bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasma Motion in a Time Changing Toroidal Octupole Magnetic Field
Authors: Lencioni Donald E.
Published: February 2004

A gun-injected hydrogen plasma was contained in a toroidal octupole magnetic field. The plasma motion due to the changing magnetic field was studied and compared to a model based on the flux invariance of the motion. For early injection (while the field was rising) there was a strong motion toward the multipole rods while for late injection the motion was toward the wall. Magnetohydrodynamic theory shows that the plasma becomes unstable near the separatrix due to this motion. Although fluctuations were observed in this region, the plasma was found to be distributed stably.
Stability of a High β, Helically Symmetric Pinch
Authors: Freidberg J. P. , Marder B. M.
Published: February 2004

Previous results obtained with a sharp boundary model on the stability of a high β theta pinch with l = 1 windings are generalized to include diffuse profiles. The encouraging sharp boundary result is found to be valid for a large class of diffuse profiles: To lowest order the system is weakly stable to the m = 1 mode.
The New Stokes Paradox
Authors: O'Brien Vivian
Published: February 2004

Viscous shear flow in a shallow box is computed numerically. Superposition of the flow due to a rotating cylinder at the center of the box produces a flow configuration investigated recently by Robertson and Acrivos. Their results are discussed and clarified.
Mean Period of the Turbulent Production Mechanism in a Boundary Layer
Authors: Laufer John , Narayanan M. A. Badri
Published: February 2004

Based on experimentally observed scaling laws, the interaction between the motion in the sublayer with that of the wakelike outer flow is described in terms of a limit cycle.
Effect of Oblique Incidence on Optical Absorption of Laser Light by a Plasma
Authors: Shearer J. W.
Published: February 2004

The reflection coefficient of laser light is an increasing function of the angle of incidence relative to the density gradient at a diffuse plasma boundary, because refraction bends the light away from denser regions where the absorption coefficient is high.
Electrostatic Instabilities in Multicomponent Plasmas
Authors: Schulz Michael , Koons H. C.
Published: February 2004

A commonly employed heuristic method for evaluating phase velocities and growth rates of ion and electron plasma oscillations is generalized here to multicomponent plasmas. The new formulation exhibits the correct Galilean transformation properties.
Effects of Couple Stresses in Fluids on Dispersion of a Solute in a Channel Flow
Authors: Soundalgekar V. M.
Published: February 2004

An analysis of the dispersion of a solute in a channel flow of fluid with couple stresses has been carried out. It is observed that couple stresses are more effective for α < 20 where α is a nondimensional parameter. When α > > 20, the effects of couple stresses on the dispersion of a solute are negligibly small. For α → ∞, the dispersion of the solute is not affected by the couple stresses.
Particle Orbits in Two Waves of Arbitrary Amplitude
Authors: Kaw P. K. , Kruer W. L.
Published: February 2004

The effect of a second wave, of arbitrary amplitude and phase, on the one-dimensional motion of a particle trapped in a large-amplitude electrostatic wave has been analytically investigated.
Microwave Propagation in the Presence of a Finite Amplitude Helical Instability
Authors: Ventrice Carl A.
Published: February 2004

Phase shift measurements are made in the presence of a finite amplitude instability, using a 30 GHz microwave interferometer. A large discrepancy exists between the measured phase shifts and those calculated from the time-averaged particle density profiles.
The Stellarator as a Nonlinear Plasma Current Transformer
Authors: Furth H. P.
Published: February 2004

Oscillation of the helical winding current of a stellarator induces toroidal plasma currents proportional to the square of the winding current.
Harmonic Generation in Cold Nonuniform Plasma in a Magnetic Field
Authors: Blum F. A.
Published: February 2004

Theoretical discussion of harmonic generation in cold bounded nonuniform magnetoplasmas predicts weak even order harmonic generation (compared to odd order) and strong resonances near cyclotron and maximum upper hybrid resonances for small collision frequencies.
Slip in the Thermal Creep Flow
Authors: Loyalka S. K.
Published: February 2004

A simple and accurate expression for slip in the thermal creep problem is obtained via the use of the Roussopolous variational principle. The linearized Boltzmann equation is used and it is shown that, contrary to the results obtained by Yalamov, Ivchenko, and Deryagin, the Bhatnagar-Gross-Krook model, and the Maxwell molecules give essentially the same numerical values for the slip coefficient. Interestingly, the result for the rigid sphere molecules is about 12% lower than these values. Further, it is shown that some variational principles used previously in the kinetic theory are, in fact, only a special case of the Roussopolous principle.
Kinetic Theory of Wave Propagation. I. One-Component Systems
Authors: Bramlette T. Taz , Huang A. Ben
Published: February 2004

The problem of wave propagation in one-component systems is treated using the discrete ordinate method. Forced and free oscillations in a monatomic gas and longitudinal electrostatic oscillations in a one-component plasma are considered. The governing equation is the linearized ellipsoidal model of the Boltzmann equation. When the ratio of collision frequency to a characteristic frequency of the wave is greater than one, the present technique yields results which are in excellent agreement with other theories and experimental data. For values of this ratio less than one, the present theory is very similar to the polynomial expansion theories.
Experimental Study of the Magnetic Piston-Shock Wave Problem in a Collisionless Plasma
Authors: DeSilva A. W. , Dove W. F. , Spalding I. J. , Goldenbaum G. C.
Published: February 2004

The time-dependent problem of piston and shock wave formation in a low density (collision-free) magnetized plasma has been experimentally studied in a high voltage theta pinch. The applied field strongly interacts with the plasma: either exciting instabilities that cause a fast resistive penetration and very low force density, or exerting a sufficiently large force density to produce high Mach number (5-20) shock waves. The data on piston formation is discussed in terms of a magnetic field-dependent resistivity such as might be expected from an ion plasma drift wave instability. The piston ejects ions possibly by the interaction of ions with ion plasma waves. The shock wave is seen to evolve from an initially one-dimensional disturbance.
Ion Heating in the Dense Plasma Focus
Authors: Toepfer A. J. , Smith D. R. , Beckner E. H.
Published: February 2004

The collapse phase of a dense plasma focus gun operating in deuterium was studied using streak photography and time resolved x-ray and neutron measuring techniques. The streak photographs, showing the radial motion of the luminous front at various axial positions, indicate a collapsing luminous front at the time of the current collapse followed by an expanding front and a recompression. The luminosity then disappears for a period of several hundred nanoseconds, during which time the neutrons are emitted. Estimates of shock heating and magnetic compressional heating were made from the streak pictures, and a calculation of plasma heating due to viscous forces arising from axial motion of the plasma was carried out. The effects of shock heating, magnetic compressional heating, and viscous heating are shown to be sufficient to produce an ion temperature of several kilovolts.
Far-Wake Structure in Rarefield Plasma Flows past Charged Bodies
Authors: Sanmartin Juan R. , Lam S. H.
Published: February 2004

The asymptotic structure of the far-wake behind a charged body in a rarefied plasma flow is investigated under the assumption of small ion-to-electron temperature ratio and of flow speed hypersonic with respect to the ions but not with respect to the electrons. It is found that waves are excited even if the flow is subacoustic (flow velocity less than the ion-acoustic speed). For both superacoustic and subacoustic velocities a steep wave front develops separating the weakly perturbed, quasineutral plasma ahead, from the region behind where ion waves appear. Near the axis a trailing front develops; the region between this and the axis is quasineutral for superacoustic speeds. The decay laws in all of these regions, the self-similar structure of the fronts and the general character of the waves are determined. The damping of the waves and special flow detail for bodies large and small compared with the Debye length are discussed. A nonlinear analysis of the leading wave front in superacoustic flow is carried out. A hyperacoustic equivalence principle is presented.
Instabilities of the Ekman-Hartmann Boundary Layer
Authors: Gilman Peter A.
Published: February 2004

Gilman and Benton have demonstrated the existence of composite Ekman-Hartmann layer flow in rotating, electrically conducting fluids permeated by a magnetic field normal to the boundary. This flow was shown to evolve smoothly from a pure Ekman layer to a pure Hartmann layer as the parameter α ≡ (2μρλΩ0)−1/2 B0 increases (μ is magnetic permeability, ρ is density, λ is magnetic diffusivity, Ω0 is the rotation rate, and B0 is the imposed magnetic field). Here, it is shown that in the Cartesian, low magnetic Prandtl number limit, this flow exhibits the two instabilities to two-dimensional rolls characteristic of the pure Ekman layer, but at Reynolds numbers that increase rapidly as α increases. Both rolls decrease in horizontal scale, orient more nearly parallel to the flow far from the boundary, and acquire smaller phase velocities. Coriolis forces are seen to give a parallel roll instability of the Hartmann layer, at much lower Reynolds numbers than given by Roberts for Hartmann layer instability in the absence of rotation.
Snowplowing in a Plasma Rail Gun
Authors: Collier D. W. , Zinke O. H.
Published: February 2004

Agreement between data from a plasma rail gun as analyzed by a time-of-flight technique and predicted by snowplow theory indicates that there is no necessity for any theory of drag force in the gun and seems to indicate that one theory for drag force which also accounts for the conduction of electrical current into a moving plasma should be re-examined.
Nonlinear Plasma Waves
Authors: Klozenberg J. P.
Published: February 2004

A numerical solution of the equations for unstable electrostatic plasma waves propagating in a uniform infinite plasma with a weak beam is performed. Space dependent variables are Fourier transformed and the computations are done first with only one and then with two harmonics included. In both cases the first harmonic electric field reaches a maximum amplitude and thereafter oscillates periodically, the period being different in the two cases. Thus, the time evolution of the field depends strongly on the presence of the second harmonic. The second harmonic electric field itself has negligible amplitude compared with the fundamental but the corresponding perturbed distribution functions are comparable in the vicinity of the wave resonance. In the frame of the background plasma the frequency of the first harmonic electric field is close to the plasma frequency ωp but the nonlinearly generated second harmonic frequency is 2ωp. Because of this it is found that the wave-wave interaction terms are important and resonant processes occur. The neglect of such terms in quasilinear theory is questioned.
Theory of the Dynamic Stabilization of the Rayleigh-Taylor Instability
Authors: Troyon F. , Gruber R.
Published: February 2004

Recent experiments by Wolf have demonstrated the possibility of dynamically stabilizing the Rayleigh-Taylor instability of the interface between two heavy fluids. This problem is considered and it is shown quite generally that both viscosity and interfacial tension are necessary to stabilize the short wavelength perturbations. As an example the experimental results obtained with a liquid-air interface are reproduced.
Flow in a Turbulent Trailing Vortex
Authors: Govindaraju S. P. , Saffman P. G.
Published: February 2004

The structure of turbulent line vortices is examined. A general argument is constructed to show that the vortex must develop an overshoot of circulation if it entrains fluid at a rate greater than that due to molecular diffusion. A weak hypothesis on the distribution of Reynolds stress leads to the logarithmic profile of Hoffman and Joubert and an estimate of the maximum Reynolds stress. The results of a turbulence model due to Saffman are presented and shown to be poor.
Chemical Instabilities. V. Hydrodynamic Stability of a Simple Dissociating Fluid in Plane Couette Flow
Authors: Bdzil J. , Frisch H. L.
Published: February 2004

A linear stability analysis was performed of a horizontal layer of the reactive fluid mixture (A2, A) which is undergoing both a simple surface catalyzed dissociation and plane Couette flow. When only transverse disturbances were considered, it was found that the instabilities for this system are similar to those discussed previously. By including the longitudinal disturbances, it was found that the shear has a stabilizing influence on the overstable S>0 instability.
Brownian Motion from Boltzmann's Equation
Authors: Montgomery David
Published: February 2004

Two apparently disparate lines of inquiry in kinetic theory are shown to be equivalent: (1) Brownian motion as treated by the (stochastic) Langevin equation and Fokker-Planck equation; and (2) Boltzmann's equation. The method is to derive the kinetic equation for Brownian motion from the Boltzmann equation for a two-component neutral gas by a simultaneous expansion in the density and mass ratios.
Velocity Fluctuations of a Body in a Fluid
Authors: Case K. M.
Published: February 2004

An extension of the usual treatment of Brownian motion is given. The motion of a body in a fluid is considered to be described by a quite general form of retarding force. To describe the expected fluctuations, correlation functions are obtained from a fluctuation-dissipation theorem. Under very modest conditions on the retarding force the “equipartition theorem” is obtained. Frequently, such correlation functions are obtained by postulating certain fluctuating forces. Here, no such assumption is made. However, it is possible to exhibit those fluctuating forces which would give our correlation functions. Some examples are discussed. Finally, the results for a realistic retarding force are obtained.
Measurements on a Magnetohydrodynamic Shock
Authors: Sommer E. J. , Barach J. P.
Published: February 2004

An electrically driven shock wave is launched axially down a tube filled with Te = 1−2-eV plasma, carrying an axial current and associated azimuthal magnetic field (250 G). The number density is between 1016 and 1017 cm−3 and the shock Mach numbers range from 1.2 to 6.5. Flux compression of 10-25% at the front is observed, but this amount is very much smaller than ideal theory predicts and its duration is briefer. The flux increase is closely followed by diamagnetic discharge plasma producing an abrupt flux decrease. Mixing with this plasma and boundary-layer flow to the walls of the shock tube account for the small and brief field compression observed. Rough calculations support this picture and include an effective fraction q1 of the flow not undergoing compression. This q1 is found to be as high as 50%.
Strong Shock with Radiation near the Surface of a Star
Authors: Sachdev P. L. , Ashraf S.
Published: February 2004

The propagation of a shock wave, originating in a stellar interior, is considered when it approaches the surface of the star and assumes a self-similar character, “forgetting” its initial conditions. The flow behind the shock is assumed to be spatially isothermal rather than adiabatic to simulate the conditions of large radiative transfer near the stellar surface. The adiabatic and isothermal flows behind such a shock are compared. The exact shock-propagation laws, obtained by solving the equations in similarity variables, for different values of the parameter δ in the undisturbed density law, ρ0∞δ, and γ, the ratio of specific heats, are compared with the approximate values calculated by Whitham's characteristic rule and the two show a generally good agreement.
Numerical Simulation of Spark Discharges in Air
Authors: Plooster Myron N.
Published: February 2004

A numerical model is presented which describes the evolution with time of a short segment of a spark channel in air and its associated acoustic wave. The model assumes a straight, cylindrical conducting column in which local thermodynamic equilibrium exists at every point. The electrical energy input to the column is determined by a prescribed electrical current waveform, coupled with a computation of the plasma conductivity. The evolution with time of the conducting column and its surrounding flow field is then found by numerical integration of the equations of gas dynamics. The model employs a realistic equation of state for air at high temperatures, and incorporates kinetic and radiative energy transport processes. It is shown that a satisfactory description of the properties of a spark channel cannot be achieved when radiative transport processes are neglected. The model agrees well with experimental measurements of spark channel radii, temperatures, pressures, and electron densities, and predicts the resultant shock wave strengths closely. The voltage gradients along the spark channel predicted by the model, and the total energy input to the channel, are not as uniformly in agreement with experiment. Possible reasons for these discrepancies are discussed.
Production and Investigation of Very Strong Ionizing Shock Waves
Authors: Halmoy Einar
Published: February 2004

Experiments are described in which shock speeds up to 1% of the speed of light were achieved in gaseous hydrogen or deuterium. Separation between the transverse shock wave and the drive current are clearly observed. The density and magnetic field shock compressions are measured and the post-shock electron temperature, determined from plasma x-ray bremsstrahlung spectra, is found to be about 107 °K. Neutron emission was detected from shocks in deuterium. The axial electric field in the shock structure is measured and interpreted as resulting from a combination of Hall effect and ion displacement current.
Nonisothermal Theory of an Electrostatic Probe in a Weakly Ionized Gas
Authors: Jou Wen-Huei , Cheng Sin-I
Published: February 2004

The isothermal assumption for electrons is removed from the continuum theory of the electrostatic probe. Asymptotic analyses based upon small Debye length are developed for both cold and warm ions with an appropriate electron energy equation. The structure of the asymptotic expansion is essentially changed from that of the isothermal theory. In particular, the current-voltage characteristic is expressed as a series in which the leading term, obtained under quasineutral approximation, is of the order of unity and the subsequent terms are small in the asymptotic sense. The results may be used to explain the discrepancies between the isothermal theory and some experimental results of Little and Waymouth.
Nonlocal Behavior of Ion Sound Instability in Collisionless Shock Wave
Authors: Bajaj N. K. , Krall N. A.
Published: February 2004

The stability of a magnetic pulse with respect to ion acoustic-electron drift waves is studied, using a realistic magnetic profile instead of the local approximation customarily analyzed. The stabilizing effect of nonlocal corrections is noted, and the condition for validity of local approximation in this case is obtained.
One-Dimensional Simulation of Relativistic Streaming Instabilities
Authors: McKee Christopher F.
Published: February 2004

A relativistic version of the one-dimensional cloud-in-cell model for plasma simulation is developed. The model is physically self-consistent despite the omission of transverse, electromagnetic waves. The conditions for the onset of relativistic electrostatic instabilities between two electron beams and between two identical counterstreaming plasmas are derived for the case in which the one-dimensional and three-dimensional results are identical. In particular, the ion-ion instability can occur only for extremely high electron temperatures. Collisional effects in the model are discussed. Supraluminous waves are shown to be generated both by collisional effects and by nonlinear interactions in unstable plasmas. The results of the simulation of the instabilities are consistent with the theory. With the exception of the behavior of vortexes in position-momentum phase space, the relativistic results correspond reasonably well to the nonrelativistic ones.
Generalized Equations for Plasma of Arbitrary Collision Frequency in Weakly Inhomogeneous Magnetic Field
Authors: Stringer T. E. , Connor J. W.
Published: February 2004

A closed set of equations relating the macroscopic variables are derived from the linearized kinetic equations with a Bhatnagar-Gross-Krook collision term. The collisional fluid limit of these expressions are in complete agreement with the most exact magnetohydromagnetic equations, including viscosity. The collisionless fluid limit provides an extension of the Chew-Goldberger-Low equations, now valid when the diamagnetic velocity is comparable to the electric drift. The generalized equations may be used to investigate the transition between the weakly collisional condition, where resonant particle effects are important, and the strongly collisional condition where viscosity becomes dominant.
Diffusion of an Equilibrium Toroidal Plasma at Intermediate and Higher Collision Frequencies
Authors: Connor J. W. , Stringer T. E.
Published: February 2004

An expression for the equilibrium diffusion rate is derived using the generalized equations previously published. Different limiting forms of this expression are compared with the intermediate collisional and highly collisional results derived earlier. The validity of these results are found to be more restricted than previously assumed. To cover the range of experimental interest, two new limiting conditions are considered. In both these the ambipolar diffusion is generally comparable to the Pfirsch-Schlüter rate. The generalized expression allows the diffusion to be evaluated in the transition zones between the different regimes.
Drift Effects on the Behavior of a Low-β Axisymmetric Toroidal Plasma
Authors: Bowers E. , Winsor N. K.
Published: February 2004

Analysis of a low-β axisymmetric toroidal plasma is reported. This predicts shock structure in the presence of resistivity and viscosity. A one-fluid model is considered which includes the Hall terms in Ohm's law and gyroviscous corrections to the pressure tensor. In analyzing this behavior two orderings are used. For typical stellarator parameters, the first ordering (in which the mean free path is less than the connection length but greater than a critical value) leads to a stable rotational equilibrium with a positive potential on axis. In the second ordering the mean free path is less than this critical value and a shock develops toward the inside of the torus, leading to diffusion an order of magnitude larger than the Pfirsch-Schlüter value. A Korteweg-de Vries equation with an added dissipation term due to parallel viscosity, governs the azimuthal density variation in the shock region. Agreement is found between theory and the results of a two-dimensional computer simulation of a toroidal plasma.
Neutron Production Mechanism in a Plasma Focus
Authors: Lee J. H. , Shomo L. P. , Williams M. D. , Hermansdorfer H.
Published: February 2004

The neutrons emitted by a plasma focus were analyzed by using a time-of-flight method. Flight paths as large as 80 m were used to obtain better than 10% energy resolution. The energy spectrum of neutrons from d—d reactions in the plasma focus shows a sharp onset with average maximum energies of 2.8 and 3.2 MeV in the radial and the axial directions, respectively. The average half-width of the energy spectrum was 270 keV with a shot-to-shot variation between 150 and 400 keV. Simultaneous measurements in the axial and radial directions showed no appreciable difference in the half-widths and thus indicated randomly oriented ion velocities in the plasma. A converging ion model is described which is found to be in agreement with the measured quantities.
Plasma Production by Molecular Ion Injection into a Magnetic Mirror Supplemented with a Radio Frequency Electric Field
Authors: Akimune H. , Kishimoto S. , Narikawa T. , Suita T.
Published: February 2004

Observations with a 27-keV molecular ion injection experiment are described. In the experiment, an rf electric field is applied transversely to a containing magnetic mirror field in the mid-region. The rf-field intensity is proportional to r4, and the frequency relation is ω = 2.5ωci = 5ωcm, where r is the radius, and ωci and ωcm are the cyclotron frequencies of protons and hydrogen molecular ions, respectively. Accumulation of plasma greatly increases with an rf potential of about 1.4 kV, and a density of 7×107 particles/cm3 is obtained with an injection current of 2 mA. Perpendicular proton velocity distribution is well spread with an rf potential of about 1.4 kV. The spreading is caused during the process of deceleration of the injected molecular ions. Emissions at the second harmonic and the fourth harmonic of the proton cyclotron frequency are observed. Intensity of the fourth harmonic is reduced with a rise in strength of the rf field. As the rf field is switched off, there are plasma loss processes other than charge exchange. The loss may be due to a low-frequency drift instability. In the presence of the rf field, however, there is no evidence of plasma loss by processes other than charge exchange. The rf field may set up a sufficiently deep well of equivalent quasipotential for ions of the present low-density plasma.
Hydromagnetic Stability of a Finitely Conducting Jet
Authors: Chakraborty B. B. , Jindia R. K.
Published: February 2004

The stability of a finitely conducting and inviscid liquid jet with uniform velocity and magnetic field is studied. Some analytical and numerical results are given. An unstable mode, not present in the infinitely conducting jet, exists for large conductivity and high magnetic field.
Bernstein Modes in a Two-Dimensional Computer Plasma
Authors: Gitomer S. J.
Published: February 2004

Stable longitudinal electron waves with K⊥B are studied using a numerical simulation approach. The dispersion properties of these waves agree well with predictions from linear theory.
Nonlinear Effects of Two Transverse Monochromatic Waves in a Cold Plasma
Authors: Das K. P.
Published: February 2004

The perturbation method of Bogoliubov, Krylov, and Mitropolsky is applied to study the nonlinear effects for two transverse monochromatic waves in a cold plasma. Amplitude-dependent wavelength and frequency shifts including relativistic corrections are derived.
Self-Consistent Relativistic Beam Equilibria
Authors: Rensink Marvin E.
Published: February 2004

Self-consistent solutions to the Vlasov-Maxwell equations are given for three types of relativistic beams: (a) The current density is hollowed out on axis; (b) the current density is peaked on axis; and (c) the current density is uniform. The models used here give beams with sharp radial boundaries.
Parametric Dependence of the Density in a Mirror-Confined Plasma Subject to an Ion-Cyclotron Instability
Authors: Foote James H.
Published: February 2004

A relation is derived predicting a τcz2/3B10/3Wi−1 variation of ion density for onset of an ion-cyclotron instability in a mirror-confined plasma. This threshold behavior may explain why no complete density limitation has been observed in strongly unstable plasmas of two relevant experiments.
Influence of Electron-Ion Collisions on Ion Acoustic Waves
Authors: Stéfant Robert J.
Published: February 2004

The critical current for the growth of ion acoustic waves in the presence of collisions is calculated by using a kinetic investigation with a collision integral of the Bhatnagar-Gross-Krook type. It is shown that electron-ion collisions facilitate the ion acoustic oscillations.
Nonlinear Development of an Instability Wave in a Turbulent Wake
Authors: Liu J. T. C.
Published: February 2004

Recent experimental observations appear to indicate that turbulent mean flow velocity profiles with points of inflection are dynamically unstable with respect to traveling wavy disturbances. As an illustration, the description of the nonlinear development of an instability wave in the turbulent wake behind a thin body is presented on the basis of integrals of the equations of mean flow momentum, kinetic energy, and the time-averaged disturbance kinetic energy, with the turbulent dissipation integrals relegated to phenomenological considerations. The over-all physical mechanisms leading to the streamwise distribution of the mean flow decay and disturbance energy amplification and decay are explained through the disturbance energy production integral and the mean flow and disturbance turbulent-dissipation integrals. The growth of the disturbance wave is limited by (1) the rapidity of turbulent mean flow decay which renders the production integral less spectacular and (2) the prominant role of the turbulent dissipation integral which draws energy away from the disturbance wave to the turbulence. These limitations and the rapidity with which events take place in the streamwise direction essentially distinguishes the instability wave in a turbulent mean flow with inflectional velocity profile from that in a corresponding laminar flow.
Disturbance Characteristics in a Plane Jet
Authors: Mattingly George E. , Criminale W. O.
Published: February 2004

An incompressible two-dimensional plane jet is analyzed using the spatial stability viewpoint. Two modes of unstable waves are found, the more unstable of which has a transverse disturbance velocity component symmetrical about the jet centerplane. Disturbance vorticity, Reynolds stress, and distributions of energetics in the cross-stream direction are presented. Also included is a mechanism through which these jet disturbances interact with the mean flow to produce a vortex street configuration in the downstream jet field.
Film Stability in a Vertical Rotating Tube with a Core-Gas Flow
Authors: Sarma G. S. R. , Lu Pau-Chang , Ostrach S.
Published: February 2004

The linear hydrodynamic stability of a thin-liquid layer flowing along the inside wall of a vertical tube rotating about its axis in the presence of a core-gas flow is examined. The stability problem is formulated under the conditions that the liquid film is thin, the density and viscosity ratios of gas to liquid are small and the relative (axial) pressure gradient in the gas is of the same order as gravity. The resulting eigen-value problem is first solved by a perturbation method appropriate to axisymmetric long-wave disturbances. The damped nature (to within the thin-film and other approximations made) of the nonaxisymmetric and short-wave disturbances is noted. In view of the limitations on a truncated perturbation solution when the disturbance wavenumber is not small, an initial value method using a digital computer is presented. Stability characteristics of neutral, growing, and damped modes are presented showing the influences of rotation, surface tension, and the core-gas flow. Energy balance in a neutral mode is also illustrated.
Stability of Boundary Layer Flow Subject to Rotation
Authors: Potter Merle C. , Chawla Mangal D.
Published: February 2004

The stability of three-dimensional infinitesimal waves moving in a Blasius boundary layer in a rotating flow is investigated for the situation where the rotation axis coincides with the leading edge of a semiinfinite flat plate. Primary interest is in the effect of rotation on the critical point of the neutral stability curve. The problem is formulated in terms of a sixth-order differential equation, which reduces to the Orr-Sommerfeld equation for zero rotation, with homogeneous boundary conditions. The eigenvalue problem thus formed is solved numerically. Results indicate a destabilizing or stabilizing effect depending on the sense of the rotation vector. This rotation effect is influenced by the spanwise wavenumber so that the effect disappears as the spanwise wavenumber vanishes. The results compare favorably with known experimental results.
Applicability of the Oldroyd Constitutive Equation to Flow of Dilute Polymer Solutions
Authors: Lumley J. L.
Published: February 2004

It is shown that the equation relating stress and deformation in a dilute solution of polymer molecules (according to the dumbell model) may be placed in the form of the Oldroyd constitutive equation with an appropriate interpretation of constants.
Some Boundary Value Problems in the Kinetic Theory of Gases
Authors: Pao Young-ping
Published: February 2004

Some one-dimensional boundary value problems are considered from the viewpoint of the Wiener-Hopf integral equation of the second kind. These include the slip flow problem and the problem of transverse oscillations in gases and use the single relaxation model equation as well as a model equation with a velocity-dependent collision frequency. The velocity slips are related to the kernel function in a simple manner. A simple formula is obtained for the microscopic slip in the case of velocity-dependent collision frequency. For the oscillation problem, solutions are obtained in quadrature form in a straightforward manner. This result is discussed along with the application of the present method to the problem of Knudsen flow through a long tube, the heat conduction problem, and the problem of evaporation and condensation.
Kinetic Models for Pressure Flow and Self-Diffusion of Rarefied Gases Through Tubes
Authors: van Eekelen H. A. M. , Smit W.
Published: February 2004

The pressure flow and self-diffusion of rarefied gases through cylindrical tubes is calculated using a kinetic model, with a velocity-independent mean free path. The model obeys the conservation laws for mass, momentum, and energy. It is shown that this “λ model” gives a consistent description of both pressure flow and self-diffusion, which is not the case for the BGK kinetic model. In addition, the slip coefficient has a value which is 8% larger than for the BGK model.
Heat Transfer to Cylinders in Binary Gas Mixtures
Authors: Baccaglini G. , Miller David R. , Libby Paul A.
Published: February 2004

Further experimental and theoretical work on the heat loss from cylinders in flows involving low Reynolds number and binary mixtures is presented. In the experimental work techniques used previously are applied to a pair of monatomic gases, helium-argon, so that the possible role of internal energy, as might arise when nitrogen is a participant, is clarified. The theoretical work involves an extension of the Lees-Liu moment method to binary mixtures and application thereof to explain the observed slip effects when one gas component is of low molecular weight. It is shown that an earlier conjecture, namely, that a nonequilibrium thermodynamic behavior is involved, is correct.
Departure from Translational Equilibrium in a Low Density Source Flow
Authors: Chen T. Y. , Cheng H. K.
Published: February 2004

A more complete solution for the near-equilibrium, supersonic region of a spherical source flow of a monatomic gas is presented. On the basis of this solution, a method for computing meaningful reference quantities from measured data for temperature-freezing studies is provided. The analysis brings out an explicit dependence of the Navier-Stokes/Fourier correlations on the anisotropy, also clarifies the relationship between integration constants and reference conditions. While the degree of anisotropy generally increases with radial distance, the difference between radial and transverse stresses reaches a local maximum in the supersonic region.
Shock-Tube Measurements of Rotational Relaxation in Hydrogen
Authors: Boitnott C. A. , Warder R. C.
Published: February 2004

Density profiles in hydrogen shock waves have been measured with an electron beam densitometer for Mach numbers from 1.2 to 3.0. The translational and rotational relaxation processes were found to be uncoupled in the shock wave allowing for a simple determination of the relatively large (from ∼270 to ∼30) number of collisions required for equilibration of the rotational degrees of freedom over the temperature range from 410-1240 °K. An intermediate relaxation point and subsequent increase in the number of collisions required above 600 °K was attributed to the participation of additional excited rotational quantum levels in the equilibration process.
Flow Properties of a Partially Ionized Free Jet Expansion
Authors: Fraser R. B. , Robben F. , Talbot L.
Published: February 2004

Diagnostic studies were carried out in an induction-heated low-density supersonic plasma jet. The neutral number densities were obtained from the calibrated intensity of the 4609-Å argon II line excited by a 25-kV electron beam, and the velocities and heavy particle temperatures were determined by measuring the Doppler shift and Doppler broadening with a Fabry-Perot interferometer in two linearly independent directions, following a technique developed by Muntz. The contribution to the 4609-Å line due to the plasma self-emission was found to be negligible. The density, impact pressure, and velocity along the free jet center line all followed the isentropic source flow model up to the Mach disc. The temperature, however, showed an unexpected rise above the isentropic prediction. Ion number densities and electron temperatures were measured with a double Langmuir probe. The fraction of ionization was frozen at about 0.1% along the free jet axis. Calculations of the fraction of the energy of recombination absorbed by the electrons and the fraction lost by radiation from an electron energy balance showed good agreement with an a priori estimate based on collisional-radiative recombination.
Instability of One-Dimensional, Oblique, Magnetic Shock Structures
Authors: Wright Thomas P.
Published: February 2004

It is shown that the whistler and/or electron-cyclotron structures which have been observed in one-dimensional computer calculations are unstable to decay by resonant three-wave interaction. The perturbing waves propagate at an angle to the primary wave. The conditions for instability to occur and the pertinent growth rates are presented.
Ion Dynamics in a High-Voltage θ Pinch
Authors: Dove William F.
Published: February 2004

The interaction of low-initial-β hydrogen and argon plasmas with a fast rising magnetic piston [Ḃ(0) = 1.4×1010 G/sec] has been studied in a θ-pinch geometry. Doppler broadened and shifted line emission of ions and fast charge-exchange neutrals is used to determine the plasma dynamics. High Mach number flow (MA≥6) diffusion, and strong ion heating are observed. In addition, large Doppler shifted intensities indicate that ion reflection from the magnetic piston occurs giving velocities up to twice the piston velocity.
Numerical Solution of the Krook-Model Boltzmann Equation for a Plasma Diode
Authors: Whipple Elden C. , Parker Lee W.
Published: February 2004

The Boltzmann equations for both ions and electrons with the Krook collision model are solved self-consistently with Poisson's equation for a plasma diode by a discrete-ordinate technique. The charged-particle mean free path may be arbitrary compared to either the electrode spacing or the Debye length. Solutions for a diode with an electrode spacing that is both one ion mean free path (approximately 2−1/2 electron mean free paths) and one Debye length show that it is possible to fit the ion results by a solution of the diffusion-mobility equation with an appropriate extrapolated end point. The electron results may not be so fitted because of their large change in temperature. Results for an “electrons only” diode agree well with a computer simulation calculation by Burger. Some results are also presented for a potential well problem involving trapped orbits which can only be populated by collisions.
Calculation of Anomalous Resistance
Authors: Hamasaki S. , Davidson R. C. , Krall N. A.
Published: February 2004

The time development of a one-dimensional electron-positron plasma subjected to a weak applied electric field, E0 = const, is calculated through the quasilinear equations. The results are in good qualitative agreement with the computer simulation experiments of Boris et al.
Ion Acoustic Waves in a Multi-Ion Plasma
Authors: Fried Burton D. , White Roscoe B. , Samec Thomas K.
Published: February 2004

An exact treatment of the multispecies ion acoustic dispersion relation is given for an argon/helium plasma. Phase velocity and damping are obtained as a function of ion-electron temperature ratio and relative densities of the two species. There are two important modes in the plasma, with quite different phase velocities, which are referred to as principal heavy ion mode and principal light ion mode. Which of these is dominant depends on the relative densities of the two components, but, in general, the light ion mode becomes important for surprisingly small light ion contamination. Approximate analytic expressions are derived from damping rates and phase velocities and their domains of validity are investigated. Relevance of the results for the investigation of collisionless shocks is discussed.
Formation of Stationary Large Amplitude Waves in Plasmas
Authors: Manheimer Wallace M. , Flynn Robert W.
Published: February 2004

Several recent nonlinear theories of one-dimensional plasmas have suggested that a stable or unstable electrostatic wave can evolve into a Bernstein-Greene-Kruskal mode. Generally, the distribution function of the total energy of a particle is computed. The self-consistency of these computed distributions is examined here by solving Poisson's equation. It turns out that the system is self-consistent only if frequency shifts are incorporated in the theory.
Instantaneous Wave Emission Model
Authors: Kruer W. L.
Published: February 2004

A useful treatment of electrostatic wave emission by fast particles in a plasma is given. First, the potential due to a fast particle is expressed as a simple integration over the particle orbit; several interesting results readily follow. The potential in the wake of an accelerating particle is shown to be essentially that produced through local excitation of the plasma by the particle freely streaming about its instantaneous orbit. Application is made to one dimension, and it is shown that the wave emission and absorption synchronize to the instantaneous velocity distribution function. Guided by these calculations, a test particle model for computing the instantaneous wave emission by fast particles in a Vlasov plasma is then formulated. This model lends itself to physical interpretation and provides a direct approach to many problems. By adopting a Fokker-Planck description for the particle dynamics, the broadening of the wave-particle resonance due to velocity diffusion and drag is calculated. This calculation readily yields the synchronization of the wave emission to the instantaneous velocity distribution, and also shows that some important nonanalytic dependences, due to velocity diffusion and drag, are retained. Finally, the emission model is used to treat electrostatic wave scattering by fast particles. It is shown that nearly resonant particles give an enhanced scattering of the waves. The maximum enhancement is derived and physically explained, in both quasilinear and strong trapping limits.
Drift Instability in Collisionless Alkali Metal Plasmas
Authors: Politzer Peter A.
Published: February 2004

Measurements of low-frequency (ω≪Ωi) oscillations in collisionless, low-β, alkali metal Q-device plasmas are reported. These oscillations are conclusively identified as density-gradient-driven drift waves by the agreement between experiment and the predictions of the linear theory with regard to frequency, wave-number, and stabilization by ion Landau damping. The linear theory of collisionless drift waves is modified to take into account effects of cylindrical geometry. Also considered are radial gradients in the zero-order diamagnetic drift and plasma rotation frequencies. The enhancement of resonant particle effects by the finite length of the plasma column is computed. The occurrence of discrete radial eigenfunctions is found to depend on the radial variation of the equilibrium plasma potential. The observed dependence of amplitude on r agrees with that predicted by the theory. The experimental results demonstrate the importance of centrifugal and Coriolis force effects in determining the oscillation frequency. Finally, the transition between collisionless and collision dominated drift waves is explored, and the relationship between the observed amplitudes and the predictions of several nonlinear theories is examined.
Nonlinear Theory of the Cross-Field Instability—Explosive Mode Coupling
Authors: Sato Tetsuya
Published: February 2004

Nonlinear evolution of low frequency drift waves in weakly ionized plasmas is investigated, including the quasilinear and mode coupling effects. An equation governing the development of these waves is presented in terms of an external parameter (electric field) under appropriate assumptions. The equation states that the plasma system experiences two types of transition when one increases the external parameter from zero to infinity. Below a certain value of the parameter any perturbations are stabilized, but at the critical point the system makes a soft-type transition and an unstable drift mode is excited which finally reaches a finite amplitude. When the parameter is increased beyond the critical point, the system sees another transition point beyond which the unstable mode can no longer remain a finite amplitude but diverges within a finite time; this implies an explosive instability. This explosive transition is caused by the mode coupling process which acts to destabilize the initially unstable (linear) mode. It is inferred thereby that in the real plasma a strong turbulence is realized in which a number of modes are strongly excited and interact with each other.
Parametric Oscillations of a Hot Magnetized Plasma
Authors: Bajwa G. S. , Srivastava K. M.
Published: February 2004

The parametric excitation of a hot plasma subjected to an externally imposed spatially uniform electric field and to a constant uniform magnetic field have been considered. For transverse propagations perpendicular to the applied electric field, it is found that instabilities may occur for frequency ω+nν≈ω0 where ω0 and ν are, respectively, the plasma frequency and the electric field frequency.
Electron Cyclotron Electromagnetic Instabilities in Weakly Relativistic Plasmas
Authors: Jacquinot J. , Leloup C.
Published: February 2004

The relativistic dispersion relation of whistlers is solved for weakly relativistic plasmas. The solution takes into account various deviations from a Maxwellian distribution found in laboratory plasmas, namely, pressure anisotropy, loss cone, and cold plasma. The relativistic effects are shown to be strongly stabilizing even for low temperature plasmas when the density is such that ωp2/ωc2≪0.25. The spectrum of unstable waves is also shifted toward smaller frequencies.
Experimental Observations of Half-Harmonic Instabilities in Hot-Electron Plasmas
Authors: Wagner C. E. , Lidsky L. M. , Blanken R. A.
Published: February 2004

The fluctuation spectrum of a two-component, hot electron plasma generated by a beam-plasma interaction in a magnetic mirror was investigated. The unstable waves were studied with specially constructed high-frequency, impedance matched probes. Correlation studies show that the wavenumbers of the unstable modes satisfy k⊥ae∼k‖ae∼1. The observed unstable frequencies (ω∼0.7ωce) and wavenumbers are in good agreement with those predicted by half-harmonic electrostatic instability in a two-component electron plasma driven by the temperature anisotropy of the hot component.