bluuebunny/crossref_metadata_2025 huggingface dataset:
Scattering of Electrons by Electrostatic Fluctuations in a Magnetized Plasma
Authors: Walsh J. E. , Bancroft D. , Hawkins C. , Layman R. W.
Published: February 2004

The scattering of beam electrons in a beam formed, magnetized plasma has been measured experimentally. Evidence for an effective inverse mean free path which depends upon the intensity and width of the beam excited fluctuations is presented. The model used to interpret the experiment is based upon an elementary application of the Fokker-Planck equation and the theory of Brownian motion. It includes the effects of velocity space diffusion. Mean free paths between 10 and 103 cm are found to be in agreement with the predictions of our model. The ordinary collisional attenuation of the beam under the same operating conditions is several orders of magnitude smaller.
Flow Visualization using Chemiluminescent Radiation
Authors: Bien F. , Davidor W. , Penner S. S.
Published: February 2004

Flow visualization using the chemiluminescent luminol oxidation is discussed. Representative results are described which show the advantages inherent in the use of this technique.
Measurement of Drift Wave Potential Oscillations in the Presence of Temperature Oscillations
Authors: Motley R. W. , Ellis R. F.
Published: February 2004

Floating potential oscillations on a Langmuir probe are found to lead density oscillations in drift wave instabilities of a thermally ionized cesium plasma. This contradiction of the isothermal theory is attributed to oscillations of the electron temperature.
Modification of the Quasilinear Equations
Authors: Abraham-Shrauner Barbara
Published: February 2004

Modified quasilinear equations are derived for the marginally and weakly stable states of an initially unstable plasma. Comparison with computer simulations indicate the equations may explain two-dimensional but not one-dimensional plasma stabilization.
Anomalous Heating of Plasma Electrons Driven by a Large Transverse Field at ∼ωpe
Authors: Kruer W. L. , Dawson J. M.
Published: February 2004

Numerical experiments on a plasma driven by a large-amplitude transverse field oscillating at nearly twice the electron plasma frequency are presented. The large wave drives the electrostatic plasma waves unstable. When these unstable waves grow to large amplitude, they efficiently transfer energy to the plasma particles. A simple theory to explain the results is presented.
Conservative Trapping of Charged Particles in a Static Magnetic Field
Authors: Hogan W. A. , Lamborn B. N. A.
Published: February 2004

A computer analysis is made of the trajectories of charged particles injected tangentially into the mid-plane of a physically reasonable static mirror field. Conditions necessary for the nonadiabatic transfer of particle energy from the plane perpendicular to the field to the direction parallel to the field are discussed. It is shown that this energy transfer can be qualitatively predicted from the Mathieu equation. Two exchange mechanisms are observed; when the requirements for parametric resonance are satisfied energy is transferred into the longitudinal degree of freedom, and when the particle exhibits the characteristic looping behavior energy may be transferred between the transverse and longitudinal degrees of freedom. The coupled nonlinear equations of motion for single particles are numerically integrated using the fourth-order Runge-Kutta method. Based on the results of the various computer experiments, an effective trapping time is obtained.
Energy Analysis of Cesium Ions in a Q Machine
Authors: Motley R. W. , Kawabe T.
Published: February 2004

Energy analysis of cesium ions in the collision-dominated plasma of a double-ended Q machine is reported. The ion temperature, found to be between 3000 and 6000°K, is always greater than the temperature of the hot ionizing plates. Also, the measured temperature is almost 50% greater than can be accounted for solely by thermal and electrostatic energy associated with the acceleration of ions in the plasma sheath.
High Temperature Viscosity Ratios for Xenon
Authors: Goldblatt M. , Wageman W. E.
Published: February 2004

Coefficient of viscosity data for xenon relative to its value at 283°K at atmospheric pressure are reported in the temperature range 1100-2000°K. Measurements were made by a capillary flow method.
Energy Balance in a Turbulent Boundary Layer on a Rough Wall
Authors: Antonia R. A. , Luxton R. E.
Published: February 2004

Measurements of the mean flow and turbulence fields over a two-dimensional roughness reveal a shear stress distribution which is very different from that on a smooth wall. The usual mean flow energy equation fails to close indicating other terms may be important.
Energy Flux in Incompressible Magnetohydrodynamic Plane Waves
Authors: Skiles Durward D. , Kunkel Wulf B.
Published: February 2004

The energy flux in plane magnetohydrodynamic waves in general includes a mechanical constribution pv in addition to the usual Poynting vector S, even when the fluid is incompressible. Thus S need not be coplanar with the group and phase velocities of such waves.
Derivation of a Connection Formula using a Partial Wronskian
Authors: Baldwin D. E. , Parlange J.-Y.
Published: February 2004

A partial Wronskian is employed to derive the previously known Stokes parameters of the fourth-order equation coupling plasma oscillations to Bohm-Gross waves.
Conditions for the Existence of Shock-Like Solutions of Korteweg-De Vries Equation with Dissipation
Authors: Pfirsch D. , Sudan R. N.
Published: February 2004

Necessary conditions on dissipative operators for the existence of shock-like solutions of the Korteweg-de Vries equation, which limit the damping tolerable at long wavelengths are derived.
Dynamic Stabilization of the Screw Pinch
Authors: Berge G. , Freidberg J. P.
Published: February 2004

A method is presented for dynamically stabilizing the m = 1 mode in a screw pinch
Experimental Investigation of Carbon Dioxide Jet Plumes
Authors: Beylich Alfred E.
Published: February 2004

Free jets, produced by issuing CO2 gas from a supersonic nozzle into high vacuum, have been investigated experimentally by measuring densities and temperatures of the gas. Gas densities are measured using electron beam absorption and luminescence methods. Rotational temperatures are measured, after a theoretical model is developed, by using an unresolved band system of the CO2 spectrum. The results indicate that condensation must take place inside the nozzle. Outside the nozzle, the expanding gas gradually leaves the saturation line. At a pressure of about 0.3 Torr the condensation is frozen, and beyond this point the gas essentially follows an isentropic expansion line.
Application of Singular Eigenfunction Expansions to the Propagation of Periodic Disturbances in a Radiating Grey Gas
Authors: Cheng Ping , Leonard A.
Published: February 2004

The effect of thermal radiation on the propagation of small disturbances generated by the harmonic oscillation of a planar wall, either in position or temperature or both, is considered. By separation of variables, it is shown that the governing linearized equations can be reduced to a homogeneous integral equation that admits both regular and singular solutions to form a complete set; thus, the problem can be solved by the application of singular eigenfunction expansions analogous to those used in neutron-transport theory. An exact closed form solution is obtained for disturbed quantities in the flow and radiation fields. The exact solution shows that the disturbances consist of a damped continuum mode with infinite wave speed in addition to two discrete modes with finite wave speed. One of the discrete modes represents the “modified classical” wave whereas the other discrete mode plus the continuum mode corresponds to the radiation-induced wave. For sufficiently small Bouguer numbers, the discrete mode of the radiation-induced wave disappears. The newly found continuum mode damps faster than the discrete mode. Consequently, only the discrete modes persist away from the boundary. The differential approximation is found to predict the modified classical wave accurately but predicts the radiation-induced wave only approximately. The implications as well as the accuracy of the differential approximation are discussed and compared.
Longitudinal Oscillations of a Lorentzian Electron Gas
Authors: Lee W. W. , Hirsch R. H. , Denavit J.
Published: February 2004

The combined nonlinear and collisional effects on the Landau damping of longitudinal electron oscillations are studied using the Lorentz gas model to represent electron-neutral and electron-ion interactions. Three types of interactions are considered: hard-sphere collisions, inverse fifth-power interactions, and inverse square interactions. A perturbation analysis of the nonlinear kinetic equation is carried out following Montgomery's expansion technique. For hard-sphere collisions, the collisional damping and the nonlinear change in Landau damping are determined analytically. For inverse fifth-power interactions and inverse square interactions, the same results are obtained numerically by expanding the distribution function in Legendre polynomials to sufficiently high order to adequately represent its variations in the resonance region.
Experimental Observation of the Deformation of the Electron Distribution Function due to a Damped Electrostatic Wave
Authors: Guillemot M. , Olivain J. , Perceval F. , Scharer J.
Published: February 2004

The change in the electron distribution function due to a damped electron plasma wave is observed by means of an electron energy analyzer. The results show that the number of particles with velocities greater than that of the wave phase velocity is increased and that the number of particles with velocities less than the wave decreases. The distance between the antenna and analyzer is varied to show the increase in the deformation of the velocity distribution due to wave-particle interaction through space. For sufficiently high wave power and large separation a plateau is formed in the vicinity of the wave phase velocity.
Nonlinear Landau Damping and Beat Wave Trapping
Authors: Ott Edward , Dum Christian Thomas
Published: February 2004

The nonlinear interaction of two coherent waves with particles of velocity near (ω1−ω2) / (k1−k2) is investigated. For times short compared with the trapping time in the beat wave we recover the usual nonlinear Landau damping result, previously derived for the incoherent (turbulent) case. For two coherent waves, however, trapping severely limits the validity of this result.
Reversed Field Equilibria in Axially Symmetric Electron Current Layers
Authors: Fisher Shalom
Published: February 2004

Self-consistent, nonrelativistic E-layer equilibria in two dimensions are calculated by numerical methods. A rigid-rotor model for the electron distribution, together with a neutralizing ion background, leads to a nonlinear equation for the magnetic flux function ψ. Solutions to this equation are displayed, and the existence of bifurcations or nonuniqueness is demonstrated.
Effects of Cold Plasma on the Negative Mass Instability of a Relativistic Electron Layer
Authors: Lau Y. Y. , Briggs R. J.
Published: February 2004

The stability of a cylindrical layer of gyrating relativistic electrons (E layer), both in vacuum and in a cold plasma, is examined. The beam model assumes concentric particle orbits and allows for a finite thickness of the E layer. It is shown that the background plasma can stabilize the lower azimuthal modes (modes with their frequency less than the cold cyclotron frequency, or azimuthal wavenumber l less than the relativistic mass factor γ). The mechanism of stabilization can be interpreted in terms of an inductive impedance at the beam edge due to the cold plasma. The interaction of the beam with the plasma at the upper hybrid frequency is discussed briefly.
Hydromagnetic Stability of the Bennett Pinch
Authors: Harris Edward G. , Kaneko Shobu
Published: February 2004

The hydromagnetic energy principle is applied to the derivation of a sufficient condition for the hydromagnetic stability of the linear Bennett pinch. The instabilities can be divided into unlocalized modes in which the most dangerous ones are the kink mode and localized modes. A sufficient condition for stability of the kink mode is βz < (9/25) (r0/R)2 for (r0/R)2<3.75 where βz is the toroidal β and r0 and 2πR are the mean radius and the length of the pinch, respectively. The linear Bennett pinch is unstable for localized Suydam modes. But these unstable modes can be stabilized if the pinch is bent into a torus. The above stability condition against the kink instability may be considered as a sufficient condition for stability of a toroidal Bennett pinch.
Measurements of Wave-Particle Interaction in a Single-Ended Q Machine
Authors: Andersen S. A. , Christoffersen G. B. , Jensen V. O. , Michelsen P. , Nielsen P.
Published: February 2004

A Green-function technique is used to solve the linearized Vlasov equation for the perturbed ion velocity distribution function, f(x, v, t), in a case where a short density pulse is released into a plasma. Some characteristic features in the calculated curves are caused by wave-particle interaction. Experimentally, short density pulses are generated in the plasma in a single-ended Q machine by application of electrical square pulses to a grid immersed in the plasma column. The perturbed ion velocity distribution function in the density pulse is measured by means of an electrostatic energy analyzer. The features showing the wave-particle interaction appear in the experimental results.
Relativistic Acceleration of Charged Particles by an Electromagnetic Pulse
Authors: Noerdlinger Peter
Published: February 2004

The kinetic energy imparted to a charged particle by an electromagnetic pulse is 12q2φ2/mc2, where φ is the “magnetic flux” in the pulse. The particle can acquire any velocity < c in the propagation direction, but not more than 2−1/2c in the transverse direction. An ionized medium is able to perturb the wave significantly whenever ω2<ωp2, no matter how powerful the wave.
Role of Droplets and Bubbles in the “Condensation” of the One-Dimensional Gas of Kac, Uhlenbeck, and Hemmer
Authors: Jalickee John B. , Wiegel F. W. , Vezzetti David J.
Published: February 2004

The functional integral representing the grand canonical partition function of the Kac, Uhlenbeck, and Hemmer model is approximated, in a systematic way, to give a much simpler integral representing one-dimensional Brownian motion with absorption. It is shown that the paths which make the dominant contributions to this integral are those which correspond to alternating regions of high and low density in the fluid. An interpretation of these paths as representing configurations of droplets and bubbles is given. The pressure of the system is obtained by summing over the droplet-bubble configurations, and it is shown that there is no phase transition for any finite value of the range of the attractive potential. A number of properties of the droplets are determined. The relation of this work to inverse range expansions and other recent works is discussed.
General Hydrodynamic Equations from the Linear Boltzmann Equation
Authors: Bixon M. , Dorfman J. R. , Mo K. C.
Published: February 2004

A derivation of hydrodynamic equations from the linearized Boltzmann equation is presented which is based upon Zwanzig's projection operator method. This is obtained in the simple compact form of linearized Burnett equations with frequency and wavelength dependent transport coefficients, for which explicit expressions are given for well-behaved intermolecular potentials. The effects of the initial distribution function may be included, although for long times the initial state terms disappear. This disappearance of the initial state terms implies that for long times the general hydrodynamic equations and the Chapman-Enskog hydrodynamic equations agree. The latter are exact for all times for a special initial state. As an application of the theory, an expression is found for the dispersion equation for sound propagating in a gas, that holds for any well-behaved intermolecular potential.
Interacting Motion of Rectilinear Geostrophic Vortices
Authors: Morikawa George K. , Swenson Eva V.
Published: February 2004

The kinematic motion of (N+1) geostrophic (Bessel) vortices is studied. Initially, the vortices are positioned near a uniformly rotating equilibrium configuration which consists of N vortices of equal strength γ equally spaced on a circle of radius a, and one vortex of strength γ0 at the center of the circle. One length scale κ−1 is associated with each of the vortices, the limiting case κ = 0being the classical logarithmic vortex. The linearized stability of this equilibrium configuration is studied over the range of the three parameters: N≥2, 0≤ (κa) < ∞, and − ∞ <(γ0/κ) < ∞. Over the entire range of the parameters, there are double-zero eigenvalues, which imply that the motion of the center vortex is inherently nonlinear. Numerical computations show that nonlinear effects are important in a parametric transition region embracing both the stable and unstable sides of the neutral stability curves for the circle vortices, even for small initial perturbations. The stability of the center vortex is not well represented by the neutral stability curves. In addition, the nonlinear motion away from an unstable equilibrium toward a stable equilibrium configuration is studied numerically.
Use of Retarded Motion Expansions for Simple Fluids in Hydrodynamic Stability Analysis
Authors: McIntire Larry V.
Published: February 2004

The limits of using retarded motion expansions of simple fluid theory are examined. The possible existence of two types of instability for parallel flows of second-order fluids is shown. For one of these instabilities the second-order fluid assumptions are not valid and mathematical stability results do not bear any relation to real fluid behavior in this region. Apparent contradictions in previous papers are resolved.
Chemical Instabilities. IV. Nonisothermal Chemical Surface Reactions and Hydrodynamic Instability
Authors: Bdzil J. , Frisch H. L.
Published: February 2004

A linear stability analysis of a horizontal layer of the reactive fluid mixture (A2A) which is undergoing the surface catalyzed nonisothermal reaction (A2⇋2A) is performed. It has been found that including the heat of reaction in our analysis leads not only to a modification of the convective instability observed for the isothermal reactive fluid, but also to a whole new class of instabilities for fluids with negative (gravitationally stable) steady-state density gradients. This new class of instabilities resulting from the heat of reaction is referred to as “thermochemical” instabilities. The mathematically similar thermosaline evaporation problem, describing the evaporation of water from the surface of a salt solution, is also examined and found to exhibit similar stability characteristics.
Elastico-Viscous Flow Near a Rotating Disk
Authors: Elliott L.
Published: February 2004

The Navier-Stokes equations are solved numerically for the flow of elastico-viscous fluid near a rotating disk by expanding the velocity components in powers of a small parameter K0*. The main effect of elasticity is to increase the magnitude of the velocity components and to decrease the magnitude of the turning moment on the disk.
Stability of Electrically Charged Viscous Cylinders
Authors: Saville D. A.
Published: February 2004

A characteristic equation describing the stability of an electrified fluid cylinder is derived taking into account effects due to the electric field, surface tension, viscosity, and inertia. The electric field causes the cylinder to be unstable subsequent to nonaxisymmetric deformations of the interface. For relatively inviscid fluids electrification can make the growth rates for nonaxisymmetric disturbances almost as large as the rates for axisymmetric forms. It is found that viscous effects tend to damp axisymmetric motions more than motions accompanying a sinuous deformation; thus, the sinuous mode may be the most unstable form of disturbance in many situations. The combined effects of viscosity and the electric field act so that the cylinder manifests the greatest instability at wavelengths about as large as the circumference of the cylinder, when viscous effects are paramount, in contrast to Rayleigh's result for an unelectrified fluid cylinder.
Free Stream Velocity Measurements in a High Enthalpy Shock Tunnel
Authors: McIntosh M. K.
Published: February 2004

Two independent methods (spark tracer and magnetohydrodynamic) are described for the measurement of the velocity of the gas in the free stream of a high enthalpy shock tunnel. Comparison is made with calculated results.
Numerical Study of the Magnetic Shock Tube
Authors: Schneider S. H. , Chu C. K. , Leonard B. P.
Published: February 2004

Unsteady, one-dimensional magnetohydrodynamic shock formation in a shock tube has been studied by numerical solution of the single-fluid continuum equations, using numerical dissipation as the only diffusion mechanism. The results are qualitative inasmuch as the exact shapes of the various profiles are not predicted. However, considerable physical insight has been gained, particularly concerning the early-time evolution of the shock wave and its separation from the drive-current layer. By appropriate scaling, these results can be compared with experiments, and are useful in their interpretation. Many of the departures of experimental results from ideal theory can be explained in terms of finite dissipation, without introducing anomalous effects.
Propagation of Coherent Radiation in a Cylindrical Plasma Column
Authors: Steinhauer Loren C. , Ahlstrom Harlow G.
Published: February 2004

Refraction plays a very significant role in the absorption of laser energy in high temperature plasmas. The geometry considered here is a long cylindrical magnetically confined plasma. The laser pulse is assumed to enter the plasma from the ends. It is then necessary that the radiation propagate the full length of the plasma so that it will be absorbed. The refraction of the laser radiation in the plasma column depends on the radial distribution of the density. Several representative density profiles are considered and solutions for the propagation are presented. It is shown that a profile with the maximum density on the axis is very difficult to heat over long distances; but, if the density has a minimum on the axis, then the plasma column acts like a “light pipe” and traps the laser beam. In this case the effective absorption length of the laser beam is also reduced.
Continuum Theory of Slender Electrostatic Probes
Authors: Whitman Alan M. , Chien Chung-Jen
Published: February 2004

The continuum theory of electrostatic probes is developed for axisymmetric probes of arbitrary shape under the restriction that their maximum diameter is much smaller than their length. The current-voltage characteristic is not computed explicitly, but it is shown that the saturation currents drawn by this class of probes as well as the current drawn by them at the plasma potential are all proportional to each other. This proportionality constant, a function of the probe shape, is calculated for a cylindrical probe which has spheroidal ends.
Electrostatic Probe Measurements in a Collisionless Plasma Sheath
Authors: Yamada Hideo , Murphree David L.
Published: February 2004

Experimental data are presented on electrostatic probe measurements in the collisionless plasma sheath of a 3.2-cm-diam conducting plate. The plate was immersed in a glow discharge-produced argon plasma in which the pressure was varied from 0.2 to 0.8 μ. A movable probe of 0.0064 cm diam, 0.64 cm length, tungsten wire was used as a Langmuir probe, emissive probe, and floating emissive probe. The data explicitly shows that experimental measurements to determine the local sheath potential based on Langmiur probe theory are meaningless. However, it is explicitly shown that the experimentally measured floating potential distributions of the emissive probe and the floating emissive probe in the sheath of a positive plate do follow the expected trend of the local potential of the plasma sheath.
Exact Nonlinear Evolution of Alfvén Modes in the Guiding-Center Model
Authors: Patterson Blake
Published: February 2004

Alfvén waves parallel to a uniform magnetic field in a uniform but anisotropic plasma are studied in the Chew-Goldberger-Low and guiding-center models. Exact solutions are found in the stable and unstable cases. When the plasma is stable, an arbitrarily large constant amplitude perturbation perpendicular to the uniform field can propagate without distortion parallel to the uniform field. The exact nonlinear behavior of an unstable circularly polarized Alfvén mode is obtained: growth of a finite perturbation is quenched in a finite time, and decay begins immediately.
Parametric Amplification of Alfvén Waves
Authors: Vahala George , Montgomery David
Published: February 2004

A calculation describing the parametric amplification of Alfvén waves in a uniform, perfectly conducting, magnetohydrodynamic fluid is reported. The calculation has been motivated by a recent experiment of Lehane and Paoloni. A magnetically supported uniform column of the magnetohydrodynamic fluid is imagined to be subjected to an externally imposed, sinusoidally varying, magnetic field which can be idealized as spatially uniform. It is shown that a certain class of Alfvén waves which have an axial wavelength long compared with the radius of the column can be parametrically amplified in the case where their frequency and the modulating frequency satisfy certain integer quotient relations. The mathematical behavior is determined by Mathieu equations.
Resistive Instability of the Sheet Pinch
Authors: Van Hoven Gerard , Cross Mark A.
Published: February 2004

An investigation of the linear “tearing mode” instability of the sheet pinch with uniform resistivity is described. A first integral of the coupled perturbation equations for magnetic fields and fluid velocities is used to find constraints on the growth rate which detail the possible regimes of instability. The existence of pure exponential growth for long wavelengths is shown explicitly in two examples.
A Theory of Collision Dominated Electron Density Fluctuations in a Plasma with Applications to Incoherent Scattering
Authors: Hagfors T. , Brockelman R. A.
Published: February 2004

The problem of thermal electron density fluctuations in a weakly ionized gas is considered from the point of view of particle diffusion in single particle phase space (μ space). When ion-neutral and electron-neutral two-body collisions constitute the only important force on the charged particles apart from an electrostatic self-consistent field, it is shown how the fluctuation theory may be developed from a transition probability describing the random walk of a single charged particle in the absence of the interaction field. Specific calculations of thermally excited low frequency electron density fluctuation spectra are carried out on the assumption that the random walk may be described in terms of classical Brownian motion or in terms of a combination of free flight and classical Brownian motion. The latter model is shown to be a first approximation to a more exact solution which may be obtained by solving an integral equation for the transition probability. First-order calculations are carried out for the case where the ion-neutral collisions may be treated as hard sphere elastic ones. The computational results are compared with those of earlier theories of fluctuations in a weakly ionized gas.
Kinetic Theory of Plasma in a Magnetic Field
Authors: Price John C.
Published: February 2004

The Krylov-Bogoliubov transformation is used to simplify the guiding center equations for a charged particle in electric and magnetic fields. The resulting transformation of variables is then applied to the Vlasov distribution function, yielding a magnetic Vlasov equation which describes the low-frequency behavior of a system with no statistical effects. The equation is generalized to include effects of high- and low-frequency fluctuations by a procedure developed by Klimontovich and Dupree. A consistent treatment of the conservation laws and Maxwell's equations is given to complete the kinetic description.
Three-Wave Interaction and Nonlinear Wave-Particle Scattering
Authors: Krishan S. , Fukai J.
Published: February 2004

A study has been made of three-wave interaction and nonlinear wave-particle scattering for waves propagating parallel to the external magnetic field using quantum techniques. The three-wave interaction refers to longitudinal, transverse, and Alfvén or whistler modes. The waves taking part in the nonlinear wave-particle scattering are transverse, Alfvén, and whistlers. Kinetic equations containing these effects have been derived. It is established the three-wave interaction for Alfvén or whistler modes is impossible.
Amplitude Dispersion in the Electromagnetic Modes
Authors: Selim A. A. , Krishan S.
Published: February 2004

Amplitude dependent frequency shift for whistlers, Alfvén, and light waves has been calculated. Unlike the previous work of this nature, which makes use of the Krylov-Bogoliubov-Mitropolskii method, the diagrammatic method of field theory was used. The result for light waves agrees closely with Tidman, but for whistler modes, it disagrees with Tam.
Onset of Anomalous Plasma Resistivity after Application of a Step Electric Field
Authors: Robin James E. , MacKenzie K. R.
Published: February 2004

A photoionized argon plasma was subjected to a step E field of the order of 10−2 V/cm (1<E/Eτ<80,where Eτ is the runaway field). In a magnetic field free plasma the electron current rose linearly to a maximum value (the time of which varies as E−1/2) and then fell as the result of the rapid growth (in a few wave periods) of ion wave turbulence (consisting almost entirely of waves traveling at large angles to the E field). In the presence of a magnetic field parallel to E (zero to 150 G) the time of the current maximum decreased by 40% to a minimum at 40 G (presumably due to finite geometry effects) and then rose almost linearly from this point by a factor of 2 at 150 G. Wave propagation was still at large angles to E. Parameters were 4×108<n<4×109ions/cm3; kTe≃0.36 eV; kTi≃0.025 ev.
Collision Free Shock Formation in Finite Temperature Plasmas
Authors: Auer P. L. , Evers W. H.
Published: February 2004

A one-dimensional macro-particle code is used to investigate the effect of finite initial ion temperature on large amplitude magnetosonic disturbances. Time-dependent piston problems closely related to the earlier work of Auer, Hurwitz, and Kilb are studied. It is shown that at even relatively small plasma pressure to magnetic pressure ratios, large scale field fluctuations accompanying orbit crossings produce quasistationary shocks for all values of Mach numbers investigated. This is in contrast to cold plasma results, where similar results were observed only if the Mach number was chosen well in excess of the critical value (MA,cr = 2). The mechanism of electron heating is not treated in this study.
Microwave Probing of Plasmas Including Electron Collision Interactions
Authors: Fogelson Stephan A. , Grimwood Paul R.
Published: February 2004

Slightly ionized plasmas with a Maxwellian electron velocity distribution and non-Maxwellian electronneutral molecule interaction are treated by using a modified Langevin equation having a complex dissipative factor g in the manner proposed by Molmud. At frequencies near the average electron collision frequency, this factor is evaluated and plotted for two plasma types in which the electron-neutral molecule interaction is non-Maxwellian. The interactions approximate that between an electron and an air or nitrogen molecule, and that between an electron and a helium molecule. The results are used to compute the microwave power transmission coefficient and transmission phase shift, assuming a plane wave-uniform plasma slab geometry, for weakly ionized plasmas with the above interactions, at frequencies near the average electron collision frequency. Composite parametric plots are developed from the computations which provide a convenient means for obtaining the plasma electron number density and average electron collision frequency from experimentally measured values of the power transmission coefficient and transmission phase shift.
Reflection and Transmission Measurements on a Magnetized Plasma Slab
Authors: O'Brien B. B. , Kuehl H. H.
Published: February 2004

Experimental observations of microwave reflection from and transmission through a magnetized plasma slab are reported. The incident wave has a frequency below the second cyclotron harmonic and an electric field perpendicular to the static magnetic field. It is found that the reflection and transmission coefficients exhibit a resonant structure due to longitudinal wave resonances in the interior of the plasma. The observations are shown to be consistent with a theory based on the Pearson equations.
Microwave Scattering from Unstable Electron Plasma Waves
Authors: Arunasalam V. , Heald M. A. , Sinnis J.
Published: February 2004

An analysis is presented of an experimental study of the scattering of microwaves by the density fluctuations due to electron plasma-wave instability in a beam-plasma system. Reasonably good agreement with the general predictions of the Shapiro and the Drummond and Pines nonlinear theories of plasma oscillations is obtained. In particular, at the “quasilinear” steady state, the experimentally measured values of the scattering cross sections, the angular spread of the scattered radiations, the functional dependence of the scattering cross sections on the wavenumber of the most unstable plasma wave mode, and the increase in the thermal energy of the plasma electrons were all in reasonably good agreement with the corresponding theoretically expected values. In a few cases, a rather weak satellite line corresponding to scattering at the “bounce frequency” was seen. In these cases, the satellite line appeared only on the low-frequency side of the main plasma line.
Return Current Induced by a Relativistic Beam Propagating in a Magnetized Plasma
Authors: Lee Roswell , Sudan R. N.
Published: February 2004

The propagation of a high current relativistic beam in a cold magnetized plasma is investigated using a model developed by Hammer and Rostoker for the unmagnetized case. In this model, the beam electrons are assumed to be undeflected from their zero-order orbits and the fields associated with the beam are switched on at time t = 0. The return current induced in the plasma is calculated as a function of beam and plasma parameters. It is demonstrated that the return current does not extend indefinitely but dies away inversely as the distance from the head of the beam with a characteristic length Ln = v0τa2/λE2, where v0 and a are the beam velocity and radius, τ is a phenomenological momentum relaxation time for the plasma electrons, λE = c/ωp, and ωp is the plasma frequency of the plasma electrons. When the beam is injected either parallel or perpendicular to a static magnetic field B0, it is found to be magnetically neutralized by a return current over a length of order Ln if a2/[λE2(1+Ω2/ωp2)]≫1, where Ω = eB0/m0c.
Finite Beta Equilibria of Relativistic Electron Beams in Toroidal Geometry
Authors: Ott Edward , Sudan R. N.
Published: February 2004

Vlasov equilibria of axisymmetric toroidal plasma pinches are obtained by a perturbation expansion with the inverse aspect ratio, rp/R, as the small parameter (rp and R are the minor and major toroid radii). The particle distribution function is a delta function in the two constants of motion, the canonical azimuthal angular momentum and the total energy. The equilibria studied include a plasma pinch contained within a conducting toroidal vessel and a plasma ring such as might be formed by transverse injection into a mirror field.
Observations of Anomalous Plasma Transport Produced by Magnetic Field Errors
Authors: Jernigan T. , Prater R. , Meade D. M.
Published: February 2004

The plasma transport to the internal ring of a multipolelike device was increased by over an order of magnitude by the addition of a 1% magnetic field error which causes field lines to spiral across the confinement region. Magnetic field perturbations which keep the field lines closed produce a negligible increase in plasma loss to the internal ring. The plasma is observed to flow radially toward the loop at the region of the perturbation and then E × B drifts azimuthally affecting the density profile everywhere in the device. The increased loss under the influence of a 1% perturbation corresponds to an effective diffusion coefficient that is ≃20% of the Bohm value. Detailed experimental studies of the plasma transport and azimuthal density profiles are in qualitative agreement with a model which considers diffusion of plasma along the perturbed magnetic field to the internal ring.
Constants of the Motion for Toroidal τ and Screw Pinches
Authors: Enoch Jacob
Published: February 2004

A technique is developed for computing the constants of the motion for particles in toroidal τ and screw pinches. The technique uses classical perturbation theory with the inverse aspect ratio as the perturbation parameter. In addition, the evaluation of certain matrix elements requires the expansion of certain singular integrals in powers of the radial amplitude of the motion. The technique for carrying out expansions of this type is developed in detail.
Viscous Inner Structure of Zero Prandtl Number Shocks
Authors: Cohen Ira M. , Moraff Charles A.
Published: February 2004

Inviscid, heat conducting (zero Prandtl number) gasdynamic shock waves have a discontinuous jump (inner shock) in velocity for all but very weak shocks. The viscous structure of this inner isothermal discontinuity is obtained here explicitly.
Motion of Charged Particles in a Circularly Polarized Wave Packet
Authors: Laird M. J.
Published: February 2004

An integral is derived for the motion of a charged particle in a circularly polarized wave packet, propagating along a uniform magnetic field, and a longitudinal electric field. The integral may be used to reduce the order of the equations of motion.
Feedback Control of Plasma Flutes with Finite Enforcer Electrodes
Authors: Crowley Joseph M.
Published: February 2004

The finite size of enforcer electrodes in the feedback control of a low density flute instability limits the maximum density which can be obtained in an experiment.
Classical Model of the Roton-Quantized Vortex Interaction with an Application to Rotating Liquid He II
Authors: Goodman S. E.
Published: February 2004

A simple classical model is used to investigate the roton-quantized vortex line interaction, and the behavior of the roton in the vortex field is studied in detail. A process is found which results in a sizeable, long-range transfer of momentum between a roton and the core. The scattering is unsymmetric about the forward direction. From this model it is possible to derive the Hall-Vinen mutual friction terms that appear in the phenomenological equations of motion for liquid He II. Calculated values of the B and B′ coefficients are in agreement with experiments for T<1.6°K. The parameters in the theory are chosen from considerations independent of the present problem.
Spin-Up and Spin-Down of Rotating Flows in Finite Cylindrical Containers
Authors: Bien F. , Penner S. S.
Published: February 2004

A simplified theoretical model is used for the successful description of measured impulsively started spin-up and impulsively stopped spin-down times in a finite cylindrical geometry at a Reynolds number R of 1002. The essential physical idea used in the analysis is very rapid establishment of steady-state boundary-layer flows in times that are short compared with spin-up and spin-down times in the interior (core) of the liquid (water).
Lateral Motion of the Two-Dimensional Jet Boundaries
Authors: Wygnanski I. , Gutmark E.
Published: February 2004

Two intermittency signals on each side of a two-dimensional jet were correlated to determine the manner in which boundaries move relative to one another. With some minor reservations it is concluded that each boundary moves independently.
Channel and Tube Flows with Surface Mass Transfer and Velocity Slip
Authors: Sparrow E. M. , Beavers G. S. , Hung L. Y.
Published: February 2004

An analysis of internal flows with surface mass transfer is performed in which account is taken of velocity slip at the surface of the porous bounding wall. The solutions for channel and tube flows reveal a variety of interesting effects of velocity slip, which depend upon whether fluid is injected or withdrawn at the bounding wall and upon the sign of the streamwise pressure gradient. For example, relative to the situation in which there is no slip, the streamwise pressure gradient may either increase or decrease in the presence of slip and may even undergo a change of sign.
Linear Stability of Turbulent Flow Profiles
Authors: Potter Merle C.
Published: February 2004

The stability of turbulent plane flow profiles subject to infinitesimal disturbances is studied. Neutral stability curves are found for a number of velocity profiles varying from parabolic Poiseuille flow to a profile approaching that of turbulent flow. As the profile varies from the parabolic case, the flow is always stabilized.
Turbulent Mixing of Two Rapidly Reacting Chemical Species
Authors: O'Brien Edward E.
Published: February 2004

The evolution of moments of the concentration of each of the species in a two-species, very rapid, isothermal, irreversible, second-order, chemical reaction in a homogeneous turbulence is described in terms of assumed initial distributions of the concentration fields. The fields decay in two stages. In the stage dominated by chemical kinetics, exact stochastic solutions are derived for a class of initial distributions. These solutions exhibit asymptotic concentration fields having an extremely high relative intensity and skewness associated with the spatial segregation of the species. In the second or diffusion controlled stage exact solutions are obtained in terms of the turbulent mixing of a nonreacting species when the molecular diffusivities of the species are equal. An approximate solution is proposed when they are unequal. In both cases the time scale of decay in the second stage is entirely characterized by turbulent mixing parameters. It is shown that in final period turbulence the reactants decay with an effective diffusivity of the same order as the smaller of the two diffusivities.
Unsteady Boundary-Layer Induced Pressures at Hypersonic Speed
Authors: Gupta Roop N. , Rodkiewicz Czeslaw M.
Published: February 2004

The first-order transient contribution to the strong-interaction induced pressure has been obtained for a suddenly accelerated semi-infinite flat plate moving at hypersonic speed and zero angle of attack. The unsteady compressible laminar two-dimensional boundary-layer equations are employed in self-similar form incorporating the Dorodnitsyn-Howarth and similarity transformations. The linear viscosity-temperature law is used in the analysis. The solution to the coupled set of governing equations has been found numerically for Prandtl number unity and for zero and nonzero wall heat transfer. The obtained solutions are utilized to compute the unsteady displacement thickness and subsequently the induced pressure. Numerical results have also been obtained for the transient distribution of the wall shear and wall heat transfer for one percent change in the plate velocity. There is a discontinuity in the solutions which corresponds to Stewartson's singularity at τ = 0.
Temperature and Density Jumps in the Kinetic Theory of Gases and Vapors
Authors: Pao Young-Ping
Published: February 2004

The problem of evaporation from an interphase and the problem of heat conduction in a gas are studied on the basis of the linearized single-relaxation model equation. Both problems lead to the same set of integral equations. Exact values are obtained for the microscopic temperature and density jumps. It is found that the macroscopic temperature and density jumps of the evaporation problem can be expressed in terms of the macroscopic jumps of the heat conduction problem and vice versa. A proof for the existence and uniqueness of the solutions is also given.
Influence of Water Vapor upon the Properties of Shocked Air in Thermodynamic Equilibrium
Authors: Horton T. E. , Menard W. A.
Published: February 2004

The role of water, initially mixed with air, upon the properties of shock compressed air has been investigated using a thermodynamic equilibrium computer program. The principal effect of the inclusion of water in the computation of the shock parameters of air is to reduce the temperature of the products. This reduction in temperature results in a reduction in the equilibrium electron concentration by reducing the ionization of NO. The maximum effect occurs at shock velocities of 4.0 to 4.3 km/sec. A procedure is presented for estimating the effect of the addition of water.
Theory of Continuum Flush Probes
Authors: Stahl Neil , Su C. H.
Published: February 2004

Methods are discussed for determining both the density gradient at the surface and the free-stream density of charged particles in a weakly ionized flowing gas by means of flush electrostatic probes. It is shown that the values of the density gradients of the ions and electrons at the surface can be determined by current-voltage characteristics. The determination of the free-stream charged-particle density is studied by means of an analysis in the sheath region which, for highly negative probe potentials, gives sufficient boundary conditions to, in general, overspecify the density solution in the quasineutral region. This overspecification makes possible the determination of the boundary of the quasineutral region for a large class of continuum model equations describing the region. Using this information, current-voltage characteristics can be drawn for various values of free-stream charged-particle density, and the density thus determined by comparison with experiment. These characteristics are drawn for two models.
Response of a Langmuir Probe in a Strong Magnetic Field
Authors: Brown Ian G. , Compher Alan B. , Kunkel Wulf B.
Published: February 2004

A comparison was made of plasma density measurements obtained using cylindrical Langmuir probes and a high-sensitivity microwave interferometer in magnetic fields between 1 and 7 kG. The experiment was carried out in a current-free stream of ionized hydrogen with electron densities ranging from 3×109 to 4×1011 cm−3. A set of probes of different sizes was used so that the ratio of probe diameter to ion gyroradius 2rp/ρi covered the critical range from 0.2 to 5 or more. It was found that (1) the shape of the probe characteristics was not affected very much by the presence of the strong magnetic field; (2) the electron temperature derived from the slope seemed to be the true temperature; but (3) the apparent ion density inferred from the characteristic using Laframboise's calculation, which applies in the absence of magnetic fields, was consistently low by a factor which depended primarily on the ratio rp/ρi and seemed nearly independent of the Debye length. This reduction factor was considerably larger in the streaming plasma than in a stationary one, presumably because of the wake or “shadow” cast by the probe when rp/ρi is not negligible.