bluuebunny/crossref_metadata_2025 huggingface dataset:
Shock tube study of ionization rates of NaCl-contaminated argon
Authors: Schneider Klaus-Peter , Park Chul
Published: March 2003

Electron density, electron temperature, and concentration of excited sodium atoms are measured in the weakly ionized regime behind a shock wave in impure argon in a shock tube using microwave techniques and spectrally resolved radiometry. Evidence is presented to show that an apparent increase in the rate of ionization is due to electron detachment of negative chlorine ions produced from sodium chloride vapor contained as an impurity. To be consistent with this chemical model, rate coefficients are found for 5500<T<8600 °K to be as follows: for NaCl+Ar+5.8 eV→Na++Cl−+Ar, k4=0.082exp(−67 315/T)/T2 cm3 sec−1; for Cl−+Ar+3.61 eV→Cl+e+Ar, k5=6×10−12exp(−41 900/T) cm3 sec−1; and for the branching ratio between the reaction NaCl+Ar+5.8 eV→Na++Cl−+Ar(k4) and reaction NaCl+Ar+4.27 eV→Na+Cl+Ar(k3), k4/k3=1.6×104exp(−17 760/T). Electron temperature is lower than heavy particle temperature by roughly 1000 °K. The electron-argon impact ionization rate coefficient is a weak function of electron temperature in contradiction to expectation.
Transverse diffusion of particles and energy in a laser-heated plasma column
Authors: Bethe H. A. , Vlases G. C.
Published: March 2003

In a laser-heated magnetically confined column of plasma separated from material walls by a vacuum field, laser energy absorption near the center leads to a ’’light pipe’’ effect essential to the concept of heating long columns to fusion temperatures. Outward diffusion of particles at the vacuum-plasma boundary tends to move the position of maximum density inward, and hence to narrow the light pipe, while over-all expansion of the heated column against the field tends to widen it. A model is formulated to describe these effects and is treated analytically and numerically. The results indicate that for conditions of interest, the light pipe will persist long enough to permit heating of reactor-scale columns.
Dynamics of the dense plasma focus as determined from an analysis of laser scattering spectra
Authors: Downing J. N. , Eisner M.
Published: March 2003

Time resolved 90° scattering spectra have been observed from a dense plasma focus illuminated by a pulse of laser light, for two axial positions, 0.6 cm and 1.3 cm from the face of the center electrode. Scattered laser light was observable in the time interval from 10 nsec prior to the arrival of the collapse on axis until the time when the visible light bremsstrahlung from the dense pinch decreased below the background illumination of the plasma sheath. The frequency spectrum was markedly asymmetric about the laser frequency, and a model has been postulated which attributes the asymmetry to the effects of a nonisotropic velocity distribution. Analysis of the data based on this model has given the radial collapse velocity (≈3.5×107 cm/sec), density (2–4×1019 cm−3), and ion temperature (?70 eV) in the plasma sheath. No scattering from the dense pinch region was observed, and an implied axial flow velocity of ≳ 108 cm/sec was inferred from the experimental results.
Two-dimensional relativistic simulations of resonance absorption
Authors: Estabrook K. G. , Valeo E. J. , Kruer W. L.
Published: March 2003

Resonant absorption has been simulated for radiation of energy density E20/4πnT ranging from much less than to somewhat greater than unity. Characteristic features of the absorption process are an absorption efficiency of approximately 50%, generation of suprathermal particles, and strong modification of the density profile in the vicinity of the critical density. The latter effect, the appearance of a finite density variation over the distance of a few Debye lengths, is forced by strong gradients in the plasma wave intensity and electron temperature. Such a density discontinuity greatly enhances the range of incidence angles for which resonance absorption is effective and decreases the effects of the oscillating two-stream and ion-acoustic decay instabilities.
Poloidal field measurements in the ST tokamak by harmonic generation at the upper hybrid layer
Authors: Cano R. , Fidone I. , Hosea J. C.
Published: March 2003

An extraordinary incident wave propagating along the major radius through the ST tokamak plasma is used to generate a second harmonic wave at the upper hybrid layer. Remote polarization measurements of the harmonic yield the poloidal magnetic field profile. The estimated over-all error in the measurement of the rotation angle of the total magnetic field is ≃0.3×10−2 rad. Further improvements in the accuracy of the measurements which are required to specify the current density profile unambiguously are discussed.
Velocity shear driven instabilities of an unneutralized electron beam
Authors: Antonsen Thomas M. , Ott Edward
Published: March 2003

The stability of a planar electron beam with a linear velocity shear both parallel and perpendicular to a fixed, uniform magnetic field is examined. In the case of a beam bounded by conducting walls, an exact criterion for stability is determined for perturbations of arbitrary wavelength. A similar, although more involved, criterion is given for a beam isolated from conducting walls. Estimates of the growth rate of the instabilities are determined for both long and short wavelength perturbations.
Surface waves at the interface separating two slipping plasma streams
Authors: Seshadri S. R.
Published: March 2003

The characteristics of the electromagnetic surface waves supported by the interface separating two plasma streams slipping along the interface in opposite directions with the same speed are analyzed.
Energy of plasma waves
Authors: Schmidt G.
Published: March 2003

A new definition of the sign of wave energy is given, which is valid where the old definition based on an expansion procedure breaks down. It is shown that a beam-plasma wave does not produce explosive instabilities.
Some dissipative effects on stratified shear flows over an obstacle
Authors: Su C. H.
Published: March 2003

Some aspects of dissipation due to viscosity and heat conduction are investigated for a linear two-dimensional unbounded stratified flow over obstacles. Under the assumption of hydrostatics and small dissipation, an explicit formula for calculating the flow field in the vicinity of the obstacles is given, which is essentially nondissipative. Far above the obstacles, an asymptotic expression is obtained showing how the disturbance caused by the presence of the obstacles is damped.
Drag on a small sphere moving through a gas
Authors: Phillips Warren F.
Published: March 2003

An approximate theoretical solution is presented for the drag force on a small sphere moving through a gas. The result is based on a moment solution to the Boltzmann equation which places no restriction on the Knudsen number. The equation which is obtained for the drag force reduces to the exact solution in the case of both large and small Knudsen number and gives excellent agreement with experimental data.
Superposition of the modes of sound propagation in rarefied gases
Authors: Lin Maw-Rong , Ward C. A.
Published: March 2003

It follows from an examination of the dispersion relation in the free-molecule flow limit that the superposition of the different modes can lead to a solution of the boundary value problem of sound propagation in the low density limit. Therefore, a procedure, based on the moment method for solving the full Boltzmann equation, is developed to superimpose the modes found to be present from the dispersion relation. This procedure can be used to determine the boundary value sound distribution function to any order of approximation. Applying this technique to the 13-moment equations, the boundary value problem of sound propagation in a monatomic gas is solved by superimposing the two modes associated with this approximation.
Atom-molecule and molecule-molecule potentials and transport collision integrals for high-temperature air species
Authors: Cubley S. J. , Mason E. A.
Published: March 2003

Molecular-beam scattering results are analyzed to obtain a consistent and reliable set of potentials for the atom-molecule interactions N-N2, N-O2, O-N2, O-O2, N-NO, and O-NO, and the molecule-molecule interactions N2-N2, N2-O2, O2-O2, N2-NO, O2-NO, and NO-NO. These are used to generate a set of transport collision integrals over the range 300–15 000 °K with an estimated uncertainty of about 5%.
Magnetic forces and the surface instability in ferromagnetic fluids
Authors: Miller C. W. , Resler E. L.
Published: March 2003

Ferromagnetic fluids are a colloidal suspension of subdomain iron particles dispersed in a carrier fluid. Experiments were performed to determine the pressure exerted by the fluid in a uniform and a gradient magnetic field. The pressure measurements were not the same as predicted by the continuum theory. An expression for the pressure jump at the surface of the fluid was proposed for the particular ferromagnetic fluid used based on the experimental measurements. This pressure jump was then used to predict the shape of the surface of the ferrofluid that results when a magnetic field is applied normal to an initially flat ferrofluid surface (ferrofluid spike). An expression for the radius of the shape ρ as a function of its distance from the base z, ρ=ρ (z), was calculated and compared to an enlarged photograph of the particular shape. In the region ρ≳0, a simple analytical solution was found. When ρ is zero or in the region close to zero, surface tension must be included and a numerical solution was necessary to determine the profile.
Numerical simulation of regular and Mach reflections
Authors: Schneyer Gary P.
Published: March 2003

The results of an M∞=2 shock wave propagating in air down a shock tube and impinging on a wedge were calculated using both a two-dimensional Eulerian code and a two-dimensional Lagrangian code. The air was considered to be an ideal gas with γ=1.4. Both 2:1 and 1:2 wedges were used; these angles are known to generate regular and Mach reflected shock waves, respectively. The calculated results agreed quite well in both shock angle and overpressure with the appropriate theoretical or experimental results. A comparison of the two methods showed that the Eulerian calculation was easier and cheaper, gave equally good shock and expansion wave results, but ’’washed out’’ the slip line whose approximate position was still observable in the Lagrangian calculation.
Strong plasma shock structures based on the Navier–Stokes equations
Authors: Abe Kanji
Published: March 2003

The structure of a plasma collisional shock wave is examined on the basis of the Navier–Stokes equations and simultaneously on the basis of the Fokker–Planck equation. The resultant structures are compared to check the validity of the Navier–Stokes equations applied to the structures of strong shock waves. The Navier–Stokes equations give quite correct structures for weak shock waves. For the strong shock waves, the detailed structures obtained from the Navier–Stokes equations differ from the results of the Fokker–Planck equation, but the shock thicknesses of the two shock waves are in relatively close agreement.
Plasma motion induced by laser heating
Authors: Steinhauer Loren C.
Published: March 2003

Laser-induced motion is calculated for an underdense magnetically confined plasma column subjected to axial laser heating. Perturbation velocities and densities are determined for small values of the disturbance parameter defined as the ratio of the speed of sound to the speed of plasma growth due directly to laser absorption. The calculation confirms that for small values of the disturbance parameter, laser-induced plasma motion is unimportant. A number of relevant laser heating experiments are examined and classified with respect to induced plasma motions.
Strong self-focusing due to the ponderomotive force in plasmas
Authors: Max Claire Ellen
Published: March 2003

Self-focusing of cylindrical beams due to the ponderomotive force behaves quite differently for the full exponential nonlinearity than for the weak, cubic-nonlinearity limit. Steady self-trapped propagation becomes possible for arbitrary incident powers. Self-focusing becomes a periodic oscillatory phenomenon, rather than a catastrophic process in which the light intensity increases without limit.
Turbulent pusher behavior
Authors: McCrory R. L. , Morse R. L.
Published: March 2003

Model calculations suggest that turbulence resulting from instability of laser driven ablatively imploded high aspect ratio pusher shells in which the unstable region is, in general, distinctly narrower than the shell will degrade, but not exclude, useful compression of these systems.
Theory of parametric heating of plasma in the lower hybrid frequency range
Authors: Rogister André , Hasselberg Günter
Published: March 2003

Lower hybrid turbulence can be driven parametrically by a whistler pump wave. Destabilization occurring through the resonant interaction of the whistler, an electrostatic mode, and a particle, either electron or ion, which mechanism is akin to the well-known phenomenon of inverse nonlinear Landau damping, is considered. A nonlinear theory of turbulence is developed for a range of parameters characteristic of tokamaks on the basis of the wave kinetic equation for weakly turbulent plasma in a uniform magnetic field. This yields an estimate of the saturation level of the turbulence which is, in turn, responsible for the anomalous absorption of the pump wave electromagnetic energy. Both the anomalous absorption rate and the plasma heating rate are evaluated. The theoretical results are very promising: lower hybrid parametric heating should be realizable up to densities typically of order 3×1014 cm−3 (for larger densities, the poor tunneling of the pump wave through the evanescent region between the launching structure and the turning point leads to too high electric fields in the waveguide). A decisive advantage of this form of ratio frequency heating is that energy can also be deposited directly in the ion component.
End shorting induced rotation in a ϑ pinch
Authors: Kadish Abraham
Published: March 2003

A possible explanation for the observed rotation in open ended ϑ-pinch devices is shown to result from the shorting out of electric field components at the insulating boundary. The propagation of rotation into the plasma is primarily via torsional Alfvén waves preceded by dispersive precursors. The precursors have spatially and temporally modulated amplitudes. They are due to gyrofrequency oscillations of the plasma and are seen throughout the plasma immediately following the shorting out of the electric field components at the insulators.
Dispersion of a line source in grid turbulence
Authors: Sullivan P. J.
Published: March 2003

The root-mean square value of concentration of a passive scalar is found to grow linearly with downstream distance in decaying turbulent grid flow. Experimental evidence appears to support this conclusion.
Interferometric measurements in ionizing radiating flow of carbon dioxide behind normal shock waves
Authors: Ebrahim N. A. , Hornung H. G.
Published: March 2003

Experimental studies of normal shock waves in carbon dioxide in the velocity range 3 to 17.3 km/sec show that above a velocity of 11 km/sec, the thermodynamic model of carbon dioxide used in equilibrium calculations is inadequate and that above 13 km/sec, significant radiation losses can be expected.
Resistive interchange quasi-modes in a plasma cylinder
Authors: Dagazian R. Y.
Published: March 2003

A resistive interchange quasi-mode is derived in a cylindrical magnetically confined plasma.
Optimum coupling condition for the two-stream instability
Authors: Mross M. R. , Walsh J. E.
Published: March 2003

The power transferred from an electron beam to longitudinal electrostatic fluctuations in a low energy beam-plasma system is found to be optimal when the beam velocity and the long wavelength asymptote to the phase velocity of the longitudinal modes are approximately equal.
Probe theory for arbitrary shape in a large Debye length, stationary plasma
Authors: Chang Jen-Shih , Laframboise J. G.
Published: March 2003

The exact analytic current-voltage characteristic recently obtained by Fendell and by Chapkis and Baum for spherical probes in the continuum Laplace limit, is shown to be valid for arbitrary probe shape. This result has important diagnostic implications. The form of the characteristic suggests a basic modification to the usual ’’retarding potential’’ technique, in which the retarded current divided by probe potential is graphed logarithmically to measure electron temperature. An approximate extension to finite mean free paths is made. This leads to a prediction that a long cylindrical probe will be much more sensitive to departures from collisionless conditions than a sphere of equal diameter. Another extension of the theory includes negative ion current. The effects of departure from Laplace conditions are investigated by presenting self-consistent numerical calculations for spherical probes. Formulas for triple-probe use are presented. A widespread misuse of the Druyvesteyn method is critically examined.
Nonlinear wavenumber of an electron plasma wave
Authors: Vidmar P. J. , Malmberg J. H. , Starke T. P.
Published: March 2003

The wavenumber of a large-amplitude electron plasma wave propagating on a collisionless plasma column is measured. The wavenumber is shifted from that of a small-amplitude wave of the same frequency. This nonlinear wavenumber shift, δkr, depends on position, frequency, and initial wave amplitude, Φ. The observed spatial oscillations of δkr agree qualitatively with recent theories. Experimentally δkr∝kiS (Φ) √Φ where ki is the linear Landau damping coefficient, S (Φ) ≡ki(Φ)/ki, and ki(Φ) is the initial damping coefficient which depends on Φ.
Current flow in a high-voltage diode subjected to a crossed magnetic field
Authors: Orzechowski T. J. , Bekefi G.
Published: March 2003

The space-charge limited electron current (∼50 kA) flowing in a pulsed, high voltage (∼200 kV) vacuum diode is studied as a function of magnetic field applied at right angles to the diode electric field. The observations compare favorably with predictions from self-consistent theory which takes account of space-charge and allows for the presence of the magnetic field. Time-resolved measurements of the diode current and voltage lead to a determination of the expansion velocity of the cathode and anode plasmas. It is shown that a magnetic field of ∼5 kG suffices to stop plasma motion, in agreement with magnetohydrodynamic computations. Thus, diode closure is inhibited, at least over the 40 nsec time span of the voltage pulse.
Kinetic theory of a relativistic beam
Authors: Lee Edward P.
Published: March 2003

A Fokker–Planck equation is derived to study the evolution of a stable, low-current beam propagating in a gas-plasma medium. Small-angle scattering of the beam particles by the medium causes diffusion in the phase space projected transverse to the direction of propagation. The projected components of dynamical friction vanish. As a result, there is a continued input of energy into the transverse particle motions, which is taken up in expansion against the pinch field. A quasi-static Bennett equilibrium, with isothermal distribution of transverse momenta, is shown to be a similarity solution of the Fokker–Planck equation with scale radius increasing in accord with Nordsiéck’s formula. An H theorem is proved and the Bennett distribution is shown to minimize both H and −dH/dt; hence, it is the time-dependent asymptotic state. The predicted current profile and radius are shown to be in fair agreement with experiment.
Oscillation-center formulation of the classical theory of induced scattering in plasma
Authors: Johnston Shayne
Published: March 2003

Particle trapping in the beat potential produced by the mixing of two coherent waves lies outside the domain of the conventional weak-turbulence theory of induced wave–particle scattering in plasma. A reformulation of the theory is presented which is applicable to this extended domain. The formulation is based upon a canonical transformation to ’’oscillation-center variables’’ and in particular affords a simpler method for deriving the ’’linear’’ matrix elements of weak-turbulence theory. This method is first illustrated in the problem of the nonlinear Landau damping of longitudinal plasma modes. The power of the method is then usefully exploited in two more difficult situations, namely, the cases of electrostatic waves in the presence of a uniform magnetic field, and electromagnetic waves in an arbitrarily relativistic plasma. The application of the transformation to the extended strong-interaction regime is demonstrated.
Nonlinear ion motion in a slow ion cyclotron mode
Authors: Vella M. C. , Aamodt R. E.
Published: March 2003

The nonlinear cyclotron resonance of a single ion in a coherent slow ion cyclotron wave is treated analytically, at first, for an arbitrary angle of propagation in a homogeneous magnetic field. It is found that for tokamak plasma parameters the nonlinear phase space orbits are characterized by parallel propagation, and, for this case, simple approximate expressions are obtained for the gyroradius and parallel velocity of the resonant particle. The nonlinear period is obtained, and an invariant is found which extends the theory to a system with slowly changing parameters. It also is found that heating occurs in the perpendicular direction, and cooling in the parallel direction.
Ion acoustic waves at a plasma sheath
Authors: Gary S. Peter , Alexeff I. , Hsieh S.-L.
Published: March 2003

The propagation of ion acoustic waves toward a plasma sheath is considered, using a fluid model which allows charge separation. It is assumed that wavelengths are sufficiently short to apply the WKB approximation and that amplitudes remain sufficiently small to use the linear approximation. Under these approximations, ion acoustic waves are not reflected from a plasma sheath, and in general are somewhat damped, although they may undergo weak growth deep in the sheath.
Plasma behavior with a separatrix magnetic surface in JFT−2a tokamak
Authors: Shimomura Y. , Maeda H. , Ohtsuka H. , Kitsunezaki A. , Nagashima T. , Yamamoto S. , Kimura H. , Nagami M. , Ueda N. , Funahashi A. , Matoba T. , Kasai S. , Takeuchi H. , Takahashi K. , Kumagai K. , Tokutake T. , Anno K. , Arai T.
Published: March 2003

Results from the JFT−2a (DIVA) experiments made with a separatrix magnetic surface are described. The main conclusions are: (1) A separatrix magnetic surface is stably located inside the material surface. (2) A plasma enclosed in a separatrix magnetic surface is similar to that of a conventional tokamak as far as the magnetohydrodynamic properties are concerned. (3) Measured parameters of the main plasma column are consistent with those expected from a conventional tokamak. (4) The electron density and temperature in the scrape-off layer are about ten times less than the values at the center of the main plasma column. (5) Heat and particle fluxes to the divertor region are axisymmetric and several times less than those of the total loss fluxes from the main plasma column. (6) Runaway electrons are well guided to the divertor region.
Velocity profile in the thermal creep slip problem
Authors: Loyalka S. K.
Published: March 2003

The effect of velocity dependence of collision frequency on the flow profile in thermal creep sip problem is studied. A simple variable collision frequency model is used, and it is found that the flow profile is quite sensitive to the velocity dependence of the collision frequency.
Unstable normal modes induced by magnetic shear
Authors: Lau Y. Y.
Published: March 2003

A simple mathematical model is presented to describe instabilities resulting from the transferral of energy in different regions of an inhomogeneous plasma. The normal mode solution and the stability criterion are computed.
Warm plasma stabilization of drift-cone mode at finite beta
Authors: Berk H. L. , Gerver M. J.
Published: March 2003

The fraction of warm plasma needed to stabilize the drift cyclotron loss-cone mode in a mirror machine is computed. With warm plasma present, a remnant short wavelength instability persists.
Comments on ’’Taylor instability of an inverted atmosphere’’
Authors: Chakraborty B. B.
Published: March 2003

The instability of an inverted atmosphere as an initial-value problem, studied by Case, is re-examined. The growth rate of instability which he obtained is modified and is found to be same as that obtained through normal mode analysis. Some further comments are made to supplement his discussion.
Temperature anisotropy and beam type whistler instabilities
Authors: Hashimoto Kozo , Matsumoto Hiroshi
Published: March 2003

Whistler instabilities have been investigated for two different types, i.e., a temperature anisotropy type instability and a beam type instability. A comparison between the two types of whistler instabilities is made within the framework of linear theory. A transition from one type to the other is also discussed, which is an extension of the work on electrostatic beam and Landau instabilities performed by O’Neil and Malmberg for electromagnetic whistler instabilities. It is clarified that the essential source of the whistler instability is not a beam kinetic energy, but a temperature anisotropy even for the beam type whistler instability.
Energy and momentum of a superfluid vortex ring for large core radius
Authors: Blood Frank A.
Published: March 2003

The free energy and momentum of a vortex ring with a large core radius in superfluid helium near the lambda point are investigated by a method similar to that of Ginsburg and Pitaeviskii. It is assumed the velocity field of the vortex ring is that of a vortex ring in a classical fluid. The free energy is found to vary from 95% of its classical value at a ratio of core radius to vortex ring radius of 0.1, to 86% at a ratio of 0.318, while the momentum varies from 88% of its classical value at a ratio of 0.1 to 56% at a ratio of 0.318.
Hydrodynamic forces and moments acting on a body emerging from an infinite plane
Authors: Chow S. K. , Hou A. Y. , Landweber L.
Published: March 2003

An iteration procedure has been developed for calculating the time-dependent velocity potential on the wetted surface of a prescribed body emerging into a fluid from an infinite, moving plane at an arbitrary angle of attack. The mathematical singularities encountered in the velocity-potential computations are removed by exact, analytical means. The classic motion equations of Kelvin–Kirchhoff have been extended for the present case to include the effects of the time-varying inertia terms. A simple illustrative example, that of a half-emerged sphere, is given. Numerical values obtained are compared with those of the pressure integration method, and of an exact analytically derived solution. Numerical solutions for a spheroid of fineness ratio 2 with linear and angular velocities emerging from an infinite, moving plane at two different angles, are presented.
Modeling of the final period of decay for the axisymmetric turbulent temperature wake
Authors: Freymuth Peter
Published: March 2003

The theory of the final period of turbulent decay for the axisymmetric turbulent temperature wake is modified with the result that agreement between theory and experiment is improved.
Implosion characteristics of deuterium–tritium pellets surrounded by high density shells
Authors: Fraley Gary S.
Published: March 2003

The effect of high density shells on deuterium–tritium pellets imploded by laser energy deposition or other means is investigated. Attention is centered on the inner parts of the pellet where hydrodynamics is the dominant mechanism. The implosions can then be characterized by a pressure boundary condition. Numerical solutions of the implosions are carried out over a wide range of parameters both for solid pellets and pellets with a central void.
Study of plasma density distribution produced by irradiating a 50 μ deuterium pellet on one side with a ruby laser
Authors: Jarboe T. R. , Kunkel W. B. , Lietzke A. F.
Published: March 2003

Freely falling 50-μm diam deuterium pellets are irradiated on one side with a ruby laser pulse of 1 nsec rise time and beam diameter larger than 100 μm. It is found that the freely expanding plasma has an asymptotic density distribution which is shell like. The observed laser-pellet interaction time, expansion velocity, and asymptotic density distribution are found to be in good agreement with a simple model for the ablation and acceleration of the pellets. Reasonably symmetric clouds are formed provided the beam envelops the pellet and the laser pulse is long enough to ’’burn through’’ the entire target. The total number of ions produced is about 5×1015. This is consistent with complete ionization of the 50-μm pellets. The plasma is given an energy on the order of 100 eV per particle when the laser intensity is 1012 W/cm2.
Enhanced microwave scattering at the upper hybrid frequency
Authors: Cano R. , Fidone I. , Mendonca J. T. , Zanfagna B.
Published: March 2003

The results of an experiment of wave scattering by coherent phase density fluctuations at the upper hybrid resonance are presented. Enhanced microwave scattering from small amplitude density fluctuations at 110 kHz in an argon plasma is observed. The results show that the scattered field is generated in a small region where the frequency of the incident microwave beam equals the local upper hybrid frequency. The measured angle of the direction of maximum scattered power is in agreement with the conservation of momentum in the direction of the confining magnetic field. An absolute calibration of the detection chain leads to a value of the scattered flux in good agreement with the theoretical calculation. Possible applications of the present results as a diagnostic tool for high temperature dense plasma are discussed.
Single-mode saturation of the bump-on-tail instability: Immobile ions
Authors: Simon Albert , Rosenbluth Marshall N.
Published: March 2003

A one-dimensional collisionless electron plasma is considered with a velocity distribution of the ’’bump-on-tail’’ type. The ions are immobile and the eigenmodes are separated by finite periodic boundary conditions. The electron number density is increased above the neutral-stable value by a small fractional amount Δ. A single mode moves on to the positive slope region and grows until saturated at small amplitude by nonlinear effects. The saturated amplitude, frequency shift, and modified electron distribution function are determined in terms of Δ. The solution is shown to be stable and conserves energy and momentum. All singular functions appearing in higher harmonics are identified as generalized functions, and a correction to the class 1c mode adjoint is obtained. The solution of the ’’inflection-on-tail’’ problem is also given.
Laser beam-plasma coupling in laser solenoid plasmas
Authors: Steinhauer Loren C.
Published: March 2003

A model has been constructed to analyze the gross beam-plasma interaction in a laser solenoid plasma. The model includes a simple solution for a slab plasma response to a given laser beam, and a solution for axial beam size variations in response to arbitrary axial plasma structure. The two solutions are combined to determine the coupled behavior. Trapping of the focused laser beam where it enters the plasma is a significant problem, but can be achieved by a minimum level of imbedded field in the plasma. If the beam is trapped, it first focuses and then defocuses near the front of the bleaching wave (front of the laser heated plasma). In order to avoid divergence of the beam near the front, it is essential to have a pre-formed favorable density profile in the plasma. Such a condition is probably achieved automatically in the early stages of plasma heating. Several techniques are discussed which can be used to avert unfavorable refractive behavior (catastrophic self-focusing and defocusing).
Space–time formulation of plasma turbulence theory
Authors: DuBois Donald F.
Published: March 2003

A formulation of plasma turbulence theory is developed which is based on the concept of the response function of the turbulent system to an infinitesimal, localized external perturbation. This infinitesimal response function describes the normal modes of the turbulent system. The theory is developed as an expansion in powers of the assumed small ratio of the incoherent wave energy to the particle kinetic energy. It is also assumed that while the wave fluctuations are weakly correlated, strong coherent fields may also be present which make the system arbitrarily nonstationary in time and inhomogenous in space. The equations of the system are therefore developed in physical space and time rather than in Fourier space. The first two orders of iteration are carried out to obtain the space–time analogs of all the familiar weak turbulence processes.
Plasma multistreaming and the viability of fluid codes
Authors: Manheimer Wallace M. , Lampe Martin , Clark Robert W. , Liewer Paulett C. , Chu K. R.
Published: March 2003

For plasmas in the collisionless regime, the absence of bulk viscosity permits multistreaming; if this occurs, fluid codes, which by definition prohibit multistreaming, give unphysical results. It is shown that a fluid code, using an energy propagation equation, will conserve energy, but nevertheless can give totally incorrect results if multistreaming occurs. If a temperature propagation equation is used instead, the system continuously loses energy when multistreaming occurs. This energy nonconservation, which is completely independent of cell size and time step, can be used as an internal test for multistreaming, requiring no data outside the fluid code itself.
Observation of magnetic islands in the FM−1 spherator
Authors: Davis S. L. , Hawryluk R. J. , Schmidt J. A.
Published: March 2003

Time independent spatially periodic variations in the density and floating potential have been observed in the FM−1 spherator. On the exterior of the plasma Δn/n and Δφ/φ are found to be as much as 0.3. Experimental evidence indicates these variations are due to magnetic islands created by small field errors produced by the levitated ring. Calculations of the expected island size agree well with observations.
Nonlinear effects for the Taylor column for a hemisphere
Authors: Crisalli A. J. , Walker J. D. A.
Published: March 2003

When a flow is forced past an obstacle in a rapidly rotating fluid, a Taylor column forms. This is defined by a set of vertical detached shear layers circumscribing the obstacle which provide the smooth transition from an external inviscid potential flow to a stagnant core above the obstacle. For a hemispherical object, the main adjustment takes place in an external E1/4 layer and an internal E2/7 layer; here, the nonlinear flow in these layers is investigated. The problem in the E1/4 layer is identical to a problem occurring in magnetohydrodynamic flow; in addition, some features of the magnetohydrodynamic problem have been resolved. Numerical solutions are obtained for the steady nonlinear external E1/4 layer flow up to the point where unsteady flow separation from the Taylor column is imminent. The response of the internal E2/7 layer to the flow in the E1/4 layer is calculated and the results suggest the internal shear layer is unlikely to play any significant role in the separation process.
Surface waves on viscous fluid of variable depth
Authors: Shen M. C.
Published: March 2003

An asymptotic method based upon ray theory is developed for the study of surface waves on a viscous fluid of variable depth. An asymptotic solution involving a phase function and an amplitude function is constructed. Uniform asymptotic expansions at and away from caustics and shorelines are obtained. To illustrate the method, an example concerning the spreading of a bore over a sloping beach is considered.
Bursts in turbulent shear flows
Authors: Antonia R. A. , Danh H. Q. , Prabhu A.
Published: March 2003

The burst frequency or frequency of regions in a turbulent flow where the energy dissipation is large has been measured in both laboratory and atmospheric shear flows. The laboratory measurements were made in two slightly heated flows, a boundary layer in zero pressure gradient and an axisymmetric jet with a co-flowing external system. The atmospheric data were obtained in the first few meters above a wheat canopy. For the laboratory data, the burst frequency, as determined from either velocity or temperature signals, is found to be approximately equal to one half the zero crossing frequency of these signals. In the atmosphere, the burst frequency is very roughly twice the zero crossing frequency. The burst intermittency factor and the ratio of the burst width to Kolgomoroff length scale are found to be very weakly dependent on the Reynolds number. Available data in the literature on the intermittency factor and width of bursts exhibit extensive scatter and conflicting Reynolds number trends.
Critical surface bubbles and corrugations and their implications to laser fusion
Authors: Estabrook Kent
Published: March 2003

Bubbles are concentrations of electromagnetic energy in the region of the critical density that force the plasma out to form a cavity. Since the critical density surface becomes cratered, absorption may be greater than for a smooth surface. A larger area is available for absorption and the reflected light has a large probability of restriking the critical density. The distance between bubbles is several wavelengths and consequently, they may encourage Rayleigh–Taylor instabilities. Two different kinds of two-dimensional simulation models are used to study the cases of light polarization in and out of the plane of incidence. With the electric field in the simulation plane, corrugations appear in the critical surface. Resonant absorption can occur on these angular surfaces even with the pump light perpendicularly incident. Since the problem is inherently three-dimensional and kinetic, the limitations of the models are described. The threshold, magnetic field generation, and possible experimental evidence for bubbles are discussed. Also, the competition between sidescatter and self− focusing in an entirely underdense plasma is studied, and it is found that sidescatter dominates for polarization out of the simulation plane.
Skewness of temperature derivative in turbulent shear flows
Authors: Freymuth P.
Published: March 2003

Based on dimensional arguments, the Reynolds number dependence of the temperature derivative skewness is derived in the two cases where the skewness is solely indicative of the large scale structure of temperature fluctuations and where it is solely indicative of their small scale structure.
Poiseuille−like flow in a rotating gas
Authors: Gans Roger F.
Published: March 2003

An extension of Hagen–Poiseuille flow in a gas to the case where the gas has a superposed solid rotation is given. It reduces to Hagen–Poiseuille flow in the absence of rotation and uniform plug flow in the limit of infinite rotation.
Time analysis of the shock flow using dual microwave and dual schlieren systems
Authors: Rothkopf E. M. , Low W.
Published: March 2003

The microwave attenuation and the pressure gradients in the shock flow of a pressure driven shock tube at an axial and at a nonaxial position are compared. A dual cookie cutter microwave system and a dual beam laser schlieren system are used to probe the shock-heated air.
Plasma return currents in a magnetic field
Authors: Berk H. L. , Pearlstein L. D.
Published: March 2003

Whereas plasma return currents along a magnetic field arise for an electromagnetic diffusion time, it is found that appreciable plasma return currents perpendicular to a magnetic field are not induced for built-up times slow compared with an Alfvén transit time.
Particle motion and diffusion in geometric mirrors
Authors: Schulz Michael
Published: March 2003

Expressions are derived for the full bounce period and second adiabatic invariant of a charged particle trapped in a geometric mirror (which confines plasma by means of a magnetic surface layer). Field-free regions of double-conical and ellipsoidal shape are treated explicitly as special cases.
Ion sheath motion in plasma-filled diodes
Authors: Widner M. M. , Poukey J. W.
Published: March 2003

The time development of the ion space charge sheath in a plasma-filled planar diode is considered in reference to the behavior of relativistic diodes used for electron and/or ion beam production.
Influence of density variation on the stability of a vortex with a top-hat jet core
Authors: Lessen Martin , Hadji-Ohanes Bernard
Published: March 2003

The stability of a potential vortex with an injected rotating and nonrotating jet core is considered for different density ratios of the vortex to the jet. Growth rates are given for different ratios of the vortex strength to the axial jet velocity. It is shown that the vortex is less unstable as the density ratio increases.
Spatial waves of higher modes in an axisymmetric turbulent jet
Authors: Chan Y. Y.
Published: March 2003

It is shown theoretically that higher modes of wave-like disturbances can be propagated in the turbulent shear layer of an axisymmetric jet. Both the amplitudes and the extent of the spatially growing waves decrease as the order of the mode increases.
Positivity of eigenfunctions in time dependent problems of kinetic theory
Authors: Ronen Yigal
Published: March 2003

The positivity of eigenfunctions in the time dependent foreign gas problem is treated using the linear integral transport equation. It is concluded that there is no eigenvalue with a positive eigenfunction except the asymptotic one.
Nonequilibrium effects on shock structure in a fully ionized gas
Authors: Greywall Mahesh S.
Published: March 2003

The effect of initially unequal electron and ion temperatures on the structure of a collisional shock wave propagating through a fully ionized gas is investigated and is found to be restricted to a small region at the beginning of the shock.
Neutron yield calculations from self-similar spherical compressions
Authors: Mayer F. J. , Johnson R. R. , Tanner D. J.
Published: March 2003

The neutron yield from the compression-expansion cycle of a deuterium–tritium gas sphere is calculated using a self-similar hydrodynamic model.
Multispecies transport in collisional tokamaks
Authors: Boley C. D. , Gelbard E. M. , Stacey W. M.
Published: March 2003

Neoclassical radial particle and energy fluxes are computed, in the disparate mass limit, for a multicomponent collisional tokamak plasma. Contributions due to charge-exchange friction are included in the fluxes.
Spatially decaying array of vortices
Authors: Rogler Harold L. , Reshotko Eli
Published: March 2003

An analysis of two-dimensional vorticity disturbances introduced at a grid and propagating downstream reveals that viscosity causes the x wavenumber to diminish and the phase speed to increase from their inviscid values, while also causing the amplitude to decay exponentially downstream. This decaying disturbance field introduces an adverse mean pressure gradient of strength O (1/RΛ), where RΛ is the Reynolds number based on freestream velocity and vortex diameter. Viscous effects introduce a discrepancy between the two-point and two-time velocity correlations when Taylor’s hypothesis r=U∞t is used to relate the space and time separations. This discrepancy arises because the vortices propagate at a phase speed c greater than the freestream. As RΛ→∞, c→U∞. If Taylor’s hypothesis is modified to r=ct, then the two-point and two-time correlations agree.
Rayleigh–Taylor instability in the presence of rotation
Authors: Chakraborty B. B. , Chandra Jyoti
Published: March 2003

A heavy uniform fluid is superposed on a lighter one. The two uniform fluids are separated by a layer of transition of finite thickness in which the density increases exponentially in the vertical direction. The growth rate and the wavenumber of the mode of maximum instability are obtained when the whole system rotates uniformly about a vertical axis.
Mechanism of tornado funnel formation
Authors: Hsu C. T. , Fattahi B.
Published: March 2003

The mechanism of formation of a tornado funnel was observed in a specially designed facility for tornado simulation. In this facility, a tornado cyclone is first simulated at the exit of a vortex generator. Interaction of this vortex with a ground plane is found to be responsible for the funnel formation. Time-averaged velocity measurements indicate that a smaller, but highly concentrated vortex core is developed upward from the ground plane due to the horizontal convergence motion induced by the above interaction. The flow visualization technique has revealed that the funnel cloud is the downward extension of its parent cloud inside this invisible concentrated vortex core. This is possibly the fluid mechanical phenomenon of axial flow reversal usually occurring in a converging or diverging swirling flow.
Experiments on vortex stability
Authors: Singh Param Indar , Uberoi Mahinder S.
Published: March 2003

The tip vortex of a laminar flow wing was studied at a sectional lift-to-drag ratio of 60. The vortex Reynolds number was Γ0/ν=7.8×104, where Γ0 is the total circulation and ν is the kinematic viscosity. At and near the wing the vortex core was turbulent with an axial jet. Downstream of the wing the jet rapidly dissipated and a wake developed in the core and intensity of turbulent velocities decreased. From 13 to 40 chord length periodic oscillations dominated the velocity fluctuations with little background turbulence. These instabilities had a symmetric and a helical mode with wavelength of the same order as the core diameter. In this range of distances along the vortex core the maximum axial, swirl, and fluctuating velocities vary slowly. At 40 chord lengths behind the wing there is a rapid change in these velocities. This change of state of the vortex core is accompanied by change of velocity fluctuations from periodic to turbulent. The core showed spatial excursions. Measurements up to 80 chord lengths downstream showed no self-similar decay.
Statistical properties of the interface in the turbulent wake of a heated cylinder
Authors: LaRue John C. , Libby Paul A.
Published: March 2003

The statistical properties of the interface between turbulent and nonturbulent fluid in the two-dimensional wake of a heated cylinder are presented. The following are the principal results: distributions of the intermittency factor and crossing frequency; probability density functions of the durations of the passages of turbulent and nonturbulent fluid, indicating that the longer durations are exponentially distributed; the mean and rms slope angles of the interface at upstream and downstream edges, showing an asymmetry of the mean shape with a steeper downstream edge; and the relative number of overhangs at the two sets of edges, namely, 25% at the downstream edge and only 6% at the upstream edge.
Free boundaries for plasmas in surface magnetic field configurations
Authors: Fried Burton D. , VanDam J. W. , Lee Y. C.
Published: March 2003

Exact analytic solutions for the plasma/magnetic-field free-boundary problem are derived for three planar, surface magnetic field configurations: the picket fence, the simple magnetic slab, and the staggered magnetic slab. In the ideal magnetohydrodynamic limit, conformal mapping techniques yield explicit closed-form solutions for the free boundaries, the magnetic field lines, and the magnetohydrodynamic stability criteria. For configurations with plasma confined to one side of a continuous, sharp free boundary, it is found that with a given choice of the physical parameters (i.e., dimensions, current, and plasma pressure), there may be only one stable solution; only one unstable solution; two solutions, one stable and one unstable; or no solution at all. For the staggered slab, parameters can be chosen so that the conductors nearest the plasma are force free, an arrangement which could minimize the size of physical supports and the associated plasma loss in confinement applications.