. Neutral stability curves and axial variations of the critical Reynolds number are presented, showing greater stability for more skewed inlet profiles.
Linear Stability of Axial Flow in an Annular Pipe
Authors: Carmi S.
Published: February 2004

Rigorous estimates are obtained for amplification rates and wave speeds in the three-dimensional linear stability problem, with the radius ratio nη as parameter. For the axisymmetric case, stronger results are obtained and limits for sufficient stability are derived.
Stability of the Flow of a Slightly Viscoelastic Fluid
Authors: Platten J. , Schechter R. S.
Published: February 2004

The eigenvalues of the generalized Orr-Sommerfeld equation for a slightly viscoelastic fluid are found for a constant velocity profile. The result shows that the flow is always unstable.
Ion Temperatures and Increased End Losses in Q Devices
Authors: Von Goeler S. , Motley R. W.
Published: February 2004

Negative plasma potentials and imperfect radial plasma confinement in Q machine alkali plasmas disturb the plasma equilibrium, raising the ion temperature and the end losses. Calculations pertinent to typical cesium and potassium plasma columns are presented.
Drift Mode Free Plasmas
Authors: Kadish Abraham
Published: February 2004

It is shown that drift modes of other theories cannot be accounted for by a linear analysis of the kinetic guiding center plasma model.
Ion Drift Wave Instability
Authors: Freidberg J. P. , Wesson J. A.
Published: February 2004

In hydromagnetically unstable, shearless plasmas the flute mode, k‖ = 0;, is stabilized for sufficiently large k⊥ by finite Larmor radius effects. It has been widely assumed that this mode is the worst. It is shown that this is not generally correct. In particular, those modes which are finite Larmor radius stabilized for k‖ = 0 are unstable for 0 < k‖ < kc, where kc is identical to the hydromagnetic marginal wavenumber. The instability is due to an ion resonance with the ion drift wave.
Propagation of Low-Frequency Electrostatic Waves in a Magnetic Field
Authors: Joyce Glenn , Dory R. A.
Published: February 2004

The properties of low-frequency electrostatic waves propagating at various angles to a magnetic field in a plasma are studied. Numerical calculations are used to determine the phase velocities, group velocities, damping decrements, and propagation directions for frequencies between zero and twice the ion cyclotron frequency. A model is presented which simulates experimental time-of-flight studies of finite wave packets generated by sine wave bursts.
Quasilinear Stabilization of the Transverse Instability
Authors: Albright Norman W.
Published: February 2004

The transverse instability is studied for the case of an infinite unmagnetized plasma with small electron temperature anisotropy. Growth rates and normal modes are found. Relativistic corrections to the growth rate have a stabilizing effect. The distribution function satisfies a diffusion equation with an additional flow term. The diffusion term causes the anisotropy to disappear and thus stabilizes the instability. The flow term is a perfect time derivative and makes no contribution to the net change in the distribution function between initial and final states which have negligible wave spectra.
Structure of Evolving Ion-Acoustic Fronts in Collisionless Plasmas
Authors: Mason Rodney J.
Published: February 2004

Exact analytic solutions are obtained to the linearized, two-species Maxwell-Vlasov equations for the evolution of an initial step-function density discontinuity in an initially neutral, collisionless plasma. These solutions have been evaluated numerically for hydrogen plasmas with starting temperature ratios 0 ≤ θ = Te/Ti ≤ 30, for times 0 ≤ τ = ωpit ≤ 100, and over distances into the original low-density region 0 ≤ η = x/Ait ≤ 12, where Ai is the mean thermal speed of ions. For τ ≪ 1 both species simply free stream. By late times (τ ≳ 30) quasineutrality of the perturbation has been established, and it is found that: (1) the ion profiles for θ ≲ 1 exhibit the appearance of free streaming at an enhanced ion temperature, suggesting that the strong Landau damping usually attributed to the low-θ limit might better be termed “ambipolar free streaming,” (2) for θ ≃ 5 they are self-similar and monotonic with a steep leading edge near η = θ1/2 followed by a broad, arched trailing edge accounting for half the density rise, and (3) for θ ≳ 30 they have a steep but spreading leading edge near θ1/2 and general resemblance to the integrated Airy function profile obtainable through a moment equation treatment retaining only the last damped collective mode.
Plasma Shielding
Authors: Friedman Herbert W. , Levi Enrico
Published: February 2004

Necessary and sufficient conditions are established for the shielding of current-carrying plasmas by means of space charge sheaths. These conditions reduce to Bohm's shielding criterion in the particular case of zero current and, in general, are consistent with measurements obtained by means of Langmuir probes and their current interpretation.
Collisionless Sheath—An Experimental Investigation
Authors: Goldan Paul D.
Published: February 2004

An electron beam probing technique has been utilized to measure the sheath electric field distribution near a planar floating plate immersed in a low-pressure argon arc discharge plasma. The static sheath field determined by this nonperturbing measurement is compared with the predictions of the collisionless or free-fall model of the sheath. The agreement is found to be so satisfactory that such static sheath field measurements, supplemented by a floating potential measurement, are sufficient to yield accurate values of the plasma electron density and temperature.
Sheath Structure in a Plasma Diode
Authors: Sockol Peter M.
Published: February 2004

The plasma diode is proposed as a vehicle for testing theories on sheath structure with collisions. A kinetic theory model of the plasma-sheath transition is used to analyze the operation of the diode. In particular the sheath structure at the cold collector is obtained in the limiting cases where the local Debye length is much larger than and much smaller than the mean free path. Comparison of the theoretical current-voltage characteristics with experimental ones obtained in a cesium thermionic converter shows that the slopes of the theoretical limiting curves bracket the experimental behavior quite closely. The theory is used to obtain values for the electron and ion diffusion coefficients and the collector work function.
Alternating Current Diagnostic Study of Diffusion in a Highly Ionized Plasma in a Magnetic Field
Authors: Flannery D. L. , Brown Sanborn C.
Published: February 2004

A new ac diagnostic technique has been used to study the radial diffusion of a highly ionized hollow cathode discharge plasma in a magnetic field. The method involves generating very low-frequency density waves in one region of the plasma and observing the diffusion of these waves through the remaining plasma. The spatial variations of phase and amplitude of the density modulation were measured with a Langmuir probe and compared with theoretical predictions corresponding to two possible diffusion mechanisms: Bohm and collisional-ambipolar. The diffusion coefficient entered as a variable parameter in each theory and was adjusted for best agreement with data in each case. Best agreement was obtained with the collisional-ambipolar theory using approximately the value of diffusion coefficient predicted for that diffusion mechanism for the plasma used.
Faraday Rotation of a Far-Infrared Laser Beam by a Small Theta-Pinch Plasma
Authors: Turner R. , Poehler T. O.
Published: February 2004

Faraday rotation measurements have been made on a small theta-pinch plasma using the 337, 128, 119, and 79 μm wavelength radiation of the HCN and H2O gas lasers. Rotation angles of up to 50 deg have been measured with an accuracy, set mainly by the laser source, estimated to be better than 10%. Enhancement or attenuation of the transmitted signal produced by density gradients in the plasma has been measured simultaneously to correct the rotation measurements. The Faraday rotation measurement confirms that a magnetic probe placed in the plasma perturbs the actual field present.
Mode Coupling at the Boundary of a Relativistic Collisionless Plasma
Authors: Imre Kaya , Ozizmir Ercument
Published: February 2004

The exact solution of the linearized transmission and reflection problem for electromagnetic waves obliquely incident on a half-space relativistic Vlasov plasma is obtained in the case when the electric field is polarized in the plane of incidence. It is assumed that electrons are reflected specularly at the boundary, and ion dynamics is ignored. Coupling of transversal and longitudinal components at the boundary and their propagation characteristics are studied in detail. Numerical results for the calculation of the skin depth and the phase velocity of the discrete modes in the first Riemann sheet are included.
Cyclotron Harmonic Emission by Mode Conversion in a Nonuniform Plasma Slab
Authors: Alper A. T. , Gruber S.
Published: February 2004

Electromagnetic emission from a warm collisionless nonuniform plasma slab is considered for frequencies of observation near the second electron cyclotron harmonic. The model for the emission mechanism is that fast electrons in the dense plasma core generate electrostatic waves which are then trapped in the high-density region between the upper hybrid resonance points where the electrostatic waves drive the extraordinary wave which propagates out of the plasma. The energy lost by the fast particles to longitudinal waves is evaluated by retaining collisionless damping using a dressed test particle approach. The electromagnetic radiation field is calculated using an equation which includes coupling between the longitudinal and transverse fields in the density region encompassing the upper hybrid frequency [ωp2(x) = ω2−ωc2]. The calculation shows that the emission spectrum contains a fine structure and that as much as 90% of the longitudinal wave energy is converted into electromagnetic wave energy.
Thermal and Electromagnetic Forces Induced by the Interaction of Laser Radiation with a Plasma
Authors: Steinhauer Loren C. , Ahlstrom Harlow G.
Published: February 2004

The interaction of laser radiation with a hot nonuniform plasma is examined. Two types of forces, thermal and electromagnetic, have been shown to be important. The magnitudes of these forces are determined for the interesting ranges of temperature and density.
Collisionless Electrostatic Shocks
Authors: Andersen H. K. , Andersen S. A. , Jensen V. O. , Nielsen P. , D'Angelo N.
Published: February 2004

An attempt was made in the laboratory to observe the standing collisionless electrostatic shocks described by Tidman in connection with the bow shock of the earth.
Scattering of Electromagnetic Waves by a Nonuniform Magnetized Plasma Column
Authors: Greenwald R. A.
Published: February 2004

A comparison is made between the complete electromagnetic and a quasistatic solution for the upper hybrid resonance scattering spectrum from an infinitely long, radially inhomogeneous, magnetoplasma column to determine when the latter solution is in error.
Instability of the m = 1 Mode of a Rotating θ Pinch
Authors: Freidberg J. P. , Wesson J. A.
Published: February 2004

It is shown here that in contrast to previously published results, the m = 1 mode of a rotating θ pinch is magnetohydro-dynamically unstable.
Nonlinear Stability of a Liquid Jet
Authors: Nayfeh Ali Hasan
Published: February 2004

A nonlinear analysis is presented for the capillary stability of a cylindrical column of liquid, of circular cross section. A second-order expansion is obtained using the method of multiple time scales. It is found that the cutoff wavenumber which separates stable from unstable disturbances is amplitude dependent, in agreement with Yuen, and contrary to the linearized analysis. Axisymmetric disturbances with wavenumbers greater than k′ = (1+3a2/4R2)R−1 where a is the disturbance amplitude and R is the radius of the undisturbed jet, oscillate and are stable. However, the frequency of oscillation is amplitude-dependent, contrary to the linearized results. Below this cutoff wavenumber disturbances grow with time. It is also found that the application of the method of straining of coordinates to this problem leads to erroneous results for wavelengths near the circumference of the jet.
Stokes' Problems in Kinetic Theory
Authors: Scharf G.
Published: February 2004

Stokes' problems, concerning the steady flow of a viscous fluid past a sphere and a circular cylinder, have been solved using the linearized Boltzmann equation. The solutions obtained are well behaved at infinity; Stokes' and Whitehead's paradoxes do not occur. For the sphere the well-known drag formula P = 6πvrηρ(1+38R...) is found. The results for the drag on the cylinder are in better agreement with experimental values than the classical formula of Lamb.
Growth and Decay of Curved Acceleration Waves in Chemically Reacting Fluids
Authors: Doria Michael L. , Bowen Ray M.
Published: February 2004

The propagation of curved acceleration waves in a mixture of ideal fluids in which chemical reactions are taking place is discussed. The purpose is to investigate the strength of the attenuation induced by geometric factors for expanding waves relative to the growth induced by thermochemical instabilities. Solutions for the wave amplitude are given for waves of general shape and are specialized to the case of spherical and cylindrical waves.
Radiatively Driven Acoustic Waves Independent of the Substitute-Kernel Approximation
Authors: Cogley Allen C. , Compton Dale L.
Published: February 2004

Analytical solutions for radiatively driven waves in one-dimensional radiative acoustics are obtained by an approximation for the radiative heat addition. The gas is nongrey, in molecular equilibrium, and for simplicity assumed to be thermally perfect. The resulting approximate, but asymptotically exact, wave equation is solved for the problems of (1) the discrete wave produced in a half-space by a step input of radiation from a wall and (2) the pressure response at one boundary of a confined gas due to a sinusoidal input of radiant energy from the other. Closed-form solutions per unit spectral frequency are obtained in terms of exponential-integral functions. The accuracy of the corresponding substitute-kernel solutions is found by comparison with these asymptotically exact results.
Characteristics of a Spherical Electrostatic Probe in a Bounded Plasma
Authors: Cohen Ira M.
Published: February 2004

Spherical electrostatic probes immersed in a slightly ionized, collision-dominated plasma bounded by a large concentric spherical electrode of radius Rw are treated by asymptotic continuum theory when the sheath thickness is small compared with the probe radius rp but large compared with a mean free path. It is found that when Rw/rp is large, the saturation currents are modified by only O(rp/Rw). However, the maximum slope of the characteristic increases by 20% as Rw/rp increases from 100 to infinity. Since this slope increases similarly as the electron to ion temperature ratio τ increases, it is concluded that reduction of data for measurements in bounded plasmas using continuum theory for unbounded plasmas leads to values of τ (and usually T_) that are smaller than the true values.
Non-Maxwellian Equilibrium Distribution for Free Electrons in a Plasma
Authors: Wright T. P. , Theimer O. H.
Published: February 2004

A free (bound) electron in a plasma is defined by requiring that its total energy ε be larger (smaller) than some negative value E*, which may be thought of as the energy E(ν*) of an electron in a Bohr orbit with principal quantum number ν*. This separation of bound and free states is explicitly incorporated into the electron partition function. The free electrons can then be treated by classical statistics without encountering the familiar Coulomb divergence. It is found that an electron moving in the potential well of a nearest neighbor ion has a non-Maxwellian kinetic energy distribution given by f(w) = (β/a)(βw)1/2G(βw) exp (−βw), with w = 1/2mυ2, β = (kT)−1, and a is a normalization constant. The non-Maxwellian term clearly resides inG(κ =  ∫ t0κ + t0 exp (t)dtt4, where κ = βw, t0 = βe2/r0, r0 is the average interparticle distance, and e is the magnitude of the electronic charge. G(κ) can be expressed in terms of tabulated functions. The average kinetic energy of an electron with a nearest-neighbor ion has a dominant correction term proportional to the Debye-Hückel energy e2/D, where D is the Debye length, in agreement with previously published results. The consequences of this distribution function on the Einstein relation and Wiedemann-Franz law are investigated.
Plasma Motion Induced by High-Intensity Laser Heating
Authors: Rehm Ronald G.
Published: February 2004

The macroscopic plasma response to absorption of laser radiation is examined in a one-dimensional geometry. Euler's equations with inverse bremsstrahlung energy absorption and the radiative transport equation neglecting emission and reabsorption are the governing model equations. The parameters deriving from this model are the Bouguer number, measuring the ratio of the characteristic plasma length to the absorption length at the laser frequency, and the Boltzmann number, measuring the ratio of the characteristic convective energy flux to the laser radiative energy flux. The response to incident laser radiation of an absorbing plasma slab, bounded on one side (the side from which the laser radiation impinges) by a cold, nonabsorbing gas and on the other side by a reflecting wall, is examined in detail. The initial types of plasma response are classified according to the magnitude of the Bouguer and Boltzmann numbers. For large rates of energy addition the plasma will undergo either a radiatively driven shock-wave response or a heating wave response, which is characterized by high temperatures with no induced plasma motion. An analytical solution for the heating wave and numerical solutions for each type of response are presented.
The Problem of Ambipolar Diffusion of Finite Magnetoplasmas
Authors: Geissler Klaus H.
Published: February 2004

The diffusion of weakly ionized plasmas across a magnetic field is studied by measuring their decay rates. The variation of the experimental data with magnetic field and pressure is found to be in agreement with the theory of classical diffusion. However, the absolute values of the experimental data cannot be explained in terms of ambipolar diffusion. A comparison of the data with experimental results from different authors is given. The combined experimental evidence suggested that the assumption of ambipolarity is inappropriate for the treatment of actual problems of plasma diffusion across a magnetic field. The influence of mixed boundary conditions on transverse diffusion is discussed.
Radiative Reactions in the Resistive-Diffusion Problem
Authors: Newcomb William A.
Published: February 2004

In the problem of resistive diffusion of magnetic flux lines in a one-dimensional magnetohydrodynamic system, there is an apparent indeterminacy due to insufficient boundary conditions. The indeterminacy is here resolved by the use of radiation conditions at infinity. There is an outflow of momentum from the diffusive region by radiation of magnetoacoustic waves.
Wave Instabilities in Partly Ionized Gases
Authors: Morin Stephen , Kahn David
Published: February 2004

A collisional theory of longitudinal wave propagation in partly ionized, multitemperature gases is formulated from a coupled set of Maxwell and Boltzmann equations. Equations of motion for the three plasma constituents (electrons, ions, and neutrals) are developed by expanding the particle distribution functions in series of Hermite polynomials about equilibrium, Maxwellian distributions which are specified by the macroscopic temperatures of the various plasma species. Employing the equations of continuity, momentum, and energy (inviscid approximation), we obtain a dispersion equation relating the propagation constant to the wave frequency for small amplitude, longitudinal waves. It is found that all three propagation modes (neutral, ion, and electron waves) exhibit instabilities under conditions determined by the wave frequency and the temperature differences among the plasma components. Numerical and analytic data are presented to illustrate these wave instabilities, with particular emphasis being placed upon propagation in weakly ionized gases.
Interactions of Waves and Particles in an Inhomogeneous One-Dimensional Plasma
Authors: Kaufman Allan N. , Nakayama Toshio
Published: February 2004

When a one-dimensional plasma is confined by a static potential, the electric field fluctuations can be described in terms of normal modes. A mode interacts resonantly with a particle whose bounce frequency is an integral submultiple of the mode eigenfrequency. This leads to energy exchange and quasilinear diffusion of particles. Kinetic equations are derived for the evolution of mode energy, due to wave emission and to damping or growth; and for the evolution of the particle distribution in action space, due to radiation reaction and quasilinear diffusion. These equations have an H theorem, implying an approach to thermal equilibrium (in the absence of neglected effects). The mode-particle coupling coefficient is expressed explicitly, and is approximated for the limiting cases of high eigenfrequency and of short wavelength.
Temperature Effects on High-Frequency Beam Plasma Interaction
Authors: Seidl M.
Published: February 2004

The dispersion equation corresponding to the interaction of an electron beam with a Maxwellian plasma has been solved in quasistatic and infinite geometry approximations. Two representative beams are considered: a parallel beam with isotropic velocity spread and a helical beam with different longitudinal and transverse temperatures. The aim of the work is to predict the frequency, growth rate, and wavenumbers of the most unstable waves as functions of the basic beam and the plasma parameters. The results of the calculations are presented in graphs suitable for comparison with the experiments. The effect of plasma and beam temperatures on the spectrum of the instabilities is discussed in detail. It is shown that the plasma temperature reduces the growth rate of the instabilities at cyclotron harmonic frequencies while a velocity spread in the helical beam suppresses the instabilities everywhere, except in the vicinity of the cyclotron harmonics.
Phase Space Hydrodynamics of Equivalent Nonlinear Systems: Experimental and Computational Observations
Authors: Berk H. L. , Nielsen C. E. , Roberts K. V.
Published: February 2004

The one-dimensional Vlasov equation describes the behavior of an incompressible self-interacting classical fluid which moves in the (q, p) phase plane. This type of phase fluid occurs in many physical problems and its hydrodynamic properties can be examined from a general point of view. A characteristic feature with initially unstable spatially homogeneous configurations is the development of stable nonlinear phase structures. Such examples occur as the result of the gravitational Jeans instability, or the two-stream and negative-mass instabilities of charged-particle beams. These structures can be related to one another by extending a duality principle due to Dory. The stable cavities in phase space which have been observed in numerical calculations on the two-stream instability are compared with stable proton clusters which develop from the negative-mass instability in the mirror experiment DCX-1.
Technique for Determining the Propagation Characteristics of Instabilities
Authors: Lee D. A. , Soper G. K.
Published: February 2004

A method for obtaining an approximation to the large-time behavior of instabilities which are represented by multidimensional Fourier integrals of a type which arises in dispersion relation studies is discussed. Applications to moving striations, the beam-plasma instability, and to the ion-cyclotron resonance instability are given and the results compared with those of other methods.
Instability of Time-Periodic Flows of Stratified Fluids
Authors: Li Chin-Hsiu
Published: February 2004

The instability of two liquid layers with a free surface set in motion by an oscillatory lower boundary is analyzed for two superposed fluids with different viscosities and different densities. There are two modes of wave motion: the interfacial and the free-surface modes. When the Froude number is less than about 3, the interfacial mode governs the instability of the flow. For this case the free-surface mode is always stable. The two surfaces of discontinuity are always in the phase for the free-surface mode of disturbance, but may be in phase or 180 deg out of phase for the interfacial mode. The two modes, however, are found to compete with each other for governing the instability of the flow when the Froude number is larger than 3. The two surfaces of discontinuity can be out of phase by an angle different from 180 deg.
Collapse of Spherical Cavities in Viscoelastic Fluids
Authors: Fogler H. S. , Goddard J. D.
Published: February 2004

An analysis is given of the collapse of a spherical cavity in a large body of an incompressible viscoelastic liquid. Proceeding from a linear rheological model for the liquid, one obtains a nonlinear integro-differential equation for the motion of the cavity. Analytical solutions are derived for certain limiting values of the parameters governing collapse, and some numerical solutions are presented for various other values. As one of the more interesting results of this work, it is found that elasticity in the liquid can significantly retard the collapse of a void and produce prolonged, oscillatory motion whenever the relaxation time of the fluid is moderately large in comparison to the Rayleigh collapse time. This is in sharp contrast to the catastrophic collapse which will aways occur for voids in purely viscous liquids. Both numerical and approximate analytical solutions are presented to demonstrate the damping effect of liquid viscosity on the cavity motion.
Experimental Model for High-Speed Rarefied Flow over a Sharp Flat Plate
Authors: Lillicrap D. C. , Berry C. J.
Published: February 2004

A flow field survey has been made of the shock layer development on a flat plate, at M = 6, from just upstream of the leading edge to downstream of the merged layer. The electron beam fluorescence technique has been used to measure density profiles from which a comprehensive description of the flow field is constructed. Close to the leading edge the flow is near free molecular and can be described in terms of two effective mean free paths, as proposed by Hamel and Cooper. The results suggest that continuum flow is not established for a distance approximately four times the mean free path for the collision of a free stream molecule with a body molecule. An upstream disturbance occurs a few free stream static mean free paths ahead of the leading edge, although this was aerodynamically sharp.
Self-Similar Strong Shocks with Radiation in a Decreasing Exponential Atmosphere
Authors: Laumbach Dallas D. , Probstein Ronald F.
Published: February 2004

The self-similar one-dimensional flow behind a plane shock propagating upward into an exponentially decreasing atmosphere is considered. The flow is taken to be isothermal in view of the large radiation mean free paths associated with high altitudes and the intense radiation heat transfer accompanying the high temperatures characteristic of an accelerating shock wave. The equations of motion are formulated in Lagrangian coordinates and are integrated exactly for all values of the shock density ratio. Solutions are presented for the cases where the boundary conditions at the shock correspond to a Hugoniot shock and to a Chapman-Jouguet shock. A significant result of the analysis is that in both of these cases the shock propagates much faster than for the case of adiabatic flow.
Perturbations of Plane Blast Waves
Authors: Gerwin Richard A. , Hall Richard B.
Published: February 2004

The disturbance of a plane blast wave by surface ripples is examined. A thin sheet approximation to the geometry makes it possible to obtain a set of ordinary differential equations which describe the sheet motion. Numerical solutions of these equations show that the ripples grow rapidly at first but are eventually limited in amplitude, within the linearized theory. A variety of types of oscillation are sustained. Since the thin sheet model breaks down at large times for finite wavelengths, the question of stability of the plane blast wave for finite wavelengths cannot yet be solved. However, for infinite wavelengths, the sheet model proves to remain valid, and is found to be weakly unstable.
Exact and Chapman-Enskog Solutions of the Boltzmann Equation for the Lorentz Model
Authors: Hauge E. H.
Published: February 2004

The Boltzmann equation for the Lorentz model, where noninteracting classical point particles move through a random array of stationary scatterers (hard spheres), can be solved exactly. Also the corresponding Chapman-Enskog solution, and thus the hydrodynamical equation, can be found in closed form, i. e., to all orders in the gradients. A detailed explicit discussion of the relationship between the two solutions is given. The limitations of the Chapman-Enskog development (in the standard meaning of the term) as a method for solving the initial value problem of the Boltzmann equation are discussed, and the resolution of the Hilbert paradox is given.
Electron Distribution and Transport Phenomena in a Lorentzian Magnetoplasma
Authors: Buti B.
Published: February 2004

The electron distribution functions, required for the evaluation of the transport coefficients in a homogeneous Lorentzian plasma, are derived in the presence of a uniform external magnetic field which is strong enough to affect the interparticle collisions but still small enough for ωc/ωp (ωc and ωp being the electron cyclotron and plasma frequencies) to be used as an expansion parameter. The coefficients of electrical conductivity, thermal diffusion, and viscosity are determined through these functions. The effect of magnetic field, through collisions, up to second order in (ωc/ωp) vanishes identically for conductivity and diffusion; for viscosity although it does not vanish, it is negligibly small.
Electron-Beam Echo
Authors: Hinton F. L. , Kawabe T.
Published: February 2004

The existence of an electron-beam echo is demonstrated, and its properties are described. The use of the beam echo as a diagnostic for fluctuations in a plasma is discussed.
Ion Correlations due to a High-Frequency Electric Field and Their Effect on the Nonlinear Plasma Conductivity
Authors: Sanmartin Juan R.
Published: February 2004

The influence of a strong, high-frequency electric field on the ion-ion correlations in a fully ionized plasma is investigated in the limit of infinite ion mass, starting with the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy of equations; a significant departure from the thermal correlations is found. It is shown that the above effect may substantially modify earlier results on the nonlinear high-frequency plasma conductivity.
Power Spectrum of Radar Returns from an Underdense, Turbulent, Ionized Gas
Authors: Johnson Kent R.
Published: February 2004

An analysis is given of the time autocorrelation function and the power spectrum to be anticipated in electromagnetic scattering from an underdense, turbulent, ionized gas. The autocorrelation function and power spectrum are obtained in terms of a parameter describing electron density decay and of parameters describing the turbulence. It is shown that when electron density decay is significant, broader spectra, and slower decay of spectral width, may be obtained than might be anticipated by the application of the usual Doppler formula to the rms turbulent velocity fluctuation.
Transverse Resistive Shock Waves
Authors: Coffey T. P.
Published: February 2004

The existence and structure of transverse resistive shock waves is discussed within the framework of the two-fluid theory. The analysis incorporates the effects of electron inertia, finite pressure, charge separation, and electrical resistivity. Critical Mach numbers above which resistive shock waves cannot exist are obtained as functions of the fluid-to-magnetic pressure ratio. These critical Mach numbers are not related to the critical Mach numbers obtained in the cold plasma theory. It is shown that the wavelength of the downstream oscillations can be considerably different from that predicted by cold plasma theory, especially in the vicinity of the critical Mach number. Where possible, comparison is made with the results obtained from cold plasma theory.
Penetration of an Electromagnetic Wave into a Hot Plasma Slab
Authors: Blevin H. A. , Reynolds J. A. , Thonemann P. C.
Published: February 2004

The penetration of a small-amplitude high-frequency electromagnetic wave into a plasma slab is calculated making allowance for the thermal motion of electrons. For low collision rates the electromagnetic field distribution in the plasma is strongly dependent on the ratio of the wave period to the transit time of electrons crossing the slab.
Ion Temperature Sensitive End Effect in Cylindrical Langmuir Probe Response at Ionosphere Satellite Conditions
Authors: Hester S. D. , Sonin Ain A.
Published: February 2004

Computations and experiments are presented for an end effect which can dominate the ion current response of long, cylindrical Langmuir probes in high-speed collision-free flows. The end effect, which takes the form of an increase in ion current when the probe is aligned with the flow direction, depends strongly on the plasma properties and flow speed, and can be large even for very long probes when the speed ratio is large and the probe radius small compared with the Debye length. Experimental data are compared with theory, and some apparently contradictory results reported in the literature are reconciled in terms of the end effect.
Linear Instability of Some Finite Amplitude Ion Waves
Authors: Su C. H.
Published: February 2004

The linear instability of periodic wave trains in a plasma consisting of cold ions and equilibrium electrons without magnetic field is studied. Small but finite amplitude wave trains with infinitesimal disturbances are considered using the method commonly used in parametric resonance. It is found that periodic waves are unstable if the square of their wave speed [normalized by the ion acoustic speed (KTe/mi1/2] is less than 13.
Landau Damping of Ion Acoustic Waves in a Uniform Magnetic Field
Authors: Hirose A. , Alexeff I. , Jones W. D.
Published: February 2004

Landau damping of ion acoustic waves in a relatively weak magnetic field has been experimentally studied. Both artificially created contaminant Landau damping and electron Landau damping have been examined for arbitrary propagation angles from 0° (parallel)to 90° (perpendicular). It has been found that for perpendicular propagation, the contaminant Landau damping disappears for wave frequencies ω such that ω < ωciHe. Also, for ω > 4ωciHe, the damping without magnetic field has been completely recovered. Electron Landau damping is observable only when the waves propagate almost perpendicularly to the magnetic field. The wave frequency has been kept much higher than the major ion cyclotron frequency so that the ion acoustic waves can propagate in any direction.
Pressure Distribution in the Structure of a Propagating Current Sheet
Authors: York Thomas M. , Jahn Robert G.
Published: February 2004

The structure of the current sheet in a dynamic z pinch in argon is studied with a specialized highspeed piezoelectric pressure transducer capable of following profiles of axial and radial pressure within the discharge. Correlation of these data with electric and magnetic field profiles, luminosity, and voltage records, indicates three distinct zones within the sheet in sequence, regions of electron current conduction, mass accumulation with ion current conduction, and induced flow of unswept gas. Profiles of particle density, velocity, and temperature are evaluated on the basis of a simplified gas-kinetic model. The current sheet is found to entrain a large percentage of the gas encountered, and a momentum balance across the sheet is in approximate agreement with snowplow predictions, but the distributions of current and mass density differ categorically from conventional piston-shock wave models.
Instabilities in Parametric Oscillations of a Plasma in a Magnetic Field
Authors: Prasad R.
Published: February 2004

A dispersion relation for transverse waves with a propagation vector along the direction of a constant magnetic field pervading a plasma medium in response to an externally applied circularly polarized or hybrid electric field with the electric vector perpendicular to the magnetic field has been obtained. The zero-order state of the plasma is defined by these external fields with a zero-order plasma current and a zero-order external current, both of which have oscillatory parts with frequencies ν (frequency of the applied field) and Ω (the electron cyclotron frequency). It has been shown that in all cases the left-hand mode is excited with frequency ≃ Ω − ω0, where ω0 is the electron plasma frequency, and instabilities may occur provided Ω is large. Excitation and instabilities are also possible with frequency ≃ ν − ω0 in both modes under certain restrictions. The principal criterion for these restrictions is the validity of the assumption of spatial homogeneity of the imposed electric field.
Effects of a Magnetic Guide Field on the Propagation of Intense Relativistic Electron Beams
Authors: Andrews M. , Bzura J. , Fleischmann H. H. , Rostoker N.
Published: February 2004

In the absence of a magnetic guide field, intense relativistic electron beams will not propagate because the electrostatic repulsive forces always dominate the magnetic pinching forces. It is necessary to have some background ions to reduce the space charge of the beam. With a sufficiently strong magnetic guide field in the direction of propagation, it is, in principle, possible to have an equilibrium with no ions. The theoretical basis for un-neutralized propagation and beam focusing is presented. Experiments have been carried out that indicate qualitative changes in beam propagation and focusing with a guide field.
Convective Losses in a Thermionic Plasma with Shear
Authors: Mosher David , Chen Francis F.
Published: February 2004

Experiments on anomalous transport in a Q machine with a hard core providing magnetic shear show shear-dependent particle losses in the absence of oscillations. It is demonstrated that these Bohmlike losses are caused by steady plasma convection in asymmetric electric fields produced by small temperature gradients in the end plates and that the effect of shear is to symmetrize the convective patterns by twisting the equipotentials into tight spirals. A finite-Larmor-radius theory of transport by convection is presented which correctly predicts the observed increase of confinement with shear. Estimates of the absolute magnitude of losses by this mechanism indicate that at least half of the anomalous transport in Q machines is due to plasma convection, at least in magnetic fields below 4 kG.
Effects of Spatial Variations on Collisional Losses in a Mirror-Confined Plasma
Authors: Marx K. D.
Published: February 2004

The results of a numerical procedure for solving a spatially dependent Fokker-Planck equation for plasmas in mirror-confinement systems are presented. Ion distributions are evaluated as functions of speed and angle in velocity space, while the electron distribution is assumed to be approximately isotropic and Maxwellian (except for the absence of particles in the loss region). Ion-electron interactions are accounted for, as well as ambipolar potential effects. In addition, the effects of variations in plasma parameters along field lines are included by integrating sources and losses along guiding center orbits. Data from several sample calculations are given to illustrate the effects of spatial dependence, variations in particle current and mirror ratio, and slow-ion trapping.
Comparison of Three Sets of Higher Order Adiabatic Plasma Equations
Authors: Wilson Gerald E.
Published: February 2004

A comparison is made among three methods of obtaining highly accurate approximate expressions for the average motion of plasmas in slowly varying electric and magnetic fields. It is shown that no inconsistencies are revealed by this comparison and that, in fact, two of the techniques are completely equivalent while most of the results of the third can be obtained from the equivalent pair. As a by-product of the comparison, a function is obtained which can be shown to be conserved along the guiding center trajectory.