bluuebunny/crossref_metadata_2025 huggingface dataset:
Plural and Multiple Scattering of Fast Electrons in Gases
Authors: Center R. E.
Published: February 2004

The scattering of fast electrons in nitrogen and argon has been investigated under conditions resulting in approximately 1-100 small angle scattering collisions. Experimental measurements have been made of the spatial distribution of the scattered electrons for highly collimated incident electron beams. Electron energies of 20, 40, and 100 keV and gas target thickness of 3-1000 Torr cm at room temperature were used. The experimental distributions are much wider than predicted for single scattering and were approximately Gaussian for thick targets with many electron collisions. The dependence of the measured half-current beamwidth on the target thickness varied from a 32 power law at small target thicknesses to a 12 power law in thick targets. Direct analog Monte Carlo calculations have been made based on a screened cross section including the large contribution by inelastic collisions at very small scattering angles. Despite the approximate nature of the cross-section data the calculated spatial distributions of scattered electrons agree well with the experimental results except at the smallest target thicknesses where the calculated distributions are wider than the experimental results.
Cross Field Convection of Plasma in a Partially Ionized Gas
Authors: Hooper E. B.
Published: February 2004

The E × B instability generates a drift wave in a partially ionized gas which causes plasma transport across the magnetic field. It is believed to be important in reflex arcs and in the ionosphere. A non-linear model of the transport is given in the limit of collisionless electrons. A solution is found which demonstrates that the transport in the model is convective in nature with characteristics similar to results obtained in a reflex arc.
Low Reynolds Number Flow Past a Heated Circular Cylinder
Authors: Hodnett P. F.
Published: February 2004

The Stokes region (where diffusion dominates) is shown to contain two subregions of distinct character—an inner region near the cylinder where the variable transport properties of the gas are of secondary importance and an intermediate region (remainder of Stokes region) where they are of primary importance.
Measurements of the Universal Constant in Kolmogoroff's Third Hypothesis for High Reynolds Number Turbulence
Authors: Gibson Carl H. , Stegen Gilbert R. , McConnell Steve
Published: February 2004

The viscous dissipation εr averaged over regions of size r is assumed log normal with variance σlogεr2 = A + μ log (L/r) in Kolmogoroff's third hypothesis, where A depends on the large scale motions, L is the energy scale of the turbulence ≫ r, and μ is a universal constant. The constant μ was measured from the slope of squared velocity derivative spectra using an expression derived by Yaglom. μ was also inferred from measurements of velocity derivative kurtosis K at various L/r values from the defining expression and the fact that σlog εr2 = log K for log normal εr, where r ≪ (ν3 / ε)1/4. An average value of 0.51 ± 0.02 was obtained from the spectral slopes over a 6:1 range of Reynolds number. A value of 0.44 ± 0.25 was indicated by the other method. Previous measurements range from 0.33 to 0.64.
Laminar Boundary Layer on a Rotating Sphere
Authors: Singh Shiva N.
Published: February 2004

The problem of laminar boundary layer on a sphere, rotating uniformly about a diameter, is studied by the momentum-integral method. The meridional and the radial velocity components are assumed to be nonzero at the outer edge of the boundary layer. Instead, the condition of zero vorticity is imposed. It is found that an inflow at the poles changes into an outflow near the equator and this transition takes place at an angle measured from the pole of 77.5°.
Swirling Axisymmetrical Laminar Jet
Authors: Wygnanski I.
Published: February 2004

A similarity solution for the complete Navier-Stokes equations describing the flow of an incompressible laminar swirling jet was obtained. The solution clearly shows the effect of swirl on the other velocity components, and it is valid for all degrees of swirl. It thus differs from the previous solutions which were of the perturbation type.
Phase Velocity of Surface Capillary-Gravity Waves
Authors: Walbridge N. L. , Woodward L. A.
Published: February 2004

An experimental test of Kelvin's equation for the phase velocity in shallow water was made at a frequency of 20 Hz at various depths down to 0.006 cm. The experimental values agreed with the theory except for depths less than the thickness of the boundary layer. Measurements were also made of the wavelengths in narrow, deep channels for frequencies of 20 and 60 Hz. Due to boundary conditions at the edges, a cutoff wavelength exists, which is about one-fourth the wavelength in open water. An equation was derived from fundamental hydrodynamics for wavelengths in channels less than a wavelength wide. An empirical constant was added to the channel width to reach agreement with the experimental results.
Measurement of the Viscosity of Atmospheric Argon from 3500 to 8500°K
Authors: Aeschliman Daniel P. , Cambel Ali Bulent
Published: February 2004

A direct-current, wall-stabilized arc, constrained to cylindrical symmetry by a precision-bore Vycor tube, was used to measure the viscosity μ(Tg) of atmospheric pressure argon over the heavy-particle temperature range 3500 ≤ Tg ≤ 8500°K. Streak photography from perpendicular directions of 20-30 μ graphite particles yielded the velocity profile u(r), from which the velocity gradient du/dr was obtained; the axial pressure gradient was determined with a micromanometer attached to taps in the arctube wall. These data were employed to solve the axial-component momentum equation for μ(r). Tg(r) was determined from a linear similarity relation between u(r) and the heavy-particle enthalpy, hg(r). Tg on the axis was found from absolute line and continuum measurements of the electron temperature, allowing for a small departure from kinetic equilibrium. The radius r was eliminated from μ(r) and Tg(r) to yield μ(Tg); the data are represented to within about 1% by μ(Tg) = 3.094 × 10−6 Tg0.740 g/cm-sec, with an experimental uncertainty of about ± 12%.
Thermal Effects in Rarefied Binary Gas Mixtures
Authors: Jenkins R. E. , Mason E. A.
Published: February 2004

Expressions are derived for the radiometer force and the thermomolecular pressure difference (thermal transpiration) in a binary gas mixture as a function of pressure from the free-molecule to the continuum regime. The pressure dependence of the effective thermal diffusion factor is also obtained, including the effect of the simultaneously occurring thermomolecular pressure difference. Inelastic collisions are neglected. Qualitatively new features arise for mixtures that are not present for single gases.
Heat Conduction between Concentric Cylinders in the Slip Regime
Authors: Yu E. Y.
Published: February 2004

An analysis is made of heat conduction of a rarefied gas in the slip regime confined between concentric cylinders maintained at a small temperature difference. From the linearized Krook equation, two integral equations in the perturbed density and temperature are obtained, which are solved separately in the continuum region away from the walls and in the Knudsen layers adjacent to the walls. The Navier-Stokes continuum solution involves some unspecified constants which are determined by matching the solution to the first-order Knudsen-layer solution. The density and temperature jumps at the walls and the correction to heat flux are evaluated from the Knudsen-layer solution.
Validity of the Local Thermal Equilibrium Assumption in Electromagnetic Shock Tubes
Authors: Lie T. N. , Rhee M. J. , McLean E. A.
Published: February 2004

In order to check the assumption of local thermal equilibrium in a transient plasma with kTe ∼ 4 eV and Ne ∼ 1017 cm−3, the electron temperature has been determined by measuring both the spectral line intensity ratio of He II 4686 Å to He I 5876 Å, and the laser light scattered by the plasma. The former method is strongly dependent on the local thermal equilibrium assumption, whereas, the latter method is independent of this assumption. These measurements were made on incident and reflected shock waves produced in an electromagnetic T-tube which had been prefilled with helium or hydrogen to a pressure of 0.5−1.0 Torr. Within the experimental uncertainty of ± 15%, the two electron temperatures agreed, indicating that the assumption of local thermal equilibrium used in the spectroscopic temperature determination is a reasonable approximation. Validity criteria for local thermal equilibrium given by Griem are examined for these conditions.
Wave Propagation in Partly Ionized Viscous Plasmas
Authors: Morin Stephen , Kahn David
Published: February 2004

An analysis of longitudinal wave propagation in partially ionized, viscous plasmas is presented. Equations of motion for three plasma constituents (electrons, ions, and neutrals) are formulated from a coupled set of Maxwell and Boltzman equations. It is found that under suitable conditions all three plasma wave modes (neutral, ion, and electron waves) can be unstable.
Experimental Investigations of a Streaming Plasma Column at Low Magnetic Fields
Authors: Cataldo Joseph C.
Published: February 2004

An experimental study of a low β surface-ionized streaming plasma column is presented for low magnetic fields. As the magnetic field is lowered to 400 G a hollow plasma column sets in and edge oscillations are suppressed. At 175 G a distinct hollow cellular pattern is observed by plasma camera photographs. Below 100 G a hollow plasma column with larger inner and outer diameters reappears. These lower magnetic field phenomena result in an order of magnitude increase in the plasma density. The large increase in density was always accompanied by a change in the ionizer sheath conditions, from ion to electron, as the magnetic field was lowered below 400 G.
Electromagnetic Wave Scattering within a Plasma in the Transport Approximation
Authors: Watson Kenneth M.
Published: February 2004

The radiation transport equation is studied as a means of describing the scattering of electromagnetic waves by a plasma. The approximations required to replace Maxwell's equations by a transport equation are reviewed. The form of the transport equation expressed in terms of Stokes' parameters is given and special expressions for backscatter are developed.
Motion of Newly Created Magnetoplasma
Authors: Zinn John
Published: February 2004

The motion of a nonuniform collisionless plasma that is created at t = 0 in a region containing a magnetic field is considered. Approximate integrals are obtained for the electron and ion Vlasov equations coupled with Maxwell's equations. The results include expressions for the E and B fields, the electron and ion velocities, and the particle densities. The expression for the E field contains a smooth part equivalent to the sum of an ambipolar field and the v × B field associated with a steadily increasing drift velocity. In addition, there are large oscillatory terms with frequencies close to the plasma frequency. The B field is, in an average sense, frozen in the expanding plasma; however, it oscillates with the E field, and the oscillations become progressively stronger with time. In the framework of the approximations used, the oscillations grow without limit, until the approximations fail.
Ion Acoustic Wave Excitation and Ion Sheath Evolution
Authors: Widner M. , Alexeff I. , Jones W. D. , Lonngren K. E.
Published: February 2004

A series of computer simulations and experiments has been performed to investigate the time evolution of an ion space-charge sheath from a solid electrode in a plasma. A large negative step potential (eΔV ≫ kTe) is applied to the boundary of a uniform plasma and the response computed. A fluid model is used for cold ions, and hot electrons in thermal equilibrium are assumed as a neutralizing background. Both the computer simulations and the experiments show the formation of an ion space-charge sheath in a few ion plasma periods and a rarefying disturbance propagating into the plasma with the ion acoustic speed. For a plane electrode this disturbance extends to the electrode, resembling a rarefaction wave as found in ordinary fluid dynamics. For cylindrical and spherical electrodes this disturbance breaks away from the sheath and propagates as an ion acoustic wave into the plasma. The addition of substantial ion-neutral collisions is found to prevent separation of the wave from the sheath. The results of the computer simulations and the experiments agree.
Effects of Bunched Ion Bursts on Apparent Nonlinear Ion Acoustic Waves
Authors: Ichikawa Yoshi H.
Published: February 2004

The bunching effects of ions at the excitation grid in a typical ion acoustic wave experiment are examined by applying the generalized quasilinear theory of Al'tshul and Karpman to a simple model of the grid-plasma system. The resulting bunched ion bursts exhibit amplitude modulation at a distance far from the grid. The characteristics of this amplitude modulation appear to be similar to the recently observed results of Sato, Ikezi, Takahasi and Yamashita. who interpreted their results in terms of nonlinear Landau damping of ion acoustic waves.
Spatial Damping of Large Amplitude Waves
Authors: Lee A. , Schmidt G.
Published: February 2004

The spatial damping of a large amplitude plasma wave was studied to permit direct comparison with experimental data. Using both the quasilinear treatment of Al'tshul and Karpman, and following exact particle trajectories of resonant particles as done by O'Neil for the temporal case, it was found that the spatial damping results are analogous to the temporal ones. The spatial damping formula is obtained by replacing the nondimensional time t/τ and damping coefficient γLτ for the temporal case by the distance x/L and spatial damping coefficient ΛLL, respectively. Here, τ = (m/eEk)1/2,γL is the linear Landau damping coefficient, ΛL = γL∂ω/∂k, and L = τω/k. Damping curves have been plotted for comparison with measured data. The validity condition of the spatial case, namely, ΛLL ≪ 1, is far more stringent than for the temporal one.
Microinstabilities in Inhomogeneous Plasmas: Theory
Authors: Beasley C. O. , Farr W. M. , Grawe H.
Published: February 2004

A formalism is presented for the determination of unstable electrostatic oscillations in a model mirror-confined plasma with a Gaussian density variation of arbitrary scale length along the magnetic field. A formal solution to the collisionless Boltzman equation is obtained for a plasma confined in a parabolic well. Using this solution, one may numerically solve Poisson's equation to obtain the eigenfunctions (perturbed potentials) and eigenvalues (densities) of the system for a given frequency and growth rate. As no mathematical limits on plasma length exist for obtaining these solutions, the infinite-plasma results may be recovered in the limit of very long plasmas.
Main Electron Resonance of a Bounded Plasma at High Magnetic Fields
Authors: Messiaen A. M. , Vandenplas P. E.
Published: February 2004

The main electron resonance, whose behavior up to ωce/ω ≃ 1 is well understood, has now been experimentally followed up to high magnetic fields (ωce/ω ≃ 50) in a very quiet plasma. There is very good agreement with recent theoretical predictions based on the hydrodynamical description of a bounded, hot, electron-ion plasma, thereby confirming, for the values of the plasma parameters involved, the validity of the theory used.
Adiabatic Compression of Tokamak Discharges
Authors: Furth H. P. , Yoshikawa S.
Published: February 2004

Adiabatic compression in minor and major radius is shown to facilitate the attainment of dense, high-temperature plasmas in the tokamak configuration.
High-Beta Plasma Injection into Linear Multipole Fields
Authors: Turner R.
Published: February 2004

Two linear multipole fields, a 3 kG octopole and a 2 kG Ioffe field have been studied experimentally as guide fields for the high-beta output of a plasma gun. In the octopole field a large fraction of the original plasma was lost to the walls; the amount and location of the loss depended on the direction of the octopole field. The loss is attributed to unstable plasma in the region behind the octopole bars that short circuits the polarization field necessary for the plasma to move along the guide field. The octopole field does not offer any advantage over the simpler Bz field as a guide field for the present plasma. A rotational instability, at a frequency of up to 1 MHz, resulted in a large plasma loss through the cusp regions of the Ioffe field. As a result, it also proved to be a much poorer guide field than a Bz field.
X-Ray Spectra from Dense Plasma Focus Devices
Authors: Van Paassen H. L. L. , Vandre R. H. , White R. Stephen
Published: February 2004

X-ray spectra with energies up to 350 keV are reported for two paraboloidal plasma focus devices, the Mark I and Mark III device. Low energy x rays with energies between 5.46 and 29.2 keV were measured with Ross filters. Both time resolved and time integrated spectra were obtained. The higher energy x rays from 60 to 350 keV were measured with K-5 nuclear emulsions. The energies of the individual electrons produced by the photoelectric effect and by Compton scattering in the nuclear emulsion were measured and the x-ray spectra were deduced. The x-ray spectra from each device can be represented by the function (dN/dE)E = AE−m. In the Mark I device, A = (0.85 ± 0.28) × 108 ergs (keV)1.5 and m = (2.5 ± 0.8); in the Mark III device, A = (3.8 ± 1.0) × 108 ergs (keV)1.5 and m = (2.5 ± 1.0), where E is the photon energy in kiloelectron volts. Both spectra are similar in shape, but the x-ray intensity from Mark III, with four times the bank energy, is greater. The x rays appear to be produced by thick target bremsstrahlung on the anode surface by electrons with maximum energies greater than 350 keV and total energy distributions that vary as E−3.3. The start of the x-ray pulse is found to be coincident in time with the current discontinuity in the plasma pinch device.
Experimental Study of Fully Developed Laminar Flow in a Porous Pipe with Wall Injection
Authors: Bundy Roy D. , Weissberg Harold L.
Published: February 2004

Pressure drops and exit centerline velocities were determined for nonswirling laminar flow in a porous pipe with wall injection. The measurements confirm earlier theoretical results except for the recent additional solutions obtained by Terrill and Thomas.
Thermal Diffusion Effects on the Electrohydrodynamic Rayleigh-Taylor Bulk Instability
Authors: Turnbull Robert J.
Published: February 2004

A dielectric liquid heated from above becomes unstable when a vertical alternating electric field of sufficient magnitude is applied. The effects of thermal diffusion on that instability are explored. The voltage for incipient instability is compared with experimental results.
Transient Solution for Stokes' Second Problem in Magnetohydrodynamics
Authors: Rudraiah N.
Published: February 2004

A closed form solution for the transient solution of Stokes' second problem is given in terms of exponential and error functions of a complex argument. The transient dies out rapidly with an increasing Hartmann-type number m as distance from the plate increases.
Temperature Gradients, Resonance, and the Interchange Instability
Authors: Emmert Gilbert A.
Published: February 2004

Temperature gradients and wave-guiding center resonance modify the usual finite gyroradius stabilization criteria and growth rate for the interchange instability in a collisionless low-β plasma. The growth rate is given for a few examples.
Relativistic Beam Equilibria with Back Currents
Authors: Benford Gregory , Book David L. , Sudan R. N.
Published: February 2004

A generalization of the Bennett distribution leads to a hollowed-out beam with back currents. The system becomes more and more unstable to the resistive firehose mode as the beam is hollowed out.
Deviations from Maxwellian in the Electron Velocity Distribution Function of a θ-Pinch Plasma
Authors: Gondhalekar A. M. , Kronast B. , Benesch R.
Published: February 2004

Incoherent scattering of laser radiation from a high temperature θ-pinch plasma has been used to determine the electron velocity distribution. Differences from Maxwellian, namely, a blue shift and a deviation in the red wing of the spectrum are noted.
Influence of Retarded Time on Jet Noise
Authors: Jones Ian S. F.
Published: February 2004

The acoustic radiation from a region of turbulence can be expressed in terms of the fluctuating turbulent stresses and for estimates of the noise, it is common to neglect the change in retarded time between different regions of correlated turbulence. From measurements of the wavenumber frequency spectrum of one of the turbulent stresses in a jet, the influence of retarded time on the acoustic radiation is shown to be small for sound radiated at right angles to the jet axis but to be significant at small angles to the jet axis. This provides a partial explanation of the success of Lighthill's U8 law even when convection is important.
Transport Equations in Turbulence
Authors: Daly Bart J. , Harlow Francis H.
Published: February 2004

Turbulence transport equations, describing the dynamics of transient flow of an incompressible fluid in arbitrary geometry, have been derived in such a manner as to incorporate the principles of invariance (tensor and Galilean) and universality. The equations are described in detail and their applicability is demonstrated by comparison of solutions with experiments on turbulence distortion and on the turbulence in the flow between flat plates.
Shock Waves from Line Sources. Numerical Solutions and Experimental Measurements
Authors: Plooster Myron N.
Published: February 2004

The cylindrical pressure wave resulting from instantaneous energy release along a line in a quiescent atmosphere has been studied by numerical integration of the equations of gas dynamics. Atmospheres obeying both the ideal gas law, and a realistic equation of state for air at high temperatures, were employed. The effects of varying the initial distribution of mass and energy in space were also investigated. The computations were carried well into the weak shock region, and agree well with asymptotic solutions for very strong and very weak shock waves. The effects of deviations from the initial assumptions of the strong shock asymptotic solutions are discussed. An approximate equation for the radial dependence of shock strength, applicable to most of the numerical solutions, is presented. Experimental measurements of shock strengths from detonation of long high explosive charges are shown to be in good agreement with the numerical solutions.
Measurements of Gaseous Diffusion Coefficients
Authors: DuBro G. A. , Weissman Stanley
Published: February 2004

Diffusion coefficients for He-Ne, He-Ar, and 3He-4He systems have been measured as a function of temperature using a two-bulb method. The theory of the method has been developed to account for the removal of samples of nonnegligible volume for concentration analysis. The temperature range for the experimental values of the diffusion coefficients for 3He-4He has been extended to 900°K. The results of this investigation agree well with values in the literature and exhibit good mutual consistency with other transport properties. Theoretical diffusion coefficients also show reasonable agreement with the present results.
Self-Diffusion Coefficients for Krypton
Authors: Weissman Stanley , DuBro G. A.
Published: February 2004

Self-diffusion coefficients for Kr have been measured in the temperature range from 195°K to 1036°K. The present results are the only self-diffusion coefficients reported as a function of temperature which are consistent with viscosity and thermal conductivity data for the pure gas. A relation between the isotopic thermal diffusion factor, and the self-diffusion coefficient and the viscosity which takes into account higher approximations in the Chapman-Enskog theory has been developed. The derived values of the thermal diffusion factor show surprisingly good agreement with the directly measured values.
Transport Properties of a Plasma in a Strong Magnetic Field
Authors: Gilbert B. J. , Radin S.
Published: February 2004

The longitudinal electrical and thermal conductivities of a fully ionized plasma in a strong external magnetic field are calculated. The magnetic field is strong enough to significantly affect the collision process, but it is not so strong as to dominate.
Experimental Study of Magnetic Flux Transfer at the Hyperbolic Neutral Point
Authors: Bratenahl A. , Yeates C. M.
Published: February 2004

A laboratory study is reported herein of a plasma flow process sometimes referred to as the severing and reconnecting of magnetic field lines at a hyperbolic or X-type neutral point. It is found that a hyperbolic pinch develops at the neutral point resulting in plasma compression. The Ohmic electric field of the pinch current enables field line reconnection to take place through resistive diffusion. The reconnection rate is substantially increased by a reduction in the size of the pinch region effected by flow adjustment through pairs of stationary slow mode shocks in a manner similar to that deduced and described by Petschek. Strong evidence is presented for this wave-dominated configuration. However, it is found that the pinch current becomes progressively concentrated at the neutral point and along the shock loci until eventually a critical current density is reached marked by a sudden and large anomalous increase in resistivity as predicted by Friedman and Hamberger. At this point the wave-assisted diffusion mode is terminated and there is observed: (1) a cutoff in pinch current, (2) a large increase in the electric field, (3) corresponding increase in reconnection rate, and (4) generation of a system of large amplitude fast-mode waves. The waves, bearing evidence of the onset of plasma turbulence, effect a rapid and gross redistribution of flux among the cells defined by the separatrix, and blow the slow mode shocks off downstream. The increased electric field raises the possibility of rapid magnetic energy dissipation through acceleration of particles to high energy.
Interaction between Hydromagnetic Waves and a Time-Dependent, Inhomogeneous Medium
Authors: Dewar R. L.
Published: February 2004

Consider a system made up of a hydromagnetic wave and the slowly varying background fluid in which it propagates. It is shown that both the effect of the background on the wave and that of the wave on the background may be derived from Hamilton's principle using the averaged hydromagnetic Lagrangian density. The waves propagate adiabatically, conserving the wave action, and act on the background via a wave pressure term. Total momentum, angular momentum, and energy are conserved. When many waves are superimposed, as in weak turbulence, the wave kinetic equation replaces the adiabatic conservation equation. The accuracy of the averaging approximation is examined, and it is shown that it may be extended to all orders in the inhomogeneity. Also, Eulerian and Lagrangian averaging are discussed.
Parametric Excitation of Purely Growing Modes in Magnetoplasmas
Authors: McBride John B.
Published: February 2004

Excitation of purely growing modes in magnetoplasmas by high-frequency, dipole electric fields oscillating at ω0 is discussed. Analytic expressions are given for the threshold and growth rate just above threshold for long wavelengths when k ⊥ B0.
Stability of a Bulged Theta Pinch
Authors: Bodin H. A. B. , Newton A. A. , Wolf G. H. , Wesson J. A.
Published: February 2004

An experimental and theoretical study has been made of the hydromagnetic instability of an axisymmetric bulged region in the midplane of a theta pinch 8 m long. The bulged region was generated adiabatically after the initial implosion in such a way that it fulfilled most of the assumptions of the theoretical model; in particular, it was free of end effects for the time of observation. At a filling pressure of 20 m Torr D2 and with a peak magnetic field of 20 kG the plasma, which was collision dominated, had values of temperature, density, and beta on the axis of 120 eV, 3 × 1016cm−3, and 0.7 ± 0.2. The predicted m = 1 instability was observed and for a range of bulge amplitudes its measured growth and propagation along the column agreed to within a factor of less than 2 with the theoretical values. It is concluded that the m = 1 instability of such bulged plasmas is well described by ideal hydro-magnetic theory. Modes with m ≥ 2 were not observed during the m = 1 growth and their absence is attributed to finite Larmor radius stabilization.
Sideband Instability
Authors: Kruer W. L. , Dawson J. M.
Published: February 2004

Computer experiments on one-dimensional sheet plasmas show that large amplitude electron plasma oscillations with trapped particles can be unstable. This behavior is consistent with both a recent experiment and a recent theory predicting a trapped particle instability.
Low Density Cyclotron Instability in a Two-Component Electron Plasma
Authors: Blanken R. A. , Lazar N. H.
Published: February 2004

A velocity space instability with frequency near the electron cyclotron frequency f c has been observed in a hot electron plasma. Measurements of the frequency shift above f c, the stability boundary and the growth rate agree well with calculations for the two-component instability.
Nonlinear Theory of the Drift-Dissipative Instability
Authors: Sleeper Arthur M. , Simon Albert
Published: February 2004

The drift instability of a weakly ionized plasma is analyzed in a semi-infinite slab geometry. Analytic expressions are obtained for the unstable eigenmodes and all critical linear parameters. By choosing the appropriate operating regime (in terms of background pressure and applied magnetic field), it is possible for only one mode to go unstable as the pressure decreases by an appreciable amount below the critical value. Nonlinear theory is then used to solve for the saturated mode amplitude and frequency shift as functions of the fractional decrease in pressure. The anomalous flux is also obtained. One interesting result is that the frequency shift is very small for this instability.
Rotor Equilibria of Non-Neutral Plasmas
Authors: Bogema Bernard L. , Davidson Ronald C.
Published: February 2004

Equilibria are considered within a Vlasov-Maxwell model for an electron gas column rotating about an axis parallel to a uniform external magnetic field B0. A condition is derived which restricts the values of ωR (angular speed of mean rotation), Ωc (electron cyclotron frequency), and ωp (electron plasma frequency on axis) in order that the general class of rigid-rotor distributions f0(H⊥ − ωRL, pz) corresponds to radially confined equilibria in the nonrelativistic, nondiamagnetic case. It is demonstrated that rigid-rotor distributions have the property that a specification of the radial equilibrium density profile n0(r) uniquely determines the distribution ∫  dpzf0(H⊥ − ωRL, pz) of electrons perpendicular to B0. Explicit examples in this regard are discussed in both the nonrelativistic, and relativistic, diamagnetic cases. This can serve as a useful experimental diagnostic whereby a determination of n0(r) yields the perpendicular distribution ∫  dpzf0(H⊥ − ωRL, pz).
Relaxation Processes in Plasmas with Magnetic Field. Temperature Relaxations
Authors: Ichimaru Setsuo , Rosenbluth Marshall N.
Published: February 2004

The Fokker-Planck coefficients of a plasma in the magnetic field are calculated in terms of the spectral function of the electric-field fluctuations and the dielectric response function; the results are used for the investigation of temperature relaxation processes. It is found that the relaxation rate between the electron and ion temperatures contains, in addition to the usual Spitzer rate, an anomalous term which diverges logarithmically as the mass ratio approaches zero. The physical origin of this anomalous term is the strong coupling between the spiral motion of the electrons and the long-wavelength, low-frequency fluctuations produced by the ions; its magnitude can become comparable to the Spitzer rate for a strong magnetic field. In the case of the temperature relaxation between the parallel and perpendicular directions to the magnetic field, the screened Coulomb interaction provides the major relaxation mechanism; the effects of the fluctuations associated with the Bernstein modes are negligibly small.
Conductivity of a Weakly Ionized Plasma as Related to Particle Diffusion in μ Space
Authors: Hagfors T.
Published: February 2004

A method is developed whereby the conductivity tensor of a collision dominated plasma is expressed in terms of the correlation function for microcurrents as in the case of a collisionless plasma. When collisions are important, the motion of particles through phase space must be considered as a stochastic, diffusionlike process rather than as a dynamical one as in the collisionless plasma. Some examples of the diffusion process are considered and the resulting conductivity is related to previous work.
Frequency Spectrum of Microwaves Scattered by Turbulent Plasma
Authors: Granatstein V. L. , Philips T. O.
Published: February 2004

Microwaves are scattered from plasma fluctuations produced by forcing gas in turbulent flow through a discharge tube. The frequency broadening of the scattered wave is studied as a function of several experimental variables including the magnitude and orientation of the wave vector and the extent of the scattering volume. The experiment is compared with a theoretical result that expresses the frequency broadening in terms of three distinct contributions: a Doppler broadening due to random convection of the plasma turbules; transit time broadening; and a non-Gaussian broadening due to spatial gradients in the mean convection velocity. It is shown that measurement of the frequency broadening can be used to estimate the level of gas velocity fluctuations with about 25% accuracy.
Formation and Heating of Laser Irradiated Solid Particle Plasmas
Authors: Haught Alan F. , Polk Donald H.
Published: February 2004

High energy, spherically symmetric, free plasmas are produced by electrically suspending a small, solid, lithium hydride particle in vacuum at the focus of a lens where the particle is vaporized, ionized, and the resulting plasma heated by the focused beam of a Q-spoiled laser. A two-temperature, integated similarity model has been developed for calculation of the plasma time development and gives plasma energies in good agreement with those determined experimentally. Charge collector and expansion velocity measurements show that the plasma expansion is spherically symmetric with a linear velocity profile as assumed in the calculations. While line radiation studies indicate that some recombination occurs in the plasma, from mass spectrometer measurements the plasma consists primarily of Li3+ and H+ for plasma energies above 100 eV. Calculations have been carried out to define the optimum conditions of particle radius, focal spot size, pulse duration, and laser peak power for both maximum plasma energy and maximum plasma quantity at a given energy. Based on the results of these calculations, average plasma energies in excess of 5 keV can be produced with 10 J, 0.1 nsec laser pulses, and a laser system with these characteristics is being developed for high-energy plasma production experiments.
Acceleration Mechanism for Neutron Production in Plasma Focus and z-Pinch Discharges
Authors: Bernstein Melvin J.
Published: February 2004

A model has been developed for the acceleration of deuterons in the tightly compressed column of a z-pinch discharge, in particular, that of a plasma focus discharge. It was assumed that an annular distribution of current undergoes a rapidly contracting transition to a distribution peaked on axis and the resulting crossed fields, Bθ and Ez, were used to calculate deuteron trajectories in the plasma. These results show that a significant number of ions can be accelerated to energies of up to 600 keV and that they have a large value for their time-averaged axial velocities. The orbiting motion in the magnetic field produces an anisotropic distribution of collision velocities and a neutron-production model based upon nuclear collisions by these deuterons can account for the measured characteristics of neutron energies, neutron fluxes, and rates of production.
Spontaneous Field Reversal in Theta Pinches
Authors: Morse R. L. , Stovall E. J.
Published: February 2004

A model is proposed to account for spontaneous magnetic field reversal which is observed in high temperature θ-pinch plasmas early in the compression phase. The model assumes a large anomalous viscosity in the electron cloud and collisionless ion behavior.
Propagation of Ion Cyclotron Harmonic Wave
Authors: Ault E. R. , Ikezi H.
Published: February 2004

Low-frequency electrostatic waves which propagate across the magnetic field are studied experimentally. The observed dispersion relation agrees with that of the ion cyclotron harmonic wave. Strong damping of the wave is observed.
Navier-Stokes Initial Value Problem for Boundary-Free Incompressible Fluid Flow
Authors: Rosen Gerald
Published: February 2004

Convergence proofs are reported for a general local iteration solution to the Navier-Stokes initial value problem and estimates of the accuracy of the nth iterative approximation are derived. Without appeal to methods of functional analysis, it is shown that a Kiselev-Ladyzhenskaya weak solution is, in fact, a classical solution. Any one of three alternative conditions on the initial velocity field is found to be sufficient to guarantee the existence of a global solution. Breakdown phenomenon which may prevent a local solution from being continued for all t ≥ 0 to a global solution is analyzed. The mathematical theory suggests that breakdown is precluded for a suitably smooth initial velocity field, irrespective of the over-all initial velocity field magnitude.
Stability of Steady Flow in a Diverging Channel
Authors: Nakaya C. , Hasegawa E.
Published: February 2004

An angle formed by two intersecting planes and maximum velocity are chosen as two characteristic parameters for steady flow. It is shown that for a given maximum velocity there exists a certain critical angle at which steady perturbation appears.
Some Results on the Nonoscillation of Salt Fingers
Authors: Yih Chia-Shun
Published: February 2004

Salt-finger convection in water discovered by Stommel, Arons, and Blanchard is discussed, and conditions under which the principle of exchange of stabilities holds are given.
Decay of Weak Turbulence
Authors: Ling S. C. , Huang T. T.
Published: February 2004

A detailed experimental investigation of the structure of weak turbulence generated by various single and multiple-stage grids has been made. The weak turbulent fields were limited to those having no interaction with the linear momentum wake of the grid. The present study covers a range of Reynolds numbers of turbulence between 70 and 3. Components of turbulence were found to have equipartition of energy within this range. When the Reynolds number of turbulence is <30, the kinetic energy of turbulence decreases inversely as the square of decay time. All the length scales of turbulence increase as the square root of time, while the Reynolds number of turbulence decreases as the square root of time. Both the measured spectral and correlation functions show self-preserving forms. The longitudinal correlation function is closer to a Cauchy than to a Gaussian distribution function. The resultant three-dimension energy spectrum shows a weak but nonvanishing transfer of energy from low to high wavenumbers.
Influence of High-Pass Filtering on Third-Order Correlation Measurements
Authors: Helland K. N. , Stegen G. R.
Published: February 2004

An experimental investigation has been made of the influence of high-pass filtering on third-order correlations in grid turbulence. It has been found that for sufficiently small cutoff frequencies, the third-order correlations remain unchanged by high-pass filtering.
Finite-Amplitude Instability of the Compressible Laminar Wake. Strongly Amplified Disturbances
Authors: Liu J. T. C. , Lees Lester
Published: February 2004

The interaction between mean flow and finite-amplitude disturbances in certain experimentally observed unstable, compressible laminar wakes is considered theoretically without explicitly assuming small amplification rates. Boundary-layer form of the two-dimensional mean-flow momentum, kinetic energy and thermal energy equations and the time-averaged kinetic energy equation of spatially growing disturbances are recast into their respective von Kármán integral form which show the over-all physical coupling. The Reynolds shear stresses couple the mean flow and disturbance kinetic energies through the conversion mechanism familiar in low-speed flows. Both the mean flow and disturbance kinetic energies are coupled to the mean-flow thermal energy through their respective viscous dissipation. The work done by the disturbance pressure gradients gives rise to an additional coupling between the disturbance kinetic energy and the mean-flow thermal energy. The compressibility transformation suggested by work on turbulent shear flows is not applicable to this problem because of the accompanying ad hoc assumptions about the disturbance behavior. The disturbances of a discrete frequency which corresponds to the most unstable fundamental component, are first evaluated locally. Subsequent mean-flow and disturbance profile-shape assumptions are made in terms of a mean-flow-density Howarth variable. The compressibility transformation, which cannot convert this problem into a form identical to the low-speed problem of Ko, Kubota, and Lees because of the compressible disturbance quantities, nevertheless, yields a much simplified description of the mean flow.
Traveling Waves of Arbitrary Amplitude in Compressible Hydrodynamics under Gravity: An Exact Solution
Authors: Chiu Y. T.
Published: February 2004

Exact traveling-wave solutions to the hydrodynamic equations for an isothermal atmosphere stratified by a uniform gravitational field are obtained in two Cartesian spatial coordinates and one temporal coordinate and represent simple Riemannian waves of arbitrary amplitude and wave form which reduce directly into acoustic waves in the absence of gravity. While a number of characteristics are similar to the theory of small amplitude acoustic-gravity waves, these solutions exhibit features such as shock formation and phase dispersion which cannot be treated in small-amplitude theory. Solutions are given in terms of relations between physical wave characteristics and hydrodynamic variables. Comparison with traveling atmospheric disturbances are proposed.
Properties of High Current Free-Burning Arcs in Air
Authors: Nicolai Leland M.
Published: February 2004

The measured characteristic curves for free-burning arcs in air at pressures from 0.019 to 1.0 atm and high currents from 190 to 400 A are presented. The experimental results show that the characteristic curves are flat (E = const) at these high currents. Characteristic arc dimensions were determined from arc photographs. The results show the arc diameter to be proportional to I12. Heated solid cylinder heat transfer ideas are applied to the free-burning arc data and the functional form for the Nusselt number in terms of the Grashof and Prandtl number is determined.
Electrohydrodynamic Stability: Fluid Cylinders in Longitudinal Electric Fields
Authors: Saville D. A.
Published: February 2004

The stability of a fluid cylinder, stressed by an axial electric field, has heretofore been studied assuming that the cylinder and its surroundings behave as perfect dielectrics and viscous effects are ignored. With many fluids this is unrealistic since the existence of even a small conductivity implies that the deformed interface carries an electric charge. Upon deformation of the interface the charge interacts with the field to produce an electrical shearing stress. Thus, to avoid singular behavior viscous shear must be considered from the outset. The analysis is applicable to situations where the relaxation time for free charges is short compared with the time scale for fluid motion. It is found that electrical shearing forces can, under some conditions, completely stabilize the cylindrical interface to axisymmetric deformations. On the other hand, the conditions under which these same forces produce instability are delineated. In instances where both fluids have low viscosities a boundary layer effect produces additional damping and, in the presence of an axial electric field, electrical shearing stresses in this boundary layer may render an otherwise stable oscillation unstable.
Ion Cyclotron Instability
Authors: Weibel Erich S.
Published: February 2004

Electrostatic ion cyclotron waves are investigated for a plasma consisting of two groups of counter-streaming ions in a background of stationary electrons. Under certain conditions such waves are weakly amplified. Analytic and numerical conditions for instability are presented.
Ordinary-Mode Electromagnetic Instability in Counterstreaming Plasmas with Anisotropic Temperatures
Authors: Bornatici M. , Lee Kai Fong
Published: February 2004

The instability of the electromagnetic linearly polarized mode propagating perpendicular to a uniform magnetic field is studied by using the Vlasov equation for a counterstreaming electron plasma with anisotropic temperatures. An instability occurs if the streaming velocity exceeds a certain threshold value which can be below that required to excite the electrostatic two-stream instability. It is found that temperature perpendicular to the field has a stabilizing effect, while parallel temperature enhances the electromagnetic instability. Typical growth rates are of the order of the electron cyclotron frequency.
Lyapunov Stability of an Inhomogeneous Two-Stream Plasma
Authors: Chervin Robert M. , Sen Amiya K.
Published: February 2004

Lyapunov's direct method has been adapted to the study of an electrostatic instability of a plasma by using Zubov's extension of the method to distributed parameter systems. Specifically, the linear stability of two inhomogeneous interpenetrating electron streams in a finite one-dimensional system is considered. Proper Lyapunov functionals are constructed for both stability and instability. It is seen that, as in the homogeneous case, the stability or instability depends on whether or not the thermal speed is greater or less than the streaming speed. In contrast to the methods of energy principle, the complete generality of Lyapunov's direct method is discussed.
Thermal Equilibrium and Stability of Tokamak Discharges
Authors: Furth H. P. , Rosenbluth M. N. , Rutherford P. H. , Stodiek W.
Published: February 2004

Steady-state temperature and magnetic field profiles are derived in cylindrical geometry, including classical electron-ion equilibration, Ohmic heating, and the classical ion thermal transport appropriate to tokamak geometry. To fit the experimental data, a direct electron heat loss must accompany any appreciable resistivity anomaly. The classical equilibrium can be thermally stable only if Ti/Te ≳ 2/3. Direct electron heat loss by radiation is further destabilizing; but for typical parameters, stability can be achieved by a moderate amount of anomalous electron thermal conduction. The growth time of thermal instabilities is generally limited by the resistive skin time. The presence of a runaway component of the current allows shorter growth times, and this may be related to the present high-density limit in tokamaks.
Explosive Plasma Instabilities
Authors: Fukai J. , Krishan S. , Harris E. G.
Published: February 2004

The interaction of three monochromatic waves (two positive energy longitudinal waves and one negative energy wave) is investigated. When only the first-order nonlinear interactions are considered, an explosive instability occurs. However, this instability is stabilized by the higher order nonlinear interactions. The matrix elements of the three-wave and the four-wave interactions in a magnetized plasma are calculated.