bluuebunny/crossref_metadata_2025 huggingface dataset:
Kelvin-Helmholtz Instability for a Collisionless Plasma Model
Authors: Smith Craig G. , von Goeler S.
Published: February 2004

The dispersion relation of the Kelvin-Helmholtz instability due to a shear in ion fluid velocity parallel to the magnetic field is calculated from the Vlasov equation to account for effects of ion Landau damping and finite Larmor radius. Due to the relatively short wavelength parallel to the magnetic field, resonant particle effects are strong and the dispersion relation is considerably modified from that obtained by D'Angelo with a fluid treatment.
Nonlinear Development of the Two-Stream Instability
Authors: Freidberg J. P. , Armstrong T. P.
Published: February 2004

The nonlinear development of the two-stream instability is investigated analytically and numerically using as a model two cold interpenetrating electron and ion streams. When periodic boundary conditions are chosen so that only one linearly unstable wave is excited, it is found that whether or not the instability levels off nonlinearly before overtaking is directly dependent upon the choice of the spatially averaged electric field E0. Simple choices of E0 are given for stabilization and no stabilization. Also, even though there is strong nonlinear coupling, there is no continuous flow of energy into higher harmonics, for those waves which stabilize.
Fluid Equations for a Collisionless Plasma including Finite Ion Larmor Radius and Finite β Effects
Authors: Bowers E. , Haines M. G.
Published: February 2004

The distribution function is systematically expanded in the finite Larmor radius ordering scheme for a collisionless plasma in an axial magnetic field Bz(x, y, t), where the magnetic field variation is a direct result of finite plasma pressure (β ∼ 1). Fluid equations are evaluated in both the guiding-center frame and the center-of-mass frame. These equations are complicated by the velocity dependent ∇B drift which prevents strict closure of the moment equations. The effect of finite β is to include further terms in the stress tensor and in the energy equation in the form of a heat flux. An alternative derivation by a direct moment expansion is included. From these fluid equations the mechanism for producing radial differential rotation is rigorously shown. Secondly the stability of a rotating theta pinch is studied showing two finite β effects which can contribute to stability. The first is due to the increase in diamagnetic angular velocity (a result of creating a magnetic well) and the second due to the azimuthal equilibrium heat flow if the ion temperature decreases with radius.
Electromagnetic Microinstabilities of Plasmas in a Uniform Magnetic Induction
Authors: Hamasaki Seishi
Published: February 2004

Electromagnetic instabilities associated with transverse plasma waves propagating perpendicular to an external uniform magnetic induction B0 are investigated for a two-temperature Maxwellian distribution function. The analysis shows that no instability develops if V‖e2 < V⊥e2 where V‖e2 and V⊥e2 are the electron temperatures parallel and perpendicular to B0. For V‖e2 > V⊥e2 an instability develops if ωce2/ωpe2 < V‖e2/c2 [1 − (32)12 (V⊥e/V‖e)] where ωce and ωpe are the cyclotron and plasma frequency, respectively, and c is the velocity of light. The allowable frequency regions for this type of electromagnetic wave to exist across B0 are studied. It is found that below the plasma frequency there is always a narrow allowable frequency band just below any harmonics of the ion or electron cyclotron frequencies. Each width of the allowable frequency band is calculated.
Diffusion of Fast Electrons in Stochastic Magnetic Fields
Authors: Massel G. A. , Feix M. R.
Published: February 2004

The diffusion of fast electrons in a stochastic magnetic field is considered for the simple case of the fluctuating field parallel to the steady field. The assumption defining the fast electrons is that their particle velocity is greater than the phase velocity characteristic of the fluctuating field. In the limit of observation times greater than both the Larmor period and the correlation time of the stochastic field, the diffusion coefficient can be obtained explicitly as a function of the ratio of the correlation time to the Larmor period and the result holds for all values of the ratio of these characteristic times. The result and hence the assumptions in the derivation are checked by Monte Carlo calculations.
Current Decay in a Streaming Plasma due to Weak Turbulence
Authors: Ossakow Sidney L. , Fried Burton D.
Published: February 2004

A low-β plasma can stream across a “slab” of magnetic field provided the spatial extent L of the field along the streaming direction is small compared with the geometric mean cyclotron radius and provided the magnetic field is not too strong (ωce ≲ ωpc). The behavior of the plasma which emerges from the magnetic field region is discussed here. On a scale large compared with L, the effect of the magnetic field is simply to impart an impulsive transverse velocity to the electrons of the streaming plasma. If this velocity exceeds the stability limit for the two-stream instability, long-wavelength, longitudinal thermal fluctuations should grow to such an amplitude that the resulting weak turbulence reduces the transverse velocity to zero, the associated kinetic energy being converted to electron thermal energy. A solution to this problem within the quasilinear approximation for a “collisionless” plasma is given here, together with numerical calculations of the spatial decay of the current and the associated electron heating. As expected, the length of the turbulent transition region, in which the directed transverse energy is thermalized, is an increasing function of the initial plasma density, but a decreasing function of the initial electron temperature and transverse velocity. A small charge separation (ni − ni ≲ 10−4 ne) provides an electric field just sufficient to balance the pressure gradient, n dT / dx.
Fundamental Approach to High-Frequency Breakdown of Gases
Authors: Epstein Melvin , Lenander Carl J.
Published: February 2004

An evaluation has been made of the net ionization frequencies of air inferred from breakdown measurements. This has been accomplished by comparison of such data with the corresponding values obtained from numerical solutions of the Boltzmann equation. Good agreement is found at high pressures, but the comparison deteriorates with decreasing pressure. This trend is attributed to the use of the effective field concept and the absence of nonuniform field corrections in the processing of the experimental data. Calculations are presented that show that breakdown fields calculated with data obtained from solutions of the Boltzmann equation and combined with an appropriate nonuniform field analysis are in good agreement with experimentally measured breakdown fields. It is concluded that the latter approach provides a more rational and accurate method for predicting high-frequency breakdown than previously available methods.
Lagrangian Wiener-Hermite Expansion for Turbulence
Authors: Canavan G. H. , Leith C. E.
Published: February 2004

The use of an advected white noise base for a truncated expansion is shown to provide an approximation for turbulence which has the inviscid equipartition solution and is invariant to random Galilean transformations.
Viscous Flow in a Rectangular Cut Out
Authors: Ratkowsky D. A. , Rotem Z.
Published: February 2004

A new approximation method as applied to closed streamline flow in a rectangular cavity is described. The particular boundary condition of constant shear stress over the open end of the cavity is examined in detail.
Stability of an Unsymmetrical Plane Flow
Authors: Potter Merle C. , Smith Mahlon C.
Published: February 2004

The results show that the unsymmetrical flow is more stable than the symmetrical flow. An interesting feature of the unsymmetrical flow is the existence of two critical points in the neutral stability curve.
Double-Adiabatic, Hydromagnetic Equations for Electrons with Pressure Gradients
Authors: Abraham-Shrauner Barbara
Published: February 2004

Double-adiabatic hydromagnetic fluid equations for electrons and ions are given that reduce to the Chew-Goldberger-Low equations or adiabatic, nonlinear ion-acoustic equations in special cases.
New Kinetic Equation for Plasmas
Authors: Wigley T. M. L. , Green H. S.
Published: February 2004

A new form is derived for the plasma kinetic equation in which an operator replaces the distribuion function. Transport coefficients can be obtained by a method similar to that of Chapman and Enskog and, under certain conditions, an exact solution can be found.
Multifluid Theory for Stagnation Flow of Partially Ionized Plasma
Authors: Shelton G. A. , Touryan K. J. , Johnson D. H.
Published: February 2004

The profiles for the flow of ionized argon past a blunt body are obtained by employing a series truncation method to reduce the partial differential equations to ordinary differential equations and a band-matrix technique for numerical computations.
Parametric Study of Sheath-Boundary Interactions
Authors: Hassan H. A. , McDonald P. W.
Published: February 2004

A parametric study of the effects of emission, reflection, and surface ionization on the current densities and heat fluxes to a cathode is presented. The computations were carried out for cesium and argon assuming a tungsten electrode.
Nonexistence of Toroidal Plasma Equilibrium in Ring Devices with Conventional Supports
Authors: Yoshikawa S.
Published: February 2004

Multipole plasma confinement devices with conventional, magnetically shielded supports do not possess toroidal equilibria because the devices are no longer topological tori.
Interaction of Free-Surface Waves with Viscous Wakes
Authors: Lurye Jerome R.
Published: February 2004

A method of investigating the interaction of free-surface waves with viscous wakes is described. The method consists in constructing a viscous-wake solution to the Oseen equations that satisfies the three linearized free-surface conditions appropriate to a viscous fluid. The solution is characterized by a singularity which simulates approximately the effect of a body. More general flows of the same type can be formed by superposition. The solution obtained is believed to be the first one to represent explicitly a viscous wake in the presence of a free surface.
Stokes Paradox in Kinetic Theory
Authors: Cercignani Carlo
Published: February 2004

The flow past a solid body is analyzed by means of the Boltzmann equation. It is shown that for small Mach numbers a formal linearization is affected by the same difficulties as the Stokes linearization in continuum fluid mechanics. In particular, it is proved that the linearized Boltzmann equation does not provide bounded solutions for the flow past an axisymmetric body. As a consequence, an inner-outer expansion must be constructed, and the linearization is to be reinterpreted as the first step of the inner expansion; the outer one being very similar to the Hilbert and Chapman-Enskog expansions.
Kinetic Theory of Partially Ionized Gases
Authors: Yen James T.
Published: February 2004

An approach for evaluating the thirteen moments of the Boltzmann collision integral for electronion and electron-neutral collisions in an ionized gas is developed. It is an approximation based on the smallness of the electron mass and is different from the approach of Enskog, Chapman and Cowling, Grad, Burgers and others. The initial inspiration is conceived after a study of the works of Lorentz, Druyvesteyn, Davydov, Allis and others. With the new approach, it is easy to include even higher-order moments and to treat distribution functions which are not locally Maxwellian even in the zeroth order, as well as to study problems with large diffusion velocities and enhanced electron temperatures. The approach is valid, however, only for electron-ion and electron-neutral collisions. For these collisions, the thirteen-moments results agree with those of Burgers when the distribution functions are locally Maxwellian in the zeroth order and the electron temperatures is not enhanced. Application of the new approach to various problems is demonstrated.
Kinetic Theory of a Self-Gravitating Stellar System with Uniform Rotation
Authors: Wu C.-S.
Published: February 2004

A kinetic equation for a homogeneous and uniformly rotating stellar system is established, based on statistical theory. The theory includes both the effects of direct gravitational encounters and collective processes. The expressions for the dynamic friction and diffusion tensor are provided. Based on these results, characteristic relaxation times may be discussed readily.
Evolution of a System with a Random Hamiltonian
Authors: Kaufman Allan N.
Published: February 2004

An exact equation of evolution, with the structure of the diffusion equation, is derived for the phase-space probability density of a system whose Hamiltonian is random. No assumption need be made about the magnitude of the fluctuations nor about their time scale. In the limit of short correlation time and weak correlations, the equation reduces to the equation of Birmingham, Northrop, and Fälthammar. The reduction of the Fokker-Planck equation to diffusion form is also demonstrated.
Various Expressions of the Kinetic Equation for a Plasma
Authors: Aono Osamu
Published: February 2004

On the basis of the unified theory, it is proved that the four kinetic equations obtained by Kihara, Baldwin, Frieman and Book, and by Perkins are equivalent to each other and exact in the sense that the Coulomb logarithms with exact numerical factors in the arguments can be obtained by use of any one of them.
Aspects of Collisional Diffusion Transverse to a Stable Magnetic Plasma
Authors: Weinstock Jerome
Published: February 2004

An autocorrelation function method is given which permits one to treat, in a relatively simple and concise manner, some aspects of transverse diffusion in stable plasmas that are generally omitted or difficult to formulate by other methods. An expression for the transverse diffusion coefficient is thereby obtained which is valid under a wide set of circumstances including non-Maxwellian, but stable, velocity distributions, arbitrary ratio of gyrofrequency to collision frequency, and weakly nongyrotropic velocity distributions. It is also emphasized that the diffusion coefficient is not simply an eigenfunction of the collision operator, and the correction factors are explicitly given for magnetic non-Maxwellian plasmas.
Absorption of Electrostatic Waves by Plasma Electrons
Authors: Decker James F. , Hirshfield J. L.
Published: February 2004

Experimental observations with supporting theory are described of the energy exchange between a plasma column and an externally applied rf electric field that was nearly longitudinal. When electron collisions may be neglected and the wave-particle interaction can be considered weak, the frequency-dependent power absorption, as predicted by solution of the linearized Boltzmann equation, is a resonant process involving electrons having velocities near the phase velocity of the applied field. Similarities between absorption of rf energy in this experiment and collisionless absorption of electron plasma waves are evident, and the experimental results support the ideas of Landau damping. Application of “strong” rf fields to a drifting electron plasma produces a nonlinear deformation of the time-averaged distribution. Measurements of this deformation compare favorably with a quasilinear calculation for weak nonlinear behavior.
Numerical Investigation of Collisionless Compression of a Plasma with Anomalous Friction
Authors: Chodura R.
Published: February 2004

The effect of friction on the time development of the profile of a strong compression pulse propagating perpendicular to a magnetic field is studied in cylindrical geometry using two-fluid equations. The friction term roughly describes the action of a two-stream instability by limiting the electron velocity to a critical value. Depending on this critical value and on the ratio of electron inertial skin depth to initial plasma radius, the steepening process during compression may or may not lead to a discontinuity. The time history of the profiles and conditions for the occurrence of the discontinuity are investigated for the case that no magnetic field is initially present in the plasma.
Strong Negative-V" Torus
Authors: Furth Harold P. , Hartman Charles W.
Published: February 2004

The restriction of helical stellarator windings to the large-major-radius side of the torus minor circumference, combined with the use of an axisymmetric poloidal field, gives markedly improved negative-V" properties.
Free-Streaming and Spatial Landau Damping
Authors: Hirshfield J. L. , Jacob J. H.
Published: February 2004

The interpretation of experiments on the spatial Landau damping of an electrostatic disturbance is shown to be complicated by the contribution of the free-streaming, initially perturbed particles. In particular, unless measurements give the ratio of the imaginary part to the real part of the wave-number to be somewhat less than about 0.4, the observation may be explained using a simple model which neglects the mutual interaction between the plasma particles.
Supra-Luminous Waves and the Power Spectrum of an Isotropic, Homogeneous Plasma
Authors: Lerche I.
Published: February 2004

Using the collisionless Boltzmann equation, equations are set up to describe the electric field auto-correlation function of both longitudinal and tranverse waves in a three-dimensional homogeneous, isotropic plasma. The calculation is performed relativistically for mobile electrons and stationary ions and a general form for the power spectrum is derived. It is demonstrated that as well as the adiabatic power spectrum of Rostoker there are also contributions to the power from waves with phase velocities greater than the speed of light, which persist asymptotically in time. There are also “branch cut” contributions which decay in time and C○erenkov wake-background plasma contributions which possess zero energy density asymptotically but which mix the C○erenkov wakes of individual test particles with the supra-luminous wave contributions. This calculation suggests that, in an isotropic, collisionless plasma, the “memory” of the plasma may be many orders of magnitude larger than the Landau damping time.
Longitudinal Oscillations in Bounded One-Dimensional Nonuniform Plasmas
Authors: Harker K. J. , Kino G. S. , Eitelbach D. L.
Published: February 2004

A study has been made of the longitudinal oscillations in a one-dimensional nonuniform plasma bounded by specularly reflecting walls. The nonuniformity is assumed to arise from a parabolic shaped static potential distribution. Static magnetic fields are not included. Using Maxwell's equations and the linearized Boltzmann-Vlasov equation, a linear integral equation for the longitudinal electric field is derived. This equation is solved numerically to yield the frequencies and damping rates of the various modes of the plasma. An alternative solution is obtained by using the continuum model. Comparison of results obtained by both methods shows good agreement, in contrast to earlier results for an infinite plasma, for which the agreement was poor.
Production of Negative Eddy Conductivities and Viscosities in the Presence of Buoyancy and Shear
Authors: Deissler R. G.
Published: February 2004

An analysis of weak turbulence indicates that under certain stabilizing conditions, the eddy conductivity and viscosity can become negative. It is shown that for the model considered, the occurrence of the negative values depends on the fact that the turbulence decays with time.
Laser Doppler Velocimeter for Measuring Flow-Velocity Fluctuations
Authors: Lewis R. D. , Foreman J. W. , Watson H. J. , Thornton J. R.
Published: February 2004

Instantaneous flow velocities in an unsteady liquid flow have been measured using optical heterodyning techniques. Flow in the transition region, as well as fully developed turbulence, was measured and compared with existing data and theory.
Turbulent Spectra from the Kraichnan-Spiegel Approximation
Authors: Walton John J.
Published: February 2004

Both stationary and decaying turbulent spectra are obtained using the two-point approximation for inertial energy transport due to Kraichnan-Spiegel, for a particular form of the interaction function.
Viscous and Joule Heating Effects on the Heat Transfer from a Flat Plate
Authors: Fillo John A.
Published: February 2004

In addition to reducing the local heat flux, the effect of the magnetic field (Joule plus viscous heating) is to make heat flow from wall to fluid or in the reverse direction for smaller temperature differences between the wall and free stream.
Comparison between Arc-Driven and Pressure-Driven Shock Tubes
Authors: Radcliffe S. W. , Hobson R. M.
Published: February 2004

A direct comparison is reported between the shocked gases generated by an arc-heated driver and a pressure driver operating in the same downstream conditions, from 0.5 to 3 Torr, and shock Mach number range from 8-17.
Kinetic Theory of the Transient Couette Flow Problem
Authors: Huang A. B. , Giddens D. P.
Published: February 2004

The discrete ordinate method is used to solve the linearized Bhatnagar-Gross-Krook Boltzmann equation for the transient Couette flow problem. Of particular interest is the velocity “overshoot” at the wall which occurs for d/μ < 2.
Fifth and Sixth Approximations to the Electron Transport Coefficients
Authors: Li C. P. , Devoto R. S.
Published: February 2004

Expressions are given for the fifth and sixth Chapman-Enskog-Burnett approximations to the electron contributions to the transport coefficients of ionized multicomponent mixtures.
Interaction between a Steady-State Plasma and a Magnetic Field
Authors: Kim Nak Nien , Singer Stanley
Published: February 2004

The interaction of a plasma with 5 × 1013 proton/cm3 at a velocity of 2 × 106cm/sec and a dipole magnetic field of 130 G is studied. The magnetic pressure of this field approximately balances the pressure of the plasma at about 7 cm from the center of the dipole.
Propagation of Transverse Electromagnetic Waves in a Magnetized Laboratory Plasma
Authors: Brand G. F. , Hooker C. A.
Published: February 2004

The collisional, cold plasma, dispersion relation adequately describes the propagation of electromagnetic waves along the magnetic field in a laboratory plasma. The collision frequency is estimated and its linear dependence on electron density is demonstrated by a new method.
Reflection and Transmission of Waves from Magnetized Nonuniform Plasma Slabs
Authors: Kuehl H. H.
Published: February 2004

A theory is outlined which gives the reflection and transmission coefficients for a transverse wave, with propagation direction and electric field perpendicular to the static magnetic field, incident on a thin nonuniform plasma slab.
Relativistic Correction to Plasma Bremsstrahlung
Authors: Quigg Chris
Published: February 2004

A simple relativistic correction to the electron-ion bremsstrahlung spectrum from a Maxwell-Boltzmann plasma is reported. The need for, and accuracy of, the correction are briefly noted.
Pressure Measurements in Subcritical Pure Superfluid Helium Flow
Authors: Corke Henry E. , Hildebrandt Alvin F.
Published: February 2004

The measurement of pressure in He II with flowing superfluid superimposed in a stationary normal fluid was undertaken to demonstrate ideal fluid character of the superfluid below critical velocities. Quantitative agreement with Euler's equation with zero curl is shown with slip-flow boundary conditions. Thus, Bernoulli's equation holds for potential flow and superfluid accelerations occur without dissipation. The method of pressure measurement demonstrates that net forces on an object in non-uniform potential flow can be measured.
Effects of Surface Curvature and Property Variation on Cellular Convection
Authors: Davis Stephen H. , Segel Lee A.
Published: February 2004

For a fluid layer heated from below, a calculation is made of the nonlinear effect of surface curvature which turns out to be of the same type as the non-Boussinesq effect. Results are given for the effects of variable fluid properties.
Fluid Motion Induced by Surface-Tension Variation
Authors: Yih Chia-Shun
Published: February 2004

Fluid motion in a long straight channel induced by longitudinally varying surface tension has been discussed by Levich. This problem is re-examined and a different solution is given. In addition, the stability of laminar flows involving surface-tension variation is briefly discussed, and a correction of a previous result [C.-S. Yih, J. Fluid Mech. 28, 493 (1967)] is made.
Application of the Nocilla Wall Reflection Model to Free-Molecule Kinetic Theory
Authors: Hurlbut F. C. , Sherman F. S.
Published: February 2004

The Nocilla wall reflection model has been applied in the calculation of coefficients for aerodynamic lift and drag for simple shapes in free-molecule flows. The desirability of a model more general than the Maxwellian re-emission model is underscored through a brief discussion of recent experimental results. This discussion also serves as a guide for the selection of parameters essential to the present calculations. The Nocilla model is shown to constitute a formalism within which the free-molecule kinetic theory can be carried forward with comparative ease. Normal and tangential momentum transfer are calculated on a mutually consistent basis and thermal accommodation is introduced in a manner which is consistent with the sources of such information relevant to highly directed flows.
Effect of Gas–Surface Interaction on Sound Propagation in Highly Rarefied Gases
Authors: Toba K.
Published: February 2004

Previous theoretical investigation of sound propagation in rarefied gases is clarified and extended with emphasis on the role played by gas–surface interaction effects. The problem is formulated for the case of one-dimensional motion generated by a piston undergoing small amplitude sinusoidal oscillation where the Knudsen number based on the distance from the piston is large. The resulting dispersive properties such as phase velocity and attenuation rate are in qualitative agreement with experimental data and previous theoretical predictions. However, the dependence of dispersion on the molecule–surface interaction is found to be quantitatively different from that suggested by earlier investigators.
Matrix Elements of the Linearized Collision Operator
Authors: Ford G. W.
Published: February 2004

The matrix elements of the linearized Boltzmann collision operator with respect to the Burnett functions are constructed for arbitrary power law potentials. The result of Mott-Smith for elastic spheres appears as a special case.
Class of Exact Solutions of the Magnetohydrodynamic Equations
Authors: Wang Chang-Yi
Published: February 2004

A class of exact solutions of the full, viscous magnetohydrodynamic equations are generalized. This class of solutions has the property that the nonlinear terms in the governing equations are not zero identically but as a whole they cancel each other such that the remainder is linear and solvable. The governing equations are formulated using general orthogonal coordinates. Examples in Cartesian coordinates are illustrated. These exact solutions represent a wide variety of flows with probable astrophysical or engineering applications. In each case, the velocity field and the magnetic field are completely coupled.
Thermonuclear Detonation Wave Structure
Authors: Fuller Ann L. , Gross Robert A.
Published: February 2004

The structure of a very strong detonation wave (a shock wave followed by a thermonuclear reaction zone) propagating through a deuterium-tritium gas mixture is studied. The shock is sufficiently strong so that it heats the gas to a temperature at which thermonuclear reaction probabilities are large. The characteristic times for collisions and reactions are examined to determine when the von Neumann-Zeldovich model (separate shock and reaction zone) of detonation structure is applicable. Appropriate nuclear reaction kinetics equations are developed for the reaction zone and the effect of energy loss due to bremsstrahlung is included in the analysis. A set of wave structure equations is derived and solved numerically for several different cases. The physical effects expected from a laboratory fast-shock experiment are examined briefly.
Stability of Density Waves in a Self-Gravitating Stellar System with Uniform Rotation
Authors: Wu C. -S.
Published: February 2004

The collective processes in a self-gravitating system with uniform rotation are studied with particular emphasis on the stability of density waves. In addition to the classical Jeans instability, it is shown that the so-called microinstability can also exist if the distribution is anisotropic and β ≡ longitudinal dispersion speedtransverse dispersion speed < (|1 −22|)12 ≃ 0.54. The critical wavelength is calculated as a function of β for nearly transversely propagated modes and is also estimated for the case that waves have arbitrary propagation direction and long wavelength. Finally, the stability of density waves associated with a system in the presence of the Kapteyn-Eddington star stream is examined.
Nonlinear Effects in the Propagation of Large-Amplitude Alfvén Waves in a Laboratory Plasma
Authors: Cross R. C. , Watson-Munro C. N.
Published: February 2004

In a cylindrical hydrogenous laboratory plasma source of diameter 21 cm and length 170 cm, the propagation of Alfvén torsional waves of azimuthal wave field bθ, propagating parallel to a steady magnetic field B0 in the z direction, have been studied. The perturbation ratio bθ/B0 has been increased to values as high as 2.6 and found that: (a) As the perturbation ratio is increased the wave rapidly steepens into a shock wave, but at perturbation ratios in excess of 1.2 there is no further reduction in the rise time of the leading edge. (b) The Alfvén Mach number shows a marked reduction in rate of increase at this perturbation ratio. (c) The attenuation of the wave increases rapidly at this perturbation ratio. (d) There is some evidence of the attenuation energy being expended in particle heating and in the development of a higher-frequency magnetoacoustic wave traveling radially outwards in the plasma.
Alfvén Waves in the Solar Wind
Authors: Unti Theodore W. J. , Neugebauer Marcia
Published: February 2004

Mariner II plasma and magnetic-field data are examined for explicit examples of low-frequency hydromagnetic waves. From the magnetic-field data, several sinusoidal waveforms are isolated. One of these clearly satisfies the hydromagnetic equations relating the magnetic-field variation to the ion-velocity perturbation for an Alfvén wave. This result is consistent with Barnes' theoretical prediction that only the Alfvén mode is not strongly damped in a plasma of moderate or high β.
Drift Instabilities in General Magnetic Field Configurations
Authors: Rutherford P. H. , Frieman E. A.
Published: February 2004

A theory of low-frequency drift (universal) instabilities in a nonuniform collisionless plasma is developed for general magnetic field configurations including trapped particle effects, rather than the plane geometry which has previously received most attention. A type of energy principle shows that the special equilibrium distribution F(∈, μ), of interest in minimum-B mirror configurations, is absolutely stable to these modes provided ∂F/∂∈ < 0 together with a second condition on ∂F/∂μ. For equilibrium distributions not of this special form, in particular for a Maxwell distribution with a density gradient, the case of axisymmetric toroidal configurations with closed poloidal field lines is considered in detail. Three unstable drift modes are found, a flute-like mode, a drift-ballooning mode local to the region of unfavorable curvature, and a drift-universal mode. Stability criteria and growth rates for the modes are given. The equations also describe a recently discussed low-frequency trapped-particle instability.
Local Determination of the Wave-Particle Interaction in Weakly Turbulent Plasmas
Authors: Aamodt R. E.
Published: February 2004

The nonlinear effects in weakly turbulent plasmas in the region of particle-wave resonance are shown to be derivable by determining the response of the plasma to an infinitesimal test wave. The local solutions of the test-wave responses are examined and the smearing of the particle-wave resonances and the resulting change in the dispersion relation for the gentle bump instability are determined. The lowest-order nonlinear transport equation is derived and applied to a weak homogeneous beam.
Stochastic Approach to the Theory of Fluctuations in Plasmas
Authors: Osborn R. K.
Published: February 2004

A stochastic (in contrast to kinetic theoretic) approach to the calculation of correlation functions in fully ionized plasmas is investigated. Formally different results are obtained. The question as to whether or not the differences are qualitatively and/or quantitatively significant is raised, but not answered.
Experiments on Shock Formation in a Q-Device
Authors: Andersen H. K. , D'Angelo N. , Michelsen P. , Nielsen P.
Published: February 2004

Experiments on shock formation in a Q-device are described. For equal ion and electron temperatures, Ti = Te, Landau damping prevents shock formation. When the ratio TeTi is made as large as 3-4 through ion-neutral atom collisions, shock formation is observed.
Characteristics of the Dense Plasma Focus Discharge
Authors: Mather Joseph W. , Bottoms Paul J.
Published: February 2004

The dense plasma focus discharge is produced in a hydromagnetic coaxial plasma accelerator. The final heating and compression of the plasma is accomplished by a partial conversion of the stored magnetic energy residing in the region behind the current sheath to plasma energy. The electrical behavior of the discharge is examined to determine the fraction of the initial energy involved in mechanical sheath motion, inductive storage in the accelerator, and Ohmic losses associated with the external and plasma discharge. Many analysis of this kind of datum show no definite correlation between the energy converted and neutron production. Presumably this arises from a lack of information as to how the collapse uses this energy and to the amount of plasma ejected from the dense plasma region during the collapse. From soft x-ray pinhole and Schlieren photographs, the collapse and the development of the dense plasma is unquestionably a two-dimensional pinch compression.
Analysis of a Rotating Plasma Experiment
Authors: Sockol Peter M.
Published: February 2004

In experiments with a homopolar device Fahleson has observed that for low values of the discharge current the voltage drop across the plasma is proportional to the magnetic field and independent of the current and pressure. The rotational velocity corresponds to a kinetic energy for the ions equal to the ionization potential of the gas. These experiments have been analyzed using a steady-state continuum model of the flow in which the bulk of the gas rotates at a uniform velocity and the current is confined to thin Hartmann boundary layers on the end-walls. The voltage drop has been calculated as a function of current, pressure, magnetic field, and atomic species. The dependence on these parameters is in good agreement with the measurements under all conditions, while the magnitude of the voltage is generally smaller than the observed value by a factor of 2.
Investigations on the Drift of a Plasma Ring in a Toroidal Magnetic Field
Authors: Junker J.
Published: February 2004

A plasma ring confined by a toroidal magnetic field drifts outward in a radial direction. This drift is caused by an acceleration proportional to an average plasma temperature. Measuring this temperature spectroscopically using the Hβ line intensity and the intensity of a continuum interval allows us to calculate the acceleration. Integrating this acceleration twice with respect to time yields the motion of the meridional center of mass of the plasma. The drift motion obtained in this way is compared with the motion directly observed by smear photographs. Within the margins of error of the temperature determination both results give the same drift motion. As a consequence of successive compression and decompression of the plasma ring, magnetohydrodynamic theory shows an oscillating motion of the plasma center in the meridional plane in addition to the gross drift motion. This oscillation can be observed and agrees well in phase but not in amplitude with the theoretical results. The investigations described here were conducted on a toroidal θ-pinch plasma in a tube with a major diameter of 50 cm and a minor diameter of 6 cm. The preionized plasma is compressed and heated by a 4-kJ capacitor bank. The average temperature rises to 7 eV. At a time 2.5 μsec after the onset of the compression, the plasma touches the outer wall of the glass vessel.
Electron Temperatures and Densities from Transient Helium-Like Ion Line Emission
Authors: Kunze H.-J. , Gabriel A. H. , Griem H. R.
Published: February 2004

Measurement of plasma electron temperature is based upon the observation of the decay rate, through ionization, of lines from helium-like ions. Ionization from the ground state is supplemented at higher densities by stepwise ionization through the triplet metastable levels. In an experiment on C v ions in a 15-kJ theta-pinch plasma, this method gives a temperature of 230 eV ±18%, compared with 240 eV measured by the Thomson scattering of laser light. In addition, measurement of the intensity ratio of resonance to intercombination lines in C v as a function of density gives the rate for triplet-singlet transfer collisions, together with the ratio of singlet to triplet excitation, thereby yielding the high-density corrections for the above ionization rate. With this theory, measurements of the intensity ratio can now be used for the determination of electron density in the range 2 × 1014 to 1019cm−3, by selecting the appropriate helium-like ion from B iv to Ne ix, with accuracies of the order 30%. An alternative method for measuring the electron temperature from the absolute intensity of the 23S – 23P multiplet of helium-like ions, based upon the above model together with the Seaton semi-empirical formula for the singlet excitation, gave a value of 265 eV ±25% when the temperature measured by scattering was 210 eV.
Simple Model for the Small-Scale Structure of Turbulence
Authors: Tennekes H.
Published: February 2004

The small-scale structure of turbulence may be modeled as vortex tubes of diameter η, which are stretched by eddies of scale λ. The skewness and kurtosis of ∂u/∂x-type signals are calculated.
Decay of Passive Scalar Fluctuations in Isotropic Homogeneous Turbulence
Authors: Sutton GeorgeW.
Published: February 2004

A relation is given for the decay rate of passive scalar fluctuations in terms of the decay rate for velocity fluctuations in isotropic homogeneous turbulence for a −53 spectrum. For the velocity-fluctuation decay exponent of −1.2, the two rates are equal.
Diffusion Approximation for Two-Dimensional Turbulence
Authors: Leith C. E.
Published: February 2004

A diffusion approximation to inertial energy transfer in two-dimensional isotropic turbulence is derived in such a way that energy and squared vorticity are conserved. The −53 and −3 power inertial ranges are predicted.
Development of Magnetohydrodynamic Waves behind an Ionizing Shock Wave
Authors: Cowley M. D. , Morin S. J.
Published: February 2004

A transverse perturbation to a longitudinal magnetic field is introduced upstream of an ionizing shock. The dominant length scale is given by Ohmic diffusion. Either a transverse structure develops, and one wave is emitted, or two slow waves are emitted.
Possibility of Radiation-Induced Sound Amplification in a Gas
Authors: Schulz Michael
Published: February 2004

Sound amplification should occur in a gas having an internal mode excited nonthermally, e.g., by sufficiently intense electromagnetic irradiation of the gas at a frequency of the rotational, vibrational, or electronic spectrum of a gas molecule.
Structure of Plasma Turbulence due to Nonlinear Cross-Field Instability
Authors: Tsuda Takao , Sato Tetsuya
Published: February 2004

Evolution of spectral distribution of charge-density fluctuations in a strong plasma turbulence is studied by computer. It is demonstrated that components of sufficiently short wavelengths are strongly modulated by long wavelength components, but not the other way.
Landau Damping in Maxwellian Plasmas as t → 0
Authors: Denavit J.
Published: February 2004

The linear electric field for longitudinal plasma oscillations is given by a series which does not converge uniformly as t → 0. The difference between the limit of the infinite sum and the sum of the limits of each term is evaluated.
Stability of a Nonstationary Plasma
Authors: Wu C. -S.
Published: February 2004

The stability of a nonstationary plasma is studied. It is concluded that the single-humped distribution is not necessarily stable. The result is applied to the case of the electron plasma wave.
Waves at Plasma-Magnetic Field Interface
Authors: Nakagawa Y. , Trehan S. K.
Published: February 2004

It is shown that the velocity discontinuity between a plasmavacuum interface is always unstable to small perturbations when the effect of gravity is taken into account.
Comparison of a Modified-Langmuir-Probe Analysis with Computer Solutions of Electrostatic Probes
Authors: Scharfman W. E.
Published: February 2004

A quantitative comparison is made between numerical solutions for the current to a free-molecular electrostatic probe and a modified Langmuir analysis. The maximum difference is about 60% over a range of rp/λD from 1 to 10 000.
Observation of the Negative-Mass Instability in a Plasma Betatron
Authors: Ferrari L. A. , Rogers K. C. , Landau R. W.
Published: February 2004

The beam disruption times observed in a plasma betatron experiment are compared with those predicted by the negative-mass instability. Agreement with theory is found for a wide range of data.
Explosions due to Pressurized Spheres at the Ocean Surface
Authors: Chan B. C. , Holt M. , Welsh R. L.
Published: February 2004

The effect of an explosion due to the rupture of a pressurized sphere, centered at the ocean surface, is determined. The field of disturbance near the vertical axis through the center of the explosion is determined by Friedman's analytic approach, based on a perturbation of the linear-shock-tube solution. The interaction of the main blast wave with the ocean surface is determined by fitting a locally plane shock with a Prandtl-Meyer expansion, which reduces the shock pressure to atmospheric value. The main object of the calculation is to determine the shape of the distorted ocean surface (or crater). Calculations are made for initial sphere pressures of 619 and 7000 atm, respectively. The shape of the disturbed ocean surface flattens at the base as the strength of the explosion increases, in agreement with the behavior found for intense point source explosions.
Growth of Disturbances in Both Space and Time
Authors: Gaster M.
Published: February 2004

Betchov and Criminale found certain singularities in the eigenvalue relations for the combined stability problem in space and time. It is shown why these singularities must occur, and how they influence the perturbation generated by a pulse.
Stability of Rotating Couette Flow. I. Asymmetric Waveforms
Authors: Snyder H. A.
Published: February 2004

Experiments are described which show that the waveform at onset of instability in rotating Couette flow may be asymmetric about the rotational axis. Thus, the prediction of Krueger, Gross, and DiPrima is verified. The waveforms have been observed using various cylinders with gap ratios ranging from 0.20 to 0.96. The data covers the complete range where simple asymmetric modes occur. A complicated transient motion is described which leads to the spiral waveforms observed at onset. All predictions of Krueger et al. are in accord with experiment and previous experimental work can be reconciled with both the theory and the present observations. A waveform which is subharmonic in the axial direction is also studied.
Nature of Electron-Fluid-Dynamical Waves
Authors: Shelton G. A. , Fowler R. G.
Published: February 2004

A one-dimensional, inviscid, multifluid model is employed to describe a constant velocity, steady-profile, ionizing electron-fluid-dynamical wave propagating into a pure atomic gas subjected to an applied electric field E0. It is demonstrated that the electron-fluid equations can be decoupled from the remaining equations allowing description of the wave in terms of electron variables only. Wave speed and resultant degree of ionization are derived as functions of applied field and initial gas pressure. Certain limiting conditions governing the existence of such steady-profile waves and comparison with the experimental work on breakdown waves are also presented.
Thermal Instability of a Magnetofluid in a Vertical Rectangular Channel
Authors: Yu C. P.
Published: February 2004

The onset of the instability of an incompressible, viscous and electrically conducting fluid heated from below and confined within a vertical, rectangular channel is investigated when a uniform magnetic field is applied normally to one side of the channel. The condition for the stability revealed by the critical Rayleigh number is found to be dependent upon both the Hartman number which is a measure of the magnetic effect and the aspect ratio of the channel.
Properties of the Fokker-Planck Equation
Authors: Lewis M. B. , Hogan J. T.
Published: February 2004

The expansion of the Boltzmann collision term up to second order in small deflections is shown to agree with the corresponding expansion of the Smoluchowski equation for arbitrary potentials. A general relation is obtained for the nth Fokker-Planck coefficient and (velocity) derivatives of higher coefficients.
Computer Experiments on Low-Density Crossed-Field Electron Beams
Authors: Levy R. H. , Hockney R. W.
Published: February 2004

A Lagrangian computer model consisting of 1000 electron rods has been used to investigate the long-wave diocotron instability in a low-density (ωp2 ≪ ωc2), re-entrant, crossed-field electron beam. A thick and thin beam were found to be stable and unstable, respectively, as predicted by theory. Excellent agreement was obtained between the theoretical growth rate and that observed in the model. The computer model was able to follow the nonlinear behavior of the system. The unstable beam broke up into a vortex street which remained for a long time. The size of the vortex was not enough to transport electrons to the wall of the system and the beam remained confined to the interior.
Electrostatic Equilibrium of Electron Clouds in Magnetic Fields
Authors: Levy R. H.
Published: February 2004

An electron cloud surrounding a toroidal satellite and held in place by a strong magnetic field (B2/2μ0 ≫ 12ε0E2 ≈ neeV ≫ nekTe) has been suggested as a means of raising the satellite to a large positive potential. Symmetry insures that the E × B drift of the electrons satisfies the continuity equation, and the problem of steady equilibrium is reduced to finding electron density distributions such that E·B = 0 wherever electrons are present; in other regions ne = 0. It is shown that the development of a “hole” in the electron cloud at large distances from the axis of symmetry is likely. Representative two-dimensional models are analyzed. At the edge of the electron cloud the appropriate boundary condition is closely related to the Kutta-Joukowski condition of elementary aerodynamics.