bluuebunny/crossref_metadata_2025 huggingface dataset:
Asymptotic Theory of a Spherical Electrostatic Probe in a Stationary Weakly Ionized Plasma
Authors: Bienkowski George K. , Chang Kuo-Wei
Published: February 2004

The electrical effects of a charged sphere immersed in weakly ionized gas of infinite extent are analyzed on the basis of kinetic theory. Approximate solutions are obtained by the application of a moment method in which velocity space is split on the basis of exact orbit calculation, self-consistent with the field. The theory is shown to reproduce both the collisionless and the continuum results in the appropriate limits. Detailed analysis is performed asymptotically for small Debye length but arbitrary mean free path. For quantitative calculations a completely absorbing probe surface at a highly negative potential is chosen. Criteria for the collisionless or collision-dominated sheath are obtained explicitly. The voltage-current characteristics are presented in a form useful for direct prediction of electron number density in terms of measured voltage and current, provided the mean free path is known. If the mean free path is only estimated, the results can be used directly to check self-consistency of that estimate.
Ion Velocity Distributions in a Partially Ionized Plasma
Authors: Banks Peter M. , Lewak George J.
Published: February 2004

Calculations have been made of the steady-state ion velocity distribution functions for a partially ionized gas which is not in thermal equilibrium. The electron and neutral gases are assumed to have Maxwellian distributions such that Te≤ Tn. The effects of ion-electron and ion-ion Coulomb collisions are represented by appropriate Fokker-Planck terms, while the ion-neutral collision term has been derived for resonance charge exchange. It is found for the case of atomic oxygen ions that little distortion of the ion distribution from Maxwellian occurs for ranges of electron and neutral temperatures and particle number densities of geophysical interest. Further, even if ion-ion collisions are neglected, a nearly Maxwellian distribution results for steady-state conditions.
Measurement of Low Plasma Densities in a Magnetic Field
Authors: Chen Francis F. , Etievant Claude , Mosher David
Published: February 2004

Absolute measurements of plasma density in the range 8× 108 to 3× 1011cm−3 were made in a potassium plasma by four methods: (1) Langmuir probes, (2) microwave cavity, (3) microwave interferometry, and (4) propagation of electrostatic waves. Agreement to ≈25% between the probe and microwave measurements was achieved by careful application of probe theory. By contrast, indiscriminate use of probe theory would lead to an error of 600% at low densities. The fourth method, though less accurate, was found to be a useful independent check.
Nonadiabatic Behavior of Plasma Oscillations
Authors: Bartlett Charles J.
Published: February 2004

The nonadiabatic behavior of electrostatic oscillations in an initially unstable, collisionless, field-free plasma is discussed. The equations of ordinary quasilinear theory are generalized to include the time rates of change of the oscillation frequency and the spatially homogeneous part of the distribution function. Certain aspects of the more general theory are illustrated by a discussion of the problem of interpenetrating electron and ion beams. The behavior of the instability is found to differ markedly from that predicted by quasilinear theory. Many of the findings are verified by a direct comparison with the results obtained by Buneman from computer experiments.
Physical Interpretation of the Unified Theory of Relaxations in Plasmas
Authors: Aono Osamu
Published: February 2004

An elementary analysis of frictional force suffered by a test particle traveling fast through a plasma is considered. The action of the system on the particle is described as a result due to the nonlinear polarization of the plasma. The friction thus calculated is in good agreement with that obtained on the basis of the unified theory.
Kinetic Theory of Plasma-Wave Motion in the Presence of Collisions
Authors: Porkoláb Miklós
Published: February 2004

Utilizing a Krook-type collision integral, we carry out a systematic analysis of electrostatic waves and instabilities in a fully ionized, low β, inhomogeneous plasma (where β is the ratio of particle pressure to magnetic pressure). The model employed is that of a plasma slab supported by magnetic and gravitational fields. In particular, the dispersion relations for drift waves, appropriate to a short system, and for ion cyclotron waves are derived and discussed. Thus, for drift waves it is found that in the presence of collisions, ion motion parallel to the magnetic field can provide a strong stabilizing effect for sufficiently large values of the axial wave vector. For the two-stream ion cyclotron instability we find that ion-ion collisions can provide strong damping even for collision frequencies well below the ion cyclotron frequency.
Effects of Collisions on Landau Damping
Authors: Rand S.
Published: February 2004

The quasilinear theory of Drummond and Pines has been extended in order to include the effects of collisions, and the resulting equations have been solved in the steady state. The extent to which collisions cause a reduction in Landau damping is demonstrated. Results are given in terms of the two parameters, ω/kv¯ and e2E02/m2v¯3kβ where ω and k are the frequency and wavenumber of the propagating wave field, of peak electric field strength E0, v¯ is the electron thermal speed, and β is the 90° deflection frequency of Spitzer, corresponding to an electron which moves with the phase velocity of the wave.
First-Order Orbit Theory of the Rotational Discontinuity
Authors: Su Shin-Yi , Sonnerup B. U. Ö.
Published: February 2004

A study is made of the propagation properties and internal equilibrium structure of a large-amplitude Alfvén wave which conserves the magnitude of the magnetic-field component tangential to the wave front but changes its direction. The propagation properties are found to be identical with those of small-amplitude sinusoidal waves. The equilibrium wave structure is shown to involve an electric field along the wave normal. The sign and magnitude of this field are related to the rate and sense of rotation of the tangential magnetic field component as well as to the particle distributions. In certain cases the electric field may be sufficiently large to cause nonnegligible variations in particle and magnetic pressures within the wave. Observed polarizations of the magnetopause current layer may be explained by the theory.
Longitudinal Waves Excited in an Inhomogeneous Magnetized Plasma Slab
Authors: Gruber S.
Published: February 2004

Excitation of short wavelength longitudinal oscillations in a plasma slab is considered for frequencies near the second harmonic of the electron cyclotron frequency. For the uniform plasma slab a long and short wavelength plasma oscillation coupled at the boundary and the relative amplitudes are governed by the boundary conditions. In the nonuniform plasma slab these two fields are continuously coupled within the slab as well as at the boundaries. When the boundaries are removed, these fields are coupled by the density gradient and the rapidly varying field is of amplitude λ2/L2 less than the long wavelength field where λ is the wavelength and L is the scale size. The slab plasma exhibits a series of resonances and antiresonances as a function of field B when B> mω/2e and shows an antiresonance for an excitation frequency slightly greater than the second harmonic. An experiment verified this predicted antiresonance.
Low-Frequency Limit of Interchange Instability
Authors: Rosenbluth Marshall N.
Published: February 2004

It is shown under a wide range of conditions, that if any mirroring particles in an axisymmetric toroidal confinement system have a time-averaged unfavorable drift then a low-frequency localized instability can result. An example of a geometry in which all particles have time-averaged favorable drift is given.
Nonlinear Evolution of a Resonant Interchange Mode
Authors: Pearlstein L. D.
Published: February 2004

A resonant instability due to the presence of a small number of superthermal particles with an adverse spatial gradient in a hydromagnetically stable well configuration is examined. It is found that resonant diffusion leads to a stable quasilinear plateau in the distribution function. Wave scattering redistributes the wave spectrum from the linearly unstable region to a region of lower wavenumber, at the same time transferring energy to the particles. The nonlinear wave particle scattering leads to a diffusion equation in which only electrons can interact resonantly. In addition, there is a nonresonant contribution to diffusion due to the adiabatic response of electrons and ions to the time changing wave spectrum after stabilization. The net result is that ions and electrons diffuse at an equal rate with no charge separation developed.
High-Frequency Flute-Like Instabilities in Multicomponent Plasmas
Authors: Farr W. M. , Budwine R. E.
Published: February 2004

Detailed calculations have been made to determine thresholds for flute-like instabilities in a plasma containing both cold and hot, mirror-confined ions. The effect of a density inhomogeneity on these thresholds is also considered.
Inhomogeneous Two-Stream Instability
Authors: Knorr Georg
Published: February 2004

It is shown that the well-known two-stream instability can under certain conditions be stabilized by the introduction of a periodic stationary electrostatic potential which is produced by the particle beams themselves.
Theory of Collisionless-Plasma Drift Mode in Multipoles
Authors: Jukes J. D. , Rohlena K.
Published: February 2004

A particular mode of drift/acoustic wave is considered in collisionless plasma in a closed multipole confining field. Stability criteria and the anomalous diffusion time of unstable plasma are estimated.
Equilibrium of Toroidal High-β Plasmas
Authors: Yoshikawa S.
Published: February 2004

A toroidal theta-pinch magnetohydrodynamic equilibrium configuration of a diffuse boundary is calculated analytically for β = 1 plasma. Equilibrium can be obtained even if the toroidal magnetic field is present, provided that the ratio, toroidal field over poloidal field, is less than the square root of the aspect ratio.
High-Frequency Breakdown of Nonuniform Gases in Spatially Varying Fields
Authors: Epstein Melvin
Published: February 2004

A method is described for predicting the field strength required to produce continuous wave breakdown of gases with spatially varying properties subjected to electric fields of nonuniform intensity. The proposed method is based on a variational principle derived from the electron continuity equation. A Ritz method is used to generate solutions of the variational problem. The approximate solutions are evaluated by comparing them with several exact solutions which are also developed. The use of a one-term trial function in the Ritz method is found to give very good agreement with the exact solutions. A two-term approximation provides greater accuracy than is presently available from experimental data.
Temperature Dependence of the NO+ + e Dissociative-Recombination-Rate Coefficient
Authors: Hansen C. Frederick
Published: February 2004

If constant transition probability at the N + O and NO-potential crossing is assumed, the NO+ + e recombination rate is shown to vary from a T−12 to T−32 dependence as T increases. This result is found consistent with most of the experimental evidence.
Small Perturbation Method in Kinetic Theory
Authors: Chi L. K.
Published: February 2004

Oseen's equations for compressible fluid flows are shown to be approximations of the Bhatnagar-Gross-Krook equation. The linearized Burnett equations with different coefficients, are obtained as corrections to Oseen's equations.
Theory of Flat-Plate Ion-Density Probe
Authors: de Boer P. C. T. , Johnson R. A.
Published: February 2004

Theoretical results are presented for the ion sheath which forms on a flat plate parallel to the stream direction of a slightly ionized gas. The boundary layer is assumed to be thin compared with the sheath. The solution obtained has a simple algebraic form.
Mobility Tensor for a Strongly Turbulent Lorentz Gas in a Magnetic Field
Authors: Frank Eugene N.
Published: February 2004

The magnetic field terms of the Fourier analyzed momentum equation of a turbulent Lorentz gas are linearized using a phenomenological approach. The perpendicular mobility is found to vary as B−q where 0.6 < q < 2.0.
Effect of Neutral Impurity Levels on the Oscillation Spectrum of a Magnetoplasma
Authors: Eastlund B. J. , Leheny R. F. , Granatstein V. L. , Schmidt P. H.
Published: February 2004

Neutral gases were added to a chamber containing a fully ionized magnetoplasma. Above certain critical background pressures, naturally occurring drift waves were quenched and a new low-frequency wave appeared. The wave quenching is attributed to ion-atom collisions.
Normal Modes of a Nonuniform Plasma
Authors: Leavens W. M. , Larson R. W. , Love C. H.
Published: February 2004

The spectrum of undriven electron plasma oscillations of a realistic, nonuniform, collisionless plasma with a sheath is determined. The spectrum is found to be discrete.
Integral Equation Treatment of the Linearized Theory of Electrostatic Plasma Oscillations
Authors: Lee D. A. , Soper G. K.
Published: February 2004

It is shown by an example that it is convenient and physically revealing to solve certain initial value problems for the Vlasov equation directly, in the form of an integral equation for the disturbance in electron-number density, without using integral transforms.
Two New Results in Cylindrical Diocotron Theory
Authors: Levy R. H.
Published: February 2004

Two new results on the diocotron wave are presented. One is a linearized solution valid for arbitrary unperturbed density profiles, but restricted to the fundamental mode. The other exhibits a special family of exact nonlinear solutions to diocotron type motion.
Shock-Tube Measurements of Cr i and Cr ii gf Values
Authors: Wolnik S. J. , Berthel R. O. , Larson G. S. , Carnevale E. H. , Wares G. W.
Published: February 2004

Absolute gf values for 41 lines of Cr i and 2 lines of Cr ii have been determined from measurements of shock-heated gas emission. The lines are distributed over 12 multiplets and fall in the spectral range 3805-5410Å. The values presented here show disagreement with those reported by other investigators on an absolute scale ranging from a few percent to factors of approximately 10. Application of the gf values to computed solar abundances is discussed.
Unsteady Flow in the Shock-Tube Magnetohydrodynamic Generator
Authors: Fishman Frank J.
Published: February 2004

In order to obtain some insight into unsteady magnetohydrodynamic channel flow, the flow in an idealized shock-tube generator is investigated theoretically. The treatment is limited to weak shocks, but is valid for arbitrary interaction parameters. The natural time scale of the flow is ω0−1 = ρ1/σ B2 (1−α), where ρ1 is the density in front of the shock, σ the (constant, scalar) conductivity of the test gas, B the (constant) magnetic field, and α the (constant) load parameter. The shock decays in the time ω0−1, but the over-all flow persists for times orders of magnitude longer. The electric power extracted initially rises linearly with the length of the test gas, but reaches a broad maximum after several characteristic times and delays only slowly thereafter. A detailed description of the flow is presented until it becomes a classical diffusion at values of ω0t greater than about 100.
Classical Diffusion Limit of One-Dimensional Hydromagnetic Flow
Authors: Bineau M.
Published: February 2004

The hydromagnetic flow of a plane sheet of plasma with scalar pressure is represented by a set of equations for which the Cauchy problem is well posed. If the Alfvén speed is made infinite in this system with dimensionless variables, one obtains the classical diffusion limit. The velocity of diffusion is then defined purely by boundary conditions at each time.
Solution of the Linearized Vlasov Equation for a Space-Time-Dependent Distribution Function
Authors: Bloomberg H.
Published: February 2004

A solution is given for the one-dimensional linearized Vlasov equation when the background distribution function f0 is a sufficiently weak function of space and time; the field is given self-consistently through the Poisson equation and the initial value problem is explicitly considered. An eikonal solution, common to geometrical optics, is found, and the appropriate combination of such solutions so as to conform to given initial conditions is specified. Results are given for the modification of the Landau damping through the variation of f0, as well as for the coefficient of the eikonal exponential, which change is directly due to the space-time variation of f0. An example is given for an eikonal wave, in which wave-particle energy transfer is initially small, which is “driven” through the change of f0 to a condition where the solution breaks down due either to strong wave-particle effects or to the invalidity of the basic eikonal ordering assumption. Estimates for the times at which these limiting effects occur are given.
A Fundamental Solution for the Linearized Guiding-Center Equations
Authors: Kadish Abraham
Published: February 2004

The linear one-dimensional propagation of an initial perturbation in an infinite, homogeneous, stable guiding-center plasma is studied. The dominant mode of decay after long periods of time is shown to be that of a reciprocal power of time.
Dispersion Relations in Relativistic Vlasov Plasmas
Authors: Prentice A. J. R.
Published: February 2004

The complete solution, for all temperatures and wavenumbers, of the longitudinal and transverse dispersion equations of a relativistic Maxwellian plasma, is presented. It is assumed that the ions are immobile and that there is no zero-order magnetic field. Analytical methods are used for the very small and very large wavenumber cases, and in the intractable intermediate wavenumber regions numerical results are displayed graphically. The existence at all temperatures of very slightly damped longitudinal plasma waves and slightly damped nonoscillatory transverse excitations is established and the damping constants are evaluated. Necessary and sufficient conditions for the existence of slight Landau damping of longitudinal plasma waves in any general isotropic relativistic Vlasov plasma are also derived. Several new dispersion relations for undamped oscillations, which have phase velocity greater than c, are recorded. One of these, which describes transverse oscillations for large wavenumbers, corresponds to the propagation of light waves in the plasma.
Depolarization of Light Scattered by a Relativistic Plasma
Authors: Theimer O. , Hicks W.
Published: February 2004

The depolarization ratio ρ for the single particle light scattering spectrum of a relativistic plasma with a displaced Maxwell velocity distribution is calculated to the lowest significant order in β = v/c. (c is the light velocity; v is the electron velocity.) It is found that ρ reaches the order of magnitude 0.1 if the temperature increases beyond 108 °K, and that the plasma temperature can be determined by one single polarization measurement without spectral decomposition of the scattered radiation.
Plasma Waves and Rotation in the Gas-Fed Hollow-Cathode Arc
Authors: Kretschmer C. B. , Boeschoten F. , Demeter L. J.
Published: February 2004

Mass rotation and azimuthally propagating waves have been observed in gas-fed hollow-cathode arcs having ne ≈ 1014cm−3, Te ≈ 1 eV, Ti = 3 to 30 eV, and Bz = 1 to 6 kG. The column rotates as a rigid body at an angular velocity of 12 ωci; it is shown theoretically that at this velocity the radial density gradient has the maximum value at which equilibrium is possible in the absence of a radial electric field. This maximum gradient corresponds to an exp [− r2/(2ρi)2] dependence of density on radius, where ρi is the ion Larmor radius. The observed waves propagate in the electron drift direction exactly perpendicular to the axis of the arc, but have nonzero k‖ because of the azimuthal field of the arc current. They are identified as resistively unstable drift waves, modified torsional Alfvén waves, and ion cyclotron waves. The drift and ion cyclotron waves occur as coherent oscillations with phase-locked harmonics, while the Alfvén waves are noncoherent. Because of the dependence of the density gradient on Bz, the drift wave frequency is proportional to Bz and the Alfvén wave frequency is independent of Bz. The Alfvén and ion cyclotron waves are excited by a feedback mechanism involving electron flow across the anode sheath.
Some Measurements on a Hydrogen Plasma in a Magnetic Well
Authors: Cilliers W. A. , Driver H. S. T.
Published: February 2004

The behavior of a hydrogen plasma inside a coil which gives a vacuum magnetic field with minimum |B| properties, has been studied in some detail. Streak and framing pictures were taken and the variation of electron density with time was measured. During the first half-cycle of the coil current, the plasma appeared to be stable. The experiment were carried out at relatively low energy. For purposes of comparison, a theta pinch was studied using the same capacitor bank.
Free-Free Bremsstrahlung from a Plasma with an Anisotropic Electron Velocity Distribution
Authors: Shohet J. L.
Published: February 2004

Measurements of two properties of the emitted free-free bremsstrahlung from an electron cyclotron resonance plasma were made. These were the radiation intensity and the spatial distribution of the photons as a function of angle with respect to the magnetic field axis. The intensity was maximum for directions of observation along the field lines. The spectral distribution showed that the average emitted x-ray photon was more energetic along the field lines than across them. A theoretical development has been made which considers quantum-mechanical, nonrelativistic transitions, which correspond to the conditions of the experiment. The theory predicts the observed measurements and also, in the limit of low energy photons, (nonquantum mechanical transitions) corresponds to previous developments.
Measurement of Plasma Temperature Using a Waveguide Probe
Authors: Aro T. O. , Walsh D.
Published: February 2004

The central portion of the plasma produced in a shock tube was sampled by allowing it to flow into a length of X-band rectangular waveguide, coaxial with the shock tube. The temperature of the portion of ionized gas inside the waveguide was determined from the measurement of the microwave noise emitted by the shock-heated gas and its absorption coefficient measured at the same frequency, 9.05 Gc/sec. The measured temperatures were between 4700 and 6000°K for shocks of Mach numbers between 7.0 and 10.6 in argon at an initial pressure of 4 mm Hg. The selection of the middle axial portion of the shock eliminates the boundary layer present at the walls of the shock tube.
Surface Effects on the Structure of a Collisionless Sheath near an Electrode
Authors: Hassan H. A.
Published: February 2004

The effects of emission, reflection, and surface ionization on the structure of a collisionless sheath near a planar electrode are considered. The model assumes the distribution functions to be Maxwellian and employs boundary conditions which relate fluxes of incoming, emitted, and reflected particles. It is shown that the need for imposing the usual sheath criterion, to insure the existence of a stable sheath, depends to a large extent on the value of the thermal accommodation coefficient of the collected particles. If it is unity, the usual sheath criterion need not be imposed. On the other hand, if it is less than unity, two possible solutions can exist, one with a minimum drift velocity different from zero. The reflection and thermal accommodation coefficients are assumed given, and the validity of the model does not depend on the existence of any special relations among these coefficients.
Cold-Electrode Characteristics in Shock-Ionized Air Plasmas
Authors: Hoppmann R. F.
Published: February 2004

The conduction of electric current between cold electrodes in a high-velocity, shock-ionized air plasma has been studied experimentally in order to investigate conduction mechanisms in continuum boundary layers and sheaths. Current-voltage measurements were made in the test flow behind the incident shock wave in an arc-driven shock tube. The electrode configuration employed was of a shielded, parallel-plate type. The data for the lowest, presaturation range of electrode voltages are shown to be in satisfactory agreement with the results of a recent theoretical analysis. Several mechanisms are postulated to explain the observed behavior at the higher values of electrode potential. The current density is shown to be fairly uniform over both electrodes prior to the occurrence of breakdown. The data further indicate that breakdown phenomena occur in the vicinity of the cathode surface.
Use of Langmuir Probes in Low-Pressure Rare Gas Plasmas
Authors: Hart D. A. , Oleson N. L.
Published: February 2004

Evidence is presented which indicates that the assumption of zero ion energy yields best agreement between the results of probes and other methods for charge densities in the range of 109 to 1011cm−3 in a xenon discharge of several mTorr.
Stationary Equilibrium of a Toroidal Plasma
Authors: Viswanathan K. S.
Published: February 2004

Studies are made of the effects of resistivity, inertial forces, viscosity, pressure anisotropy, and especially gyroviscosity on the stationary equilibrium of a low-density plasma in toroidal geometry. The conditions imposed by viscosity on the two arbitrary functions occurring in the expression for the zero-order velocity vector have been derived. It is shown that gyroviscosity does not impose conditions on these two arbitrary functions. It is suggested that among the perturbing forces considered, dissipative forces such as the collision-dominated viscosity and resistivity will give rise to conditions on the two arbitrary functions at the higher approximations.
Confinement of Injected Plasmas in Stellarators
Authors: Ellis R. A. , Eubank H. P.
Published: February 2004

Plasmas produced by a washer plasma gun have been injected into B-3, which is a twisted figure-eight stellarator, and Etude, which is a racetrack stellarator. Both have l = 3 helical windings. In the injected plasmas ne ≤ 5 < 109, Te ≈ 5-8 eV, and Ti is probably greater than Te. The mean free paths for electron collisions were in the range 10-100 machine lengths. The observed confinement times varied with confining field as Bm with 0.6 < m < 1.2 for B ≤ 20 kG in B-3. In Etude, the confinement times varied from the Bohm value at zero rotational transform ι and increased by a factor 20 when ι = 5.43 rad. In B-3 the confinement times varied from about twice the Bohm value when only the geometric transform was present and increased by a factor 30 when ι was increased to 19 rad. It was not possible to decide if the increase of confinement time was due to effects of shear or rotational transform.
Influence of a Toroidal Field on Plasma Confined in a Toroidal Octupole
Authors: Lencioni D. E. , Poukey J. W. , Schmidt J. A. , Sprott J. C. , Erickson C. W.
Published: February 2004

A toroidal magnetic field Bθ of up to 360 G was added to the Wisconsin toroidal octupole producing a stellarator-like field with a large rotational transform and large shear. The influence of this Bθ on plasma injection, transport, density distribution, lifetime, and electric-field fluctuations was studied. Injection and transport were not inhibited by Bθ and proceeded in much the same way as for Bθ = 0. The density distribution after filling was unchanged and remained peaked slightly off the separatrix toward the hoops. The lifetime was smaller with Eθ, but was still consistent with expected losses to the hoop supports. In the originally V″ unstable region outside the last stable field line, the amplitude of the electric field fluctuations decreased when Bθ was added, but in the interior of the plasma, the fluctuations increased monotonically with Bθ. In the plasma interior the maximum diffusion coefficient derived from the fluctuations increased from 10−4 DBohm to 10−2 DBohm as Bθ was increased from zero to 140 G, but the observed lifetime, limited by hoop supports, was always ∼10 τBohm. Large potential deviations which were affected by magnetic field perturbations occurred in the region of zero average shear. Large external-field perturbations were added with no effect on the lifetime. Fluctuations associated with stable inverted density gradients were reduced or eliminated by Bθ.
Measurement of θ-Pinch End Loss Using a Gas Laser Interferometer
Authors: Thomas K. S.
Published: February 2004

A He–Ne gas laser interferometer has been used to make plasma density measurements outside the central plasma core of a θ-pinch plasma. At the θ-pinch coil midplane, the average plasma density is less than the sensitivity of the interferometer, that is, less than 5 × 1013cm−3. Outside the ends of the coil line densities (particles per cm of tube length) of the order of 1015cm−1 are measured. When compared with previous data from the same θ pinch, a streaming velocity out the coil ends in the neighborhood of the ion thermal velocity is obtained.
Effects of Couple Stresses in Fluids on Hydromagnetic Channel Flows
Authors: Stokes Vijay Kumar
Published: February 2004

Two boundary value problems have been solved. It has been shown, that for large Hartmann numbers, the effects of couple stresses are quite large for Poiseuille flow between two parallel plates subjected to a transverse magnetic field.
Interaction of a Charged Particle with Moving Current Layer
Authors: Kuliński S.
Published: February 2004

The equations of motion for a charged particle overtaken by a moving current layer are written and solved. It is shown that a particle can (a) be reflected by the layer, (b) be captured by it, and (c) penetrate through the layer.
Steady Laminar Forced Convection from a Circular Cylinder at Low Reynolds Numbers
Authors: Dennis S. C. R. , Hudson J. D. , Smith N.
Published: February 2004

Comparison of experimental data for the heat transfer between a circular cylinder and a steady stream of viscous, incompressible fluid at low Reynolds numbers with the only available theoretical solution, that based on Oseen type linearization of the heat transfer equation, indicates considerable discrepancies. This question can only be resolved by obtaining solutions of the heat transfer equation based on the correct velocity distribution in the field of flow according to the full Navier-Stokes equations. This problem is considered for a range of Reynolds numbers from 0.01 up to 40. Solutions of the equation for forced heat convection are obtained using numerical methods. The mean and local Nusselt numbers are calculated and compared with available experimental data and correlations. The results are found to compare favorably. At the upper end of the Reynolds number range the solutions are examined to see if their trend checks with boundary-layer results at high Reynolds numbers and with some recent predictions as to the nature of the heat transfer in separated flow past a circular cylinder at high Reynolds numbers. Again some evidence of satisfactory comparison is found.
Viscous Fluid Flow over a Corrugated Bottom in a Strongly Rotating System
Authors: Hsueh Y.
Published: February 2004

The problem of a laterally unbounded viscous flow across slight bottom corrugations at a right angle in a strongly rotating system is considered. It is shown that when the ratio of the Rossby number to the Reynolds number δ2 ≡ Ro/Re ≪ 1 and Re = δ−m, m < 1, the flow far away from the bottom is both geostrophic and hydrostatic to a high degree and that flow near the bottom is of the boundary-layer type with negligible inertia. A steady-state solution for the entire flow field is obtained in which boundary-layer suction maintains the mass continuity as fluid is pushed across the uneven bottom at a constant speed. Experimental results for a bottom of constant slope are presented which are in good agreement with theory.
Gas-Density Fluctuations in the Wakes from Hypersonic Spheres
Authors: Herrmann J. , Clay W. G. , Slattery R. E.
Published: February 2004

The correlation functions, spectra, and variances of the gas density in the turbulent wakes of spheres of 0.5-, 1.0-, 1.6-cm diameter, traveling at 5.6 km/sec, are compared with previous work on 2.5-km/sec spheres [W. G. Clay, J. Herrmann, and R. E. Slattery, Phys. Fluids 8, 1792 (1965)]. The wakes appear to be statistically homogeneous and isotropic, as were the measurements at lower velocities. The normalized correlation functions and spectra of the gas density in the wakes are independent of pressure in the region of 10 to 80 Torr and are independent of the position behind the sphere out to about 1600 body diameters but change beyond that distance. The rms density fluctuations of the wakes peak also at about 1600 body diameters behind the sphere which is further behind than is the case at lower velocities. The level of the spectrum of the gas-density fluctuation increases out to that distance without change in its form. Beyond that distance the decrease of the spectrum is faster at large wave-numbers than at small ones. The correlation length of the wake edge profile is much longer than the correlation length of the gas density fluctuations at the same positions in the wake.
Nonlinear Gas Oscillations in a Resonant Tube
Authors: Temkin S.
Published: February 2004

Nonlinear gas oscillations in a resonant tube are considered analytically and experimentally. Approximate formulas for the velocity and pressure fluctuations are obtained assuming that, due to nonlinear convective effects, the waves emitted by the piston distort rapidly to form a sawtooth with a weak discontinuity at each wavelength. The interaction between incident and reflected waves yields the velocity and pressure inside the tube. These solutions are used to determine, by means of energy considerations, the limiting values of pressure amplitudes, assuming that the leading dissipative mechanisms are the shock wave and the boundary layer. The results obtained compare favorably with amplitude measurements in a piston-driven tube under nonlinear conditions.
Similarity Solution for Cylindrical Gas Cloud in Rarefied Atmosphere
Authors: Klein Milton M.
Published: February 2004

The analysis of Stuart for an expanding spherical gas cloud in a rarefied atmosphere is extended to the case of cylindrical flow. The equations of motion are expressed in similarity form from which early and late time solutions are obtained. The spherical and cylindrical flows are numerically compared for the case of negligible frictional heating by the atmosphere.
Effect of Radiative Heat Loss on the Subsonic Region of the Hypersonic Shock Layer
Authors: Bloor M. I. G.
Published: February 2004

An analytic, uniformly valid solution for the subsonic region of the hypersonic shock layer is found when the gas is losing energy by radiation. For simplicity the gas is assumed to be perfect and the density ratio across the shock is assumed to be large. Use is made of the von Mises transformation, the transformed equations being solved by interchanging the roles of an independent and a dependent variable. The solutions for the sonic line and a stream line are compared with a nonradiative solution. The comparison of the shock stand-off distance in the stagnation region with previous numerical results shows favorable agreement.
Interaction of the Magnetized Solar Wind with the Moon
Authors: Whang Y. C.
Published: February 2004

The experimental results obtained from the Explorer 35 spacecraft indicate that a detached bow shock wave does not exist in the vicinity of the moon. Thus, the flow conditions near the moon do not resemble those near the magnetosphere of the earth. The solar-wind flow around the moon is treated theoretically as a free-molecule flow of guiding-center plasma. Analytical results are obtained to describe the ion flow in the vicinity of the moon. The disturbed region forms a long wake in the downstream of the moon. The thickness of the wake, measured perpendicular to the plane of the solar-wind velocity and the interplanetary magnetic field, is constant at one lunar diameter. On the other hand, the width of the wake, measured parallel to that plane, increases with distance from the moon.
Collision Effects on Charged Particle Densities in the Trail of a Satellite
Authors: Albini F. , Rand S.
Published: February 2004

The effects of ion-electron collisions, on the structure of the satellite wake, have been studied. It is found that, in the daytime ionospheric F layer, due to these collisions the periodic variations in the ion and electron densities have largely disappeared at distances behind the vehicle greater than about 1 km. In other regions of the ionosphere, the distance required for the diffusing of the periodic structure scales with density as n0−1/3, where n0 is the ambient electron density. It is suggested that, in their effects on the wake structure ion-electron collisions are generally more important than ion-ion collisions.
Electric Field ahead of Normal Ionizing Shock Waves
Authors: Cross R. C.
Published: February 2004

Measurements of the transverse electric field ahead of a normal ionizing shock wave are presented for Alfvén Mach numbers in excess of the ideal-gas limit of two. A simple expression is derived to explain the results.
Experimental Study of Cylindrical Magnetohydrodynamic Blast Waves
Authors: Vlases George C. , Jones Donald L.
Published: February 2004

The interaction of a cylindrical ionizing blast wave with a uniform axial magnetic field is studied under conditions such that the magnetic Reynolds number is very small and the interaction parameter is of the order of unity. The source of the blast wave is an inverse pinch operating in the mode where the energy deposition time is short compared with the time required for the shock to traverse the chamber. The flow consists of an ordinary shock followed by ionized gas which interacts with the magnetic field to alter the trajectory and flow-field profiles from those given by the classical theory. Piezoelectric probe measurements show that while the shock is slowed by the magnetic field, the classical similarity is preserved, i.e., Rshock ∼ t1/2. Static pressure measurements indicate that in a magnetic field, p/pshock rises rapidly behind the shock in direct contrast to the classical behavior. A mapping of the magnetic field indicates that large perturbations are found only near the axis and last only for short times. These results are in qualitative agreement with those predicted theoretically by Lykoudis in the limit of small magnetic Reynolds number.
Afterglow Measurements of a Laser Breakdown Plasma
Authors: Lampis G. , Brown Sanborn C.
Published: February 2004

A highly ionized plasma in helium at a pressure of 10 atm was produced by a giant laser pulse. The properties of the plasma were studied by a dc helium-neon gas laser. Measurements of the variation of the shape and size of the plasma, its electron density and temperature, and its absorption coefficient at 6328 Å were made during the afterglow between 100 and 600 nsec. The shock wave emitted by the plasma was also studied.
Observation of Plasma Wave Echoes
Authors: Malmberg J. H. , Wharton C. B. , Gould R. W. , O'Neil T. M.
Published: February 2004

Experimental observation of a new nonlinear plasma phenomenon, the plasma wave echo, is reported. A recent theory predicts that if a longitudinal electron plasma wave is excited at one position in a collisionless plasma and Landau damps away, and a second wave is excited at another position and also damps away, then a third wave (i.e., the echo) will spontaneously appear at a third position. The existence of various echoes, associated with various orders of the perturbation theory, is demonstrated experimentally. The echoes appear at the predicted position in the plasma. The frequency of the echo wave and the dependence of its amplitude on the amplitude of the initial wave are also in agreement with the theory. Experimental data on the saturation of echo amplitude with increasing initial wave amplitude and increasing distance are given. Data are also presented on another new, but related, phenomenon “the sheath echo.”
Exact, Stationary Wave Solutions of the Nonlinear Vlasov Equation
Authors: Abraham-Shrauner Barbara
Published: February 2004

A procedure for systematically calculating a wide class of exact, nonlinear wave solutions of the Vlasov equation that are stationary in the wave frame is given. The essential feature of the method is the expansion of the current density in an infinite series of the vector potential or the expansion of the charge density in an infinite series in the scalar potential. The potentials obey a differential equation of the form of the equation of motion for a point particle in a conservative potential. This nonlinear differential equation has numerous analytic solutions depending on the choice of physical parameters.
Electron-Plasma Wave Amplitudes Associated with Particle Phase Mixing
Authors: Rand S.
Published: February 2004

The Landau decrement associated with sinusoidal electron-plasma wave propagation undergoes decaying oscillations in time. The weakening of the oscillations between growing and damped waves is due to phase mixing of resonance particle motions. The rate of phase mixing is increased by the effects of collisions between resonance electrons and the bulk of the plasma particles. The phase mixing problem has been studied, and it is found that the amplitude of the oscillations in the Landau decrement decreases inversely with the square root of the time for early times, and inversely with the seven-halves power for late times.
Stability of Electromagnetic Waves Propagating Perpendicular to a Uniform Magnetic Induction
Authors: Hamasaki Seishi
Published: February 2004

The general dispersion formulas of plasma waves propagating perpendicular to an applied uniform magnetic field B0 in an infinite plasma are derived. Stability of one of the wave modes, a linearly polarized electromagnetic wave whose electric field is directed along B0, is analyzed under the assumption that the wavelength is much larger than the cyclotron radii of electrons. The analysis shows that the waves are stable for a low-density plasma. However, if the plasma density becomes sufficiently high such that the plasma frequency becomes higher than the electron cyclotron frequency, then an instability may develop. The stability criterion is compared with and is analogous to the criterion for the firehose instability. the allowable frequency range for this mode is analyzed, and it indicates that there is no longer a low-frequency cutoff in the rigorous sense for a hot plasma.
Effects of Ion-Atom Collisions on the Propagation and Damping of Ion-Acoustic Waves
Authors: Andersen H. K. , D'Angelo N. , Jensen V. O. , Michelsen P. , Nielsen P.
Published: February 2004

Experiments are described on ion-acoustic wave propagation and damping in alkali plasmas of various degrees of ionization. An increase of the ratio Te/Ti from 1 to approximately 3-4, caused by ion-atom collisions, results in a decrease of the (Landau) damping of the waves. At high gas pressure and/or low wave frequency a “fluid” picture adequately describes the experimental results.
Nonlinear Transport in Weakly Ionized Plasma
Authors: Simon Albert
Published: February 2004

A set of equations are derived for the amplitudes of the oscillating modes which arise in a slightly unstable weakly ionized plasma. The plasma is initially in a time-independent but spatially dependent and linearly stable equilibrium. It becomes unstable upon a small fractional increase Δ of some external parameter. The amplitudes of the final steadily oscillating states, the frequency shifts of these states, and the transport rates are determined in terms of Δ.
Convection of Weakly Ionized Plasma in a Nonuniform Magnetic Field
Authors: Simon Albert
Published: February 2004

A weakly ionized plasma in a nonuniform magnetic field exhibits an instability analogous to the well-known flute instability of a fully ionized plasma. The instability sets in at a critical magnetic field. When this external field is slightly increased above the critical value by the fractional amount Δ, to begin with only one mode goes unstable and it grows in amplitude to a finite limiting value. Using a general theory of the nonlinear behavior derived in an accompanying paper, we evaluate the mode amplitude and frequency shift as functions of Δ, as well as the corresponding enhanced particle transport. The results are first obtained in the quasilinear approximation, but it is then shown that the mode-coupling contribution is negligible and hence that the result is generally valid for small Δ.
Stability of Plasma Sheaths
Authors: Schindler K. , Soop M.
Published: February 2004

The stability of plasma in a magnetic field against collision-free tearing of current layers is considered in plane geometry. While previous studies were confined to specific equilibria without charge separation, the present (variational) approach allows for a large class of distribution functions and for an equilibrium electrostatic field, thus also applying to strongly inhomogeneous equilibria. A simple criterion is obtained, which is necessary and sufficient for stability against perturbations that do not vary along the direction of the equilibrium current (tearing mode). Strictly one-dimensional perturbations requiring a somewhat modified procedure are discussed separately.
Whistler Type Wave Penetration of Hot Plasmas
Authors: Drummond James E.
Published: February 2004

The attenuation of plane, right circular polarized electromagnetic waves propagating along an axial magnetic field into a thermal plasma is computed by an adaptation of Weibel's analytical and numerical results for nonmagnetic field cases.
Magnetically Induced Current Chopping in Low-Pressure Discharges
Authors: Tuma D. T. , Ware A. A.
Published: February 2004

Current chopping has been magnetically induced in low-pressure (2 × 10−5 − 5 × 10−3 Torr) arcs carrying currents of 50-200 A. The chopping was achieved in a time duration of 1-10 μ sec using a θ-pinch or an axially uniform magnetic field. Voltage spikes across the arc larger than 80 kV accompanied the chopping when an 8-mH inductor was connected in series with the arc circuit. Irregular oscillations of frequencies higher than 10 MHz were detected during current chopping; the amplitude of the oscillations was proportional to the voltage spike. Other oscillations whose frequency range extended from 100-200 kHz were detected, preceding and following the current chopping. x rays were emitted from the arc at current chopping whose flux depended on the voltage spike.
Operation of a Theta Pinch at Extremely Low Filling Pressures
Authors: Kunze H.-J. , Gabriel A. H.
Published: February 2004

Observations are reported that by adding methane to the hydrogen or deuterium filling in the discharge tube of a theta pinch the absolute density at which it is possible to achieve breakdown in the preheater phase can be lowered. Plasma conditions have been investigated for a filling gas pressure of 0.8-m Torr pure CH 4 or CD 4, respectively, using light scattering and neutron emission. Measurements on impurity concentrations indicate that for low filling pressures and low absolute impurity concentrations, selective injection and loss of impurities to the walls during the preheater phase of a theta pinch may become important. Large errors can then arise in determining the concentration of elements with physically stable condensable forms (e.g., carbon and boron) when using the method involving the measurement of the intensity of an emitted spectral line as a function of added impurity concentration.