bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Field Asymmetry on Neoclassical Transport in a Tokamak
Authors: Hazeltine R. D. , Rosenbluth M. N.
Published: February 2004

The effect on transport of a local increase (“bump”) in the confining field of a large aspect ratio tokamak is studied in the small collision frequency regime, in which trapped particles—particles reflected by the bump—make a dominant contribution. From solution of the drift-kinetic equation with boundary conditions appropriate to trapped and untrapped particles, explicit expressions for the cross-field particle and energy fluxes are obtained; the density, temperature, and potential gradients, and a parallel electric field, are considered as driving terms. While the diffusion and energy fluxes have an easily anticipated form, similar to superbanana transport, the influence of the bump on the Ware flux, resulting from the parallel electric field, is surprisingly large.
Low-Frequency Beam-Plasma Interactions in a Finite-Sized Plasma
Authors: Bhatnagar V. P. , Getty W. D.
Published: February 2004

Results are presented for an experimental and theoretical investigation of low-frequency waves in a beam-generated plasma. Waves are excited at frequencies immediately above the ion-plasma frequency by sinusoidally modulating the electron beam current. The study is aimed at obtaining ion heating at the lower-hybrid resonant frequency. An electron beam of 400-1000 V energy and a few milliamperes of current is used to generate plasmas with densities in the range of 109 cm−3 in a magnetic field of a few hundred gauss. Hydrogen, argon, deuterium, and neon gases are used. The rf electric field is probed as a function of r, z, and frequency, and energetic ions are detected by a gridded probe. Two or three resonances are found in the probe response above ωpi, and are shown to be multiple half-wavelength resonances of standing plasma waveguide axisymmetric modes. A normal-mode analysis is used to calculate the probe responses and is found to correctly predict the effects of varying beam voltage, plasma density, ion mass, and dc axial magnetic field. The excited wave may be viewed as an electrostatic wave propagating at an angle very close to 90 deg from the magnetic field.
Elevated Ion Temperature in a Double-Ended Q Machine
Authors: Brown Ian G.
Published: February 2004

The perpendicular ion temperature of a barium plasma contained in a double-ended Q machine has been measured by a spectroscopic technique. When the plasma is “ion-rich”, good agreement is found between the measured ion temperature and the hot-plate temperature, while in the “electron-rich” regime, the ion temperature is elevated above the hot-plate temperature. The increased ion temperature can be well accounted for by the energy input through the acceleration of ions through the electron sheath and their consequent thermalization.
Inherent Electrostatic Instability in a Low-Density Single-Ended Q Machine
Authors: Estabrook K. , Doucet H. J. , Rouille C.
Published: February 2004

An inherent electrostatic instability in a low-density single-ended Q machine is investigated theoretically and experimentally. Using the Penrose and Jackson analysis, the plasma is shown to be unstable with respect to ion-acoustic waves for all negative potentials of the cold plate except for a narrow band of values slightly more negative than the plasma potential. The prediction is experimentally confirmed.
Shear Stabilization of the Drift-Cyclotron Instability
Authors: Liu Chuan S. , Bhadra Dilip K.
Published: February 2004

Drift-cyclotron instability is shown to be stabilized by the shear of the magnetic field for Ln/Ls>(m/M)1/2, where Ln is the density scale length and Ls is the shear length.
Quasilinear Theory of the Mirror Flute Instability
Authors: Simon Albert , Weng C. I.
Published: February 2004

The nonlinear small-amplitude behavior of a collisionless plasma is studied at the mirror flute instability threshold. A treatment assuming a “constant gravity” model of the mirror field predicts saturation of the m = 1 mode amplitude in disagreement with experiment. A model using nonconstant gravity yields the previous threshold mode and an upper damped mode. Nonlinear analysis shows the upper mode to be nonlinearly unstable. If the lower mode reaches sufficient amplitude, it triggers the upper and is itself shut off. The resulting behavior is in general agreement with experiments.
Nonlinear Frequency Shift of a Plasma Mode
Authors: Lee A. , Pocobelli G.
Published: February 2004

The nonlinear frequency shift of an electron plasma mode is calculated without restriction to part of the electrons. A time-dependent dispersion equation solved numerically in the time-asymptotic limit yields, for phase/thermal velocity ratios ≳4, frequency shifts significantly larger than previously calculated. The relative contribution of trapped and untrapped electrons to the frequency shift varies widely with the wave amplitude and the phase/thermal velocity ratio.
Anomalous Resistance due to Cross-Field Electron-Ion Streaming Instabilities
Authors: Lampe Martin , Manheimer Wallace M. , McBride John B. , Orens Joseph H.
Published: February 2004

New computer simulations show that the nonlinear stage of the beam cyclotron instability is stabilized if Ti/Te≳υd/υe, similar to ion sound, as has been predicted theoretically. In this case, the instability makes no significant contribution to anomalous resistance, for the conditions of typical laboratory resistive shocks. In the opposite case, a theoretical study of the later development shows that after the onset of ion trapping, both wave energy and electron temperature grow linearly with time, and the anomalous electron-ion collision frequency becomes constant at ∼0.02 times the electron plasma frequency. These conclusions are supported by simulation studies.
Lifetime of Plasma Fluctuations in a Discharge Tube with Turbulent Gas Flow
Authors: Rhinewine M. , Granatstein V. L.
Published: February 2004

A direct measurement of the lifetime of plasma density fluctuations in turbulent pipe flow has been made; this measurement determines the range of validity of the frozen flow assumption in past studies of microwave scattering from plasma fluctuations.
Hydrodynamic Stability of the Flow between Parallel Porous Walls
Authors: Sheppard D. Max
Published: February 2004

The linear stability of the flow of an incompressible Newtonian fluid between two porous parallel walls is analyzed using the Galerkin method. The flow parallel to the plates is maintained by a constant pressure gradient. The effects of small “cross flows” from one wall to the other on the stability is examined. Two Reynolds numbers are defined, one based on the maximum symmetric plane Poiseuille velocity (R) and one on the cross-flow velocity (r). Both use half the wall spacing for the characteristic length. A closed form sufficient condition for stability that indicates the flow becomes more stable with increasing r is obtained. The numerically obtained neutral stability curves for r = 0.1, 0.2, 0.3, 0.4, and 0.6 are in agreement with the sufficient condition showing a substantial shift toward increased stability for increased r.
Radiative Transfer Effects on Reflected Shock Waves. II. Absorbing Gas
Authors: Su F. Y. , Olee D. B.
Published: February 2004

Radiative cooling effects behind a reflected shock wave are calculated for an absorbing-emitting gas by means of an expansion procedure in the small density ratio ε across the shock front. For a gray gas shock layer with an optical thickness of order unity or less the absorption integral is simplified by use of the local temperature approximation, whereas for larger optical thicknesses a Rosseland diffusion type of solution is matched with the local temperature approximation solution. The calculations show that the shock wave will attenuate at first and then accelerate to a constant velocity. Under appropriate conditions the gas enthalpy near the wall may increase at intermediate times before ultimately decreasing to zero. A two-band absorption model yields end-wall radiant-heat fluxes which agree well with available shock-tube measurements.
Linear Time-Dependent Vlasov Equation; Case-Van Kampen Modes
Authors: Bateman Glenn , Kruskal Martin D.
Published: February 2004

The multiple-time-scale method is used to find a succinct solution for the linearized Vlasov equation when the background state of the plasma is a slowly varying function of time. It is found to be necessary to consider normal modes of the equation because the slow and fast time variables synchronize separately for each mode. The asymptotic series for each normal mode and for its associated frequency are computed to all orders in the expansion parameter. The lowest-order results are the Case-Van Kampen modes in WKB form. The corrections represent a diagonalization of the results of Baldwin, Trocheris, and Imre. In particular, the dispersion function is corrected by higher-order terms and the frequencies of the discrete spectrum have complex-valued shifts.
Formation and Interaction of Ion-Acoustic Solitary Waves in a Collisionless Warm Plasma
Authors: Sakanaka P. H.
Published: February 2004

The formation and interaction of solitary waves in a warm-ion, hot isothermal electron plasma have been studied with the Vlasov equation for ions and Boltzmann distribution for electrons. An arbitrary initial potential pulse having a width smaller (or larger) than that of a solitary wave decomposes into one (or several) solitary wave(s) with (or without) ion-acoustic oscillations behind. In the interaction of two solitary waves, it has been found that: (1) If the initial amplitude ratio is not too large, the two waves exchange their amplitudes and bounce apart; (2) if the initial amplitude ratio is large, the larger wave first absorbs the smaller, subsequently re-emits it behind. A steady-state solitary wave solution for the ion fluid equations with a scalar pressure and Boltzmann electrons presents a smaller width and a larger velocity than the solution of the Korteweg-de Vries equation with the same amplitude. The limiting Mach number is smaller than Sagdeev's value.
Theory of Phase Space Density Granulation in Plasma
Authors: Dupree Thomas H.
Published: February 2004

A novel state of turbulent plasma characterized by small scale phase-space granulations called “clumps” is proposed. Clumps are produced when regions of different phase space density are mixed by the fluctuating electric field. They move along ballistic orbits and drive the turbulent field in a manner similar to that in which thermal fluctuations are driven by particle discreteness. In the coherent wave limit the clumps become the familiar trapped particle eddies of a Bernstein-Green-Kruskal mode. The turbulent state can exist in the absence of linear instability although it is more likely to occur in a linearly unstable plasma. The spectrum contains a ballistic portion as well as resonances at the wave (collective) frequencies. The discreteness of the clumps produces collision-like process. For example, the average distribution function satisfies a Fokker-Planck equation instead of a quasilinear diffusion equation.
Dependence of Fluctuation Level on the Magnetic Field Configuration in the Spherator
Authors: Okabayashi M. , Freeman R.
Published: February 2004

The fluctuation level and the plasma confinement time were investigated by changing the shear length and average magnetic well in the spherator, a toroidal plasma confinement system. The experimental results show that the plasma is unstable when the mirror-trapped particles are located in the bad curvature section, even if the average curvature is favorable.
Integrability of the Magnetohydrodynamic Equations for Rotational Symmetric Configuration of Plasma with Infinite Conductivity
Authors: Badr O.
Published: February 2004

The integrability condition for the magnetohydrodynamic equations for rotational symmetric stationary plasma with infinite conductivity is obtained. It is found that the total enthalpy is conserved on a magnetic surface. Using this condition, a geometrical representation of the flow (sub- and supersonic) is given.
Intense Relativistic Electron-Beam Propagation in Preionized Gas
Authors: Benford James , Ecker Bruce
Published: February 2004

An experiment is described which demonstrates that high current relativistic electron beams that contain substantial transverse electron motion expand rapidly when injected into field-free preionized gas.
Thermonuclear Reaction Waves at High Densities
Authors: Chu M. S.
Published: February 2004

The initiation, development, and propagation of thermonuclear reaction waves in a solid density deuterium-tritium plasma are presented. Physical effects due to thermonuclear reactions, heat conduction, electron-ion equilibration, bremsstrahlung, and fluid dynamics are contained in the analysis. The qualitative behavior of the physical variables is discussed and solutions of the equations are obtained by employing finite difference numerical techniques. Due to plasma properties and the form of the fusion reaction cross section, important differences exist between fusion and chemical detonation waves. Threshold ignition energy is found for simple geometries and the complete history of the development of the wave is studied. The structure of a fully developed fusion reaction wave is presented. Finally, the thermonuclear energy yield from small D-T pellets is presented.
Velocity Space Instabilities in a Hot Electron Plasma
Authors: Schwartz M. J. , Lichtenberg A. J.
Published: February 2004

An instability driven by anisotropy in velocity space has been studied in a hot electron plasma created by adiabatic compression in a pulsed magnetic mirror. Early in the compression history of the plasma, bursts of radiation occur, with frequencies below the electron cyclotron frequency and its harmonics, with no apparent loss of plasma. The anisotropy in velocity space of the plasma was determined by comparing the measured axial plasma distribution with theoretical profiles. The observed values of plasma density (cold plus hot), temperature and anisotropy are used to find the unstable modes of the complete electromagnetic dispersion relation for all angles of propagation. The fastest growing mode early in the compression cycle is electrostatic occurring below the second harmonic; here, ωp/Ω (cold) = 1.5, ωp/Ω (hot) = 0.35. Later in time, ωp/Ω (cold) = 0.5, ωp/Ω (hot) = 0.25, and the fastest growing mode is electromagnetic, occurring below the fundamental. These predictions are in agreement with the observed spectrum and polarization measurements.
Stability of a Steady, Large Amplitude Whistler Wave
Authors: Palmadesso P. J. , Schmidt G.
Published: February 2004

The behavior of weak electrostatic waves in a collisionless magnetoplasma supporting a steady large amplitude whistler wave has been studied. All waves are assumed to propagate parallel to a uniform backgound magnetic field B0. In the presence of the whistler wave fields each particle executes an oscillatory motion parallel to B0, in addition to a translation along B0 and transverse motions. This oscillation causes the Landau resonance to be replaced by a series of new resonances between particles and the electrostatic modes. A distribution function for the perturbed plasma is constructed by solving the Vlasov equation, linearized in the electrostatic wave amplitudes. A dispersion relation is obtained and solved approximately for the growth/damping rate of the perturbations. Growing electrostatic modes are found to be approximately uncoupled. Trapped particles have a strong influence on the stability of the system.
Modified Schottky Boundary Condition in a Wide Plasma Column
Authors: Ventrice Carl A.
Published: February 2004

Axial current density measurements are made in a wide argon magnetoplasma. From these measurements, a “modified Schottky” boundary condition is found to apply.
Numerical Solutions for Time-Dependent Flow Past an Impulsively Started Sphere
Authors: Dennis S. C. R. , Walker J. D. A.
Published: February 2004

A numerical method is given for determining the transient flow past a sphere which is impulsively started from rest with constant velocity in a viscous fluid. One of the features of the method is that the calculation of the flow at early times is performed using boundary-layer variables, which leads to very accurate solutions. The problem is formulated in terms of the stream function and the vorticity. The method used is the semi-analytical one of series truncation in which the stream function and vorticity are expanded in a series of Legendre functions with argument z = cosθ, where θ is the polar angle. The governing equations are thus reduced to sets of time-dependent differential equations in the radial variable. In theory the number of these equations is infinite but in practice only a finite number can be solved to give an approximation to the flow. They are solved numerically by the Crank-Nicolson procedure. Numerical solutions are given for the cases R = 20, 40, 100, 200, 500, 1000, and ∞, where R is the Reynolds number based on the diameter of the sphere. For R = 20, 40, and 100 the equations are integrated to times at which the solutions may be considered close to steady motion. The developments of various physical properties of the flow are calculated and compared, where possible, with the results of other calculations.
Convective Stability of a General Viscoelastic Fluid Heated from Below
Authors: Sokolov M. , Tanner R. I.
Published: February 2004

The stability problem for a plane layer of a general viscoelastic (simple) fluid heated from below is investigated. The nature of the problem suggests that linear viscoelasticity assumptions are sufficient to fully describe the phenomena. It is shown that under certain conditions the fluid is overstable; namely, an oscillating cell structure will be created before the classical (Bénard) steady secondary-flow instability appears. Stability criteria for the oscillatory modes have been found as well as wavenumber and oscillation periods for both rigid and free boundaries. The theoretical results have been applied to a Maxwell fluid and to some real viscoelastic solutions. The numerical results for the latter suggest that although oscillation of Bénard cells is theoretically possible, very high-temperature gradients or high gravitational fields would be required before the oscillating cells could be observed in common polymer solutions of moderate viscosity.
Burgers' Turbulence Model with Two Velocity Components
Authors: Lee Jon
Published: February 2004

Burgers' turbulence model with two velocity components has a periodic motion as the equilibrium turbulent state. Numerical experiments have shown that this equilibrium state is a stable limit cycle and hence attainable from the arbitrary initial conditions except for some singular ones. Since the equilibrium state is continuous with respect to the Reynolds number, no evidence has been found of the finite-jump and turbulence-turbulence transitions of the sort that Case and Chiu have suggested.
Magnetohydrodynamic Stability of the Developing Laminar Flow in a Parallel-Plate Channel
Authors: Chen T. S. , Eaton T. E.
Published: February 2004

Linear stability of the developing laminar flow of an electrically conducting, incompressible fluid in a parallel-plate channel under a transverse magnetic field is investigated. The case of small magnetic Reynolds numbers is treated. The developing flows whose stability characteristics are studied correspond to those induced by a uniform and a parabolic velocity distribution at the channel inlet. The stability of the fully developed Hartmann flow is also reexamined. Neutral stability curves and axial variations of the critical Reynolds number are presented for a range of Hartmann numbers between 0 and 4. It is found that for Hartmann numbers larger than one, the developing flow induced by a uniform inlet velocity distribution is the least stable, while the flow induced by a parabolic inlet velocity distribution could be the most stable in the entrance region of the channel. A comparison with the available experimental data shows that for a given Hartmann number the transition Reynolds number is about two orders of magnitude lower than the critical Reynolds number.
Stability of Bernstein-Greene-Kruskal Wave with Small Fraction of Trapped Electrons
Authors: Wong H. Vernon
Published: February 2004

For ω≫ωB = (k02e∅0/me)1/2, the normal modes are essentially oscillations of the background plasma and these can be made unstable due to coupling to the periodic motion of the trapped electrons with bound frequency ωb, where ω = nωb and n is an integer. However, the most unstable waves have frequency ω∼ωB, and in this regime, plasma oscillations with wave number k + k0 and k − k0, where k≪k0, are coupled; instability is associated with coupling due to resonant and nonresonant interaction with the trapped electrons. If the trapped electron distribution function is monotonically increasing (decreasing) in energy, then the lower (upper) frequency side band with wavenumber | k | − k0(| k |+k0) is dominant.
Effect of Finite β on the Drift Cyclotron Instability
Authors: Bajaj N. K. , Krall N. A.
Published: February 2004

The effect of finite β (particle pressure/magnetic pressure) on the drift-cyclotron instability is investigated. It is shown that for β<[(B2/4πnMc2)+(m/M)]1/4 the instability range is shifted but not reduced, whereas, for β>[(B2/4πnMc2)+(m/M)]1/4 the growth of the drift-cyclotron mode is much reduced.
Lifetime of Hot-Ion Plasma in a Mirror Machine
Authors: Stirling W. L.
Published: February 2004

A neutral particle analyzer has been constructed to investigate the flux of energetic neutral particles emitted from the midplane of the hot-ion plasma, Burnout V. Energy and momentum analysis reveal that the energy confinement time is limited to 15 μsec by charge exchange of the hot ions on the background flux of Franck-Condon neutral atoms.
Microwave Combination Scattering from Plasma Waves in an Electron Beam-Plasma System
Authors: Bollinger L. D. , Böhmer H.
Published: February 2004

The spatial development of the electron beam excited plasma wave spectrum is investigated by determining the wavenumber, amplitude, and frequency by means of incoherent microwave scattering. The angular dependence, relative to the beam direction, of the most unstable wavenumber is determined. In the initial linear growth stage of the plasma waves, the finite beam radius is found to give a constraint on the angular direction in which the plasma waves grow. Furthermore, microwave scattering from the harmonic of the electron plasma wave shows this to be a wave on the beam branch of the dispersion relation.
Time-Dependent Wiener-Hermite Expansion for the Nearly Gaussian Turbulence in the Burgers' System
Authors: Yano Masafumi , Imamura Tsutomu
Published: February 2004

The proper choice of the time-dependent ideal random function improves the approximation of the truncated Wiener-Hermite expansion in the Burgers' system. The quasistable energy spectrum E(k)∼k−2 is supported.
Low-Current Relativistic Beam Equilibria
Authors: Leary James M. , Lee Edward P.
Published: February 2004

A simple procedure yields isotropic beam equilibria with given current profile and energy distribution in the limiting case of the beam current small compared with the Alfvén current.
Nonuniform Concentration—A Mechanism for Drag Reduction
Authors: Rivard William C. , Kulinski E. S.
Published: February 2004

A large reduction in drag coefficient has been observed in certain external flows of aqueous solutions with high molecular weight polymer additives. A change in the near wake configuration is phenomenologically responsible for the drag reduction, but the underlying mechanism is presently unknown. An analogy to known phenomena in particulate suspensions is drawn which suggests nonuniform concentration of the polymer additive as an explanation. An analysis of the boundary layer on a sphere with varying viscosity was made to investigate the effect. The results indicate early transition to turbulence for concentration variations whose length scale is small compared with the momentum boundary layer thickness. Stabilization and delayed transition are indicated for thicker concentration layers. Observations are suggested for the thin concentration layers.
Effect of Moisture on the Propagation of Internal and Acoustic Gravity Waves
Authors: Lalas Demetrius P.
Published: February 2004

The dispersion relation of small amplitude waves in an isothermal saturated atmosphere with constant specific humidity is derived. The propagation of internal gravity waves is found to be severely inhibited while the effect on acoustic gravity waves is small.
Numerical Analysis on Source Expansion Flow into Vacuum
Authors: Soga Takeo , Oguchi Hakuro
Published: February 2004

A numerical analysis of the source expansion flow into a vacuum is presented. Applying the BGK kinetic equation described in spherical coordinates to the problem, it is solved by combining a proposed computational technique with a discrete ordinate method. The actual computation is carried out for a large variety of rarefaction conditions, covering a wide extent from an equilibrium region near the sonic radius up to one sufficiently far downstream. Calculated results for the radial and perpendicular temperatures are compared with results obtained by existing methods.
Internal Rarefied Gas Flows with Backscattering
Authors: Berman Abraham S. , Maegley Wendel J.
Published: February 2004

A modification of the boundary condition describing the interaction between a gas molecule and a wall is proposed for use in the calculation of internal rarefied gas flows. The effect of the altered boundary condition on a number of flows of interest is calculated. In several cases, for which experimental data are available, comparison is made between predicted and measured transport. It is found that significant improvement in the predicted transport results from the suggested boundary condition modification.
Stability of Sheared Electron Flow
Authors: Rome James A. , Briggs Richard J.
Published: February 2004

The instabilities of a cylindrical electron stream driven by shear in the velocity parallel to the guiding magnetic field (dv11/dr ≠ 0) are analyzed. Quadratic forms are developed that bound the growth rates and provide necessary conditions for instability. An efficient numerical method for calculating the eigenfrequencies directly from the (singular) differential equation of a system with arbitrary velocity/density profiles is described. This numerical method is used to study the unstable modes of an unneutralized beam with velocity shear arising from space-charge potential depression. The computed growth lengths indicate that these modes are of practical importance in the propagation of high perveance electron beams.
Experimental Studies of Electrostatic Fluctuations in a Turbulently Heated Plasma
Authors: Hamberger S. M. , Jancarik J.
Published: February 2004

Experiments are described in which the spectra of potential fluctuations in a toroidal discharge are measured under conditions of turbulent heating using a small double electrostatic probe. Three different turbulent regimes are distinguished whose occurrence depends on the electron drift velocity and which correspond, respectively, to the excitation of ion sound, two-stream, or beam-plasma instability. The spectral distribution in the case of weakly turbulent ion sound waves agrees with nonlinear theory. The frequency of the strongly turbulent two-stream oscillations appears in the vicinity of the predicted fastest growth frequency f* = 12(M/m)1/6fpi. The relationship of the fluctuations and their correlation times with the effective conductivity is discussed.
Computer Simulation of Ion-Acoustic Shocks. II. Slug and Piston Problems
Authors: Mason R. J.
Published: February 2004

Particle-in-cell computer simulation techniques are applied to the study of ion-acoustic shocks in (a) the expansion of a narrow plasma slug, and (b) the flow produced by an impulsively started piston. Electrons are treated as an isothermal fluid. The slug fissions into pulses with structure dependent on θ( = Te/Ti). Pulse reflection from a specular boundary is characterized. For piston Mach numbers Mp = 0.25→1.25 shocks from Mach 1.10 to 1.42 are generated. The shocks are initially laminar, but an apparent onset for turbulence is observed. Jump conditions are consistent with results from previous investigations of the diaphragm problem.
Precursor of Ion-Acoustic Quasishock Wave in Collisionless Plasma
Authors: Kato Yusuke , Tajiri Masayoshi , Taniuti Tosiya
Published: February 2004

A weak, ion-acoustic quasishock wave which propagates into a uniform state is considered. A relevant initial value problem of the Vlasov equation is solved to give the long time behavior of a precursor which is a stream of ions reflected by the electrostatic potential. An asymptotic expansion in terms of the small amplitude is used. The ratio of the ion temperature to the electron temperature is assumed small so that effects of the reflected ions appear as a correction to the Korteweg-de Vries equation which governs the wave propagation due to the nonresonant ions. The connection with the stationary solution is examined.
Theory and Computer Experiment on Self-Trapping Instability of Plasma Cyclotron Waves
Authors: Hasegawa Akira
Published: February 2004

A theory explaining the self-trapping instability (modulational instability) of plasma cyclotron waves is developed and the results are compared with computer experiments using a sheet current model. The observed growth rate at an initial phase of the instability is in rough agreement with that given by perturbation theory. However, as the level of the modulation increases, the rate of the growth of the modulation increases due to excitation of additional side bands, and finally, the carrier wave is found to collapse suddenly leading to rapid thermalization. The cause of the sudden collapse of the wave is attributed to the crossing of particles which are accelerated in the direction parallel to the ambient magnetic field by a large pressure gradient force, ∇(B⊥2/2μ0), developed by the instability, where B⊥ is the transverse magnetic field associated with the wave.
Critical Length Criteria for Mirror Machines
Authors: Berk H. L. , Pearlstein L. D. , Cordey J. G.
Published: February 2004

Critical scale lengths for stability of mirror devices are determined. The analysis proceeds via a modified WKB technique which adds the effect of wave amplification due to the presence of singularities of the dielectric function. The approximate answers so determined compare favorably with the numerical solution of the appropriate equations. Results for large and small mirror ratios are presented. It is found that irrespective of the character of the wave in the infinite medium limit (e.g., drift-cone or stable negative energy wave) stabilization is effected at roughly the same magnetic scale length for all but the longest axial wavelength modes.
Parametric Instabilities of Ion Cyclotron Waves in a Plasma
Authors: Lee Y. C. , Kaw P. K.
Published: February 2004

An externally applied large amplitude circularly polarized ion cyclotron wave of long wavelength propagating along the static magnetic field can drive instabilities of ion cyclotron waves and ion acoustic waves. The dispersion relation is first derived using a kinetic equation approach. Later, it is shown that the same relation can be derived on the basis of a “KΔX” analysis. The instabilities can be classified into three classes: | k |⋙k0 corresponds to the usual purely growing instability; | k | ∼k0 corresponds to the decay instability, and | k | ≫k0 corresponds to slightly oscillatory instability which is actually the finite k0 modification of the purely growing instability. The dependence of both, the threshold and maximum growth rates, on various parameters is discussed. The relevance of the results to the anomalous ion heating for fusion research is also pointed out.
Laminar Free Convection from Vertical Thin Needles
Authors: Narain Jai P. , Uberoi Mahinder S.
Published: February 2004

A similarity solution is obtained for the problem of free-convection heat transfer over a thin vertical needle with uniform heat flux at the surface. A few errors in previous papers on “isothermal” needles have been modified.
Existence of Real Fluids with a Negative Fundamental Derivative Γ
Authors: Lambrakis Konstantine C. , Thompson Philip A.
Published: February 2004

The gasdynamic behavior of fluids is inverted if a certain thermodynamic property Λ ≡ ρ3c4(∂2υ/∂P2)8/2 is negative. Several different methods of calculation, based on published thermodynamic data and standard equations of state, yield Γ<0 for relatively complex organic compounds.
Electromagnetic Instability for Counterstreaming Plasmas
Authors: Hirshfield J. L. , Bernstein I. B.
Published: February 2004

Growth rates for unstable ordinary polarization electromagnetic waves propagating at right angles to symmetric counterstreaming finite temperature plasmas are shown to be less than growth rates derived from a slightly modified dispersion relation for cold streams.
Electron-Beam Investigation of a Hypersonic Shock Wave in Nitrogen
Authors: Smith Ronald B.
Published: February 2004

The electron-beam fluorescence technique is used to probe a Mach-26 normal shock wave. A method to determine the distribution of population among the rotational states is developed. The measured number density and rotational temperature profiles are compared with the theoretical results of Brau and Simons. A simple approximate collision model is developed, producing from the experimental results, general information about the rotational equilibration process, and the determination of a rotational excitation cross section.
Quasilinear Diffusion of an Axisymmetric Toroidal Plasma
Authors: Kaufman Allan N.
Published: February 2004

In a toroidal plasma with axial symmetry, the three adiabatically invariant actions of a particle are the magnetic moment, the canonical angular momentum, and the toroidal flux enclosed by the drift surface. Resonant interactions between particles and the normal modes of collective oscillation produce mode growth or decay and random changes in the actions. This random walk is represented by a diffusion equation in action space. Both the diffusion tensor and the growth rate depend upon a coupling coefficient which represents the work done by a normal-mode field eigenfunction on the current density of an unperturbed particle orbit. The diffusion of the plasma causes adiabatic changes in the electric and magnetic self-consistent fields. Accordingly, energy is not conserved, but is exchanged with external currents.
Ion and Electron Pressure Effects on Magnetosonic Shock Formation
Authors: Mason R. J.
Published: February 2004

Piston generated magnetosonic shocks have been investigated with a hybrid particle-in-cell simulation scheme that retains electron inertial effects and pressure but neglects resistivity. At low piston Mach numbers, Mp≤1.0, the c/ωpe scale wave-train shocks of Auer, Hurwitz, and Kilb are reproduced. For Mp = 1.7 post-frontally flat shocks with strong precursors are obtained. For Mp≥2.4 pure piston reflected flow is observed. All these flows are predominantly laminar. Electron pressure effects are found to scale as (1 +βe0)/Mp2, βe0 = Pe0/(B02/8π). Finite ion pressure smooths the post-frontal flow through ion Landau damping. Comparisons are made with results from other recent simulations, and with observations from laboratory experiments at Culham and Garching.
Growth Rates of Instabilities of a Diffuse Linear Pinch
Authors: Goedbloed J. P. , Hagebeuk H. J. L.
Published: February 2004

In order to obtain growth rates of magnetohydrodynamic instabilities, the equation of motion of a diffuse linear pinch is solved analytically in the tokomak approximation and numerically without approximation. The growth rates of kinks are calculated for the Lundquist field. The constant-pitch magnetic field is shown to be unstable to quasi-kinks, quasi-interchanges, and pure interchanges which dominate, respectively, at increasing values of the negative pressure gradient. Analytical expressions and numerical values for the growth rates of these modes are given. Interchanges in a sheared magnetic field are investigated numerically and checked by means of perturbation theory.
Vlasov-Fluid Model for Studying Gross Stability of High-β Plasmas
Authors: Freidberg J. P.
Published: February 2004

A model is presented which provides a more realistic description of the gross stability properties in high-β plasmas than that given by ideal magnetohydrodynamics.
Magnetohydrodynamic Flow between Two Rotating Coaxial Cylinders under Radial Magnetic Field
Authors: Arora K. L. , Gupta P. R.
Published: February 2004

An exact solution for the magnetohydrodynamic flow between two rotating coaxial (insulator) cylinders under a radial magnetic field has been obtained and the results are discussed graphically.
Collisional Effects on Spatial Ion Wave Echoes in a Plasma
Authors: Sasaki A. , Sato N.
Published: February 2004

Effects of ion-ion collisions on ion wave echoes are studied experimentally in a Q-machine plasma. The spatial damping of the echo peak amplitude is observed to be different from earlier measurements.
Turbulence Following Ion-Acoustic Shocks
Authors: Mason R. J.
Published: February 2004

Extended particle-in-cell investigations of ion-acoustic shocks with isothermal electrons verify predictions of a maximal shock Mach number slightly above 1.5 and demonstrate the presence of post-frontal turbulence that intensifies with both the Mach number and initial electron-to-ion temperature ratio.
Anisotropic Relaxation in Binary Mixture of Maxwell Molecules
Authors: McCormack Francis J. , Williams Anna M.
Published: February 2004

The relaxation of initial temperature difference, stresses and heat fluxes in a binary mixture of Maxwell molecules is studied by solving the two-temperature 13-moment equations for the mixture under the assumption of spatial homogeneity. For simplicity, the flow velocities for each gas are assumed to be the same, and the rates at which the stresses and heat fluxes relax are compared with the rate of relaxation of the temperature difference. It is found that, for equal densities and disparate masses, Grad's conjecture on relaxation in “epochs,” or stages, is borne out. For unequal densities, however, it is found that under certain conditions, the heat flux for the gas of larger density relaxes slower than the temperature difference.
Mechanism by Which a Two-Dimensional Roughness Element Induces Boundary-Layer Transition
Authors: Klebanoff P. S. , Tidstrom K. D.
Published: February 2004

An experimental investigation of the effect of two-dimensional roughness elements on boundary-layer transition is described. Primary emphasis is given to the nature of disturbances within the recovery zone, i.e., that region in the immediate downstream of the roughness where the mean flow has been distorted by the presence of the roughness. Detailed measurements of mean velocity distributions, of disturbance spectra, and intensity, growth, and decay of disturbances at discrete frequencies were made for a range of unit Reynolds numbers. The measurements demonstrate that the behavior can best be understood by considering wave-type disturbances, and that the basic mechanism by which a two-dimensional roughness element induces earlier transition to turbulent flow is by the destabilizing influence of the flow within the recovery zone. Comparison with the behavior expected from stability theory supports this conclusion.
Current Dependence of Convection in Electrolytically Heated Fluid Layers
Authors: Schwiderski E. W.
Published: February 2004

The Tritton and Zarraga problem of convection in electrolytically heated fluid layers under gravity has been investigated by linear and nonlinear techniques. The analysis revealed that a strictly hexagonal flow and temperature pattern is inconsistent with the pattern of an oriented electric current. In qualitative agreement with corresponding experiments any emerging hexagonal motion must be expected to be more or less disturbed by the uneven internal heating which depends on a dimensionless temperature coefficient of the fluid and on the size and current-alignment of the cells. Imperfect thermal properties of solid bottom and top plates bounding the infinite fluid layer displayed no significant distortions of the convection pattern.
Degeneracy of the Spectra of the Linearized Boltzmann Collision Operator for the Maxwellian Molecules
Authors: Yan C. C.
Published: February 2004

The degeneracy between the spectra corresponding to scalar and vector solutions to the linearized Boltzmann collision operator for the Maxwellian molecules is shown to be a consequence of the Galilean translational invariance of the equations and the spherical symmetric property of the scalar solution.
Verification of Theory for Plasma of Finite-Size Particles
Authors: Okuda Hideo
Published: February 2004

Some of the equilibrium properties of a one-dimensional plasma model for numerical simulation using finite-size particles (clouds) with spatial grids were investigated experimentally and compared with the theoretical predictions. Fluctuation spectrum of the electric field, correlation function, and Landau damping of the Fourier modes, drag on a particle, diffusion in velocity space, Debye shielding, wakes due to fast particles, and the frequency spectrum of the Fourier modes were measured. The experimental results give good agreement with the theoretical predictions of a kinetic theory for finite-size particles, showing the reduction of interactions at short wavelengths and, hence, reduction of collisional effects.
Stability of Inhomogeneous Two-Stream Plasma with a Water-Bag Model
Authors: Bertrand P. , Doremus J. P. , Baumann G. , Feix M. R.
Published: February 2004

The problem of the stability of a one-dimensional inhomogeneous electron plasma in a fixed ion background is considered, using the water-bag model with N contours with only those instabilities appearing through the point ω = 0. For marginal stability, the system of N water-bag equations is shown to degenerate into a single equation, and the stability property is simply connected to the sign of the eigenvalues of the Schrödinger operator {k2(x) − d2/dx2), where ( − k2)1/2 is the local maximum wavenumber of instability. Finally, this criterion is checked for a simplified inhomogeneous two-stream situation described by a water-bag model with only two contours.
Initial-Boundary-Value Problem of the Formation of an Electrical Discharge in a Flow
Authors: Wilhelm H. E. , Liron N.
Published: February 2004

The initial-boundary-value problem describing the relaxation of a quasineutral discharge in a gas flow with coplanar, heated electrodes of finite extension is formulated in the diffusion approximation. The relaxation occurs from an initial breakdown to a steady-state discharge in a weak electric field. The initial-boundary-value problem is decomposed into a steady-state elliptic problem considering the different boundary conditions at the walls and electrodes and a parabolic initial-boundary-value problem with vanishing boundary conditions. By means of the Fourier-integral and Green's function methods an analytical solution is obtained for the steady-state and the time-dependent electron-ion density fields. The characteristic time describing the relaxation of the discharge is derived. The criterion for the existence and sustainment of a steady-state discharge against plasma losses by diffusion and convection is discussed.
Decay of Isotropic Turbulence Generated by a Mechanically Agitated Grid
Authors: Ling S. C. , Wan C. A.
Published: February 2004

Experimental study of weak isotropic turbulence, created by a mechanically agitated grid, has indicated that in the absence of large linear-momentum wakes the energy of turbulence relaxes very quickly into a stable self-preserving structure, which, depending on the initial Reynolds number of turbulence, decays at different constant inverse powers of time. Both the longitudinal correlation coefficients and the corresponding spectral distributions, except for the difference in the parametric constants, are of the same functional type as those found previously for a passive grid.
Simple Proof of Fluid Line Growth in Stationary Homogeneous Turbulence
Authors: Corrsin S.
Published: February 2004

With the assumption that two fluid points which are far enough apart move independently in homogeneous, stationary, turbulence, it is inferred that (1) remote points will separate on the average and (2) fluid material lines will lengthen on the average. To prove monotonic line growth an additional assumption is needed.
Stability of a Two-Component Fluid Layer Heated from Below
Authors: Legros J. C. , Platten J. K. , Poty P. G.
Published: February 2004

In connection with recent experimental results, the stability of a two-component fluid layer heated from below is examined taking into account the concentration gradient due to thermal diffusion. With the use of a variational method (local potential technique) developed by Glansdorff and Prigogine, an approximate solution is proposed for dilute solutions. The critical Rayleigh number increases for negative thermal diffusion factors and decreases for positive ones.
Hypersonic Unsteady Compressible Boundary Layer Dependence on Prandtl Number
Authors: Rodkiewicz Czeslaw M. , Luft Bernard H.
Published: February 2004

The unsteady compressible laminar boundary layer on a stepwise accelerated semiinfinite flat plate at zero incidence is investigated for Prandtl numbers different from unity. A semisimilarity transformation is employed. The equations are uncoupled for the case of zero pressure gradient and are further linearized before a numerical solution is obtained for Pr = 0.72. The initial condition is obtained by assuming that at zero time the time derivative of enthalpy is zero. For a range of Mach numbers 5≤Me≤10 the transient heat transfer and weak interaction induced pressure are obtained for both the isothermal and insulated wall.
Dynamics of Stratified Liquids in the Presence of Space Charge
Authors: Zahn Markus
Published: February 2004

The dispersion characteristics of small signal electrohydrodynamic space charge and polarization waves in continuously and discretely stratified liquids are developed. The liquids, modeled as incompressible, inviscid, and perfectly insulating have distributions of mass density, charge density, permittivity, and electric field. A general set of relations for perturbation field and flow variables defined for a “prototype” layer are used to describe the dynamics of many superposed planar layers. It is shown that the general relations can be used to represent systems of coupled layers which approximate continuous distributions by a series of step functions. Specific examples of weak gradient and exponential distributions are presented showing that the solution found directly from the distributed theory is approached by the system of coupled layers, if the limit is taken in which the number of layers become large while each layer thickness approaches zero.
Flow Induced by Thermal Stress in Rarefied Gas
Authors: Sone Yoshio
Published: February 2004

A new kind of mechanism which induces a flow around a solid body in a slightly rarefied gas is proposed. In order to demonstrate the flow induced by this mechanism the behavior of gas around a sphere with a constant temperature which is placed in an infinite expanse of gas at rest with a uniform temperature gradient is investigated on the basis of the asymptotic theory for a slightly rarefied gas. A flow with magnitude of the order of the Knudsen number squared is induced from the hotter to the colder region. The sphere is subject to a force in the direction of the given temperature gradient.