bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation into the anomalous behavior of Pitot tubes in dilute polymer solutions
Authors: Halliwell N. A. , Lewkowicz A. K.
Published: March 2003

The anomalous behavior of Pitot tubes in the turbluent pipe flow of a dilute polymer solution is investigated and discussed. Pitot tube error is measured using an alternative optical means of local velocity measurement. Unlike previous research in this field a strict control is kept on the state of degradation of the solutions and Pitot tube error is measured directly whilst the tube is under test. Errors which occurred in total head pressure measurement were found to be negative and in some cases were as high as 40%. Factors which influence the Pitot tube accuracy are identified and a dynamical similarity argument is used to express the error as a function of these. Pitot tube error is attributed to the polymer solutions storing energy viscoelastically at the tube tip. A critical review of explanations previously put forward for Pitot error with reference to the results is included in the discussion. The polymer used was polyox WSR-301.
Variable viscosity effects on the onset of convection in porous media
Authors: Kassoy D. R. , Zebib A.
Published: March 2003

The onset of convection in a horizontal, isotropic, water-saturated porous medium is considered. The temperature difference between the top and bottom is as large as 250 °C. The effects of an eightfold variation in kinematic viscosity are included. The critical Rayleigh number is found to be substantially reduced from the classical value although the associated wavenumber is nearly the same. Neutral mode streamline and isotherm patterns are considerably distorted in the vertical direction in distinction to the symmetric patterns found in the constant viscosity classical calculation.
Velocity profile in the Knudsen layer for the Kramer’s problem
Authors: Loyalka S. K.
Published: March 2003

Since the BGK model is based on the assumption of constant collision frequency, and since this model has been found inadequate in describing some experimental data, the numerical study of a variable collision frequency model proposed earlier by Cercignani and Loyalka and Ferziger is described. Specifically, the Kramer’s problem for this model is solved, and it is found that the ’’velocity defect’’ in the Knudsen layer is quite sensitive to the velocity dependence of the collision frequency. In fact, for the hard sphere collision frequency, the present results agree reasonably well with the recent experimental data of Reynolds, Smolderen, and Wendt.
Resonance cones in a warm plasma for finite magnetic fields
Authors: Burrell Keith H.
Published: March 2003

The resonance cone structure excited by a localized source is studied theoretically and experimentally for a warm plasma with a finite, uniform magnetic field. The electrostatic Green’s function is evaluated by asymptotically expanding it in the limit where the observation point is far from the source. Results are obtained that are valid for all angles and for all frequencies below the upper hybrid. The theory predicts the functional dependence of the angular location of the main resonance cone peak and the angular spacing between interference peaks on the physical parameters. Experimental parameter studies were made to check the predicted functional dependence; it was found to produce a good fit to the data. Both density and temperature can be found from these measurements; thus, resonance cone measurements are a useful diagnostic technique in any magnetoplasma in which antennas can be inserted.
Nonlinear stabilization of beam plasma interactions by parametric effects
Authors: Papadopoulos K.
Published: March 2003

The nonlinear stabilization of the kinetic stage of electron beam plasma instabilities by parametric effects is investigated. It is found that within a definite range of plasma parameters parametric instatilities induced by the beam generated waves can stabilize the system at a level of wave energy density substantially lower than expected by quasi-linear theory. This occurs because at a certain level of beam-generated plasma waves, the transfer rate of wave energy outside the spectral region in resonance with the beam exceeds the beam plasma instability growth rate. A model of a quasi-steady state for the case of continuous beam injection is proposed. The possibility of utilizing ultrarelativistic electron beams for achieving ignition temperatures in a tokamak is discussed.
Kinetic theory of tearing instability
Authors: Hazeltine R. D. , Dobrott D. , Wang T. S.
Published: March 2003

The guiding-center kinetic equation with Fokker-Planck collision term is used to study, in cylindrical geometry, a class of dissipative instabilities of which the classical tearing mode is an archetype. Variational solution of the kinetic equation obviates the use of an approximate Ohm’s law or adiabatic assumption, as used in previous studies, and it provides a dispersive relation which is uniformly valid for any ratio of wave frequency to collision frequency. One result of using the rigorous collision operator is the prediction of a new instability. This instability, driven by the electron temperature gradient, is predicted to occur under the long mean-free path conditions of present tokamak experiments, and has significant features in common with the kink-like oscillations observed in such experiments.
Experimental studies of the plasma focus and evidence for nonthermal processes
Authors: Bernard A. , Coudeville A. , Jolas A. , Launspach J. , de Mascureau J.
Published: March 2003

A systematic experimental study is conducted in order to measure the density and configuration of the plasma by holographic interferometry, and the ion temperature and level of turbulence by cooperative laser scattering. The two measurements are done in various phases of the plasma, before, during, and after the filament breakup. Suprathermal scattering during the filament phase and the successive development of an ionizing wave are evidenced for the first time. The anisotropy of the neutron emission is found to exist in all regimes by the simultaneous measurement of the energy spectra in two directions. A possible explanation of the neutron emission is given. It is concluded that nonthermal processes play an essential role in the plasma focus.
Brillouin backscattering instability in magnetized plasmas
Authors: Shukla P. K. , Yu M. Y. , Spatschek K. H.
Published: March 2003

The decay of a circularly polarized electromagnetic wave propagating parallel to an external magnetic field into another circularly polarized electromagnetic wave and an ion acoustic wave in a homogeneous plasma is considered.
Stimulated diffusion scattering in ionospheric modification
Authors: Berger Richard L. , Goldman Martin V. , DuBois Donald F.
Published: March 2003

A linear stability theory is presented for stimulated backscattering of zero−mode radiation from ’’diffusion modes.’’ The uncoupled diffusion mode is an electrostatic spatially periodic disturbance which relaxes at the parallel or cross−magnetic field diffusion rate. For ionospheric modification experiment parameters, the most unstable diffusion mode is within one degree of orthogonal to the geomagnetic field, and is characterized by the parallel diffusion rate. It is found to have a maximum temporal growth rate of 20 sec−1 and a wavelength of 100 m or more at altitudes several tens of kilometers below the zero−wave reflection point. The total spatial amplification is calculated for special geometries.
Shear stability boundaries for collisionless drift modes in finite geometry
Authors: Simon A. , Gross L. , Catto P. J.
Published: March 2003

Stability boundaries for shear stabilization of the collisionless drift mode are calculated for experimental situations in which the unstable modes are broad and of the dimensions of the system. A universal diagram is obtained which enables one to easily calculate the required finite length, or magnetic field strength or shear parameter for stabilization of a given experiment. There is also an absolute value of the shear which stabilizes all these modes.
Turbulent damping of the convective cells and the lower hybrid waves
Authors: Okuda H. , Chu C. , Dawson J. M.
Published: March 2003

A detailed numerical study has been made of the turbulent damping of the convective cells and of lower hybrid waves for a plasma near thermal equilibrium. It is found that some of the theories of strong turbulence, taking into account the diffusing orbits of particles, are inadequate for describing the observations; observations are, however, in good agreement with the linear dispersion relation with a turbulent diffusion coefficient.
Theory of enhanced ion and electron heating, and dissipation, due to ion acoustic turbulence
Authors: Weinstock J. , Sleeper A. M.
Published: March 2003

A calculation is made of the enhanced ion heating rate ν+, electron heating rate ν−, and dissipation, produced by ion acoustic turbulence. The effects of turbulence on ion motions are accounted for. It is found that ν+ ≳ ν− for some experiments, leading to a decreasing ratio of electron to ion temperatures and cessation of heating. It is also shown that ν+ ∝ m+−1/2 (ion mass).
Saturation and spectrum of the oscillating two−stream instability
Authors: Weinstock J. , Bezzerides B.
Published: March 2003

A nonlinear dispersion equation for the spectrum of parametric instabilities is derived from the hydrodynamic equations. New resonant mode−coupling terms coming from ion and electron equations are found. Solution of the dispersion equation yields an oscillating two−stream spectrum which varies as k−2 in agreement with computer simulations and a numerical solution.
Generalized aerodynamic noise equation
Authors: Chandraker A. L. , Munjal M. L.
Published: March 2003

An exact aerodynamic noise equation is formulated for Newtonian fluids. The cause−effect problem is discussed. Finally, the importance of external additions of mass, momentum, and energy is examined.
Motion of aerosol particles in a temperature gradient
Authors: Phillips Warren F.
Published: March 2003

Theoretical and experimental results are presented which show that the thermal force on an aerosol particle in a temperature gradient depends on the velocity of the particle relative to the gas as well as the temperature gradient in the gas. It is shown that any motion of the particle along a line parallel to the temperature gradient tends to induce a local increase in the temperature gradient and thus an increase in the thermal force. Thermal settling velocity calculations which are made neglecting this motion−induced temperature gradient were found to be as much as fifty percent low when compared with experimental data. Calculations which account for this induced gradient, on the other hand, were able to predict the experimental data within three percent.
Collisional damping of temporal ion waves echoes
Authors: Cussenot J. R. , Fabry M.
Published: March 2003

This theoretical study of ion wave echoes is based on a model which takes into consideration ion−atom collisions. It is found that the collision model gives a damping term varying with the collision frequency ν as exp(−νt).
’’Bursting’’ frequencies obtained from wall shear stress fluctuations in a turbulent boundary layer
Authors: Strickland J. H. , Simpson Roger L.
Published: March 2003

A one−to−one correspondence between time scales indicated by histograms of short−sampling−time autocorrelations and long−sampling−time first−moment spectral densities appears to exist. Since short−time autocorrelations are indicative of ’’bursting’’ frequencies, the implication is that ’’bursting’’ frequencies may also be obtainable from spectral data.
Kinetic theory of turbulent flows
Authors: Lewis M. B.
Published: March 2003

A generalization of the Boltzmann equation is derived from the Liouville equation for a dilute gas with macroscopic correlations. For the case of weak turbulence a solution is obtained in terms of a set of generalized hydrodynamic equations which describe the average flow.
Energy transport across a magnetic field by plasma waves
Authors: Canosa José , Okuda Hideo
Published: March 2003

Cross−field energy transport by electrostatic plasma waves has been studied theoretically and numerically for a plasma near thermal equilibrium. Energy transfer by plasma waves is significant in a high temperature plasma where collisional transport is quite small. For strong magnetic fields (ωc ≳ ωp), the simulations verify the theoretical prediction that energy transport by plasma waves increases slowly with the magnetic field, and that in the limit of large field magnitudes, wave transport dominates classical collisional transport. Furthermore, in a strong magnetic field the relaxation of the temperature by wave transport may result in an anisotropic velocity distribution. For weak fields (ωp ≳ ωc), the simulation shows that collisional transport is more important than wave transport, also in agreement with the theory.
Convective instability in the presence of a nonuniform horizontal magnetic field
Authors: Thomas John H. , Nye Alan H.
Published: March 2003

Newcomb’s criterion for convective stability in the presence of a horizontal magnetic field is written in a form which explicitly shows the effect of vertical variations of the magnetic field strength. It is shown that a nonuniform horizontal magnetic field can be destabilizing as well as stabilizing.
Density perturbation influence on nonlinear harmonic excitation at the upper hybrid resonance
Authors: Cano R. , Fidone I. , Hosea J. C. , Schuss J. J.
Published: March 2003

The cold plasma theory of upper hybrid harmonic generation is examined numerically. Inclusion of the density perturbation caused by incident wave pressure gives enhanced harmonic levels (as observed experimentally) and reveals the sensitivity of the theory to the description of the incident fields.
Comments on ’’Field generating thermal instability in laser-heated plasmas’’
Authors: Manheimer W. M. , Tidman D. A.
Published: March 2003

There is an additional solution to the zero-order heat flux equations which gives no instability in laser produced plasmas.
Probability density function approach for a turbulent axisymmetric heated jet. Centerline evolution
Authors: Dopazo Cesar
Published: March 2003

The equation describing the evolution of the probability density function of the temperature field in a turbulent axisymmetric heated jet is presented. A closure problem is present and some possible ways of attacking it are suggested. A closure at the first-order level is then tentatively tried and similarity arguments are exploited. A hyperbolic first-order variable-coefficient quasi-self-preserving partial differential equation is obtained. The constants appearing in those coefficients are evaluated from available experiments. Some questions are raised on the uncertainty of the computed constants due to the experimental scattering of the velocity-temperature correlation at the centerline. The probability density function is obtained analytically as a function of downstream location along the centerline if it is prescribed at a reference centerline position. In particular, the probability density function is taken as Gaussian at ten diameters downstream. The computed mean and variance are compared with existing experiments and display a reasonably good agreement. Values for the skewness and flatness factor tend to indicate that deviations from Gaussianity along the centerline are very small.
Experiments on turbulence behind a grid with jet injection in downstream and upstream direction
Authors: Tassa Y. , Kamotani Y.
Published: March 2003

Turbulence behind a biplanar grid with jets of air injected at the grid surface either in the upstream or the downstream direction was found to be nearly isotropic for x/M ≳ 20. Turbulence level increases with the injection rate for both upstream and downstream injection. The shape of the energy spectrum functions and microscales do not vary with the injection rate. The microscales for upstream injection are larger than those for downstream injection.
Turbulent kinetic energy profile during drag reduction
Authors: Virk P. S.
Published: March 2003

Model turbulent kinetic energy profiles expected during drag reduction are synthesized from similarity arguments. At low drag reduction, it is postulated that the radial transport of turbulent kinetic energy and of axial momentum are analogous. Thus, in nondimensional terms, the maximum kinetic energy during drag reduction must exceed the Newtonian maximum kinetic energy by an amount proportional to the ’’effective slip,’’ which latter is the amount whereby the mean velocity during drag reduction exceeds that during Newtonian turbulent flow. At maximum drag reduction, the turbulent kinetic energy profile is related to the Newtonian profile by means of the respective mixing length constants, Xm and Xn; in the former case, the maximum turbulent kinetic energy is predicted to be Xn/Xm = 4.7 times the Newtonian. The model profiles are in accord with the (few) available experimental measurements of turbulence during drag reduction.
Colliding vortex rings
Authors: Fohl T. , Turner J. S.
Published: March 2003

Laboratory observations of the interaction between pairs of vortex rings during certain collisions are described. A theory is advanced, based on the resonance of the forced motion with the elliptical mode of oscillation of a single vortex, and is found to be in agreement with the observed behavior.
Calibration of a shock tube flow by analysis of the particle trajectories
Authors: Dewey J. M. , Whitten B. T.
Published: March 2003

A technique is described by which the flow properties in a conventional diaphragm shock tube were determined from an analysis of the particle trajectories within the flow. The particle trajectories were obtained by high-speed photography of smoke tracers placed at 10 cm intervals along the 8 m length of the tube. The subsequent analysis gave the space and time variation of pressure, density, velocity, and temperature of the gas throughout the tube, for a shock of intermediate strength. The results are compared with those made using other measurement devices for pressure and density and it is concluded that the technique gives the flow properties to an accuracy of about 5%. The technique also revealed some aberrations of the flow which had not been detected by other means.
Nonequilibrium phenomena in dusty supersonic flow past blunt bodies of revolution
Authors: Chang Stephen S-H.
Published: March 2003

A theory is developed for inviscid supersonic flow past blunt bodies of revolution containing small spherical cloud particles of uniform size. It is assumed that there are no collisions between the particles. The only interactions between the gas and the particles are drag force and heat exchange. The problem is solved by using the direct method of a given body and the technique of series truncation. The convergence of the series is improved by recasting it in a modified Euler transformation. It is found that the relaxation zone is much larger than the shock layer thickness, hence the flow is nonequilibrium in the entire subsonic region. The solutions for the case without the particles agree with the known blunt-body solutions, and those with the particles resemble the known dusty air solutions behind a normal shock wave.
Numerical simulation of shock-heated plasma with a magnetic dam
Authors: Todd A. M. M.
Published: March 2003

The results of the two-dimensional numerical simulation of an ideal magnetohydrodynamic high beta shock tube plasma with a magnetic dam are presented. The dam is created by an external coil and drives into the plasma behind the shock, preventing the immediate loss of the shock-heated plasma. The problem corresponds mathematically to a hyperbolic transverse flow plasma region coupled across several free boundaries to various elliptic vacuum regions, and is solved using a particle code for the plasma dynamics, and over relaxation for the vacuum regions. The results obtained show that such a dam will lengthen the lifetime of the shock-heated plasma.
Injection and drift studies of high current relativistic electron beams in a toroidal-like system
Authors: Gilad P. , Kusse B. R. , Lockner T. R.
Published: March 2003

The successful use of an external field shaping cathode to inject high current relativistic E beams (500 kV, 20 kA, 50 nsec) across a toroidal magnetic field (1–4 kG) into a metallic vessel is presented. Injection of up to 50% of the diode energy into trajectories far removed from the metal wall (≳5rL) was achieved. Drift properties if the E beam in the toroidal vessel were studied. Energy fluence down the torus was measured. Up to 60% of the injected beam was recovered after propagating a distance of 8 m. The drift time around the torus was found to be long enough to enable trapping the beam in the toroidal system.
Velocity measurements using the photon correlation technique in a separated boundary layer
Authors: Grant I. , Barnes F. H. , Greated C. A.
Published: March 2003

A photon correlation system employing a Bragg cell to frequency shift the incident laser light has been used to measure mean velocities and turbulence intensities in the separated flow behind a backward facing step. Theoretical relationships are derived relating the probability density of flow velocity to the count correlation, these results being applicable to the case of unseeded air flow. The method can be used for measuring in flow regions where there are very high local turbulence levels, outside the range of more conventional techniques. Good agreement was found with previous measurements recorded using hot-wire anemometry.
Carrier gas effects on homogeneous nucleation of water vapor in a shock tube
Authors: Barschdorff Dieter
Published: March 2003

Condensation of water vapor was studied in the expansion wave of the driver section of a shock tube by light scattering and pressure measurements. By arranging the onset of condensation to occur at the terminating characteristic of the unsteady expansion wave, the gasdynamic analysis could be simplified. The composition of the test gas was varied from pure vapor (steam) to small mole fractions of H2O in different carrier gases, yielding onset conditions in the temperature and pressure ranges of 225 to 282 °K and 2 to 62 Torr, respectivly. Steam condensation is well predicted by the classical rate expression for homogeneous nucleation, modified to account for nonisothermal effects and a variable amount of carrier gases. Results for the transition region from the pure vapor to small mole fractions of water vapor in argon, helium, and air reveal a dependence of the computed nucleation rates of several orders of magnitude on the mole fraction of the carrier gas, which is not explained by the nonisothermal theory. Possible reasons for this effect are discussed.
Exact equilibria of axisymmetric magnetic configurations
Authors: Mazzucato E.
Published: March 2003

A class of solutions of the ideal magnetohydrodynamic equilibrium equations of an axisymmetric magnetic configuration is derived. These solutions, besides including magnetic configurations with a large variety of cross sections and nonuniform current distributions, are exact solutions obtained without making any assumptions on the value of the aspect ratio. The stability of some of these configurations with respect to ideal localized modes has been numerically evaluated.
Laser heating of a plasma in a solenoidal magnetic field
Authors: Steinhauer Loren C. , Ahlstrom Harlow G.
Published: March 2003

A model representing the laser heating of a plasma in a straight solenoid magnetic field has been analyzed. The model incorporates an idealized plasma cross section, but otherwise appears to very accurately represent the real problem. The difficulty of unequal electron and ion temperatures is averted by considering only the equilibrium limit. The frozen ion limit is examined briefly and found to differ from this only by factors generally near one. The complicated exact solution of the model is approximated to good accuracy by simple expressions.
Production of hard x rays in a plasma focus
Authors: Newman C. E. , Petrosian Vahé
Published: March 2003

A model of the plasma focus is considered, in which large axial electric fields are induced by the imploding current sheet during the final few nanoseconds of the collapse phase. This field provides a mechanism for creation of a beam of electrons of highly suprathermal energies. For such a beam, having a power-law energy spectrum, the bremsstrahlung radiation above 100 keV to be expected from it, both from electron-deuteron collisions in the focused plasma itself and when the beam reaches the walls of the device, is calculated. The expected radiation from the walls is found to be several orders of magnitude higher than that from the plasma. Thus, since experimental evidence indicates that little or no radiation above 100 keV originates in the walls, the conclusion is drawn that the electrons in the beam must be decelerated after leaving the plasma and before reaching the walls. Upon comparison with experimental results, qualitative agreement of the expected angular distribution of hard x rays with experiment is found. The total energy in accelerated electrons required to produce the observed total energy in hard x rays by this mechanism is also reasonable when compared with the total energy of the device.
Decay instability of lower hybrid waves
Authors: Ott Edward
Published: March 2003

The parametric decay of an incident lower hybrid pump wave to two lower frequency lower hybrid waves only occurs for a finite wavelength (nondipole) pump wave and can be an important process in lower hybrid resonance heating schemes. The growth rates and thresholds of this instability in homogeneous and inhomogeneous plasmas are obtained and discussed.
Parametric instabilities: Evaluation of thresholds accounting for ion-ion collisions
Authors: Virmont J.
Published: March 2003

The linear ion susceptibility is evaluated for the cases of either weak or strong ion-ion collisions, starting from a Fokker–Planck collision term. The thresholds of the plasmon-phonon parametric instabilities are then computed under conditions of interest for the laser plasma-heating experiments. The values obtained are significantly lower than those previously published.
Effect of impurities on dissipative trapped ion modes
Authors: Dobrowolny M. , Ross David W.
Published: March 2003

The stability of dissipative trapped ion modes in the presence of impurity ions is investigated and compared with previous theories of these modes in pure plasma. The impurities are assumed to be either in the plateau or Pfirsch–Schlüter regime as is typical of either present day or the next generation of toroidal plasmas. The important effects of the impurities are found to be different depending on whether the parallel wave phase velocity is above or below the impurity thermal velocity. However, it can, in general, be stated that when the impurity density gradients are in the same direction as the electron and hydrogen ion density gradients, the impurity ions exert stabilizing effects on the modes. The critical density for stabilization of the modes is found to be significantly reduced, even at rather small impurity concentrations. On the other hand, cases of inverse impurity gradients are likely to be unstable. Numerical applications of the theory to nominal parameters of the PLT tokamak are given.
Self-focusing of intense radio waves in the ionosphere
Authors: Tomljanovich Nicholas M.
Published: March 2003

Nonstationary self-focusing of electromagnetic waves under the action of Ohmic heating is investigated for anisotropic inhomogeneous plasmas. This mechanism may be responsible for field-aligned structure generation by intense radio waves in the ionosphere, which, in turn, gives rise to observed artificial spread-F ionospheric striations and high-frequency scattering. For a vertical geometry, a linearized analysis is given providing a field-aligned filamentation rate as a function of perturbation transverse wavelength, incident power, and plasma parameters. For typical ionospheric parameters and incident flux of 50 μW/m2, exponentiation times of the order of 5 sec are obtained for transverse wavelengths of the order of a kilometer.
Modeling turbulent flux of passive scalar quantities in inhomogeneous flows
Authors: Lumley John L.
Published: March 2003

It is suggested that, in an inhomogeneous turbulent flow, the flux of a passive scalar admixture should be modeled to first order by a linear combination of gradient transport and convective transport, where the convective transport coefficient is proportional to the gradient of the (gradient) -transport coefficient. A simple model is presented which allows determination of the coefficient of proportionality.
Refraction of plane inertial waves
Authors: Scott Wayman E.
Published: March 2003

A plane inertial wave, traveling in an incompressible liquid of density ρ1, is incident upon the plane interface defining another incompressible liquid of density ρ2. The reflection and refraction of the wave are studied, and the mathematical results are as interesting as those for the reflection of a plane inertial wave striking a plane, rigid wall. In particular, not only the reflection, but also the refraction, can be ’’backward,’’ a backward refracted wave occurring whenever the reflected wave is forward, and vice versa. There is no possibility of total reflection.
Pressure-strain correlation
Authors: Lumley John L.
Published: March 2003

It is shown that the separation of the pressure-strain correlation into a transport and a deviatoric term is not unique, and that the customary separation appears likely to be the wrong choice.
Hypersonic self-induced separation
Authors: Brown S. N. , Stewartson K. , Williams P. G.
Published: March 2003

The theory of self-induced separation at moderate Mach numbers is extended to hypersonic flows under the Newtonian approximation. Numerical solutions of the relevant boundary-layer equations are compared with experimental data.
Boundary effects on M=0,±1 Alfvén waves in a cylindrical, collisionless plasma
Authors: Paoloni F. J.
Published: March 2003

The dispersion relations for Alfvén waves with exp(jmϑ) azimuthal dependency are calculated for a cylindrical, cold, collisionless plasma. If the electron inertia term is included in the dielectric tensor, then, in a bounded plasma, there are two transverse wavenumbers for each axial wavenumber. The phase velocities for m=0, ±1 fast and slow waves are calculated for different vacuum thicknesses between the uniform plasma and the metal walls. It is found that m=0 and −1 fast waves each experience a cutoff below a given frequency, but the m=+1 fast wave can propagate even at very low frequencies provided the vacuum layer is of sufficient thickness. The calculations are shown to agree with previously reported experimental results.
Heated electron distributions from resonant absorption
Authors: DeGroot J. S. , Tull J. E.
Published: March 2003

A simplified model of resonant absorption of obliquely incident laser light has been developed. Using a 1.5 dimensional electrostatic simulation computer code, it is shown that the inclusion of ion motion is critically important in determining the heated electron distributions from resonant absorption. The electromagnetic wave drives up an electron plasma wave. For long density scale lengths (L≃103λDe), the phase velocity of this wave is very large (ω/k≳10Vth) so that if heating does occur, a suprathermal tail of very energetic electrons is produced. However, the pressure due to this wave steepens the density profile until the density gradient scale length near the critical density (where the local plasma frequency equals the laser frequency) is of order 20λDe. The electrostatic wave is thus forced to have a much lower phase velocity (ω/k≃2.5Vth). In this case, more electrons are heated to much lower velocities. The heated electron distributions are exponential in velocity space. Using a simple theory it is shown that this property of profile steepening applies to most of a typical laser fusion pulse. This steepening raises the threshold for parametric instabilities near the critical surface. Thus, the extensive suprathermal electron distributions typically produced by these parametric instabilities can be drastically reduced.
Laser heating of a magnetically confined plasma
Authors: Yuen S. Y. , Lax B. , Cohn D. R.
Published: March 2003

The problem of laser heating of a plasma is considered in the low β limit. Spatial and temporal variations of electron as well as ion temperatures are calculated, and the shape of the laser pulse is varied to find an optimal ion heating condition. The propagation of the ’’bleaching wave’’ into the plasma column is also investigated. By an iterative approximation analytic expressions are obtained for quantities such as particle temperatures, hole burning velocity, penetration depth, and the equilibration time of electron and ion temperatures after the laser is tuned off. They can be used to find various restricted optimization conditions.
Mechanism for ion tail formation during ion-acoustic turbulence
Authors: Choi Duk-In , Horton Wendell
Published: March 2003

An acceleration mechanism producing ion tails during turbulent heating experiments is proposed. The implication of the theory in terms of the pulsed nature of the heating is shown by a simple example.
Effects of electron angle scattering in plasma waves
Authors: Koch R. A. , Horton Wendell
Published: March 2003

The collisional contribution to the fluctuating number and current density are calculated from the linearized electron kinetic equation with a Lorentz collision operator. In the weakly collisional regimes of practical importance for low frequency drift, sound, and Alfvén waves, the dominant dissipative contribution is shown to arise from the low energy electrons that contribute a damping proportional to (ωνe/k2v2e)3/5.
Stability of magnetically confined, high-beta plasma
Authors: Guest G. E. , Hedrick C. L. , Nelson D. B.
Published: March 2003

Plasma waves propagating perpendicular to the magnetic field in a high-beta, magnetically confined plasma can be unstable in configurations for which the guiding-center drifts are in the ’’favorable’’ direction. The basic instability mechanism is illustrated and the conditions for growth are obtained using the Maxwell and Vlasov equations in a slab model of the plasma.
Some experimental studies of transverse plasma shock waves
Authors: Robertson S. , Chen Y.-G.
Published: March 2003

Experimental measurements of magnetic field compression, density compression, ion temperature, and two-dimensional flow effects have been made for strong shock waves propagating at 10–30 cm/μsec in 30–400 mTorr deuterium. The results are compared with theoretical predictions.
Ion heating in a train of orthogonal magnetoacoustic shocks
Authors: Boozer Allen H.
Published: March 2003

The deposition of energy from a train of magnetoacoustic waves, which have steepened to form shocks, is considered in a collisionless plasma. It is shown that an initially lower ion temperature tends to rise to a value comparable to the electron temperature.
Effective electrical conductivity of a nonuniform plasma
Authors: Nichols L. D.
Published: March 2003

A simple nonuniformity model for calculating effective electrical conductivity and Hall parameter is proposed. The model shows that the effective conductivity can be significantly reduced by nonuniformities in the Hall parameter, even if the local conductivity is uniform.
Convective currents in a porous layer heated from below: The influence of hydrodynamic dispersion
Authors: Neischloss Hanoch , Dagan Gedeon
Published: March 2003

Heat transport in a porous medium is governed by molecular diffusion and hydrodynamic dispersion. The latter factor, represented by a second-order tensor which depends on the fluid velocity, is taken into account for the first time in the problem of thermal convective currents in a layer heated from below. The linearized and the energy analysis yield the same results and value of the critical Rayleigh number as those obtained with neglect of dispersion. Finite amplitude convective currents are influenced by dispersion, which has a stabilizing effect. Dispersion may have an influence for relatively coarse materials or at high values of Rayleigh number.
Spread of a heated plane turbulent jet
Authors: Davies A. E. , Keffer J. F. , Baines W. D.
Published: March 2003

A heated two-dimensional turbulent jet flow has been studied experimentally using conditional sampling techniques. The aim of the investigation was to establish the details of the spread of the temperature and velocity fields. Results confirmed previous observations showing that the conventionally measured mean temperature profile was wider than the velocity. However, when considered in terms of the turbulent fluid only, the spread of thermal and of momentum fields was found to be coincident.
Subsonic-supersonic condition for shocks
Authors: Fowles G. R.
Published: March 2003

The necessary conditions for stability of a shock, that the shock travel with supersonic velocity with respect to the medium ahead and with subsonic velocity with respect to the medium behind, are shown to be implied by the second law of thermodynamics for very general classes of viscous, heat-conducting fluids; the Weyl conditions are not invoked. The results are shown to be also compatible with the Le Chatelier–Braun principle. They further imply that under certain conditions it is not thermodynamically permissible to assume the existence of a shock transition layer in which entropy production is due to heat conduction alone.
Experiments with the hydraulic analogy of a shock-wave magnetohydrodynamic generator
Authors: Brocher Eric , Betton Michel
Published: March 2003

The analogy between the free surface flow of a conducting liquid and the compressible flow of a conducting gas was studied. It was shown that the analogy exists if the Joule heating is negligible and if the conductivity of the gas is proportional to the temperature. Tests were carried out with mercury to simulate the oscillating flow of a plasma in shock-wave magnetohydrodynamic generators. A single- and a twin-Hartmann–Sprenger tube configuration were used to produce the oscillating flow. The experiments performed so far showed that as much as 21% of the energy of the jet driving the Hartmann–Sprenger tubes may be converted into electricity.
Hydrodynamics and burn of optimally imploded deuterium-tritium spheres
Authors: Mason R. J. , Morse R. L.
Published: March 2003

The phenomenology of optimized laser-driven DT sphere implosions leading to efficient thermonuclear burn is reviewed. The optimal laser deposition profile for spheres is heuristically derived. The performance of a 7.5 μg sphere, exposed to its optimal 5.3 kJ pulse, is scrutinized in detail. The timing requirements for efficient central ignition of propagating burn in the sphere are carefully explored. The difficulties stemming from superthermal electron production and thermal flux limitation are discussed. The hydro-burn performance of spheres is characterized as a function of the pulse energy, peak power, time scale, pulse exponent, wavelength, and on the degree of flux limitation. The optimal pulse parameters are determined for spheres with masses ranging from 40 ng to 250 μg, requiring from 50 J to 150 kJ of input energy, and the corresponding optimal performance levels are calculated. Discussion is given to the hydro-burn performance of new structured fusion targets, in which the DT is contained as a gas or frozen as an ice shell inside a high Z pusher-tamper layer.
An attempt to observe scattering of 2 mm waves from tokamak plasmas
Authors: Motley R. W. , Ernst W. P.
Published: March 2003

No signals were observed in an experiment to detect the 120 ° scattering of 2.15 mm waves by ion wave turbulence in the ST tokamak. The upper limit to the scattering intensity was ∼ 300 times the level expected from ordinary Thomson scattering.
Singular perturbation analysis of spherical and cylindrical N waves
Authors: Sachdev P. L.
Published: March 2003

Using a singular perturbation analysis the nonplanar Burgers’ equation is solved to yield the shock wave-displacement due to diffusion for spherical and cylindrical N waves, thus supplementing the earlier results of Lighthill for the plane N waves.
Theory of stimulated scattering processes in laser-irradiated plasmas
Authors: Forslund D. W. , Kindel J. M. , Lindman E. L.
Published: March 2003

Analytic theory of the linear and nonlinear behavior of the one-dimensional Brillouin and Raman scattering instabilities is given. Results are presented for the problems of an infinite homogeneous plasma and of a finite inhomogeneous plasma. Nonlinear fluid equations can predict backscatter energies the order of the incident laser energy; however, the size of the interaction region and nonlinear effects on the excited electrostatic wave are very important in determining the amount of backscatter. In many cases of contemporary interest for a high power laser incident on a target plasma, the latter effects can play a crucial role in reducing backscatter to a tolerable level.
Plasma simulation studies of stimulated scattering processes in laser-irradiated plasmas
Authors: Forslund D. W. , Kindel J. M. , Lindman E. L.
Published: March 2003

The behavior of stimulated Brillouin and Raman scattering is studied by a number of periodic and aperiodic plasma simulations. The one-dimensional studies at low power, roughly defined by the oscillating velocity of an electron being less than its thermal velocity, tend to support the spatial theory. Typically, in the aperiodic simulations trapping nonlinearities of the electrostatic wave and electron heating can saturate the amount of backscatter at a reasonable level. At high powers in both periodic and aperiodic simulations an x-type breaking or wave collapse phenomenon occurs after saturation which leads to an equilibration between pondermotive force, electron pressure, and ion pressure. Simulations of a random frequency modulated laser are discussed. Two-dimensional simulations and their relationship to the one-dimensional results are briefly mentioned.
Effect of trapping on the saturation of the Raman backscatter instability
Authors: Klein H. H. , Ott Edward , Manheimer Wallace M.
Published: March 2003

The criterion for whether the Raman backscatter instability saturates by electron trapping or by pump depletion is determined and tested by computer simulation.
Influence of self-fields on the filamentation instability in relativistic beam-plasma systems
Authors: Davidson R. C. , Hui B. H. , Kapetanakos C. A.
Published: March 2003

The influence of equilibrium self-fields on the filamentation instability in relativistic beam-plasma systems is investigated within the framework of a macroscopic cold-fluid description. For a low-density beam (n̂b≪n̂e) propagating through a nonrelativistic plasma background, the instability criterion for ordinary-mode propagation perpendicular to B0zêz is shown to be (assuming perturbations with ∂/∂ϑ=0=∂/∂z) (ω2pbβ2bz/ω2cb) {1+(2ω2pb/ω2cb) [β2bz(1−fM)−(1−fq)]}−1≳1, where ωpb is the beam plasma frequency, ωcb is the beam cyclotron frequency, βbzc is the axial velocity of the beam, and fM and fq are the fractional current neutralization and fractional charge neutralization, respectively, by the background plasma. The azimuthal self-magnetic field has a stabilizing influence for fM<1, whereas the radial self-electric field has a destabilizing influence for fq<1.
Behavior of some singly ionized, heavy-ion impurities during compression in a theta-pinch plasma
Authors: Jalufka Nelson W.
Published: March 2003

The introduction of a small percentage of an impurity gas containing a desired element into a theta-pinch plasma is a standard procedure used to investigate the spectra and atomic processes of the element. This procedure assumes that the mixing ratio of impurity to fill gas remains constant during the collapse and heating phase. Spectroscopic investigations of the constant mixing ratio assumption for a 2 % neon and argon impurity verifies the assumption only for the neon impurity. However, for the 2 % argon impurity, only 20 to 25 % of the argon is in the high-temperature compressed plasma. It is concluded that the constant mixing ratio assumption is not applicable to the argon impurity.
Collisional losses from a mirror machine with an end stopper
Authors: McHarg B. B. , Oakes M. E.
Published: March 2003

Collisional losses from the ends of a mirror machine place substantial restrictions on the confinement time of a plasma in such a device. One method proposed to improve the viability of a mirror machine reactor is to reduce the end losses by some means other than the magnetostatic field. Such a device is called an end stopper and it has the effect of changing the loss cone of the usual mirror machine into a loss hyperboloid (two sheet). The end losses from a mirror machine with an ideal, perfectly reflecting end stopper are studied by numerically solving the Fokker–Planck equation with appropriate mirror-end stopper boundary conditions. The mirror and end stopper are assumed to be a square well system and only decay of the ions from the system is considered.
Interpreting signals of the spanwise spatial structure in the viscous sublayer
Authors: Simpson Roger L.
Published: March 2003

Correlation frequency and amplitude probability distribution methods of deducing the spanwise spacing of the streamwise vortices in the viscous sublayer are presented.
Focusing of fast plasma shock waves
Authors: Sandel F. L. , Niimura M. , Robertson S. H. , Gross R. A.
Published: March 2003

Plasma shock waves have been focused by reflection from an appropriately shaped end wall of a coaxial electromagnetically driven shock tube. The duration of the hot, dense focus, its spatial location, and the plasma properties at the focus are compared with computer simulation predictions.
Corrections to the Stokes drag near thermodynamic critical points
Authors: Foch James D. , Ackerson Bruce J.
Published: March 2003

Low Reynolds number flow is considered in a pure fluid near the thermodynamic critical point and in a binary mixture near the critical mixing ’’point.’’ It is shown that, due to the breakdown of the assumption of imcompressibility, a sphere rotating with steady angular velocity Ω in a stream U experiences an extra force proportional to Ω×U, but no extra torque.
Forced hydromagnetic oscillations of a rapidly rotating fluid
Authors: Acheson D. J.
Published: March 2003

A theoretical study is presented of the hydromagnetic waves which are generated in a rotating fluid when its boundaries are started into transverse oscillation. Particular attention is focused on the very low-frequency waves that occur when the rotation speed greatly exceeds the Alfvén speed, in view of their probable importance in connection with the dynamics of the Earth’s liquid core. Estimates of their magnetic field amplitude are obtained for the case when the viscosity of the fluid is very small, and it is found that the amplitude increases with the conductivity σs of the boundaries unless this exceeds a certain threshold value, in which case the amplitude is virtually independent of σs. When the motion of the boundaries is transient and of very high frequency, the magnetic field amplitude of the fluid oscillations at the forcing frequency may greatly exceed that of the accompanying low-speed hydromagnetic waves. The transient response is nevertheless of very limited spatial extent, and application of these results to the dynamics of the Earth’s deep interior then indicates that high-frequency magnetic fluctuations in the core (which are shielded from observation at the Earth’s surface by the skin effect in the mantle) cannot have sufficient amplitude to significantly enhance electromagnetic core-mantle coupling.