bluuebunny/crossref_metadata_2025 huggingface dataset:
Nature of the first iterate for nearly-free molecular flow
Authors: Hamel B. B. , Cooper A. L.
Published: February 2004

A critical evaluation is made of the first iterate of integral iteration of the Boltzmann equation for nearly-free molecular flow over isolated bodies. It is demonstrated that, for two-dimensional bodies with diffuse reflection, the first iterate is incapable of describing the correct physics governing nearly-free molecular flow. Spurious sources and sinks of mass are shown to exist which result in errors of the same order as is being computed.
Energy and momentum equations for disparate-mass binary gases
Authors: Johnson E. A.
Published: February 2004

Normal solutions to the Boltzmann equation are investigated using a reordering of the various collision integrals which is expected to be appropriate for binary gas mixtures in which the species masses are very different from each other but the number densities are comparable. The resulting predictions for the temperatures and flow velocities of the species are obtained and discussed. Conservation and relaxation equations are obtained and compared with results of others. Predictions for a uniform mixture indicate that the approach used is a consistent way of treating disparate-mass binary gases. Finally, it is shown that the results presented here also apply to Lorentzian mixtures.
Kinetic theory of suction flow
Authors: Ganz Anthony , Sirovich Lawrence
Published: February 2004

An exact solution is obtained for the suction flow problem. Hydrodynamical theory is shown to be valid only under a certain limit. The neighborhood of the boundary and the neighborhood of infinity are shown to always be kinetic layers. The exact solution is then used for a general determination of slip coefficients to be used as perturbation boundary conditions in the Chapman-Enskog-Hilbert method. One explicit result of this, is the resolution of the problem of slip velocity in a pressure gradient field.
Measurements of the structure of an ionizing shock wave in a hydrogen-helium mixture
Authors: Leibowitz Lewis P.
Published: February 2004

Shock structure during ionization of a hydrogen-helium mixture has been followed using hydrogen line and continuum emission measurements. A reaction scheme is proposed which includes hydrogen dissociation and a two-step excitation-ionization mechanism for hydrogen ionization by atom-atom and atom-electron collisions. Agreement has been achieved between numerical calculations and measurements of emission intensity as a function of time for shock velocities from 13 to 20 km/sec in a 0.208 H2-0.792 He mixture. The electron temperature was found to be significantly different from the heavy particle temperature during much of the ionization process. Similar time histories for Hβ and continuum emission indicate upper level populations of hydrogen in equilibrium with the electron concentration during the relaxation process. The expression for the rate constant for excitation of hydrogen by atom-atom collisions that best fit the data was kAA = 4.0×10−17 (8kT/πμ)1/2 exp (−10/kT) cm3 sec−1, where it has been assumed that the excitation cross section is the same for hydrogen and helium collision partners. The electron-atom excitation rate constant, k8 = 7.5 × 10−16 (8kTe/πμe)1/2 exp ( −10/kTe), determined from this investigation, was in agreement with recent electron beam cross-section measurements.
Continuum electrostatic probe theory with magnetic field
Authors: Niyogi Kalyan K. , Cohen Ira M.
Published: February 2004

A continuum electrostatic probe theory is developed for a slightly ionized, collision-dominated plasma in the presence of a uniform magnetic field. The governing equations are nonlinear and coupled. A quasilinearization technique is applied to solve the equations numerically using finite difference approximations, in the case of spherical probes larger than a Debye length, the magnetic field being weak. When the probe size is not very large or the probe potential is small, the detailed analysis of the sheath is not necessary. But when the probe potential is large, the sheath needs a separate treatment. The sheath equations are essentially one-dimensional and the magnetic field parameters do not appear explicitly. In the absence of an analytic solution for either the sheath or the main region, both solutions are matched numerically in an overlap region. The effect of magnetic field on the nature of the distribution of the charged particles and the potential in space and on the probe surface is investigated in detail. The phenomenon of “potential overshoot” in the case of a probe biased near plasma potential is clearly revealed. A few representative current-voltage characteristics at various magnetic fields are drawn. A systematic procedure for the interpretation of the probe characteristics is developed.
Waves in a hot uniaxial plasma excited by a current source
Authors: Singh N. , Gould R. W.
Published: February 2004

The fields excited by a short dipole antenna in a hot uniaxially anisotropic plasma (B0→∞) have been studied. When ω<ωp, the dipole effectively excites two propagating waves, a slow wave and a fast wave, inside a cone of half-cone angle sin−1(ω/ωp). Inside the cone a characteristic interference structure in the angular distribution of the fields is noted. Outside the cone fields fall off exponentially. The appearance of the cone and the characteristic interference structure in the field is useful from the viewpoint of laboratory diagnostics.
Measurement of the attenuation of an electromagnetic wave in a bounded hot electron plasma
Authors: Blevin H. A. , Reynolds J. A. , Thonemann P. C.
Published: February 2004

Under certain conditions of electron temperature and mean free path the attenuation of an electromagnetic wave incident on a vacuum-plasma boundary cannot be described in terms of the usual complex conductivity. In a cylindrical plasma with an electron density lying between 1010 and 1012 cm−3, and an electron temperature of 2.2 eV measurements of the attenuation of a small amplitude wave show resonance phenomena due to interaction between the wave and the moving electrons. A theory of this resonance for the case of a plasma slab is compared to the experimental results.
Inertial wave frequency spectrum in a cylindrically confined, inviscid, incompressible, two-component liquid
Authors: Scott Wayman E.
Published: February 2004

A theoretical and experimental study is made of the phenomenon. It is shown that for inertial waves, just as for gravity waves in a two-component liquid, there are discontinuities in the tangential particle velocities at the interface, a fact implying the existence of a vortex sheet for a real liquid. For the particular case wherein the two liquids completely fill the cylinder, other results are obtained that are analogous to those for gravity waves. In particular, if the liquids are nearly of the same density, there are two sets of frequencies, one set characterizing oscillations of the liquid mass as a whole, the other set characterizing very low frequency oscillations at the interface. For the case in which the two liquids have markedly different densities, there are again two sets of frequencies, one set characterizing oscillations of the inner liquid as though the outer liquid were a solid mass, the other set characterizing oscillations of the outer liquid as though the inner liquid were absent. For the general case, physical interpretations are difficult; hence, a table of frequencies versus composition is given.
Transport equations for dilute plasma in a magnetic field
Authors: Price John C.
Published: February 2004

Equations are derived for near-equilibrium transport of plasma in a strong magnetic field. These equations reduce to the collision dominated (fluid) equations, and to the collisionless (Chew-Goldberger-Low) equations in the respective limits.
Ray method for nonlinear wave propagation in a rotating fluid of variable depth
Authors: Shen M. C. , Keller Joseph B.
Published: February 2004

An asymptotic method based upon the principles of geometrical optics, which has been used for linear problems, is extended to nonlinear wave propagation in a rotating fluid of variable depth. It yields the same modes, the same phase function, and the same rays as does the linear theory. However along each ray the amplitude satisfies a nonlinear equation of Korteweg-DeVries form. Thus, the theory combines certain features of the linear theory of short waves and the nonlinear theory of long waves. The theory is developed for a layer of fluid with a free surface or for an atmosphere which extends upward to infinity, and also for fluid in a channel or a waveguide. It may be useful in dealing with problems of geophysical interest.
Some effects of suspended particles on the onset of Bénard convection
Authors: Scanlon John W. , Segel Lee A.
Published: February 2004

In the simplified case considered, particles decrease the critical temperature difference for the onset of convection by increasing the heat capacity of the fluid. A proof of exchange of stabilities shows that there is no effect of particle drag when instability sets in, although the rate at which unstable perturbations grow is affected by this factor. Thermal force alone can, in principle, give rise to instability in layers heated from above or below. The results are discussed with reference to experiments in gas-particle mixtures which show “columnar instabilities” at unusually low-temperature differences.
Boundary layer separation due to mass addition
Authors: Amr A. F. , Kassoy D. R.
Published: February 2004

The effects of foreign gas mass addition of classical boundary layer magnitude on the compressible flow past a hot (cold) flat plate in a high-speed uniform air flow are studied. In the case of a wall injection distribution m = C (2 x Re)−1/2, it is shown that there is a critical value of C depending upon the injected species properties, for which classical boundary layer theory fails. An interaction theory is developed which is uniformly valid in the limit Re→∞. The analysis is based on a three layer model consisting of inviscid rotational injectant region O (Re−1/3) in thickness, a free viscous shear layer O O(Re−1/2), and the potential external flow. It is shown that the displacement effect of the thick injectant layer causes a correction to the external flow which results in a weak interaction favorable pressure gradient. The formulas for the pressure interaction and the wall shear indicate that the injection of a warm, low molecular weight gas has the most dramatic influence on the flow configuration. It is also shown that heat transfer to the wall is considerably reduced from the value predicted by classical boundary layer theory.
Study of strong temperature mixing in subsonic grid turbulence
Authors: Lin Shih-Chun , Lin Shao-Chi
Published: February 2004

Strong temperature mixing in subsonic air turbulence is studied in an open-circuit wind tunnel with a 0.5 m cross section. The specially constructed heating grid consumes up to 300 kW of electric power at a mean flow velocity of 11 m/sec. The highest mean absolute temperature 〈T〉 reaches 370°K, while the rms temperature fluctuation θ′ at midtunnel is typically 6°K. Basic statistics of the temperature field are measured and discussed. It is found, in particular, that (i) the streamwise decay of the normalized mean-square temperature fluctuation (θ′ / < T >)2 is not sensitive to the applied heating rates, suggesting that so far buoyancy contributes little to the dynamics of the turbulence; (ii) the observed decay rates are much higher than those reported by others in the literature and are consistent with the higher drag characteristics of the present grid; (iii) the temperature fluctuation spectrum, when normalized by local fluid properties and dissipation rates, retains a universal form and show an inertial-convection subrange of limited extent; (iv) the one-dimensional universal scalar inertial Kolmogoroff constant, β1, determined from such subrange has a value of 0.60±0.06.
Numerical solution of the Krook kinetic equation for flow past a cylinder
Authors: Richter Gerard
Published: February 2004

The Krook kinetic equation is used as the governing equation in an investigation of a class of exterior flow problems involving flow past an elliptic cylinder. A numerical method for solving the integral equation form of the Krook equation for this class of problems is described, and several sets of solutions are presented.
Inverse problem in transport theory
Authors: Case K. M.
Published: February 2004

The conventional problem of linear transport theory is to find the distribution function given the various scattering functions. Here, the inverse question is asked. Given the results of some simple experiment how can one construct the kernels? First, the simple problem of one velocity neutron diffusion is considered, and it is found that the methods and solution are quite similar to that for the problem of deducing a potential given the scattering data. The solution given is constructive and seems to be efficient.
Interrelated structures of the transport shock and collisional relaxation layer in a multitemperature, multilevel ionized gas
Authors: Viũolo Antonio R. , Clarke Joseph H.
Published: February 2004

The gas dynamic structures of the transport shock and the downstream collisional relaxation layer are evaluated for partially ionized monatomic gases. Elastic and inelastic collisional nonequilibrium effects are taken into consideration. In the microscopic model of the atom, three electronic levels are accounted for. By using an asymtpotic technique, the shock morphology is found on a continuum flow basis. This procedure gives two distinct layers in which the nonequilibrium effects to be considered are different. A transport shock appears as the inner solution to an outer collisional relaxation layer. The results show four main interesting points: (i) On structuring the transport shock, ionization and excitation rates must be included in the formulation, since the flow is not frozen with respect to the population of the different electronic levels; (ii) an electron temperature precursor appears at the beginning of the transport shock; (iii) the collisional layer is rationally reduced to quadrature for special initial conditions, which (iv) are obtained from new Rankine-Hugoniot relations for the inner shock.
Structure of strong shock waves in xenon. II: Further experiments and theoretical interpretation
Authors: Foley William H. , Bader Jon B. , Nerem Robert M.
Published: February 2004

Electron temperature measurements in the ionized xenon gas downstream of a shock front are obtained using brightness observations of the XeII 5292-Å line. The results show good agreement with previous measurements obtained using a two line intensity ratio technique. A theoretical model of the shock structure is developed which considers nonequilibrium collisional and continuum radiative transitions. The theoretical calculations agree qualitatively with the experimental observations and indicate the paramount importance of radiative heating of the electron gas within that portion of the shock structure which is otherwise dominated by elastic and inelastic electron-heavy particle collisions. The theoretical calculations also provide a detailed time history of the populations of the first four excited levels of XeII and indicate that the higher excited levels may justifiably be assumed in equilibrium with each other in a Boltzmann sense at the local electron temperature. Considered are shock velocities between 6.0 and 10.0 km/sec at an upstream pressure of 0.1 Torr.
Structure and luminosity of strong shock waves in air
Authors: Zinn John , Anderson R. C.
Published: February 2004

A set of numerical computations of the thermal structure and optical luminosity of strong shock waves in air is described. The model includes radiation transport coupled with hydrodynamics under assumed conditions of steady flow. With shock velocities above 10 km/sec a thermal precursor develops ahead of the shock front, and increases in prominence with increasing shock strength. For velocities above 50 km/sec the precursor is partially opaque to visible light and the computed brightness is smaller than that of a blackbody at the shock temperature. At higher velocities the brightness decreases with increasing shock strength. Steady solutions could not be found for velocities above 80 km/sec.
Plasma transport in a torus of arbitrary aspect ratio
Authors: Hazeltine R. D. , Hinton F. L. , Rosenbluth M. N.
Published: February 2004

Finite aspect ratio modifications to neoclassical transport theory are considered. In the general case of arbitrary flux surface geometry, a closed set of macroscopic equations is derived. These include the equation which determines the time evolution of the flux surfaces. In the large aspect ratio case, the O (r /R ) corrections to the order O (r )1/2)R (1/2)) transport coefficients, calculated previously, are obtained. In particular, an expression for the electrical conductivity is obtained which may be regarded as exact for all experimentally interesting aspect ratios.
Observation of neoclassical diffusion effects on plasma losses produced by magnetic field asymmetries
Authors: Meade Dale M. , Fonck Raymond J.
Published: February 2004

Cross field loss of a partially ionized plasma induced by magnetic field asymmetries varies as the reciprocal of the collision frequency, ν, at large ν and as ν at small collision frequencies. The value of the collision frequency at peak loss ( ≈ 40 times classical for 1% field asymmetries) is a function of the asymmetry amplitude and wavelength. These observations can be accounted for in terms of an ambipolar neoclassical diffusion model taking into account field asymmetries in a shearless multipole-like device.
Diffusion in electron cyclotron resonance heating magnetic mirrors
Authors: Lichtenberg A. J. , Melin G.
Published: February 2004

A theory of electron cyclotron resonance heating in a mirror device is applied to the radio frequency induced particle diffusion into the loss cone. It is shown that the loss time is much slower than the heating time within the stochastic heating region, but that the losses are strongly enhanced over collisional losses alone. The effects of collisions in combination with the electron cyclotron resonance heating are considered and found to give additional heating beyond the adiabatic barrier, on the time scale of the 90° collisional deflection. The collisions also act, together with the radio frequency fields, to enhance the rate of loss cone diffusion. The major assumptions and results of the theory are confirmed by exact numerical calculations. Predictions of the performance of a 25 kW electron cyclotron resonance heating experiment are made.
Experiments on ion-acoustic solitary waves
Authors: Ikezi H.
Published: February 2004

Ion-acoustic solitary wave (solitons) have been studied experimentally by employing a double-plasma device. The solitary waves are found to be produced from both a single compressional pulse and a continuous wave. A rarefaction pulse also produces solitons if the pulse width is sufficiently wide. A theory based on the Schrödinger equation accounts for the number of solitons. Recurrence to the original state is observed when a continuous wave is launched. A simple wave-wave coupling analysis for the recurrence of the original state is given.
Enhanced incoherent scattering at the upper-hybrid resonance. I. Cold plasma theory
Authors: Fidone I.
Published: February 2004

Incoherent scattering of microwaves at the upper-hybrid resonance in an inhomogeneous plane-layered plasma is investigated. The incident and scattered waves propagate in the plane characterized by the directions of the density gradient and the externally imposed magnetic field. The frequency of the waves is close to the cyclotron frequency and therefore full account of the dispersive properties of the plasma is taken. The principal aim of the study is the investigation of collective effects on the scattered flux of energy in a toroidal machine and therefore the case of accessible resonance and frequency shift of the order of the ion frequency are specificallly considered. Except in the spectrum of the density fluctuations, thermal effects are neglected. This is the collision-dominated case. The relevant equations are solved for the case of opaque plasma and the scattered flux of energy is estimated. The result obtained indicates that enhancement of the scattering cross section with respect to the transparent scattering is expected for ν/ω ≪ 1, where ν is the electron collision frequency.
Enhanced incoherent scattering at the upper-hybrid resonance. II. Warm plasma theory
Authors: Fidone I. , Granata G.
Published: February 2004

Incoherent scattering of microwaves at the upper-hybrid resonance in an inhomogeneous stratified warm plasma is investigated. The incident and scattered waves propagate in the plane characterized by the directions of the density gradient and the externally static magnetic field. Ordinary collisions are neglected and finite Larmor radius corrections in the dielectric tensor are taken into account. The structure of the incident wave field near the hybrid layer is discussed, and it is shown that the component of the incident Poynting vector along the density gradient is totally converted into Bernstein plasma waves. The energy flux of the scattered radiation is also calculated. The result obtained indicates that for T / m c2 enhancement with respect to the usual high-frequency scattering (ω ≫ ωp , ωc) is expected.
Nonquasineutral theory of ion-acoustic resonances in bounded nonuniform plasmas and comparison with experiments
Authors: Weynants R. R. , Messiaen A. M. , Vandenplas P. E.
Published: February 2004

A theory is developed of ion-acoustic resonances in inhomogeneous plasmas of the positive column type using a fluid plasma description. Poisson's equation is properly taken into account, instead of applying the usual assumption of wave quasineutrality. The order of the differential equation describing the wave is thereby increased by two and the singularity that previously occurred as a result of the presence of a sheath region is thereby removed. It is shown that ion-acoustic resonances are confined within the plasma core, the effective boundary not being the wall, but the region in the plasma where the macroscopic ion flow velocity attains the Bohm velocity (KTe/mi)(1/2). The theoretical predictions are substantiated by a number of experiments taken from the literature and supplemented by a series of new experiments. The theory sheds new light on the problem of wave reflection from a negatively polarized wall and the damping of ion-acoustic waves propagating in inhomogeneous plasmas.
Trapped ion instability in plasmas with magnetic shear
Authors: Gladd Nevel T. , Ross David W.
Published: February 2004

The radial structure of the dissipative trapped ion mode is studied in order to determine the effect of shear and the possibility of finding ranges of tokamak operation which are stable to this mode even in the presence of a temperature gradient. It is found that owing to the presence of increasing numbers of resonant untrapped ions near the mode rational surfaces, where lq is an integer, the radial wavelengths are reduced and the modes are strongly Landau damped. These effects increase with increasing shear and with increasing values of l, the toroidal mode number. Numerical estimates of the growth rates and marginal stability conditions are obtained from eigenmode solutions of the radial differential equation and from algebraic dispersion relations which simulate the effects of the radial structure. It is concluded that if (r /q )d q / d r exceeds one, then the temperature threshold for instability is raised by approximately a factor of two from that of the no shear case. It is also proposed that even in unstable regimes, the anomalous diffusion should be less than indicated by previous estimates, since both the growth rates and wavelengths are reduced.
Laser light forces and self-focusing in fully ionized plasmas
Authors: Shearer J. W. , Eddleman J. L.
Published: February 2004

A derivation is given for the nonrelativistic equation of motion of a fully ionized isothermal plasma in the presence of an intense electromagnetic wave, such as laser light. The result can be expressed in a form similar to an equation used in the microwave confinement of plasmas. Applications of the result are made to the evaluation of self-focusing effects. The forces exerted on the plasma are found to be significant magnitude at contemporary intensity levels for neodymium laser radiation at λ = 1.06 μm.
Measurement of plasma electron temperature with an ion beam probe
Authors: Reinovsky R. E. , Jennings W. C. , Hickok R. L.
Published: February 2004

An ion beam probing technique has been developed to measure the electron temperature in a magnetically confined plasma. The technique, involving the use of two akali metal ion beams, provides accurate measurements of electron temperatures below 100 eV.
Harmonic wave propagation of low-frequency electrostatic waves in magnetic field
Authors: Ohnuma Toshiro
Published: February 2004

For ion waves propagating perpendicular to a magnetic field, the harmonic signals grow spatially in some region similarly to the case without a magnetic field. The theory of wave-wave coupling of electrostatic waves in a magnetic field is obtained to explain the experimental results.
Multipole-like solutions for an equilibrium plasma carrying nonuniform current
Authors: Bhadra D. K.
Published: February 2004

It is shown that multipole-like solutions exist for an equilibrium plasma carrying nonuniform current. A special case is obtained where flux constant surfaces resemble the figure eight.
Local temperature measurements in supercritical counterflow in liquid helium II
Authors: Dimotakis Paul E. , Broadwell James E.
Published: February 2004

In order to investigate the validity of appending the Gorter-Mellink friction term to the equations of motion of liquid helium, the temperature was measured along the axis of a channel carrying a supercritical heat current. A single thermomenter on a traversing assembly was used permitting local measurements both in the interior of the channel and in the jet formed in the free fluid. The temperature gradient in the interior of the channel is found to be in agreement with the Gorter-Mellink law up to the lambda point, but goes to zero within a channel radius, in the free jet. The Gorter-Mellink A (T ) was also measured up to the lambda point. A much stronger divergence is found as T λ is approached than was indicated by previous measurements.
Interfacial solitary waves in a two-fluid medium
Authors: Walker Lloyd R.
Published: February 2004

Solitary waves are generated on the interface between two immiscible liquids with free upper surface; their behavior is generally consistent with that predicted by the Korteweg-de Vries equation. Inviscid theory expanded to include capillary effects predicts unchanged wave speed and narrowed wave shape to first order in amplitude regardless of upper boundary condition; but measured speeds are down 8% and narrowing is substantially greater at very small amplitudes. The speed difference appears consistent with an interfacial viscous boundary layer. The critical depth ratio separating the elevation and depression modes of the stable gravity solitary wave ageees with prediction in the inviscid limit. The design of a programmed, variable flux wavemaker for efficiently generating interfacial waves is discussed.
Experimental study of Taylor instability
Authors: Cole R. L. , Tankin R. S.
Published: February 2004

An experimental study was made of the instability of an accelerated water-air interface. The measured growth rate agreed with theory. The method of analysis of the data reduced scatter in the results and allowed the growth rate of second order waves to be determined. The growth rate of second-order waves agreed reasonably well with theory of Emmons, Chang, and Watson.
Mass transfer to a rotating disk in a non-Newtonian fluid
Authors: Greif R. , Paterson J. A.
Published: February 2004

A theoretical relation has been obtained for the mass flux to a rotating disk in a non-Newtonian fluid which includes the convective transport in the radial direction. This result has then been used to obtain improved values for the diffusivities of oxygen in aqueous sodium chloride solutions which were rendered non-Newtonian by addition of Polyox WSR 301.
Velocity and heat transfer measurements in thermal convection
Authors: Garon A. M. , Goldstein R. J.
Published: February 2004

Measurements were taken of the heat transport and vertical component of the fluid velocity in a horizontal layer of water heated from below. The heat transfer results were well correlated by a simple power law relationship and indicated the possibility of flow transitions even at relatively high Rayleigh numbers. The velocity measurements were obtained optically and compared to predictions of Kraichnan.
Diffusion drag upon slowly evaporating droplets
Authors: Gal-Or B. , Yaron I.
Published: February 2004

Asymmetric distribution of interfacial mass fluxes is responsible for diffusion drag. Its contribution to over-all drag is appreciable for strongly circulating drops and less so for noncirculating ones. Both self-similar and uniformly distributed interfacial fluxes cause the separating stream line to detach from the interface.
Transport coefficients of high-temperature nitrogen
Authors: Capitelli M. , Devoto R. S.
Published: February 2004

The electrical conductivity, the translational, reactive, and internal thermal conductivity and the viscosity have been calculated for nitrogen at 1-atm pressure and temperatures from 5000-35 000°K. Generally satisfactory agreement is noted between the properties as computed and measured in the electric arc.
Experimental turbulence spectra in neutral and ion components of a weakly ionized gas
Authors: Küyel B. , Gruber S.
Published: February 2004

A weakly ionized argon gas flows in a 2 cm diam tube at 60-100 m/sec velocities and at mean pressures of 20-50 Torr, producing turbulence in the channel with Reynolds numbers ranging from 2000 to 6000. One-dimensional turbulence spectra are detected by laser interferometry and Langmuir probes. The experimental results obtained by these two methods show a new region between the Kolmogoroff and the dissipation region where the spectrum of both the neutrals and the ions vary as k −13/3 (where k is the wave number). It is concluded that this intermediary region is associated with fluid effects rather than being a consequence of ambipolar diffusion of particles in the plasma as has been suggested. Furthermore, it is suggested that compressibility may be responsible for the intermediary region of turbulence spectra.
Stability of plane Hartmann flow subject to a transverse magnetic field
Authors: Potter Merle C. , Kutchey James A.
Published: February 2004

The stability of an electrically conducting fluid flowing between parallel planes subject to a transverse magnetic field is investigated for infinitesimal three-dimensional disturbances. Primary interest is in the effect of the magnetic field on the critical point of the neutral stability curves. The governing stability equations include perturbations for both the velocity and magnetic fields and result in a sixth-order coupled set of linear differential equations. The results indicate a strong dependence of the critical eigenvalues on both the magnetic field strength and a fluid property, the magnetic Prandtl number. The effect of both is to stabilize the flow.
Unsteady magnetohydrodynamic boundary layer on a semi-infinite flat plate
Authors: Evans Norman A.
Published: February 2004

An analysis was performed on the incompressible, unsteady, magnetohydrodynamic boundary layer on a semi-infinite flat plate mounted in a duct. The stream unsteadiness was composed of a small sinusoidally oscillating component superimposed on a constant value, while the constant magnetic field was normal to both the stream and the plane of the plate. Solutions to the momentum and energy equations were obtained by numerical integration for the unsteady magnetic interaction effects, including dissipation, using a product series expansion in the Strouhal number s and a Hartmann-Reynolds number parameter χ. A time and distance dependent boundary condition at the edge of the thermal layer was properly satisfied using this expansion procedure. The results show that, while increases in skin friction and heat transfer occur both with the steady magnetic case (s = 0,0 < χ ⩽ 0.2) and with the unsteady nonmagnetic case (0 < s ⩽ 0.6, χ = 0), the full unsteady magnetic interaction produces amplitude increases in these quantities with s, but a conteracting decrease with χ. Other results presented include the unsteady magnetic interaction effects on the phases of the skin friction and heat transfer.
Resistive instability of a shearing boundary layer with imbedded shearing magnetic fields
Authors: Lessen Martin , Zien Hwa M.
Published: February 2004

The stability of a special three-dimensional shearing boundary layer with imbedded shearing magnetic fields is studied. Boundary layer solutions are obtained for a finitely, electrically conducting fluid, and then the sixth-order differential equations describing the instability are solved numerically. It is found that the flow is always unstable and that the neutral stability curves pass through the origin of the α-R diagram, where α is the wave number and R is the Reynolds number. An increase of the magnetic field tends to stabilize the flow when the conductivity is small or extremely large. An increase of resistivity has a stabilizing effect at moderate magnetic Prandtl number and a destabilizing effect at high magnetic Prandtl number.
Wall shape effects on straight doublet equilibria
Authors: Dobrott D. , Chu M. S. , Ohkawa T.
Published: February 2004

The effect on magnetohydrodynamic equilibria of conducting wall shape in a straight plasma current multipole, or doublet, is studied by examination of two extreme longitudinal current models. For the first of these models, the current is concentrated in two filaments which are symmetrically located in the cross section of the device. In the second model, the current density is uniform over the cross section. If the neck size is appropriately chosen, the two-filament case is excluded and the proper doublet equilibrium is obtained. For a neck size which allows both models, the poloidal magnetic fields at the wall are compared.
Extension of the guiding-center model to three-dimensional plasma diffusion
Authors: Vahala George
Published: February 2004

The three-dimensional plasma model of Montgomery, Lin, and Vahala [Phys. Fluids 15, 815 (1972)] is extended to include the effects of the fluctuating electric field on the particle motion along constant, uniform magnetic field lines. The particles are assumed to move across the field lines with the guiding-center E × B drift. The thermal equilibrium coefficient of spatial diffusion across the magnetic field is calculated and exhibits both a Bohm-like 1 / B dependence and a 1 / B2 dependence on the magnetic field. The 1 / B2 term is independent of the plasma volume. The 1 / B term contains a multiplicative factor which goes to zero as the plasma volume becomes infinite.
Collision-dominated plasma transport in toroidal confinement systems
Authors: Hazeltine R. D. , Hinton F. L.
Published: February 2004

The collisional regime of neoclassical transport theory is investigated, using a moment equation approach as well as a method based on the drift kinetic equation. Allowing for both density and temperature gradients, and an externally induced toroidal electric field, the transport coefficients describing particle and energy flux perpendicular to the magnetic field of an axisymmetric confinement system are derived. Relations between the parallel and perpendicular fluxes, which are exact in the collisional regime, are also derived. Charge neutrality is used to obtain the electrostatic potential variation on a magnetic surface.
Effects of dissipation on convective stability in a stratified plasma
Authors: Yu C. P. , Cheng W. H.
Published: February 2004

The instability induced by a vertical external gravitational field in a stratified plasma permeated by a uniform horizontal magnetic field is investigated by means of an expansion method. Dissipative processes arising from finite electrical and thermal conductivities are considered. It is found that a new unstable mode exists and a new condition, in addition to the Schwarzschild condition, must be satisfied for stability. The new stability condition is associated with the modes which exist in the nondissipative plasma, but are modified by dissipation. The net effect of this new condition is to destabilize the system.
Nonlinear properties of the internal m = 1 kink instability in the cylindrical tokamak
Authors: Rosenbluth Marshall N. , Dagazian R. Y. , Rutherford P. H.
Published: February 2004

An analysis is presented, in a cylindrical approximation, of the nonlinear behavior of the m = 1 magnetohydrodynamic kink instability that occurs in a tokamak when the “safety factor” q(r) = rBz / RB θ(r) falls below unity on axis. A kinked neighboring equilibrium is found, which is accessible from the initial straight equilibrium in the sense of satisfying the flux-conservation constraints. Owing to the singular nature of the fundamental, all harmonics are excited in a singular region near where q (r) = 1. The nonlinear amplitude is moderate. It is shown that growing modes of this type should produce negative voltage spikes and inward shifts in major radius, as are seen in the experiments. The predicted magnitudes of these two effects are, however, much smaller than those observed.
Nonlinear growth of the tearing mode
Authors: Rutherford P. H.
Published: February 2004

The resistive tearing mode is analyzed in the nonlinear regime; nonlinearity is important principally in the singular layer around k·B = 0. In the case where the resistive skin time τs is much longer than the hydromagnetic time τ H, exponential growth of the field perturbation is replaced by algebraic growth like t2 at an amplitude of order (τ H / τ S )4/5. Application of the theory to the unstable tearing modes of a tokamak with a shrinking current channel yields good agreement with the observed amplitudes of the m ≥ 2 oscillations. The analysis excludes the very long wavelength mode, and m = 1 in the tokamak, for which the “constant-Ψ” approximation is invalid.
Kink instabilities in a high-β tokamak
Authors: Freidberg J. P. , Haas F. A.
Published: February 2004

A toroidal, circular cross section, sharp-boundary model of a high-pressure tokamak with currents confined to the surface, is tested for stability against kink modes. It is shown that for β > 0.21 ε, where ε is the inverse aspect ratio, the model is unstable to the n = 1 kink mode (n is the mode number the long way) for all values of the safety factor above and below the Kruskal-Shafranov limit. Along the n = 1 marginal stability line m = 2 (m is the mode number the short way) is found to be the dominant harmonic.
Low-frequency waves in a weakly ionized, rotating magnetoplasma
Authors: Wheeler George M. , Pyle Robert V.
Published: February 2004

A single-fluid theory is developed which explains the experimental behavior of a low-frequency (∼ 2 kHz) flute instability in a hollow cathode discharge plasma. The effects of density gradient, centrifugal, and Coriolis forces due to plasma rotation in a nonuniform, radial electric field, and ion-neutral collisions are included in a linear fluid theory. A cubic dispersion equation results which is solved numerically using experimental plasma profiles. In the low-frequency limit (ω/Ωi ≪ 1), the dispersion relation reduces to a quadratic expression which is consistent with earlier work in the appropriate limits. Collisions are found to be stabilizing, while the Coriolis effect depends on the direction of plasma rotation. The theory is able to predict, within experimental uncertainty, the frequencies observed in two similar experiments.
Stability of a toroidal plasma subject to neutral injection
Authors: Stix Thomas H.
Published: February 2004

Neutral injection of fast atoms into a toroidal plasma can produce, after ionization, a double-humped velocity distribution with appreciable spatial inhomogeneity in the fast-ion component. Fluid instability may be excited in the Kelvin-Helmholtz and temperature gradient drift modes, and microinstability may appear in the drift wave and in the quasiperpendicular acoustic mode.
Efficient trapping of high-level E layers in a strong toroidal field
Authors: Briggs R. J. , Porter G. D. , Stallard B. W. , Taska J. , Weiss P. B.
Published: February 2004

Efficient trapping of high-level E layers in the presence of a strong toroidal field (Bθ∼ Bz) has been achieved in the astron experiment at Lawrence Livermore Laboratory. The beam was injected into hydrogen gas at pressures around 0.1 mTorr resulting in the prompt formation of plasma with a density of 1012/cm3, Single-pulse trapping efficiencies greater than 50%, circulating currents in excess of 13 kA with a typical half-life of 1 msec, and diamagnetic strengths (ζ) up to 75% were achieved. Using the multiple pulse capability of the astron linac, “maintenance” of an E layer at ζ ∼ 30% was demonstrated.
Observation of sheath excitation of electrostatic waves and ion bursts in a plasma
Authors: Hauck James P. , Rynn Nathan , Benford Gregory
Published: February 2004

A potential pulse applied to the end plate of a plasma column in a Q machine excites a high velocity electrostatic plasma mode and releases ions from the adjacent sheath. Above a critical pulse height (eV 0 ≫ k T) bursts of ions are launched which had been trapped in the potential troughs at the Q-machine end plates. The ions acquire a fraction of the pulse voltage and the bursts broaden in accord with an ion thermal spreading as they move down the column. When the electrostatic mode reaches the other end plate, the ions trapped in the sheath are also launched sending ions streaming back toward the initial plate. Ion acoustic pulses and ion acoustic resonances are also observed under certain conditions.
Self-consistent approach to anomalous resistivity applied to theta pinch experiments
Authors: Liewer Paulett C. , Krall N. A.
Published: February 2004

A theoretical model of magnetic pulse propagation in collisionless plasmas is derived starting from the Vlasov equation. The model consists of a set of fluid equations which include the effects of turbulence self-consistently through anomalous transport terms which evolve in space and time as instabilities develop and as the macroscopic plasma parameters change. Results from numerical integration of these equations explain most of the phenomena of a theta pinch experiment with no initial magnetic field and with small pulsed fields. There was similar agreement with the gross penetration times and effects of changing density in theta pinch experiments with initial bias fields and large pulsed fields. Probable causes of the remaining differences are discussed.
Frequency shift of a plasma mode of arbitrary amplitude
Authors: Lee A. , Pocobelli G.
Published: February 2004

A computer simulation of a plasma in which an electron plasma mode was excited was performed. The asymptotic frequency of the mode was determined in correspondence with a wide range of amplitudes. Results at the larger amplitudes, where existing analytical theories are invalid, show an increasingly larger shift in the frequency of the mode, with respect to the linear frequency. At the smaller amplitudes, the simulation points are in good agreement with the analytical results reported by the same authors. To complement the latter results, the nonlinear dispersion equation was solved numerically in time. At times longer than one trapped electron period [T = 2π (m / eAk )1 /2, where A and k indicate the amplitude and the wavenumber of the mode, respectively], the frequency shift is found to oscillate as predicted by Morales and O'Neil; at shorter times, however, the existence of a new, pronounced minimum for the magnitude of the frequency shift is reported.
Plasma created in a neutral gas by a relativistic electron beam
Authors: McArthur D. A. , Poukey J. W.
Published: February 2004

Theoretical and experimental studies have been made of the plasma current created by an electron beam propagating in a neutral nitrogen gas. Beams of ∼ 2 and 20 kA/cm2 and energies ∼ 3 and 0.25 MeV were investigated, and agreement within about ± 15% between theory and experiment was found for the net current. The model used includes primary and secondary ionization processes, electron-neutral and electron-ion collisions, recombination and depletion of N2 molecules. Detailed results for the spatial and temporal variation of the plasma density (∼ 1015 cm−3) and temperature (∼ 5 eV) are presented.
Behavior of vortex rings in the vicinity of a wall
Authors: Boldes U. , Ferreri J. C.
Published: February 2004

An experiment is described which shows that a vortex ring traveling toward a wall situated normal to its axis may undergo momentary inversions of its forward velocity. A qualitative analysis of the physics involved is given.
Turbulent energy production, dissipation, and transfer
Authors: Brodkey Robert S. , Nychas Stavros G. , Taraba Joseph L. , Wallace James M.
Published: February 2004

A new interpretation of production and diffusion of turbulent kinetic energy is given which results from combining terms in the turbulent kinetic energy equation. The new production term is the average of instantaneous production. The diffusion term is in the form of Fick's law of diffusion.
Convection in a vertical porous slab
Authors: Wolanski E. J.
Published: February 2004

It is shown that the basic flow of the fluid saturating a vertical porous slab, whose walls are maintained at constant, but different, temperatures, is asymptotically stable in the mean against disturbances of arbitrary amplitude, when the Rayleigh number is smaller than 4π2.
Nonaxisymmetric modes of instability in heterogeneous swirling flows
Authors: Fung Y. T. , Kurzweg U. H.
Published: February 2004

The inviscid stability of a heterogeneous swirling flow against infinitesimal disturbances of arbitrary asymmetry is examined and curves of neutral stability for several different modes are obtained. Results show that nonaxisymmetric disturbances can amplify under conditions where axisymmetric modes are stable.
Lateral penetration of a plane shock front by a rarefaction wave
Authors: Fields S. F.
Published: February 2004

The rate of lateral penetration of a plane shock front by a rarefaction wave can be calculated in terms of shock Mach number through the use of standard normal shock relations. For a given spatial variation of the shock Mach number, the extent of this penetration can also be determined.
Imploding detonations with variable heating
Authors: Strachan J. D.
Published: February 2004

The Chester-Chisnell-Whitham model for the implosion of detonations and shocks has been extended to allow for variation in the energy absorbed per particle during the implosion process.
Improved Bhatnagar-Gross-Krook model of electron-ion collisions
Authors: Greene John M.
Published: February 2004

Previous models of the BGK type for ion-electron collisions are modified to produce the correct relation between the time scales for ion-electron momentum exchange and ion thermalization.
Spatial change of ion beam by collisions
Authors: Ohnuma Toshiro , Fujita Takao
Published: February 2004

The probability of the collision of an ion with neutral-gas atoms is obtained from the decay length of the ion-beam intensity by an injection of an ion beam into a weakly ionized plasma. The damping of the ion-beam intensity is compared with the collisional damping of an ion acoustic wave.
Relativistic electron beam trajectories
Authors: Ott Edward , Lovelace R. V.
Published: February 2004

A heuristic discussion is given of the influence of the self-magnetic field on the trajectory of a high-current relativistic electron beam in different external magnetic fields.