bluuebunny/crossref_metadata_2025 huggingface dataset:
Electric Arc-Driven Shock Tube
Authors: Camm John C. , Rose Peter H.
Published: December 2004

A shock tube has been developed capable of producing a gas sample of known conditions by shocks with velocities as high as 43 000 ft/sec. The driver of this shock tube employs a capacitor bank which discharges electrical energy into helium, heating the helium to temperatures of 10 000–20 000 °K, and raising the pressure to 10 000–20 000 psi. The high-pressure bursts the scribed diaphragm and the resulting shock wave propagates into the test gas. Diagnostic techniques have been employed to investigate the resulting hot gas sample. The growth of this sample has been observed optically and correlations have been achieved with theoretical calculations. The observed radiation has been compared with and can be used to extend the known radiative properties of high temperature air. Time-resolved luminous pictures and spectra have also been taken to show the purity of the test gas. The speed and attenuation of the shock front have been measured. The observed operation of this shock tube has been compared with theoretical predictions, and although no precise correlation can be made, the driver gas energy transfer and losses in the shock tube boundary layer can be accounted for.
Boundary Effects in Viscous Rotating Plasmas
Authors: Kunkel Wulf B. , Baker William R. , Bratenahl Alexander , Halbach Klaus
Published: December 2004

The problem of current continuity and viscous drag at the boundaries in rotating-plasma experiments is discussed. We particularly emphasize a hypothetical model having a steady state with axial symmetry; it is shown that the discharge impedance derived from this model does not agree with many observations. The ``Homopolar III'' experiment is described in which the flux surfaces were strongly convex and parallel to the toroidal-shaped electrodes. In this way, friction at the insulators was reduced. But the structure of the discharge deviated drastically from axial symmetry near the outer surface. Several studies led to the conclusion that the flow pattern probably involved secondary flows. It was also found that the rotational speed could not be raised above a few cm/μsec because the insulators failed in spite of the special design of the experiment.
Plasma Instabilities Induced by Resistivity Gradients
Authors: Woods L. C.
Published: December 2004

Plasma instabilities arising from a radial gradient in resistivity are investigated for incompressible motions of a magnetized, cylindrical plasma. Hydromagnetic waves moving along an axial magnetic field B0 are normally damped by resistivity 1/σ. However if 1/σ varies with radial distance r, it is found that the resistive damping ε is reduced by a term proportional to d(1/σ)/dr = (1/σ)′. If in addition there is a small axial current j0, ε is further reduced by a term ∝ δ(1/σ)′, where δ=μj0/B0. For certain waves the direct damping is negligible, whereas the term involving δ(1/σ)′ is not, with the consequence that these waves are unstable. These unstable hydromagnetic waves occur when either the ion-cyclotron frequency is much less than vA(k2+kc2)1/2, where vA is the Alfvén speed, and k, kc are the axial and radial wavenumbers, or when k is much less than kc, i.e., when the wavelength is much greater than the radius of the cylinder. Explicit formulas are given for the growth rates of the unstable waves. Kadomtsev's current-convective instabilities due to temperature perturbations are also obtained which thus also provides an extension of his work on rectangular plasma slabs to cylindrical plasmas.
Predictions of the Structure of Radiation-Resisted Shock Waves
Authors: Heaslet Max. A. , Baldwin Barrett S.
Published: December 2004

The continuum, inviscid-flow equations of gas dynamics are used to predict the effect of thermal radiation on the internal structure of a shock wave. Numerical solutions of the governing equations show that considerable variation in the nature of the temperature and velocity profiles occurs, depending on the magnitude of the over-all velocity change and the relative strengths of the radiative and convective energy fluxes. A unique feature of the work is the demonstration that, for a range of parametric values, discontinuities necessarily arise in the temperature and velocity profiles. The results include: (a) numerical integration of the basic equations for a representative range of parameters; (b) an analytic study of the equations by means of expansion procedures; (c) a study of the uniqueness of the solutions; (d) proof that previously published investigations cannot be generally applicable since they are restricted to continuous solutions; (e) prediction within a strong shock of a temperature maximum considerably larger than that corresponding to the Rankine-Hugoniot conditions.
One-Dimensional Magnetogasdynamic Flow with Wall Friction
Authors: Liu Ching Shi , Cambel Ali Bulent
Published: December 2004

The case of one-dimensional magnetogasdynamic flow under the influence of wall friction is investigated. In particular, the case of an infinitely conducting, compressible plasma is studied when the flow direction and the direction of the magnetic field are at right angles to one another. It is shown that all flow variables can be expressed as functions of the ratio of the local flow velocity to the Alfvén velocity. It is shown that the flow has a variety of regimes delineated by specific singularities and extremities. A typical magnetogasdynamic Fanno flow chart is presented and it is noted that the flow differs markedly from that encountered in classical gasdynamics.
New Approach to Irreversible Transport Phenomena in Plasma Dynamics
Authors: Résibois P.
Published: December 2004

A factorization theorem is demonstrated for special types of contributions to the time-dependent collision operator G00(τ) which plays a central role in the classical master equation derived by I. Prigogine and P. Résibois; this theorem expresses the mutual independence of two subgroups of particles when these groups are noninteracting with each other during a given time interval (τi, τj) of the collision process. The theorem is applied to rederive in a very direct way the kinetic equation of an homogeneous stable plasma, obtained first by R. Balescu. Other possible applications of the method are also discussed.
Analytic Solution of the Thermalization of a Fast Ion in a Plasma
Authors: Ree Francis H. , Kidder Ray E.
Published: December 2004

The coefficients of friction and dispersion that appear in the Fokker-Planck equation describing the thermalization of a test ion in a plasma are approximated. The approximation is valid when the speed of the test ion is less than the average speed of the plasma electrons, but large enough that the plasma electrons interact more strongly with the test ion than do the plasma ions. The resulting Fokker-Planck equation is solved to obtain an exact analytic expression for the time-dependent energy distribution function of the test ion. This distribution function is used to examine in detail the nature of the approach to equilibrium.
Effects of Added Hexapole Magnetic Fields and Preionization in Theta Pinch Experiments
Authors: Little E. M. , Quinn W. E.
Published: December 2004

A hexapole magnetic field has been superimposed on the fast magnetic mirror compression field of the Scylla III θ pinch in an attempt to stabilize an observed plasma instability. The instability is of the flute type with a superimposed rotation. The effect of the hexapole field on the plasma stability was studied with streak camera photography and through observation of the neutron emissions. Under certain conditions the hexapole ``stabilizing'' field has an observable effect on the instability. Its main effect is to symmetrize the rotation about the axis of the compression coil and to produce a delay in the onset of the instability. There is at most a small effect tending to symmetrize the time distribution of neutron emission and to increase the neutron yield.

An ionized deuterium plasma is produced by a fast, low energy capacitor bank coupled directly to the single-turn compression coil of the Scylla III device. The ``afterglow'' of this preionization discharge, uniformly permeated by a magnetic bias field B0, forms the initial condition for the application of the main magnetic compression field. The effect of the main compression field on the preionized plasma depends strongly on the B0 which exists in the plasma.
The Interchange Instability in the Stellarator
Authors: Kulsrud Russell M.
Published: December 2004

The interchange instability is studied in an equilibrium similar to that of a stellarator with helical windings, on the basis of the combined Maxwell and Vlasov equations in the limit of small particle gyration radii. However, the first correction in the size of these radii and its effect on the stability criterion is studied. It is found that, just as in the work of Rosenbluth, Krall, and Rostoker, the stability criterion may be expressed in terms of the growth rate sH of the zero-gyration-radius theory. The stability is always improved by this correction and the new stability criterion is given by sH/Ω < ma2/R2, where Ω is the ion gyration frequency, a the ion gyration radius, R the radius of the plasma, and m the azimuthal wavenumber. The zero-gyration-radius normal mode equation and growth rates are then found and these are applied to the special case of helical windings with trefoil symmetry. It is shown that even when the gyration radius is small its effect may be significant, in many cases increasing the plasma pressure which may be stably confined by a factor of 2 or more.
Curvature of Shock Fronts in Shock Tubes
Authors: De Boer P. C. T.
Published: December 2004

Hartunian's theory for the curvature of a shock wave progressing into quiescent gas near a wall is extended to the cases of two parallel walls, of a rectangular tube and of a circular tube. Shock curvature is considered as caused both by laminar and by turbulent boundary layers along the walls behind the shock. For a completely laminar boundary layer, the axial extent of the curved shock in the cases of two parallel walls and of a circular tube is found to be 0.760 and 0.783, respectively, of Hartunian's single wall result. The correction arising from the finite length of the boundary layer is calculated. This correction is found to be negligible provided the boundary layer length is larger than approximately one-half the distance between the walls. An estimate is presented for the correction arising from the flow behind the foot of the shock. This correction is of some importance at very low initial pressures. An approximate method is given to find the curvature of shock fronts which are followed by a relaxation region. The results obtained are in good agreement with the available experimental data.
Partition Functions and Thermodynamic Properties of Argon Plasma
Authors: Drellishak K. S. , Knopp C. F. , Cambel Ali Bulent
Published: December 2004

The equilibrium chemical composition and the thermodynamic properties of argon plasmas have been calculated for five pressures (0.1, 0.5, 1.0, 2.0, and 5.0 atm) at 100 K deg increments for the temperature range 5000° to 35 000°K. The argon plasma is assumed to be a perfect gas complex consisting of six components, namely electrons, argon atoms, and the first four argon ions. The partition functions for these have been calculated using tabulated data for observed atomic energy levels and estimated energies for energy levels which are predicted although not observed. The partition functions were terminated by application of the Debye cutoff criterion and a corresponding lowering of the ionization potential was included. The calculated data are presented in graphical form and the method followed in calculating the partition functions is evaluated.
Stimulated-Emission Effects in Hot Plasmas
Authors: McCumber D. E. , Platzman P. M.
Published: December 2004

Conditions are considered for which stimulated emission modifies the sharp-line electromagnetic radiation emitted from partially ionized heavy impurities in a hot plasma. Analysis of a simple model permits a semiquantitative estimate of the radiation enhancement and of the spectral modifications which accompany superradiance in actual systems.
Asymptotic Theory of Spherical Electrostatic Probes in a Slightly Ionized, Collision-Dominated Gas
Authors: Cohen Ira M.
Published: December 2004

The problem of an electrostatic probe in a dense, slightly ionized gas is treated by techniques of asymptotic analysis. In particular, the asymptotic limits ρp = rp/λd → ∞ and ε = T+/T− → 0 are treated in considerable detail. (rp, λd, T−, T+ are probe radius, Debye length, electron, and ion temperature, respectively.) Sample integral curves for electrostatic potential, ion and electron density are given. Probe characteristic curves for three values of ε (finite and small) and ρp (large) are also given. It is noted that these characteristics do not saturate for large probe potential because the influence of the probe is felt to very great distances from the probe; the shielding due to the space-charge sheath is incomplete.
Solution of the Vlasov Equations for a Plasma in an Externally Uniform Magnetic Field
Authors: Nicholson Richard B.
Published: December 2004

An exact solution of the collisionless Boltzmann equation is presented that describes a slab of plasma contained in a magnetic field that is uniform external to the slab. The magnetic field dips in the plasma due to the diamagnetic currents in the plasma sheath separating the region of nearly constant density from the vacuum region. The currents are given by the distribution functions for ions and electrons and the fields obey Maxwell's equations. The solution has the qualitative features of real collisionless laboratory plasma distributions. The problem of a cylindrical plasma with axial magnetic field is also treated, and a solution presented for a limiting case. The solution to the slab problem is charge neutral. The limiting case in the cylindrical problem is also charge neutral, but the general cylindrical problem is not, and contains radial electric fields. The solutions have the merit of being substantially more simple than others that have previously been found for the plasma sheath problem.
Potential Distribution Method in Equilibrium Statistical Mechanics
Authors: Jackson J. L. , Klein L. S.
Published: December 2004

A general statistical mechanical relationship between the chemical potential and the probability distribution function of the micropotential in a fluid at equilibrium is derived. It is applied to a plasma and a hard-sphere gas.
Finite Amplitude Effects in an Unstable Laminar Boundary Layer
Authors: Benney D. J.
Published: December 2004

The mean flows induced by the interaction of a two- and a three-dimensional wave are calculated for a profile consisting of two straight lines. Although this is a simplified model of an actual boundary layer, the results are consistent with the experimental work done at the National Bureau of Standards.
Fluid Dynamic Studies with a Magnetohydrodynamic Generator
Authors: Louis J. F. , Lothrop J. , Brogan T. R.
Published: December 2004

The results of a study of fluid mechanics of a large linear magnetohydrodynamic generator with a field strength of 33 000G are presented. The experiment was designed to fulfill three requirements; predominant Lorenz force, important Hall effects, and substantial changes in the electrical and thermodynamic properties of the gas.

Studies of the electrical properties of the fluid of the effects of the surface temperature and geometry of the electrodes are described. The performance of the generator is analyzed under varying conditions of mass flow, magnetic field, seed concentration, exhaust pressure and channel geometry. Finally a comparison between a simple theory and the experimental results shows good agreement, indicating the feasibility of predicting magnetohydrodynamic generator performance.
Thermal Relaxation in a One-Species, One-Dimensional Plasma
Authors: Dawson John M.
Published: December 2004

Kinetic theories for a one-species, one-dimensional plasma which take into account only two-particle correlations predict all stable distributions are time independent and there is no relaxation to a Maxwellian. This is investigated by numerical experiments on a one-dimensional plasma model where the initial distribution was square. The theory is verified in that it is found that the relaxation times goes like nD2 and appears to be caused by three-particle correlations. In addition to the slow relaxation an initial transient was found which lasted for a time of the order of 1/ωp and which is accounted for by an elementary theory.
Hydromagnetic Stability at a Fluid Velocity Discontinuity between Compressible Fluids
Authors: Fejer J. A.
Published: December 2004

Formal conditions are derived for the stability of a velocity discontinuity at a plane interface between two perfectly conducting, inviscid, compressible fluids, in the presence of uniform magnetic fields. Certain special cases, in which the stability conditions can be simplified, are discussed in detail. Previous results for incompressible fluids are rederived and it is shown that the introduction of a slight compressibility always reduces the stabilizing effect of magnetic fields. It is further shown that in two special cases the magnetic field required to stabilize an interface continues to increase with the introduction of more compressibility until it reaches a limiting value that is about twice as large as the value appropriate to incompressible fluids.
Velocity Correlations in Weak Turbulent Shear Flow
Authors: Fox Jay
Published: December 2004

Turbulent energy components in a uniform shear flow with weak, homogeneous turbulence are reported. These results complement Deissler's calculations for the case of initially isotropic turbulence and provide a complete description of the effects of the mean-velocity gradient.
Diffusion of Small Particles in a Nonuniform Atmosphere
Authors: Yu Kwang , Klein Milton M.
Published: December 2004

The downward motion of small particles in an isothermal turbulence-free atmosphere has been studied for the case of variable diffusion coefficient, utilizing two models. In the first of these, the diffusion coefficient has been taken as an exponential function of altitude, while in the second the variation has been assumed parabolic. Analytic solutions have been obtained for one dimension and three dimensions for both models. The calculations, which have been restricted to the exponential case, show the development of a profile of constant shape which moves with the same velocity, independent of the mass of the particles. These results, which are derivable from our solution, are in agreement with the numerical work of Banister and Davis. It is also shown that the qualitative nature of the results for late time is independent of the initial distribution.
Equilibrium and Stability of Plasma in Arbitrary Mirror Fields
Authors: Taylor J. B.
Published: December 2004

It is shown that an appropriate choice of variables can greatly simplify the discussion of equilibrium and stability of low-pressure plasma in arbitrary mirror fields. One specifies by α and β the line of force on which a particle is moving and also specifies its adiabatic invariants μ, J; the energy of the particle is then determined as a function K(μ, J, α, β) which plays the role of a Hamiltonian. Any equilibrium distribution can then be written in the form F {μ, J, K(α, β, μ, J)} and it is shown that a sufficient criterion for such distributions to be stable against interchanges is (∂F/∂K)μJ < 0. Necessary and sufficient criteria are also derived. When approached in this way, the exact form of the field configuration only enters the problem through the determination of the function K, which may be easily calculated. In general a comprehensive view of plasma behavior, convenient for the discussions of equilibrium, confinement and stability, can be obtained from the structure of the K(α, β, μ, J) = constant contours. An example of the application of this approach to a Ioffe stabilized mirror is described. This confirms the existence of stable plasma equilibria in this field configuration.
Plasma Stability Criteria from Conservation Laws
Authors: Oberman C. , Dawson J.
Published: December 2004

It is shown that the Penrose criteria for the existence of unstable electrostatic oscillations of a Vlasov plasma can be derived simply from the energy-momentum conservation laws applied to marginally unstable modes. These criteria also are obtained variationally as necessary conditions for instability by extremizing the possible motions which can convert kinetic energy into electric field energy.
Thermal Diffusion and Diffusion in Hydrogen-Krypton Mixtures
Authors: Mason E. A. , Islam M. , Weissman Stanley
Published: December 2004

Experimental measurements of thermal diffusion and diffusion over a temperature range of about 195° to 580°K are reported for the systems H2−85Kr, D2−85Kr, and T2−Kr, and are analyzed to obtain information on intermolecular forces. The measurements are discussed from three separate points of view: (1) their internal consistency within the framework of the Chapman-Enskog kinetic theory, without reference to any specific model of intermolecular forces; (2) the applicability of the 12–6 and exp-6 models of the intermolecular potential; (3) the accuracy of various combination rules used to estimate forces between pairs of unlike molecules. The measurements are shown to be theoretically consistent, but an unresolved discrepancy in the thermal diffusion of H2−85Kr between our work and that of Ghozlan prevents any firm conclusion being drawn on (2). The discrepancy is not too large to prevent some conclusions on (3), and it is found that the exp-6 combination rules work somewhat better than the 12–6 rules.
Theory of Radiation Emission and Absorption in Plasma
Authors: Dupree Thomas H.
Published: December 2004

Starting with the basic plasma kinetic equations correct to second order in the plasma parameter, general formulas for cyclotron and bremsstrahlung emission and absorption are derived. The theory provides a rigorous description of the interaction of plasma and radiation. At equilibrium, Kirchhoff's law is recovered and the theory reduces to previously derived results.
Normal Modes for Electrostatic Ion Waves in an Inhomogeneous Plasma
Authors: Chen Francis F.
Published: December 2004

The propagation of low-frequency electrostatic oscillations perpendicular to a density gradient in a low-density, fully ionized plasma in a strong magnetic field B is studied from the point of view of the linearized macroscopic equations. Two sets of waves are found in the limits where the electrons move freely along B or not at all along B. Among these are waves which travel at the electron and ion diamagnetic drift velocities, and a physical description of this phenomenon is given in terms of microscopic motions. The transition between these two sets of modes occurs at angles of propagation very close to 90° to B; to treat this region of angles one must take into account either the electron inertia or the plasma resistivity. Dispersion curves are given for this transition region. In addition, it is found that in a small range of angles one of the cyclotron waves and the wave traveling near the electron drift velocity are unstable and can be excited by the pressure gradient, even if no longitudinal currents exist in equilibrium.
General Analysis of the Stability of Superposed Fluids
Authors: Plesset Milton S. , Hsieh Din-Yu
Published: December 2004

An analysis is made of the stability of the interface between two compressible fluids in a gravity field when the fluids have translational velocities parallel to the interface. The effects of viscosity and surface tension are not included. The general dispersion relation is found to involve Whittaker functions and their first derivatives. Appropriate limits for these functions correspond to various physical conditions. The familiar Rayleigh-Taylor and Kelvin-Helmholtz criterions for stability are obtained in the incompressible limit. It is found that compressibility in the subsonic case decreases the range of stability. In the supersonic case, the stability found by Landau holds for only one disturbance mode. In general, stratification leads to instability of the interface for the supersonic case. A simple physical discussion of the Kelvin-Helmholtz stability problem for incompressible or compressible flow concludes the paper.
Velocity Profile and other Local Quantities in Free-Molecule Tube Flow
Authors: Sparrow E. M. , Haji-Sheikh A.
Published: December 2004

The distribution function at a point in a highly rarefied gas flow in a circular tube is shown to be made up of three parts which depend on whether reversed particle trajectories through the point strike the tube wall or pass into the chambers at the ends of the tube. The distribution function is applied to the calculation of the velocity profile development along the length of the tube. It is found that the most rapid changes in the velocity profile occur near the tube inlet. For longer tubes, there is a substantial length in which the velocity profile is fully developed. In general, the velocity profile is quite flat and this characteristic is accentuated for longer tubes. Some numerical information is also given for the distribution of the particle density throughout the flow. The determination of other local quantities is discussed and illustrated.
Production and Dissipation of Magnetic Energy by Differential Fluid Motions
Authors: Clark Alfred
Published: December 2004

An exact solution is given for the time-development of a magnetic field in a two-dimensional stagnation flow, with the field lines being in the plane of the flow and parallel to the stagnation plane. The solution is given for an arbitrary initial field, and several examples are discussed in detail. The flow tends to increase magnetic energy by stretching the field lines and also tends to accentuate spatial inhomogeneities of the field by compressing the length scale in a direction perpendicular to the stagnation plane. The results show that the combination of these two effects can lead to exceptionally high rates of dissipation of magnetic energy by Joule heating.
Longitudinal Instability in a Semi-Infinite Inhomogeneous Plasma
Authors: Pearlstein L. D.
Published: December 2004

The stability properties of a semi-infinite inhomogeneous electron plasma in a uniform positive background are examined by using the Vlasov approximation. It is assumed that the perfect absorbing plane at x = 0 is a cathode emitting electrons. It is shown that equilibrium solutions with an electron excess everywhere in the half plane are stable, whereas those solutions which exhibit a positive space charge are unstable provided the maximum accelerating potential is roughly greater than 5kT. The growth rates are on the order of (1/2π)(4πe2N/m)½.
Collective Oscillations in a Cold Plasma
Authors: Auer P. L. , Hurwitz H. , Miller R. D.
Published: December 2004

The collective motions of a fully ionized cold plasma in a uniform external magnetic field are treated by standard small amplitude theory. Finite temperature and collision effects are neglected. Specializing the analysis to a neutral plasma of uniform unperturbed density containing electrons and ions of one species, one obtains a dielectric tensor and dispersion relation which is a special example of results previously given by Aström. A detailed discussion of the exact dispersion relation is given for the entire frequency spectrum, and completeness theorems are presented with the aid of scalar potentials representing the electromagnetic field quantities. It is found that when the Alfvén dielectric constant α = 4πn(m + M)c2/B02 becomes comparable in magnitude to the ion-to-electron mass ratio, the plasma space charge may play an important role in determining the nature of collective oscillations. In particular, if the axial wavelength of the perturbation is sufficiently large, the singularities of the effective dielectric constant become displaced from the neighborhood of the particle cyclotron frequencies to hybrid frequencies, which, in the limit of high plasma density, become equal to the geometric mean of the cyclotron frequencies and the plasma frequency, respectively. The last two sections discuss particle orbits in idealized oscillatory modes and simplified boundary value problems associated with plasma resonance.
Film Flow from a Rotating Beaker of Helium II
Authors: Snyder H. A. , Donnelly R. J.
Published: December 2004

A cylindrical Pyrex beaker of internal radius 0.318 cm containing He II was rotated about its principal axis at angular velocities ranging from 4 to 220 radians per second. The film flow rate during rotation was compared with the stationary rate by observing the rate of fall of the meniscus in rotation and at rest. No change in film flow rate greater than the scatter of individual runs (±4%) was observed over the entire range of rotation speeds. Deliberate introduction of contamination increased the creep rate but did not otherwise alter the above conclusion. A number of subsidiary experiments necessary to confirm the main conclusions are discussed.
Relativistic Effects on Plasma Oscillations and Two-Stream Instability. II
Authors: Buti B.
Published: December 2004

The dispersion relations and the problem of the stability of two streams, in the presence of an external magnetic field, are discussed by using the general theory developed in an earlier paper [B. Buti, Phys. Fluids 6, 89 (1963).] For wave propagation parallel to the magnetic field, a relativistic Maxwellian distribution with mass motion is used; and for wave propagation in a direction perpendicular to the magnetic field, an isotropic non-Maxwellian distribution is employed. In the latter case, gaps in the frequency spectrum occur.
Lowering of the Ionization Energy for a Plasma in Thermodynamic Equilibrium
Authors: Ecker G. , Kröll W.
Published: December 2004

In a plasma the ionization energy is decreased due to the presence of the microfield. In the past several attempts have been made to calculate this effect. These calculations, which use statistical and thermodynamical procedures, give different results. They produce either a ``polarization term'' or a ``lattice term'' or both of them. Moreover there are quantitative discrepancies. The lowering of the ionization energy is here derived by a statistical method, which is physically conceivable. The results cover a wide density range below and above the so-called critical density. The new results are compared with the results of all earlier calculations and reveal the cause of their discrepancies.
Relativistic Effects on Plasma Oscillations and Two-Stream Instability. I
Authors: Buti B.
Published: December 2004

The general theory for high-temperature plasmas, in the presence of an external uniform magnetic field, is developed by means of a Laplace-transform technique. The dispersion relations for the longitudinal and the transverse oscillations, for a relativistic Maxwellian distribution with mass motion as well as for a non-Maxwellian distribution in the absence of magnetic field are derived. The stability of two streams is investigated in detail both in the nonrelativistic and in the extreme relativistic limits. The longitudinal and the transverse modes are uncoupled only when the stream velocity and the wave velocity are parallel.
Shock-Tube Study of the Termal Dissociation of Nitrogen
Authors: Cary Boyd
Published: December 2004

The dissociation of nitrogen behind shock waves has been studied over a temperature range of 6000 to 10 000°K. A time-resolved Mach-Zehnder interferometer measured the density profiles in the reaction zone. Rate expressions based on classical collision theory and the hydrodynamic constraint equations were used to fit the experimental profiles. Inferred rate constants are presented with N2, N, Ne, and Ar as third bodies. This work differs from previous studies of nitrogen in that a measurement of the forward dissociation rate was made in N2 with N2 as the third body and in that the new data indicates that N is about as effective a third body as N2. Vibrational relaxation data indicates that to a first approximation there is no significant coupling between vibrational relaxation and dissociation over the temperature range covered. Vibrational relaxation times in N2-Ne mixtures behind combustion driven shocks indicate that Ne is about 1.4 times as effective as N2 in vibrationally exciting N2, agreeing well with predictions of the Landau theory. This agreement between theory and experiment is just as good as that obtained for Ar utilizing pressure breaks, vindicating the combustion technique.
Constants of the Linearized Motion of Vlasov Plasmas
Authors: Case K. M.
Published: December 2004

It is shown that the constants of motion for a linearized plasma can, at least in simple cases, be characterized very much as in quantum mechanics. Thus a general constant is an arbitrary function (appropriately defined) of the transport operator while the useful constants are powers of that operator.
Dynamic Structure Factor of Dilute Gases in the Fokker-Planck Approximation
Authors: Yip Sidney , Ranganathan S.
Published: December 2004

Linear density response of a dilute gas is calculated using the Fokker-Planck kinetic equation. Exact results for the initial-value problem are compared with calculations based on single-relaxation kinetic models and on hydrodynamic equations. The distinction between collisions which relax the system to local equilibrium and those which relax the system to absolute equilibrium is emphasized. The relation of the dispersion equation in the Fokker-Planck description to that for Maxwell molecules is discussed.
Gas Dynamics with Nonequilibrium Radiative and Collisional Ionization
Authors: Clarke Joseph H. , Ferrari Carlo
Published: December 2004

The dynamics of a gas undergoing nonequilibrium ionization by both radiative (bound-free) and collisional transitions is formulated. Examination of the theory leads to a number of general deductions. The ionization rates and emission and absorption coefficients are all evaluated explicitly from statistical results available for the monatomic gas considered. This makes the problem concrete; one also sees that the approach for other cross sections, transitions, and gases would be analogous in most or many respects. It is shown that spectral complexities can sometimes be removed by expansion in terms of a large thermal parameter, and there emerges rationally a gas which is approximately gray above the edge frequency. The general theory is applied to the strong normal shock wave structured by the nonequilibrium ionization processes. The nature of this problem is examined, the complete structure is computed, the photoionization in the precursor portion of the shock structure is also determined according to the black-body emitter model for comparison, and the spectral as well as a directional approximation are assessed.
Stability of Frictionally-Heated Flow
Authors: Joseph Daniel D.
Published: December 2004

Extended results relative to the existence of a critical stress (a finite shear stress or pressure gradient above which fully-developed steady solutions do not exist) in Couette and Poiseuille motions are reported. The results apply to liquids under general thermal boundary conditions including a conduction-convection balance at the boundaries. A bound which gives a close a priori estimate of the value of the critical stress is developed. Stability characteristics of frictionally-heated Couette flow in the inviscid limit are specified. Below the critical stress the steady solutions are double-valued. The stress parameter first increases, then decreases, with increasing temperature. To the previously reported temperature instability on the second branch can be added a corresponding (inviscid) instability of the motion. On the first branch of the double-valued solution the flow is stable despite the presence of a single vorticity maximum at the channel center.
Self-Consistent-Field Approach to Turbulence Theory
Authors: Herring J. R.
Published: December 2004

A self-consistent-field type perturbation theory is developed to treat the dynamics of stationary and homogeneous turbulence. The method consists of expanding the full probability distribution function about the product of the exact univariate distributions of all the Fourier modes. The theory is used in second order to find expressions for the turbulent energy spectrum and associated response frequencies. The results for the energy spectrum are identical to a simplified form of the direct-interaction approximation of Kraichnan and closely resemble the results of the generalized randomphase approximation of Edwards. The relation of the present method to both the above approaches is discussed.
Flute Instabilities at Ion Gyrofrequency
Authors: Shima Yaakov , Fowler T. K.
Published: December 2004

Flute modes at the ion gyrofrequency, propagating perpendicular to the magnetic field, are considered. A dispersion relation for inhomogeneous plasmas is obtained from which density thresholds for instabilities are derived. Several plasma distributions are considered. For a loss cone in velocity space, as in mirror machines, the density threshold is given by (ωpi/ωi) ≈ (R/rli)¾. In the case of a plasma shell with a radial density proportional to r2 at r = 0, (ωpi/ωi) ≈ (R/rli)½. Here, ωpi is the ion plasma frequency, ωi is the ion gyrofrequency, R is the plasma radius, and rli is the ion gyroradius.
Current-Driven Instabilities in Configurations with Sheared Magnetic Fields
Authors: Coppi B.
Published: December 2004

A set of instabilities which are fastest in the weakly collisional regime, being slowed down by increasing electron-ion collisions, is presented. They take place in configurations having very low pressures, sheared magnetic field, and current flowing along it. These instabilities are driven by the transverse gradient of the longitudinal current, are connected with the effects of electron inertia, and characterized by two types of mode. Modes of one type are electrostatic and localized, having eddies of relatively short scale length, and exist for small and finite wavelengths. The other modes are nonelectrostatic, nonlocalized, and result from one which is singular in the hydromagnetic limit. These exist only for wavelengths of the order of the width of the plasma column, in which limit they are faster than the electrostatic type of modes. The relationship between these instabilities and the known ``tearing'' resistive mode is studied. The growth rate of this is, in fact, increased by ion-electron collisions and corresponds to transfer of magnetic energy into plasma kinetic energy by decoupling the motion of particles and lines of force. A brief discussion of experimental results offering indication for the modes discussed above is finally given.
Propagation and Reflection of Sound in Rarefied Gases. I. Theoretical
Authors: Maidanik Gideon , Fox Herbert L. , Heckl Manfred
Published: December 2004

An analysis of sound propagation in rarefied gases is presented. The analysis emphasizes molecular surface interactions with solid boundaries, and the feasibility of their study by acoustical means. A semiphenomenological theory is developed for the regime in which molecular-surface interactions dominate. Dispersion relations are obtained which agree with experiments.
Formation of a High-Density Deuterium Plasma Focus
Authors: Mather J. W.
Published: December 2004

During the early investigation of the high-energy, low-pressure mode of a coaxial hydromagnetic gun, a second mode of action was established for large gas fillings. This particular mode, previously reported was found to lead to a high-density plasma focus situated at a distance ∼1–1.5 cm beyond the face of the center electrode. The plasma focus has the following properties; particle density ρ ∼ 2–3 × 1019/cm3, temperature T ∼ 1–3 keV, time duration t ∼ 0.2–0.3 μsec, and volume ∼15 mm3. Neutron yields >1010/burst and soft x rays are observed. These results are remarkably similar to those reported by Petrov et al. and Filippov et al. of the USSR using a metal wall pinch tube apparatus. The average velocity vz of the current sheath in the gun proper is found to depend on the fourth root of the applied voltage squares, divided by the mass density according to the simple ``snowplow'' ``M'' theory. The current sheath is found to be nonplanar and mass pickup by the advancing sheath is nonlinear with radius. The sudden collapse of the radial current sheath toward the axis at the center electrode end is most likely caused by the rapid conversion of stored magnetic energy into radial sheath motion (v̄r ∼ 3.5 × 107 cm/sec) forming in essence a super dense pinch effect.
Kinetic Theory of Dense Gases. V. Evaluation of the Second Transport Virial Coefficients
Authors: Hoffman David K. , Curtiss C. F.
Published: December 2004

Numerical calculations of the corrections to the second transport virial coefficients due to three-body collisions are made for a Lennard-Jones gas, neglecting the effect of bound states. These results are compared with experiment.
Implications of Experiments on the Weak Undular Bore
Authors: Sturtevant B.
Published: December 2004

The behavior of the nonlinear dispersive waves observed behind weak undular bores is studied using available experimental information. Calculations on cnoidal wave theory using the measured wavelengths and amplitudes lead to the unexpected result that in bore-fixed coordinates the energy and momentum of the flow under the waves are larger than in the upstream flow. This can only be due to the action in the experiments of the unsteady boundary layer on the channel bottom, for this boundary layer has a negative momentum thickness. Therefore, the dissipation near the front that is known to be a necessary condition for the existence of the steady periodic waves is shown to occur on the bottom of the channel.
Some Remarks on Plasma Oscillations and the Kinetic Theory of Plasmas
Authors: Su C. H.
Published: December 2004

In the linearized Vlasov's equation, the solution to the distribution function can be split into two parts. The one which takes the form of the free-particle propagation makes the neglected term in the linearized theory grow in t. A method of coping with such difficulty is suggested. The method is applied to some very simple cases where in the long time limit one needs a modification of the first-order distribution function, but not the first-order electric field. In general, it is believed that both these quantities have to be modified. The nature of higher-order corrections to the plasma kinetic equation is discussed. It is shown by the order of magnitude argument that the kinetic equation of a plasma cannot be extended beyond the first-order approximation with the adiabatic assumption of Bogoliubov.
Evidence of Anomalous Diffusion in a Radio-Frequency Discharge in a Magnetic Field
Authors: Powers E. J.
Published: December 2004

Experimental evidence of anomalous diffusion in argon and helium 29.3 Mc/sec rf discharges immersed in a static longitudinal magnetic field is described. It was observed that as the magnetic field is increased from zero, the rf voltage and power required to sustain a constant density discharge initially decrease but start to rise when a critical magnetic field Bc is reached. The rise is accompanied by a sudden onset of low-frequency fluctuations. The results are compared with those obtained by others for dc and ac discharges. In contrast to the ac experiments, where application of kilocycle and tens of kilocycle currents results in higher Bc than in the dc experiments, application of 29.3 Mc/sec currents results in the onset of an instability at lower magnetic fields.
Gaseous Diffusion in a Temperature Gradient
Authors: Mason E. A. , Weissman Stanley
Published: December 2004

The theory of diffusion in a temperature gradient has been tested by comparing the results of gas mixing experiments and gas unmixing experiments, the unmixing being caused by thermal diffusion. Both types of measurements have been carried out in the same apparatuses with the same temperature distributions, so that corrections cancel on taking ratios. Measurements are reported on H2-37Ar, H2-85Kr, D2-85Kr, T2-N2, T2-Kr, and T2-CO2 over a maximum temperature range of about 195° to 435°K. The theory is confirmed within experimental uncertainty, provided that account is taken of the variation of the thermal diffusion ratio during the course of the diffusion. The ratio of the experimental results to their theoretical predictions is 0.991 ± 0.023. It is therefore possible to make reliable measurements of diffusion coefficients in the presence of temperature gradients.
Nonthermal Properties of a Postshock Plasma
Authors: Michel F. C.
Published: December 2004

It is sometimes argued that either the electrons or ions get the majority of the thermal energy in a shock transition. The permissible ratio of electron to ion temperature in a postshock ``collisionless'' plasma is examined for a thermalized, preshock plasma. For weak shocks it is shown, from basic entropy considerations, that Te must equal Ti. It is argued that unless some special dissipation mechanism that applies only to strong shocks is postulated, the result Te = Ti may be generalized to the case of strong shocks.
Pressure Wave Generation in a Fissioning Gas. II. Effects of Dissociation and Multiphase Composition
Authors: Smith H. P. , Evans R. D. , Busch C. W. , Oppenheim A. K.
Published: December 2004

The analysis of pressure pulses which are generated in a fissioning gas by neutron irradiation is extended to the case of a dissociating medium including a condensed phase. After a satisfactory check of the process induced in boron trifluoride that was treated previously, the analysis is applied to borazine for which the former method would be quite inadequate since now the effects of dissociation, involving the formation of free liquid boron, become predominant in controlling the thermodynamic behavior of the substance.
Universal Instability in Complex Field Geometries
Authors: Krall Nicholas A. , Rosenbluth Marshall N.
Published: December 2004

An inhomogeneous collisionless plasma in a magnetic field B is unstable to an electrostatic oscillation propagating nearly perpendicular to B but with a large phase velocity parallel to B. We study the stability of this mode in a more complicated plasma equilibrium, including magnetic shear, finite plasma length, currents parallel to B, temperature gradients, and gravity-simulated magnetic cusp or mirror curvature. We find that many of these equilibria are stable to this mode, which has been misnamed a ``universal instability.''
Sustained Plasma Oscillations near the Crest of a Moving Striation
Authors: Swartz G. A. , Napoli L. S.
Published: December 2004

Plasma oscillations in the frequency range of 2 to 4 Gc/sec were observed with a radially directed probe in a tubular plasma column. The plasma oscillations, which are generated by application of a pulsed electric field at the plasma cathode or anode in an argon hot-cathode arc, are sustained for as long as 50 μsec after the pulsed field is removed. The oscillations occur near the crests of a moving striation. The plasma oscillations are associated with the striation and are most intense near the plasma anode. The frequency detected by the probe increases with increasing plasma density but is not related to the 300-G magnetic field which is applied parallel to the plasma column. The oscillations may be the result of the two-stream interaction of the plasma electrons with a group of high energy electrons associated with the striation.