bluuebunny/crossref_metadata_2025 huggingface dataset:
Resonant Diffusion in the Presence of Strong Plasma Turbulence
Authors: Birmingham T. J. , Bornatici M.
Published: February 2004

The diffusion equation which describes the evolution of the average one-particle distribution function for an ensemble of strongly turbulent plasmas is derived. The diffusion tensor is a time integral of the autocorrelation tensor of the fluctuations as observed by particles moving along statistically distributed orbits. These orbits contain the effects of fluctuations and thus differ from those encountered in weak turbulence theory. Two statistical orbit effects quadratic in the strength of the fluctuations affect the magnitude of the diffusion: (a) modification of the ensemble average orbits by the fluctuations, and (b) statistical dispersion in particle orbits about the average. The plasma trajectory equations are used to relate each to the diffusion tensor itself when the turbulence is electrostatic. The diffusion tensor is explicitly evaluated for a strongly turbulent unmagnetized plasma.
Wave Growth in a Strongly Turbulent Plasma
Authors: Birmingham T. J. , Bornatici M.
Published: February 2004

An equation for the average nonlinear growth (damping) rate 〈γk〉 of an electrostatic mode with wave vector k for an ensemble of electrostatically turbulent, unmagnetized plasmas is derived. Strong turbulence alters particle orbits during the course of wave growth and hence brings particles in and out of resonance with the wave. The wave-growth rate in a strongly turbulent plasma, therefore, depends on the initial velocity distribution of particles not only at u = k̂·v = αk/k , the wave speed, but in the vicinity of this speed as well. Two orbital effects are considered: turbulence modification of ensemble average orbits and turbulence-produced orbital dispersion about the average orbits. The first of these leads to a shift in the central u of the resonance. Both contribute to a resonance broadening.
Self-Consistent Electromagnetic Waves in Relativistic Vlasov Plasmas
Authors: Winkles B. B. , Eldridge Owen
Published: February 2004

It is shown that the treatment of relativistic superluminous waves can be simplified by making a Lorentz transformation to a new frame in which the spatial variable no longer appears. Self-consistent solutions of the relativistic Vlasov-Maxwell equations can be constructed in the new frame. These solutions correspond to nonlinear traveling waves in a finite temperature plasma, and reduce to the usual linear results in the small-amplitude limit. A particular example is considered in which the nonlinear waves propagate through a relativistic Maxwellian plasma, and it is shown that pure transverse waves cannot exist in such a case, but that a coupled longitudinal field necessarily appears. For this case the nonlinear effects are evaluated correct to second order in the transverse field amplitude, thus obtaining a nonlinear dispersion relation and a measure of the coupling. In addition, solutions involving pure longitudinal waves can be found, and are also investigated. In limiting cases the results agree closely with previous calculations based on hydrodynamic models.
Current-Driven Drift Wave Instability in a Sheared Magnetic Field
Authors: Rosenbluth M. N. , Liu C. S.
Published: February 2004

In a sheared magnetic field, the eigenfunction of the drift wave is asymmetrized by a current along B0. Taking into account this asymmetrizing effect, a stability condition for the current-driven drift mode in a sheared field is derived. For magnetic shear generated by the plasma current, a low limit on βe—the ratio of plasma pressure to magnetic pressure—is required for the stability of a plasma with given density and gradient.
Nonlinear Instability of Bernstein Modes Pumped by an Electromagnetic Wave
Authors: Carlile R. N.
Published: February 2004

The nonlinear decay instability of Bernstein modes pumped by an electromagnetic wave and the subsequent heating of the plasma electrons have been investigated by means of computer experiments. It was found that four pairs of Bernstein modes became unstable, and grew to large amplitudes. Each pair together with the electromagnetic wave satisfied the criteria for wave-wave interaction. The Bernstein modes would finally saturate. The kinetic energy of the plasma electrons would then begin to increase and, over the time the code was allowed to run, the electrons would have their energy increased by a factor of 4. Saturation occurred when the Coulomb force on a particle due to the electric field of the Bernstein mode became of the order of magnitude of the Lorentz force on that particle due to the magnetic field. The electron probably had its orbital motion destroyed and became trapped briefly in the potential wells of the Bernstein mode.
Nonlinear Stabilization of Single, Resonant, Loss-Cone Flute Instabilities
Authors: Crume E. C. , Meier H. K. , Eldridge Owen
Published: February 2004

The evolution of linearly unstable, high-frequency (ω≈nΩ), flutelike (k‖ = 0), electrostatic modes which can occur in a multicomponent, magnetic-mirror-confined collisionless plasma has been studied by computer simulation using a one-and-one-half dimensional model. Approximately one-quarter of the particles in the initial velocity distributions formed a warm, Maxwellian background component; the remainder belonged to a hot, linearly stable, loss-cone component. The early evolution of single wave (either traveling or standing), resonant instabilities agrees well with linear theory. A rapid, coherent heating of the warm component occurs and spatial harmonics of the unstable wave appear. The electrostatic field of the wave then saturates at an energy level as much as two orders of magnitude lower than those reported in previous simulation studies of the same and related instabilities or predicted from earlier nonlinear analysis. The saturation levels and early post-saturation behavior are in agreement with a recently reported nonlinear analysis which was motivated by the results reported here.
Finite Larmor Radius and Hall Effects on Thermal Instability of a Rotating Plasma
Authors: Sharma R. C.
Published: February 2004

Thermal instability of a rotating plasma with finite Larmor radius and Hall effects is studied. When the instability sets in as stationary convection for the case of no rotation, finite Larmor radius effects are always stabilizing for x( = k2d2/π2) greater than two and for x less than two they have a stabilizing or destabilizing influence depending on whether N( = ν0/ν) is greater than or less than its critical value Ncrit. In the limit of vanishing Hall current and for stationary convection, the stabilizing effect of the Coriolis force is observed. The conditions for the nonexistence of overstability are investigated.
Relativistic Cyclotron Resonance Heating
Authors: Faulconer David W. , Liboff Richard L.
Published: February 2004

The relativistic motion of a single particle undergoing cyclotron resonance in a magnetic mirror trap is studied. The Krylov-Bogoliubov method of averaging is employed to derive equations indicating an upper bound on particle energy. Smallness parameters necessary for the validity of these equations are made explicit. Limitation on particle energy absorption is found for a much broader class of particles than previously known. The relationship of this to experiment is discussed.
Green-Kubo Formalism and Conditions for Linear Relationships among Transport Coefficients
Authors: Mjolsness R. C. , Visscher William M.
Published: February 2004

A short, physically transparent derivation of the Green-Kubo formulas is presented and used to show that when two current operators (e.g., charge, number, energy) are proportional, so are the corresponding transport coefficients. Examples of this consequence are discussed.
Generation of Plasma Oscillation by Beam-Plasma Interaction
Authors: Khan T. P.
Published: February 2004

The frequencies of the electrostatic plasma oscillation have an angular dependence similar to that in the normal Doppler effect, the anomalous Doppler effect, and the Čerenkov effect. Light emission at the different stages of the electromagnetic interactions have also been studied.
Effect of Shear on Temporal Damping and Growth of Drift Waves
Authors: Nishida Y. , Odajima K. , Hatta Y.
Published: February 2004

The effects of magnetic shear on the damping and growth rates of collisionless drift waves are observed in a linear stellarator with l = 3 helical windings. Increasing the magnetic shear reduces the temporal growth rate and increases the damping rate of drift waves.
Numerical Simulation of the Harris Instability with Collisions
Authors: Gitomer S. J.
Published: February 2004

The Harris instability in a thermally anisotropic plasma is studied in the presence of electron-electron collisions. The plasma electrostatic field energy decreases and the electron velocity distribution Maxwellization rate increases with increasing collision frequency.
Remote Feedback Stabilization of a High-β Plasma
Authors: Chen Francis F. , Jassby D. L. , Marhic M. E.
Published: February 2004

A current-driven rotational instability in a magnetic arc plasma of density 1016 cm−3 is suppressed by a totally remote feedback system. Detection is achieved by transmission or reflection of a 337-μ laser beam, suppression by an oscillating transverse magnetic field.
Homogeneous Nucleation and Growth of Ethanol Drops in Supersonic Flow
Authors: Wegener Peter P. , Clumpner Joseph A. , Wu Benjamin J. C.
Published: February 2004

Condensation of ethanol by homogeneous nucleation of liquid droplets has been studied in a supersonic nozzle. Continuous static pressure measurements on the nozzle centerline and light scattering measurements permit the condensation process to be resolved in detail for comparison with theory. Nucleation rates found in the present work are in general agreement with previous results obtained in diffusion and expansion cloud chambers. It is seen that the predictions of the classical theory of homogeneous nucleation or that of the statistical mechanical theory with the assumptions of Dunning roughly agree with the experimental results. Various terms entering different versions of nucleation theory are given quantitatively. The pressure variations in the flow found beyond the onset point of condensation are used to study droplet growth processes. It is shown that a simple kinetic growth law with a constant mass condensation coefficient describes the condensation process well.
Nonlinear Diffusion into a Porous Material
Authors: NiCastro J. R. A. J.
Published: February 2004

A method is presented for analyzing the early behavior under either an adiabatic or isothermal assumption for the diffusion of a gas into a porous material. Viscous loss can easily be accommodated in the approximate analytical procedure.
Combined Forced and Free-Convection Heat Transfer from Vertical Thin Needles in a Uniform Stream
Authors: Narain Jai Prakash , Uberoi Mahinder S.
Published: February 2004

The problem of laminar combined forced and free-convection heat transfer from a thin needle in a uniform external stream is considered. The series and local similarity solutions have been discussed.
Analysis of Gas Expansion in a Rarefied Atmosphere
Authors: Brode Harold L. , Enstrom James E.
Published: February 2004

Similarity solutions for spherically and cylindrically symmetric gas expansions in rarefied atmospheres are refined and then compared with the corresponding numerical hydrodynamic calculations. All of the hydrodynamic solutions are then shown to be invalid except for the initial radius-time dependence in a very limited region, after which time diffusion becomes the dominant expansion method. Apparent agreement with observed gas expansions at later times is due only to the similar radial growth for hydrodynamics (∼t0.4) and diffusion (∼t0.5).
Growth of Turbulence in the Presence of Shear
Authors: Deissler R. G.
Published: February 2004

The mechanism for the maintenance or growth of turbulence in a shear flow is discussed on the basis of calculated results for some simplified models. From those results it appears (as is known experimentally) that a mean shear can produce a nondecaying turbulence field.
Turbulence Measurements with a Laser Anemometer Measuring Individual Realizations
Authors: Donohue G. L. , McLaughlin D. K. , Tiederman W. G.
Published: February 2004

A laser Doppler anemometer system is described which operates with a noncontinuous signal and measures the velocity of individual scattering centers. Histograms of the instantaneous individual velocity realizations provide accurate and unambiguous estimates of the mean velocity and rms fluctuation velocity in regions of intense turbulence levels. Measurements are presented for a fully developed two-dimensional water channel and a deflected jet of air.
Sawtooth, Solitary, and Turbulent Waves in a Weakly Ionized Plasma
Authors: Sato Tetsuya , Ogawa Tadahiko , Matsuda Yoshiyuki
Published: February 2004

Nonlinear evolution due to many-mode couplings has been studied numerically for an inhomogeneous, magnetized, weakly ionized plasma. It is found that a sawtooth (shocklike) solution is achieved for the low range of an external parameter (weak nonlinearity), and that the solution becomes localized and solitonlike for the larger parameter range (strong nonlinearity). The parameter value differentiating the solution from a shocklike to a solitonlike shape is coincident with a critical value predicted by a theory beyond which the system becomes explosively unstable. It is further shown that the turbulent spectrum obeys a power law of k−3 which is predicted by the theory.
Ion Heating by Oblique Shock Waves in a High-β Plasma
Authors: Mizui Jun-ichi , Nakai Sadao , Kasuya Koichi , Yamanaka Chiyoe
Published: February 2004

Oblique shock waves in a high-β plasma (β∼2) had a monotonic structure with fluctuations either behind or ahead of the shock when the Mach number of the fast mode wave satisfied M>1 (Alfv́en Mach number MA = 2−4). The characteristic length of the fluctuations was equal to the wavelength of the magnetoacoustic wave, and the shock width was found to be of order 2πc/ωpi, where ωpi is the ion plasma frequency in the upstream plasma. For M>1, the post shock ion temperature consisted of two components. The appearance of the high-temperature ion component occured when the fluctuations were observed. As the ion-heating mechanism, it is proposed that Landau damping of the wave energy selectively heats the resonant particles.
Momentum Transfer Interaction of a Laser-Produced Plasma with a Low-Pressure Background
Authors: Koopman David W.
Published: February 2004

The expansion of a laser-produced metallic plasma into a photoionized hydrogen background has been experimentally studied. Langmuir probe and microwave diagnostics have detected an interaction front which decelerates with a dependence on background density and time consistent with a momentum coupling between the laser plasma and the ionized fraction of the background. An ion precursor has also been observed. Calculations of scattering cross sections indicate that multiple-encounter Coulomb scattering will dominate collisional momentum transfer. The leading edge of the laser plasma contains multiply charged ions of charge state z≥5, and collisional effects appear adequate to explain the principal features of the momentum coupling. The ion precursor may have a collisionless origin.
Ionizing Gas Breakdown Waves in Strong Electric Fields
Authors: Klingbeil R. , Tidman D. A. , Fernsler R. F.
Published: February 2004

An analysis of ionizing potential waves is made which includes photoionization. It is found that photoionization plays an important role in the avalanche propagation. Velocities, electron densities, and temperatures are given as a function of electric field for both negative and positive breakdown waves in nitrogen.
Structure of the Third-Order Plasma Wave Echo
Authors: Goforth R. , Gentle K. W.
Published: February 2004

Electron plasma wave echo experiments have been performed and compared with the theoretical description from the Vlasov equation. The previous theory is extended to third order for comparison with the experiment. Measurements of the wavelengths and envelope of the echo are in good agreement with the extended theory.
Properties of Spatial Ballistic Plasma Wave Echoes
Authors: Ripin B. H. , Pechacek R. E.
Published: February 2004

Spatial electron plasma wave echo experiments are described in which the relation between the echo wavelength and frequency is given by ω3/=vc, where vc is approximately equal to the velocity at which the electron distribution function has maximum slope. It is concluded that the echo response is dominated by free-streaming electrons. Other evidence is also presented which supports this conclusion. The experimental results corroborate many of the properties of free-streaming disturbances derived from an expansion of the Vlasov-Poisson system. Numerical integrations of the derived expressions for the second-order ballistic echo electric field compare favorably with experiment. The mechanism by which electrons are perturbed by the externally applied fields (e.g., in velocity or density) is found to influence the detailed structure of the echo response.
Role of Trapped Particles in Plasma Waves and Instabilities
Authors: Rosen B. , Schmidt G. , Kruer W. L.
Published: February 2004

The role of trapped particles in large amplitude electrostatic waves is studied in computer simulation experiments. Both in waves generated by a beam-plasma instability and in waves excited externally, trapped particles are artificially untrapped or redistributed in phase space. It is found that removal of trapped particles eliminates amplitude oscillations and side-band growth while the redistribution of these particles in the trapping region leads to significant changes in damping rates, saturation levels, and sideband growth.
Resonance, Particle Trapping, and Landau Damping in Finite Amplitude Obliquely Propagating Waves
Authors: Palmadesso P. J.
Published: February 2004

The equations of motion for a particle in resonance with a small finite amplitude wave (ω, k) are solved approximately, using secularity-free perturbation theory. The wave propagates at an arbitrary angle to a uniform background magnetic field B0, in an infinite collisionless plasma. The wavefields include a longitudinal electrostatic component and elliptically polarized transverse electric and magnetic components. The trajectories of trapped and resonant untrapped particles are described, for each of the possible waveparticle resonances defined by the condition kzVz−ω≈NqB0/m, where N is an integer. These trajectories are used to construct an estimate of the nonlinear time-dependent Landau damping rate of the wave.
High-Frequency Modulation of Ion-Acoustic Waves
Authors: Albright N. W.
Published: February 2004

A large amplitude, high-frequency electromagnetic oscillation is impressed on a nonrelativistic, collisionless plasma from an external source. The frequency is chosen to be far from the plasma frequency (in fact, lower). The resulting electron velocity distribution function strongly modifies the propagation of ion-acoustic waves parallel to the oscillating electric field. The complex frequency is calculated numerically.
Nonlinear Coupling of Ion-Acoustic Waves in a Collisionless Plasma
Authors: Mix L. P. , Litzenberger L. N. , Bekefi G.
Published: February 2004

Measurements of the spatial evolution of nonlinearly generated ion-acoustic waves propagating along a collisionless, magnetically confined plasma column produced by electron cyclotron breakdown of argon gas are presented. An ion-acoustic wave is generated by applying a sinusoidal voltage (amplitude 0.25-10 V rms, frequency 0.25-3.0 MHz) to a grid immersed in the plasma. A second, movable grid and an interferometric technique are used in the determination of the damping and phase velocity of this wave and of the second harmonic wave. The observed spatial growth and subsequent decay of the harmonic wave are compared with predictions of mode-coupling theory. Good agreement is obtained provided that the ratio eΦF/κTe≲0.01, where ΦF is the potential of the fundamental wave and Te is the electron temperature. For larger values of ΦF, discrepancies between measured and computed matrix elements occur.
Simulation of the Beam-Plasma Instability in a Finite-Length System
Authors: Lin A. T. , Rowe J. E.
Published: February 2004

The electron and ion beam-plasma instabilities in a one-dimensional finite-length system are studied by computer simulation methods using the discrete charge-sheet model. The results obtained using a one-component model indicate that the region of highly concentrated oscillation energy (due to a beam-plasma instability) near the beam entrance plane shrinks with time to a limiting value and then expands to form a stationary electric-field distribution. The frequency spectrum analysis of the electric field shows that only the first few harmonics of electron plasma oscillations have been excited and only these harmonics have amplitudes significantly above the noise level in the nonlinear region. In the experiment on the ion-beam interaction with a plasma, the plasma electrons and ions achieve greater heating in comparison with the heating resulting from the interaction between an electron beam and a plasma, because the heavier ion mass yields a larger energy source, a low rate of decrease of the mean ion-beam speed, and reduced thermal spreading of the beam particles. The excited electron plasma oscillations are found to dissipate into ion-density fluctuations whenever the amplitude exceeds some threshold value.
Highly Force-Free Relativistic Electron Beam Equilibrium
Authors: Kan J. R. , Lai Hon-Ming
Published: February 2004

A non-hollowed-out relativistic electron beam model is considered in which the axial current well exceeds the Alfvén limit when the field-configuration of the beam is highly force free. In this model, the current has an axial as well as an azimuthal component. For a given ratio of these two current components, a family of solutions is obtained in which there is an upper limit on beam radius. Over a large range of the beam radius, the axial current in our model is large compared with the current carried by a beam of the same radius in Hammer and Rostoker's model.
Resonances of an Antenna Associated with the Excitation of Ion Bernstein Modes
Authors: Schmitt J. P. M.
Published: February 2004

The impedance with respect to the plasma of a wire parallel to the magnetic field is studied theoretically and experimentally. The theoretical boundary-value problem is solved through linearization and completed by numerical calculation. The wire impedance as a function of frequency is shown to exhibit peaks above the ion cyclotron harmonics corresponding to the passbands of ionic Bernstein waves. Experiments are performed in a single-ended Q machine and led to results in good agreement with theory.
General Invariance of Hydrodynamic Equations: Classical Symmetry Breaking
Authors: Rosen Gerald
Published: February 2004

Boundary-free fluid flow in n-dimensional space features approximate symmetry under the IGL(n+1, R) transformation group if the fluid motion is dominated by the inertial force. Other forces break this basic symmetry and produce equations which are invariant under subgroups of IGL(n+1, R) transformations.
Hydraulically Critical Rotating Flow
Authors: Stern Melvin E.
Published: February 2004

Uniform flow in a rotating open channel becomes “critical” when it exceeds the speed of free Kelvin waves. Transition of subcritical geostrophic flow is discussed.
Specific Refractivities of Atomic Nitrogen and Oxygen
Authors: Wettlaufer D. E. , Glass I. I.
Published: February 2004

Specific refractivities (Gladstone-Dale constants) of atomic nitrogen and oxygen were determined experimentally using dual-frequency laser interferometry over a significant wavelength range.
Shocked Layer in a Coaxial Plasma Gun
Authors: Jurak K. , Offenberger A. A.
Published: February 2004

A revised, steady-state, quasi-one-dimensional model of the shocked layer in a coaxial accelerator is numerically solved for helium for a range of shock speeds which covers up to double ionization.
Stability of the Tearing Mode in Astron
Authors: Fowler T. K.
Published: February 2004

It is shown by means of an energy principle that a neutralized astron E layer confined axially by its own magnetic forces is stable with respect to axial oscillations (the tearing mode).
Discharges Guided by Laser-Induced Rarefaction Channels
Authors: Saum K. A. , Koopman David W.
Published: February 2004

Preliminary experiments demonstrating the channeling and guidance of an electrical breakdown streamer via a laser-induced rarefaction channel are reported. The ability of this phenomenon to extend the range of a given spark is also demonstrated.
Oscillating Cylinders and the Stokes' Paradox
Authors: Williams Robert E. , Hussey R. G.
Published: February 2004

Measurements are reported of the inertia coefficient k and damping coefficient k′ for a circular cylinder (radius a) oscillating at angular frequency ω in a fluid of kinematic viscosity ν. Good agreement with the theory of Stokes is obtained throughout the range 0.286<(2ν/ωa2)1/2<4.13 even when the Reynolds number R and the relative amplitude are not small compared with 1. Stokes' theory is expressed in terms of modified Bessel functions, and values of k and k′ are tabulated for 0.001<(a2ω/4ν)1/2<0.5. The relation to Stokes' paradox is considered by examining the damping force in the limit (ωa2/ν)1/2≪1. The damping force for a cylinder, unlike that for a sphere, does not reduce to the low R drag in this limit. However, comparison with Lamb's solution of the Oseen equations suggests an expression that agrees well with drag measurements up to R = 2.5.
Closed Streamlines Associated with Channel Flow over a Cavity
Authors: O'Brien Vivian
Published: February 2004

The viscous Stokes flow induced in a rectangular cavity by a parallel shear flow is calculated by a direct finite difference method. The separating streamline and the intensity of the circulation of the closed streamline flow within the cavity are shown as a function of cavity shape, relative channel size to cavity size, and the parallel velocity profile within the channel. Application of the results to viscous flow observations are indicated.
Numerical Solution of the Navier-Stokes Equations by the Finite Element Method
Authors: Cheng Ralph Ta-shun
Published: February 2004

Occurrences of viscous fluid flows in arbitrary internal passages are numerous, an analytical solution of the governing Navier-Stokes equations cannot be obtained. Even a numerical approach faces difficulties arising from the nonlinearity and complexity of the geometry involved. To remedy these difficulties, the time-dependent Navier-Stokes equations are solved by the finite element method wherein a steady-state solution is assumed when the time-dependent solution becomes convergent. A family of locally constricted channels was considered in the computations, and in each case, the shear stress at the wall was found to be sharply increased at and near the region of constriction. Computations were carried out to Reynolds numbers when a separation eddy was established. The numerical scheme used seems to be fairly stable.
Perturbation Technique for the Study of Three-Dimensional Separation
Authors: Buckmaster J.
Published: February 2004

The three-dimensional boundary-layer equations are studied close to separation and to a plane of symmetry. Perturbation about a one-dimensional parabolic flow field leads to a sequence of linear equations which have eigensolutions, the first of which satisfies a nonlinear equation. This first eigensolution contains all the important information about the skin friction, and by appropriate choice of the perturbation problem the skin friction is shown to satisfy a first order nonlinear wave equation. The characteristics of this equation are the skin-friction lines (surface stream lines), and their behavior is described close to separation. The description obtained is a global one (that is, not restricted to the neighborhood of a plane of symmetry) when the cross flow is small. The validity of the local solution is confirmed by a Goldstein-type coordinate expansion.
Spatial Stability of Stagnation Water Boundary Layer with Heat Transfer
Authors: Wazzan A. R. , Keltner Gerlina , Okamura T. T. , Smith A. M. O.
Published: February 2004

Neglecting temperature fluctuations, assuming viscosity is only temperature dependent, and assuming all other fluid properties are constant, the two-dimensional linearized parallel flow stability problem is adequately treated by modifying the Orr-Sommerfeld equation to include viscosity variations with temperature. The resulting equation is used to study the spatial stability of stagnation water boundary layer with heat transfer. The mean flow with free-stream temperature T∞ = 60°F and wall temperature Tw ranging from 32 to 200°F is computed numerically, from the boundary layer equations with variable fluid properties. It is found that heating stabilizes the boundary layer and cooling destabilizes it. At Tw≅196°F the neutral curve degenerates to a singular point at frequency ω = 5×10−7 and Reynolds number Rδ* = 30.7×103. All disturbances become completely damped for Tw>196°F. It appears that the effect of viscosity μ is larger than the effect of its first derivative μ′ on stability, and that the effect of μ″ is negligible compared with the effect of μ′.
Nonplanar Relativistic Flow
Authors: Eltgroth Peter G.
Published: February 2004

The equations for nonplanar relativistic flow are solved by similarity analysis for a restricted set of problems. The relativistic equation of state p = 13 E is used. The solutions obtained are for flow resulting from a point source of energy at the origin, having a power law time dependence. The results are applied to the problem of spherical shock propagation into a medium and to the problem of cosmic ray generation from supernovae. It is found that the predicted spectrum of cosmic rays is somewhat steeper than is actually observed.
Radiating-Conducting Thick-Transparent Normal Shock Solution
Authors: Carlson Leland A.
Published: February 2004

An approximate solution for the radiating and conducting flowfield behind hypervelocity normal shock waves is presented. The solution is used to investigate the effects of conduction and uncertainty in radiative properties upon the flowfield enthalpy variation.
Initial Free-Surface Motion of an Impulsively Loaded Half-Space
Authors: Rae William J.
Published: February 2004

Some results are presented which describe the motion of layers near the surface of a half-space, caused by an explosion or high-speed particle impact at a nearby point. These results are found from a known closed-form solution for the flow field near the point where the shock wave propagating into the half-space intersects the free surface. Trajectories, calculated for a layer of particles which initially lie at a shallow depth beneath the surface, show the influence of the primary shock wave and subsequent expansion fan on the motion.
Atomic Oxygen Formation Times Obtained from Measurements of Electron Density Profiles behind Shock Waves in Air
Authors: Stricker J. , Low W.
Published: February 2004

Microwave attenuation and neutral gas density profiles were measured behind shock waves in air, at an initial pressure of 5 Torr in the shock Mach number range of 8-10. From these data and with the assumptions that the ionization cross section Qion is reasonably constant during the O2 dissociation process and the atomic nitrogen concentration is approximately equal to the equilibrium value during this process, the formation times of atomic oxygen and ionization relaxation times were obtained. It is shown that the formation time of atomic oxygen and the ionization relaxation time agree well with different theoretical calculations. The electron peak density was found to be 2-3 times higher than the values calculated for thermodynamic equilibrium. The neutral gas density was measured with the aid of a simple laser interferometer.
Diatomic Gasdynamic Lasers
Authors: McKenzie Robert L.
Published: February 2004

Predictions from a numerical model of the vibrational relaxation of anharmonic diatomic oscillators in supersonic expansions are used to show the extent to which the small anharmonicity of gases like CO can cause significant overpopulations of upper vibrational states. When mixtures of CO and N2 are considered, radiative gain on many of the vibration-rotation transitions of CO is predicted. Experiments are described that qualitatively verify the predictions by demonstrating laser oscillation in CO-N2 expansions. The resulting CO-N2 gasdynamic laser displays performance characteristics that equal or exceed those of similar CO2 lasers.
Steady Nonlinear Ekman-Hartmann Boundary Layers
Authors: Benton Edward R. , Chow Julianna H. S.
Published: February 2004

The steady, axially symmetric Ekman-Hartmann boundary layer on a flat insulating surface is analyzed in its fully nonlinear form. Emphasis is placed on evaluation of Ekman pumping and induced Hartmann current as functions of Rossby number, magnetic interaction parameter, and magnetic Prandtl number. Significant quantitative departures from the estimates of linear theory are found. Yet, for some purposes (such as for predicting its influence on spin-up) the strength of this hydromagnetic pump is shown to be adequately described by an analytic series solution truncated after the terms quadratic in Rossby number.
Nonlinear Thermal Convection in Conducting Fluids
Authors: Lalas D. P. , Carmi S.
Published: February 2004

The stability of an electrically conducting Boussinesq fluid subjected to a temperature gradient and a magnetic field is analyzed by the energy method. The mathematically rigorous results establish the existence of a region of certain stability near the origin of the parameter space (Ra, Re, Rm) where Ra, Re, and Rm are the Rayleigh, Reynolds, and magnetic Reynolds numbers, respectively. Furthermore, by using the calculus of variation methods, the region of certain stability is enlarged and the relevant Euler-Lagrange equations are obtained. An exact solution for the stability limit is obtained for a motionless layer of fluid heated from below and subjected to a crossed horizontal magnetic field. The region of certain stability is delineated by Ra + Rm2<1708, Re = 0. This result is compared with the results of linear theory. The pertinent regions for the design of future stability experiments are indicated.
Stability of an Electrical Discharge Surrounded by a Free Vortex
Authors: Chow Chuen-Yen , Uberoi Mahinder S.
Published: February 2004

Analysis shows that the serious unstable disturbances on a fluid cylinder carrying an axial current can be suppressed by a coaxial vortex flow, in agreement with laboratory observation on electrical discharges. The result may provide an explanation for the electrical activities found in the funnel of tornadoes.
Numerical Analysis of Magnetohydrodynamic Instabilities by the Finite Element Method
Authors: Takeda Tatsuoki , Shimomura Yasuo , Ohta Mitsuru , Yoshikawa Masaji
Published: February 2004

A finite-element method has been applied to the analysis of magnetohydrodynamic instabilities in a cylindrical current-carrying plasma embedded in a strong longitudinal magnetic field. To examine the applicability of the finite-element method to the stability analysis, the growth rate of instabilities has been calculated numerically using an electronic computer. It has been shown that the numerical results, for which corresponding analytical results are available, are in good agreement with them. Several examples of the analysis of low-m mode instabilities with various current distributions are demonstrated. It is concluded that the finite-element method is a powerful tool for the study of magnetohydrodynamic instabilities in the cylindrical plasma as well as, possibly, plasmas with more complex geometries.
Scattering of Light by Relativistic Electrons
Authors: Ward Gray , Pechacek R. E.
Published: February 2004

The differential scattering cross section for the interaction of optical photons with relativistic electrons is calculated from quantum electrodynamics. The cross section is confirmed by scattering monochromatic electromagnetic radiation from 50-keV electrons. The classical calculation of the differential scattering cross section which agrees with the quantum electrodynamic calculation and with experiment is one which takes into account the fact that scattering electrons enter and leave the scattering volume during the period of observation. These results are important for the proper intepretation of laser scattering measurements of plasma distribution functions when electron temperatures are ≥ 10 keV.
Self-Consistent Finite Amplitude Wave Damping
Authors: Oei I. H. , Swanson D. G.
Published: February 2004

An approximate self-consistent damping rate for a finite amplitude wave is obtained. In the limit of γLτ0≫1 and γLτ0≪1, where γL is the linear Landau damping coefficient and τ0 is the bounce period of the particles in the wave potential well, the linear Landau damping rate and O'Neil damping coefficient, respectively, are recovered from the generalized result, which is in the form of an integral equation. By the technique of numerical iteration, the damping coefficients for different values of γLτ0 ranging from 0.1 to 1 have been obtained. Damped wave amplitudes are also plotted which show semiquantitative agreement with the experimental data of Malmberg and Wharton.
Intermittent Behavior of a Plasma Discharge in Turbulent Gas Flow
Authors: Levine A. M. , Granatstein V. L. , Rhinewine M.
Published: February 2004

A new model to describe an arc discharge struck in a turbulent pipe flow is discussed. In this model, a randomly twisted column is convected down the pipe producing an intermittent signal on electrostatic probes. A theoretical and experimental analysis of these signals is presented. The analysis provides information about discharges in rapidly flowing gases and also develops techniques useful in studying intermittent phenomena.
Spatial Distributions of Plasma Density in a High-Frequency Discharge with a Superimposed Static Magnetic Field
Authors: Szuszczewicz Edward P. , Oechsner Hans
Published: February 2004

An experimental investigation has been carried out on the spatial distribution of charged-particle density in an inductively-coupled, cylindrical high-frequency plasma discharge with a superimposed perpendicular magnetic field. The studies were performed at and near conditions of electron-cyclotron-wave resonance and consideration was given to the influence of magnetic field and high-frequency power levels. It is shown that high-frequency power levels have relatively little influence on the volume distribution of charge, but that very unique distributions result under conditions of electron-cyclotron-wave resonance. Characteristic distributions are presented and discussed in the context of plasma anisotropy resulting from the superimposed magnetic field.
Numerical Calculations of Off-Resonance Heating
Authors: Sprott J. C.
Published: February 2004

The off-resonance heating that is observed in hot-electron plasmas is explained in terms of harmonic resonances, appropriately modified to include relativistic and Doppler effects. A theoretical expression for the heating rate is proposed and is found to agree with the results of a computer simulation over a range of parameters. The theoretical heating rate is evaluated numerically for several special cases, including a uniform magnetic field, a mirror field with a 2:1 mirror ratio, and a large-aspect ratio bumpy torus. The enhanced axial loss observed experimentally with heating below the cyclotron frequency is explained by absorption at harmonics of the electron bounce frequency.
Kelvin-Helmholtz Instability in a High-β Collisionless Plasma
Authors: Dobrowolny Marino
Published: February 2004

The stability of an inhomogeneous plasma, of arbitrary β, flowing along a straight magnetic field is studied. Both the velocity flow and the plasma density are spatially varying in a direction perpendicular to the field. For drift-type waves, very elongated along the magnetic field direction, an Alfvén wave branch and a magnetosonic branch turn out to be decoupled. It is found that both branches may be driven unstable by the velocity shear. Stability conditions are worked out, quantitatively discussed, and compared in terms of β and of the magnitude of the shear.
Propagation of an Ion Rarefaction Wave from a Growing Sheath
Authors: Andrews J. G. , Shrapnel A. J.
Published: February 2004

The structure of an ion rarefaction wave propagating from a sheath growing into a nonuniform plasma column is determined using the method of characteristics. Ionization and collisions both tend to damp out the wave. The interaction between two identical ion rarefaction waves from opposite sides of a plasma column produces a secondary ion rarefaction wave which spreads outward from the center of the column. The density profile in the column relaxes toward a new equilibrium profile, corresponding to that for the new (i.e., contracted) column width.
Mode-Coupling and Wave-Particle Interactions for Unstable Ion-Acoustic Waves
Authors: Martin Pablo , Fried Burton D.
Published: February 2004

A theory for the spatial development of linearly unstable, coupled waves is presented in which both quasilinear and mode-coupling effects are treated in a self-consistent manner. Steady-state excitation of two waves (with frequencies ω1, ω2) is assumed at the boundary x=0, the plasma being homogeneous in the y and z directions. Coupled equations are derived for the x dependence of the amplitudes of the primary waves (ω1, ω2) and the secondary waves, nω1+mω2 (n and m being integers), correct through terms of second order in the wave amplitude, eφ/Te, but without the usual approximation of small growth rates. This general formalism is then applied to the case of coupled ion-acoustic waves driven unstable by an ion beam streaming in the direction of the x axis. If the modifications of the ion beam by the waves (“quasilinear” effects) are ignored, “explosive” instabilities (singularities in all of the amplitudes at finite x) are found even when all of the waves have positive energy. If these wave-particle interactions are included, the solutions are no longer singular, and all of the amplitudes have finite maxima, at locations in reasonable agreement with experimental results of Taylor and Ikezi.
Ion-Acoustic Radiation Generated by a Pseudowave—Experiment, Theory, and Simulation
Authors: Estabrook Kent , Alexeff Igor
Published: February 2004

A pseudowave packet propagating at high velocity through a plasma is observed to generate a “wake” of ion-acoustic waves radiating outward. When the pseudowaves are cut into laminations, a short sine wave train of ion-acoustic waves is observed to propagate perpendicular to the pseudowave paths. The method may be an excellent method of exciting pure ion-acoustic waves without the nonlinear sheath effects (streaming) inherent in the direct use of exciting electrodes. A theory and simulation of the ballistic-wave coupling which predict the observed waveform is discussed.
Alfvén Cyclotron Resonance Instability in Mirror Machines
Authors: Cordey J. G. , Hastie R. J.
Published: February 2004

The stability of the collisional distribution of a mirror machine against the Alfvén cyclotron resonance mode is examined. This instability which is shown to have a growth rate which scales as γ∼ωci exp (−R3/4/β1/4) for Rβ<1 may be dangerous for low beta mirror plasmas as well as high beta plasmas.
Damping of Electron Plasma Oscillations in a Uniform Electric Field
Authors: Bateman Glenn
Published: February 2004

The damping of electron plasma oscillations with large phase velocities is computed as the combination of Landau damping, collisional damping, a growth rate or damping explicitly due to a uniformly applied, steady electric field, and a complementary effect due to the time evolution of the background distribution function. A linear form of the moment equations is used to derive expressions for the field and time-dependent effects. The derivation does not depend upon the specific nature of the resistivity or other dissipative effects. An illustrative example is given for the competition between these effects when a small electric field and classical Ohmic heating are present.
Electrostatic Oscillations in Plasmas with Cutoff Distributions
Authors: Canosa José , Gazdag Jenö , Fromm J. E. , Armstrong B. H.
Published: February 2004

When numerically solving the linear Vlasov equation with cutoff electron distributions, the well-known Landau-damped oscillation of the electric field was observed first but, after a short transition time, a constant-amplitude harmonic oscillation with a frequency distinctly higher than Landau's frequency was found. This coexistence of two distinct modes of oscillation—one damped and one undamped—has not been observed before. The behavior is explained quantitatively by comparison of the dispersion equation solution with the results obtained from the numerical solution of Vlasov's equation.
Stabilization of the Modified Negative Mass Instability
Authors: Callen J. D. , Horton C. W.
Published: February 2004

Previous studies of the resonant, modified negative mass instabilities in finite mirror-confined plasmas with highly anisotropic velocity distributions have shown that, at least when the bounce harmonic structure is ignored, a small thermal spread in the pitch-angle or energy distribution does not stabilize the modes. Bounce harmonic effects with no thermal spread have been shown to introduce new unstable modes. Combining the bounce and thermal spreading effects. It is found that the negative mass modes are all stabilized if ηΔ ≡ Δ2Ω0/ωb>0.77, where Δ∼(T‖/T⊥)1/2 is the thermal spread (half-width at half-maximum) in the pitch-angle distribution, Ω0 is the minimum gyrofrequency, and ωb is the average bounce frequency.
Nonlinear Evolution of Whistler Instabilities
Authors: Ossakow Sidney L. , Ott Edward , Haber Irving
Published: February 2004

Theoretical and computer simulation studies of whistler instabilities in anisotropic collisionless plasmas are presented. Initial bi-Maxwellian, Maxwellian with loss cone, and hot Maxwellian superimposed on a more dense cold isotropic background electron distributions were used. Many of the observed features are common to all cases. Initially, the total wave magnetic energy grows; the average growth rate is in good agreement with linear theory; and the electron distribution isotropizes rapidly with a concomitant switching off of high k number, initially unstable waves. Then, the total wave magnetic energy saturates and at this time there is a residual kinetic energy anisotropy. This anisotropy persists after saturation, although there is a further tendency toward isotropy, together with a further switching off of the higher mode numbers for the remainder of the simulation. Throughout the simulation experiments the perpendicular and parallel energy constants are conserved to good accuracy.