bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of a Simple Model for Calculating Scatter
Authors: Graf K. A. , Guthart H.
Published: February 2004

A simple model for calculating scatter from a turbulent medium has been applied to a computer experiment with good results. The proposed calculation is a modification of a first-order Born calculation that accounts for attenuation due to absorption and scatter by energy conservation. Such a nonrigorous approach requires experiments to specify the scatter attenuation in a phenomenological way. The exact computer calculations by Hochstim and Martens constitute such an experiment.
Dispersion and Stability of Collisional Drift Waves in Two-Ion-Species Plasmas
Authors: Verheest Frank
Published: February 2004

The Coppi-Perkins theory of collisional drift waves in low-β plasmas is extended to plasmas containing ions of two different types. Recent experiments call for such an extension. Before discussing the general results, the specialization to the usual plasma shows the destabilizing effect of a high ionic charge and of an electron temperature exceeding the ion temperature. As an application of the obtained criterion of marginal stability the average ion mass is computed and compared to the intuitive linear formula, based only upon concentrations. Under present-day conditions almost no difference is detected, but for future experiments with higher temperatures and higher mass ratios the correct formula is shown to give less stable results than the intuitive one at the same relative concentration. This is also true for lower densities and shorter wavelengths. The discrepancies can become quite important.
Plasma Stability in Bounded Systems with Application to a Two-Stream Instability in Spherical Geometry
Authors: Porter G. D. , Klevans E. H.
Published: February 2004

A simple procedure for numerically obtaining the solution of a linear, differential boundary-value problem is presented. For an nth-order equation, the technique requires the solution of n initial-value problems. The solution of the boundary-value problem is then a linear combination of these solutions. The technique has very attractive features that should make it a convenient method for studying a variety of stability problems in bounded systems. As an example of these applications, the initial stability of the inertial containment device proposed by Hirsch is examined. It is found that the particular model studied is marginally stable. The results are compared with computer simulation studies of the device.
Mott-Smith Solution of the Fokker-Planck Equation
Authors: Koura Katsuhisa
Published: February 2004

The nonlinear Fokker-Planck equation describing the relaxation of the fully ionized gas is solved by the Mott-Smith method. The relaxation time obtained using the lower-moment equations is found to agree with the Spitzer self-collision time.
Thermoconvective Stability of Ferrofluids
Authors: Lalas D. P. , Carmi S.
Published: February 2004

The energy stability limit is obtained for a Boussinesq ferrofluid in the presence of gravity and of thermal and magnetic field gradients. For a motionless fluid heated from below the limit is identical to the linear theory result.
Stability of a Stratified Free Shear Layer
Authors: Maslowe S. A. , Thompson J. M.
Published: February 2004

The stability of the laminar mixing region between two uniform streams is investigated by numerically solving the linear sixth-order equation for the disturbance amplitude function. This equation includes the effects of both viscosity and heat-conduction and is, therefore, regular at the critical point, where the mean flow velocity and disturbance phase speed are equal. Both the neutral stability curve and curves of constant amplification rate are computed for various Richardson numbers. The results show that the damping effects of diffusion are quite small and, therefore, that the Richardson number is the dominant parameter governing the stability of the flow. Streamlines are computed for neutral disturbances and it is found that, in the inviscid limit for long waves, the flow pattern approaches the configuration obtained previously by Taylor in his study of a discontinuous three-layer model.
Floating Bubble Configurations
Authors: Medrow Robert A. , Chao B. T.
Published: February 2004

The configurations of bubbles floating at a vapor-liquid interface are investigated both analytically and experimentally. The differential equations governing the shape of a single bubble at rest in a liquid of infinite extent are deduced under the assumption of zero dome thickness, uniform surface tension, and equal gas densities within the bubble and above the interface. These equations show that nondimensional bubble shapes depend upon the value of a single parameter. An analytical solution, valid for small bubbles, is developed and shown to be in good agreement with the general numerical solution. Good agreement with theory is demonstrated for floating air bubbles, both stationary and translating, ranging in volume from 0.01 cc (in water) to 0.83 cc (in heavy mineral oil). Theoretical results over a dimensionless bubble volume (the ratio of volume to the cube of the capillary constant) range of from 2.6 × 10−4 to 5527 are given.
Chemical Instabilities. II. Chemical Surface Reactions and Hydrodynamic Instability
Authors: Bdzil J. , Frisch H. L.
Published: February 2004

A linear stability analysis of the hydrodynamics of the isothermal two-component reactive fluid (A2, A), confined between two infinite parallel plates, and involved in the surface catalyzed reaction (A2⇋2A) is performed. The existence of solutions to the eigenvalue problem governing the state of marginal instability corresponding to pure convection is established. A variational principle for the critical eigenvalue for instability is developed and used to show that the surface catalyzed reaction enhances the instability that would occur if the reaction were frozen.
Feasibility of Measuring Radiative Amplification of Acoustic Waves
Authors: dePlomb E. P.
Published: February 2004

A calculation shows that amplification of acoustic waves by absorption of laser radiation should be measurable in the laboratory.
Sonine Polynomial Solution of the Boltzmann Equation for Relaxation of Initially Nonequilibrium Distribution
Authors: Abe Kanji
Published: February 2004

Using the Sonine polynomial expansion method the nonlinear Boltzmann equation for time-dependent spatially uniform gases is solved to examine the relaxation of an initially nonequilibrium distribution toward the equilibrium. For an inverse-fifth power law force, a simple analytical expression is presented for equations for expansion coefficients. As a result the higher-order expansion coefficients as well as the lower-order ones are obtained, so that the decay of larger initial departure of the distribution function from the equilibrium is dealt with. The resulting distribution function is compared with the corresponding one obtained on the basis of the Bhatnagar-Gross-Krook model. The latter model is shown to be adequate only when the departure of distribution function from the equilibrium becomes small.
Truncation Procedure for the Spatially Homogeneous Boltzmann Equation
Authors: Ward C. A. , Mintzer D.
Published: February 2004

The usual truncation procedure for coefficient equations is shown to be inconsistent for a certain class of initial-value problems in that it retains terms of one magnitude while neglecting terms of the same or greater magnitude. Moreover, it predicts moments which are strongly dependent on the zero-order function used in the expansion of the distribution function. A truncation procedure is developed for spatially homogeneous (time relaxation) problems which gives rise to moments which are independent of the particular zero-order function used in the expansion; and which, for certain general initial distribution functions, are correct in value and first-derivative both initially and in equilibrium. As an example, this procedure is used to solve the two-temperature single-gas mixture problem.
Kinetic Theory of Transient Condensation and Evaporation at a Plane Surface
Authors: Shankar P. N. , Marble Frank E.
Published: February 2004

The phenomenon of transient condensation onto, or evaporation from, a liquid sheet in contact with its pure vapor is treated from a kinetic theory viewpoint. The Maxwell moment method is used to formulate the detailed transient problem. A steady surface mass flux rate exists for times large in comparison with the collision time, that is, in the continuum regime, and explicit formulas are given for this limit. The complete gasdynamic field, however, is nonsteady for all times. The calculations are carried out utilizing four moments, and the effects of incorporating additional moments are negligible. Finally, the analysis is extended to incorporate imperfect mass and temperature accommodation. Examination of the transient solution and a matched asymptotic “quasisteady” solution shows that the gasdynamic field consists of a diffusion process near the liquid surface coupled through an expansion or compression wave to the constant far field state.
Influence of Boundary Conditions on the Thermomagnetic Torque
Authors: Hsu S. K. , Snider R. F.
Published: February 2004

A moment method for solving the Boltzmann equation for a gas of diatomic molecules in an external magnetic field and in cylindrical geometry is presented. It is found that the particular geometry is very important at all pressures while the specific form of the boundary conditions becomes dominant at low pressures. In the continuum region, the torque has the same features as a Burnett effect in being inversely proportional to the pressure while at lower pressures the Knudsen effect on the temperature distribution becomes the major contribution to the pressure dependence. In this case, an ansatz for a two-sided distribution function is used in solving the heat flow and temperature distribution. A comparison is made with experimental results and other theoretical investigations.
Density Distribution Measurements in Rarefied Gases Contained between Parallel Plates at High Temperature Differences
Authors: Alofs Darryl J. , Flagan Richard C. , Springer George S.
Published: February 2004

Density distributions were experimentally determined in rarefied gases at rest contained between two parallel plates maintained at widely different temperatures. The temperatures of the hot and cold plates were ∼79°K and ∼294°K, respectively, resulting in a temperature ratio of about 4:1. Both helium and nitrogen were used as test gases. Particular attention was focused on obtaining data in the temperature jump and transition regimes. The gas densities were measured by observing the luminescence produced by a high-energy electron beam traversed between the plates. In addition to the density measurements, heat transfer measurements were also made in order to estimate the values of the thermal accommodation coefficients. The experimental results for helium were compared with the analytical results of Liu and Lees, and good agreement was found between the theory and data near the cold plate. Near the hot plate the analytical results and the data differed by about 7%.
Reflection of a Curved Shock from a Straight Rigid Boundary
Authors: Pant J. C.
Published: February 2004

The situation which arises from the regular reflection of a curved shock from a straight rigid boundary is analyzed. In particular, the relation between the curvatures of the incident shock and reflected shock has been derived. The nature of the curvature of the reflected shock has also been analyzed.
Shock-Wave Interaction with an Evaporating Aerosol
Authors: Evans P. J. , Mackie J. C.
Published: February 2004

The interaction of a shock wave with a gas containing suspended particulate matter of finite thermal conductivity is considered theoretically. Mass, energy, and momentum equations specifically including the effects of particle drag and heat transfer are solved simultaneously together with the rate equation for thermal evaporation of the solid to determine the relaxation in flow properties.
Corrections for Small Values of the Logarithm Term in the Electrical Conductivity of a Fully Ionized Plasma
Authors: Viegas John R.
Published: February 2004

Correction factors which extend the range of validity of expressions for the electrical conductivity of a fully ionized gas to small values of the logarithm of the ratio of the Debye length to the mean impact parameter for a 90° deflection are developed and compared.
Comparisons of Measured and Predicted Velocity Distribution Functions in a Shock Wave
Authors: Holtz T. , Muntz E. P. , Yen S.-M.
Published: February 2004

Molecular velocity distribution functions measured in a normal shock wave in helium at M = 1.59 show deviations from equilibrium which are consistent in functional form, but not quantitatively, with the deviations predicted by the Chapman-Enskog first iterate. The measurements do appear to be in substantial agreement with a Monte Carlo solution of the Boltzmann equation, as indicated by a comparison of the half-widths of the parallel velocity distributions in the shock wave.
Propagation of Sonic Booms and other Weak Nonlinear Waves through Turbulence
Authors: George A. R. , Plotkin Kenneth J.
Published: February 2004

The structure of weak shocks propagating over long distances through turbulence modeled by sound speed fluctuations is investigated. The equilibrium wave shape is governed by a balance between non-linear steepening and a dissipative mechanism due to acoustic scattering of high-frequency energy out of the incident wave direction. This scattered energy appears as perturbations arriving behind the shock. For conditions representative of sonic boom and explosion wave propagation over long distances the mean wave structure is governed by a Burgers' equation similar to that describing viscous shocks, the difference being that parameters describing the turbulent scattering appear in the dissipative term. The theoretical predictions agree in order of magnitude with experiments on atmospheric propagation of sonic boom and explosion waves.
Asymptotic Thermochemical Relaxation Times in a Dense Plasma
Authors: Sajben M.
Published: February 2004

Relaxation processes initiated in a spatially uniform, dense plasma by a sudden change in heavy particle density, temperature, or a superimposed electric field are considered. Electron impact ionization and three-body recombination, Ohmic heating, elastic energy transfer between electrons and heavy particles of both types, and inelastic energy loss or release are taken into account. The asymptotic phase of the relaxation process is characterized by one single time scale, which is approximated by using the inverse of the logarithmic derivative of electron temperature evaluated for t → ∞. An exact, algebraic formula for this time scale is derived in terms of partial derivatives of terms found in electron energy and mass conservation equations. Specialization to argon shows that the time scale is governed by inelastic rate processes for low degrees of ionization and by electron-ion elastic energy transfer for high ionization fractions. Numerically computed results can be well approximated by simple formulas, which clearly demonstrate the relative importance of various processes present.
Measurement of Plasma Conductivity for Electric Fields Larger than the Runaway Field
Authors: Lencioni D. E.
Published: February 2004

The electrical conductivity parallel to a magnetic field of a hot ion hydrogen plasma with n ≃ 109cm−3, Ti ≃ 50 eV, and Te ≃ 5 eV was measured for electric fields larger than the runaway field. The conductivity was found to be proportional to the plasma density with a value much less than Spitzer's conductivity but larger than Buneman's turbulent conductivity. When the current became comparable to the electron thermal current, the conductivity was found to decrease.
Electric Conductivity of Weakly Turbulent Plasmas
Authors: Ichikawa Yoshi H. , Nishikawa K.
Published: February 2004

The static electric conductivity of weakly turbulent plasmas has been examined on the basis of a kinetic equation for the linear response to the one-particle distribution function. Within the regime of neglecting the mode-coupling terms, the high-frequency turbulent fluctuations associated with the electron plasma wave give rise to a modification of the ordinary collisional conductivity through the adiabatic interaction between the particles and the turbulent fluctuations. On the other hand, the low-frequency turbulent fluctuation due to the ion oscillation mode determines the relaxation process in the system through the resonant interaction, and gives rise to a finite conductivity even in the collisionless plasmas.
Strong Turbulence Theory of Nonlinear Stabilization and Harmonic Generation
Authors: Manheimer Wallace M.
Published: February 2004

A nonlinear dispersion relation for dispersionless waves in a one-dimensional plasma is obtained by examining the statistical properties of particle orbits in a random potential. New techniques are developed to deal with trapped particles. It is shown that a linearly unstable plasma stabilizes when the trapping frequency is equal to the growth rate. Also, the density fluctuations set up by the trapped particles are shown to have a power-law dependence in wavenumber. The theory is able to explain many observations in recent beam-plasma experiments.
Microscopic Theory of Density Fluctuations and Diffusion in Weakly Ionized Plasmas
Authors: Williams R. H. , Chappell W. R.
Published: February 2004

Kinetic equations for the self and distinct parts of the electron density cross-correlation function are obtained for a partially ionized gas by solving a truncated BBGKY hierarchy in the Markovian limit. Assuming a BGK model for the terms representing collisions with the neutrals, these equations are then used to calculate the self and total electron density cross-correlation functions. The expressions obtained for the correlation functions are valid for stationary, homogeneous, partially ionized plasmas. In equilibrium, the expression for the spectral density reduces to that obtained by Dougherty and Farley. In the limit of zero-collision frequencies, the results of Rostoker and Rosenbluth are recovered. For long times and large probe separations analytical expressions are obtained for the cross correlation functions. It is found that the self-correlation function depends on the electron diffusion coefficient and the total electron correlation function depends on the ambipolar diffusion coefficient.
Numerical Evaluation of the Electromagnetic Properties of a Half-Space Relativistic Plasma
Authors: Imre Kaya , Ozizmir Ercument
Published: February 2004

The results of the linearized theory are numerically evaluated in the case of perpendicularly incident electromagnetic waves on a half-space relativistic plasma. Reflection, transmission, and absorption coefficients are calculated. It is found that the surface absorption is more significant at higher temperatures. The maximum value of the absorption coefficient reaches approximately 26% for β = (mc2/kBT) ≲ 0.1The results, however, are not valid near cutoff frequencies due to the breakdown of the linearized theory upon which the present calculations are based.
Formation of Ion-Acoustic Collisionless Shocks
Authors: Sakanaka P. H. , Chu C. K. , Marshall T. C.
Published: February 2004

Formation of ion-acoustic collisionless shocks was studied by numerically solving the one-dimensional Vlasov equation. The shock propagates at about the local ion-acoustic speed, and faster than the ion-acoustic speed ahead; the oscillations behind the shock show ion-acoustic dispersion. A precursor appears with a speed of 1.6 times the shock speed. Different temperature and density ratios produce qualitatively different flows, and they are analyzed in detail.
Interpretation of Spatially Decaying Ion-Acoustic Waves
Authors: Hirshfield J. L. , Jacob J. H. , Baldwin D. E.
Published: February 2004

Detailed examination is given to circumstances surrounding the excitation and detection of spatially propagating ion-acoustic disturbances in a plasma. For relatively weak damping, a theory is presented to show the major influence on spatial signal evolution engendered by source coupling details, by source geometry, and by three-dimensional ion trajectories. In particular, near-zone and far-zone regions are identified for a disk source. Fresnel interference can dominate the near zone (within which many experiments are performed), so that serious questions can be raised as to the interpretation of observed decays. For relatively strong decays, the transition to the ballistic, three-dimensional, free-streaming solution is presented. Experiments are presented to illustrate some features of the theory, including measurements of Landau damping with 0.04 < ki/kr < 0.2 for 0.6 < ω/ωpi < 1.4. Observed Fresnel interference patterns are compared with theory.
Symmetry Considerations for Grid-Launched Ion-Acoustic Waves
Authors: Bernstein I. B. , Hirshfield J. L. , Jacob J. H.
Published: February 2004

Immersion of a fine-mesh grid (or set of parallel grids) into a plasma is widely used to stimulate ion-acoustic waves. The grid structure is usually biased so as to reflect electrons and transmit ions. The effect upon the ions due to applied rf fields in the grid region is to provide some combination of velocity and density modulation. The associated applied electric field perturbations will possess a combination of odd and even spatially symmetric parts, about the plane of symmetry of the grid system. The steady-state solution of the governing differential equation in the ion-acoustic limit is shown to depend critically upon this source symmetry, and to reduce to the usual solution only for the case of odd symmetry. Experiments designed to test these symmetry predictions have been carried out using an apparatus described previously, except that a four-grid transmitter has been substituted for the three-grid one. The outer two grids are grounded and the inner two grids can be driven either in phase (odd E-field symmetry), or 180° out of phase (even E-field symmetry). For odd symmetry, the observed spatial disturbance is similar to that reported previously with clear evidence of Fresnel interference. For even symmetry, wavelike signals are not observed near the grids, indicating a strong decrease in coupling between the free-streaming source ions and an ion-acoustic wave.
Magnetic Dipole in a Stationary Plasma
Authors: Fougere P. F.
Published: February 2004

The determination of the magnetopause or free boundary of a plasma-free point dipole immersed in a field-free, stationary plasma is treated using a moment technique first introduced by Midgley and Davis. Their results are extended in two ways. First, using their form for the bounding surface, the number of adjustable coefficients is increased from 7 to 27. Second, different forms are introduced in which true cusps are produced along the dipole axis. As the number of adjustable constants is increased, these forms converge toward the exact solution from opposite directions. Extrapolation of these results leads to a value of 0.6222485 for the cusp ratio and 1.41397752 r0 for the equatorial radius.
Upper Bound on Plasma Containment. II
Authors: Hurley James
Published: February 2004

The problem of the saturation energy of a plasma in a magnetic bottle is considered, taking special care to insure that the plasma is kept away from the sources of the field of the bottle.
Hydromagnetic Waves Generated at the Bow Shock by Tangential Discontinuities in the Solar Wind
Authors: Jaggi R. K. , Wolf R. A.
Published: February 2004

The problem of interaction of an inhomogeneity frozen into the solar wind with the bow shock has been investigated. These frozen-in tangential discontinuities produce ripples that move along the shock, ripples that can cause magnetosonic waves in the downstream medium. There are five linearly independent types of frozen-in inhomogeneities. Of the five inhomogeneities, those involving changes in the magnitude of density or velocity produce magnetosonic waves of largest amplitude. Other inhomogeneities are substantially less effective in producing magnetosonic waves in the magnetosheath. For normal solar wind parameters, a 10% density inhomogeneity upstream typically produces a magnetosonic wave with |δB| = 0.03 Bs where Bsis the field strength in the magnetosheath. A 30° fluctuation in magnetic field direction upstream typically produces a magnetosonic wave downstream with magnetic amplitude ≃ 10−3 Bs. However, for certain angles between the upstream magnetic field and the shock, the efficiency of conversion into magnetosonic waves is infinite; i.e., the shock is unstable.
Free Boundary Long Helical Wavelength Equilibria
Authors: Weitzner Harold
Published: February 2004

A straight high beta helical equilibrium approximating a theta pinch is perturbed into a large aspect ratio torus by the addition of other helically symmetric fields in such a way that stability of the torus to most significant modes is unaffected. The ideal magnetohydrodynamic free boundary model is employed. The straight helical equilibrium is obtained by an expansion in the two parameters which are small but of the same order of magnitude, the ratio of helical magnetic field to theta pinch field and the product of helical wavenumber times plasma column radius. Neither beta nor the distortion of the plasma column from a true cylinder are taken small and the helical fields are principally L = 1. The equilibrium without net z current has desirable stability properties to m = 1 long wavelength modes, although higher m modes are unstable. The stability conditions are more readily satisfied than earlier ones where it was assumed that the plasma column deformation was small and helical wavenumber times plasma radius was not small.
Tokamak Equilibrium
Authors: Greene John M. , Johnson John L. , Weimer Katherine E.
Published: February 2004

Axisymmetric hydromagnetic equilibria are obtained from an ideal fluid model by means of an asymptotic expansion in the inverse aspect ratio. The calculation is carried sufficiently far so that the equilibrium condition J×B = ≇p is satisfied to second order. This provides expressions for the eccentricity of the constant pressure surfaces as well as for their displacements, and for both the magnitude and the curvature of the external field that must be provided to support the equilibrium. Scaling considerations are invoked to show how the external field must be altered to compress the plasma to a smaller major radius and thus obtain additional heating. Elementary hydromagnetic considerations indicate that the configuration may be stable with respect to modes which have the symmetry of the equilibrium. Application is made to a specific compression heating experiment.
Dynamic Stabilization of a Linear z Pinch by a Magnetic Quadrupole
Authors: Forman Peter R. , Haberstich Albert , Karr Hugh J. , Phillips James A. , Schofield Aldred E.
Published: February 2004

The effect of high-frequency linear quadrupole magnetic fields on the m = 1 kink instabilities of a z pinch, as proposed by Osovets, is investigated. Short-wavelength instabilities of 5-12 cm are observed to be dominant and are not suppressed by the stabilization fields. This is contrary to the reported result of others that the short-wavelength instabilities do not develop if the long wavelengths of the order of the interelectrode distance are stabilized. For the experimental conditions used, magnetohydrodynamic theory predicts stabilization of wavelengths of 20-80 cm and reduced growth rate for the shorter wavelengths. The observed instabilities have a reduced growth rate in agreement with theory.
Some Toroidal Equilibria for Plasma under Magnetoelectric Confinement
Authors: Stix Thomas H.
Published: February 2004

A powerful negative bias tends to arise spontaneously by the loss, from a toroidal plasma, of suprathermal ions such as Ohmic or cyclotron heating runaway ions or fusion-product protons and alpha particles, whose Larmor radius is vastly larger than that of the electrons also scraped off at the limiting plasma aperture. By this mechanism, strong ion-confining electric fields may be expected to appear at the plasma surface in all toroidal configurations including stellarators, tokamaks, floating rings, etc. Electrons, restricted to their surfaces of constant total energy, are then also confined. A drift-kinetic description is given of a neutral plasma under such “magnetoelectric confinement” for the interesting special case of purely toroidal magnetic field (i.e., symmetric torus with zero rotational transform). Particle diffusion and the approach to quasisteady state with ambipolar particle loss are discussed. Particular attention is paid to the construction of a two-parameter family of equilibria with density profiles approximating those which, in the succeeding paper, are found favorable to stability.
Stability of a Cold Plasma under Magnetoelectric Confinement
Authors: Stix Thomas H.
Published: February 2004

Surface modes are examined for a semi-infinite cold plasma immersed in a strong magnetic field. Adjacent to the plasma appear, consecutively in space, an electron sheath, a vacuum gap, and a conducting wall. In addition, a gravitational field simulates the effect of inhomogeneity in the magnetic field. Boundary conditions appropriate to the cold-plasma fluid equations are derived and a dispersion relation obtained which is quartic in frequency. Solutions are given for a variety of cases. It is found that the presence of the electron sheath can stabilize the familiar gravitational flute instability at long wavelengths. However, a new mode, termed the “two-fluid diocotron mode,” is uncovered which is unstable for configurations where the vacuum gap exceeds a critical thickness. The critical gap for this mode is, nevertheless, significantly larger than the corresponding gap for the ordinary (i.e., plasma replaced by vacuum) long-wavelength diocotron mode. Applications of the cold-plasma stability criteria are discussed for model plasmas under magnetoelectric confinement suitable for ion stripping and for controlled fusion.
Time-Averaged Density Profile in the Presence of an m = 2 Mode Finite Amplitude Instability
Authors: Daugherty Thomas L. , Ventrice Carl A.
Published: February 2004

A weakly ionized plasma column is investigated in the presence of a finite amplitude instability. The theory of Holter and Johnson is extended to include a finite amplitude m = 2 mode instability. From the zero harmonic solution to the macroscopic equations, the time-averaged particle density is obtained. Computations are performed on a digital computer to determine the form of the particle density profile in the presence of a helical, m = 2, and mixed mode instability. The form of the profile is found to have a strong dependence on the magnitude and polarity of the amplitude factors.
Production of Energetic Highly Ionized Plasma by Laser Irradiation of Lithium Hydride Pellets
Authors: Mattioli M. , Véron D.
Published: February 2004

Spherical LiH pellets have been utilized as targets for high-power, fast-rising, nanosecond laser pulses. Using different pulse lengths, τ, it has been shown that the pellets behave as a continuous source of energetic plasma during a time tl (called “interaction time”) depending on the pellet size and on the laser flux density. For pellets 50μ in diameter and flux densities of 1.5 × 1012W/cm2, tl is 20 nsec; the degree of ionization approaches 100% (about 1016 ions in the plasma) and the root-mean-square expansion velocity is 107 cm/sec; the total plasma energy is about 0.5 J with an energy transfer efficiency of 10%. The general behavior of the burning process agrees with the extension to small pellets of the theoretical model developed for the case of massive targets.
Magnetic and Drift Surfaces, Current Configuration of Stellarator Field
Authors: Miyamoto Kenro
Published: February 2004

Magnetic surfaces and drift surfaces of a single charged particle of a stellarator field are analyzed by using an average method. The dependence of the rotational transform angle and the magnetic well depth on the parameters of the current configuration of the stellarator field are studied for the case of long and short pitch of the helical windings to find the optimum parameters. The relation of magnetic and drift surfaces are examined and a condition for their small deviation is deduced. The properties of constant |B| surfaces are examined.
Determination and Shaping of the Ion-Velocity Distribution Function in a Single-Ended Q Machine
Authors: Andersen S. A. , Jensen V. O. , Michelsen P. , Nielsen P.
Published: February 2004

An electrostatic energy analyzer with a resolution better than 0.03 eV was constructed. This analyzer was used to determine the ion-velocity distribution function at different densities and plate temperatures in a single-ended Q machine. In all regions good agreement with theoretical predictions based on simple, physical pictures is obtained. It is shown that within certain limits the velocity distribution function can be shaped; double-humped distribution functions have been obtained. The technique used here is suggested as an accurate method for determination of plasma densities within 10% in single-ended Q machines.
Nonlinear Wave Mixing at Hybrid Frequencies in an Inhomogeneous Plasma
Authors: Fidone I. , Granata G. , Teichmann J.
Published: February 2004

The nonlinear coupling of waves near the hybrid resonances for a magnetized inhomogeneous plasma is investigated. In this case, the geometric optics approximation is no longer valid and the full wave equations must be used. In contrast to the homogeneous plasma treatment no synchronism relation for the propagation vectors occurs and nonlinear processes are possible which are absent in the homogeneous case. Two special examples of wave-wave mixing are discussed in detail, namely, harmonic generation at the upper hybrid frequency and excitation of longitudinal waves of frequency near the lower hybrid.
High Temperature Viscosity Ratios for Neon
Authors: Guevara F. A. , Stensland Gary
Published: February 2004

Capillary flow viscometry measurements were made to determine neon viscosity ratios . η(T)/η(T0). T ranges from 1100 to 2100 °K and T0 is the reference, arbitrarily taken as 283 °K. Results are higher than those of previous workers.
Damping of a Large Amplitude Ion Acoustic Solitary Wave
Authors: Ott Edward
Published: February 2004

The damping of a finite amplitude ion acoustic solitary wave due to ion-neutral collisions is examined.
Görtler Instability of Boundary Layers
Authors: Rintel Lionel
Published: February 2004

The problem of centrifugal instability of the laminar boundary layer over a concave wall is posed as one of convective instability penetrating in neutrally stable fluid. It is found that the perturbations have a finite wavenumber; the mechanism of penetration is therefore essential for the selection of the shape of the perturbations. The critical conditions for a number of boundary-layer-like profiles are computed and compared with the experimental results. It is found that the stability characteristics of the boundary layer depend on the presence of points of inflection in the velocity profile.
Stability of Pipe Flow with Superposed Solid Body Rotation
Authors: Nagib H. M. , Lavan Z. , Fejer A. A. , Wolf L.
Published: February 2004

The stability of a flow consisting of solid body rotation superposed on an entrance-type pipe flow profile is investigated experimentally. Increasing the swirl ratios from zero to four reduced the axial Reynolds number at which laminar flow breaks down from 2500 to 900.
Method for Predicting the Pressure Distribution on a Sphere in a Low Degree Cavitating Flow
Authors: Bober William
Published: February 2004

A method, which was originally developed for predicting the pressure field on the walls of a two-dimensional venturi in a mild cavitating flow, has been extended to predict the pressure distribution on the surface of a sphere. The method takes into account the effects of many cavitating bubbles. Several postulates based on the experimental observations of others, make it possible to obtain a formula for the pressure on the surface of the sphere resulting from the cavitating bubbles. A statistical approach is used which bears resemblance to techniques utilized in the kinetic theory of gases. The pressure on the surface of the sphere is taken to be an expected value and, therefore, requires the evaluation of an integral. However, before the integral can be evaluated, the one-bubble distribution function must be specified. The objective of the work is to develop an approach to the problem of predicting the pressure distribution on a submerged body in a low-degree cavitating flow.
Measurements of the Hypersonic Rarefied Flow Field of a Disk
Authors: Berlin S. , Scott P. B.
Published: February 2004

Measurements of the density and rotational temperature profiles about a disk normal to a cold nitrogen flow are presented for three free-stream conditions: M∞=4.2, Re∞D=210; M∞=6.2, Re∞D=125; and M∞=9.6, Re∞D=150. The bow region was surveyed using the electron beam method. Disk support was by four free molecular wires oriented at 45° to the beam and optical axes. The shock regions are found to be diffuse and of a form closer to the free molecular solution than to the continuum limit. Essentially full rotational temperature recovery is observed at the stagnation point whereas the maximum shock layer density is slightly below the Rankine-Hugoniot value. It appears that the viscous interaction parameter provides a useful measure of transition flow effects.
Neutral Stability of an Incompressible Magnetohydrodynamic Half-Jet at Low Reynolds Number
Authors: Deshpande Narayan V.
Published: February 2004

The effect of an applied magnetic field on the instability of a laminar, free boundary layer formed between two parallel streams of semi-infinite extent has been studied. It is shown that the stabilizing effect of the magnetic field does not give rise to any minimum critical Reynolds number. The fluid is assumed to have infinite electrical conductivity.
Axially Symmetric Hydromagnetic Equilibria with Spherical Plasma-Vacuum Interfaces
Authors: Yeh Tyan , Morikawa G. K.
Published: February 2004

Solutions representing axially symmetric hydromagnetic equilibria with spherical plasma-vacuum interfaces are extended from a low-pressure paramagnetic regime to a high-pressure diamagnetic regime.
Similarities between Ion Waves in Plasmas and Gravity Waves in Incompressible Fluids
Authors: Lam S. H. , Sanmartin Juan R.
Published: February 2004

Some similarities between ion waves in plasmas and gravity waves in incompressible fluids are investigated. It is shown that for zero ion temperature the ion-wave dispersion relation is similar to that of gravity waves in a stratified liquid between rigid, horizontal walls; for large wavelength the ion waves behave as the surface gravity waves of shallow-water theory. The general character of the pattern of ion waves arising in steady plasma flows is analyzed for arbitrary ion temperature, wavelength, and acoustic Mach number (which is based on the ion-acoustic speed), and is compared to the pattern of surface gravity waves in steady water flows when surface tension is taken into account.
External Control of Ion Waves in a Plasma by High-Frequency Fields
Authors: Kaw P. K. , Dawson J. M.
Published: February 2004

It is shown that a high-frequency field, with a frequency close to the electron plasma frequency and a strength less than that required to excite parametric instabilities, can be used to externally control, in a very significant way, the frequency and damping of ion waves in a plasma.
Nonlinear Behavior of the One-Dimensional Weak Beam Plasma System
Authors: Joyce Glenn , Knorr Georg , Burns Thomas
Published: February 2004

The effect of a weak beam of electrons on a Maxwellian plasma is studied by numerically integrating the Vlasov equation in one dimension. The solution is carried past the point of maximum electrostatic energy. After reaching its maximum value, the electrostatic energy fluctuates about its maximum. Some modes which are linearly stable grow due to mode coupling with the unstable modes. The relative amount of energy in the fastest growing mode is shown to depend on the periodicity length of the system.
Electrostatic Electron Oscillations in Cylindrical, Nonneutral Plasmas
Authors: Linson Lewis M.
Published: February 2004

The character and stability of electrostatic electron waves which propagate both parallel to B (wavenumber β) and perpendicular to B (azimuthal mode numberl) in nonneutral plasmas in cylindrical geometry are studied. The background ions are taken to be infinitely massive and so provide a partial neutralization of the unperturbed electron space charge; this neutralization ranges from the completely unneutralized electron plasma case to the more familiar case of a completely neutral plasma. It is found that the axisymmetric mode (l = 0) is stable for arbitrary radial density variation when the charge density is not too high. For l ≥ 1 and electron and ion densities constant out to r = a and zero beyond, the system is stable for all frequencies independent of the degree of neutralization and the location of a conducting outer wall. The dispersion relation is analogous to that for a neutral plasma permitting separate low- and high-frequency propagation bands. For low frequencies and low, nonincreasing electron, ion, and net charge densities, it is found that the presence of a resonant layer (zero frequency as seen by the electrons) within the electron cloud is necessary but not sufficient for instability. In general, finite axial wavenumber increases the tendency towards stability.
Convection Cell Produced by Low-Frequency Flute Instabilities
Authors: Ohkawa Tihiro
Published: February 2004

The structure of convection cells in a closed line system is studied. It was found that the isothermal plasma confined in a magnetic well will not dynamically reach the steady-state convecting state. The presence of a small amount of cold plasma will lead to the formation of a convection cell.
Plasma Convection Produced by Ion-Driven Drift Instability
Authors: Ohkawa Tihiro
Published: February 2004

The low-frequency drift instability is discussed as a possible cause for plasma convection. The presence of cold plasma near the wall makes the ion-driven drift mode unstable. The resultant transport may have a rate given by the Bohm formula estimated at the temperature of the cold component.
Numerical Simulation of the Weibel Instability in One and Two Dimensions
Authors: Morse R. L. , Nielson C. W.
Published: February 2004

Particle-in-cell simulation methods for doing full electromagnetic simulations of collisionless plasma phenomena are described and applied to the Weibel instability in one and two dimensions. Magnetic particle trapping and subsequent mode coalescing are seen. Magnetic field energy is seen to reach 10% of the total particle energy. The different electromagnetic simulation methods are compared.
Effect of Helical Instability on the Radial Density and Potential Distribution
Authors: Imazu S. , Maruyama T. , Sato H. , Nakano Y.
Published: February 2004

Helical instability of a positive column in a longitudinal magnetic field is investigated, under the assumptions that the perturbed densities have finite amplitudes and that the densities of electrons and ions are perturbed independently. A relationship between the perturbed densities of charged particles and the corresponding electric field is determined by solving Poisson's equation. Furthermore, the equations describing the behavior of steady-state densities are readily solved by transforming them into the integral equation of Volterra's type. With this treatment, simplified equations of the radial distribution of the steady-state density and potential are found as functions of the amplitude of the superimposed helix for the helical mode (m = 1) and the phase shift between the perturbed densities of electrons and ions. The results are compared with experimental data and found to be in fair agreement with experimental values of the radial density and potential distribution. The measurements also show the onset of modes 2, 3, and a low-frequency oscillation as a function of magnetic field intensity.
Heating of Counterstreaming Ion Beams in an External Magnetic Field
Authors: Papadopoulos K. , Davidson R. C. , Dawson J. M. , Haber I. , Hammer D. A. , Krall N. A. , Shanny R.
Published: February 2004

Ion heating by a strong ion-ion two-stream instability perpendicular to a magnetic field in the presence of a relatively cold electron background (Te≪miVd2) is considered. The magnetic field strength is such that the ion trajectories are straight, whereas the electrons are bound to the field lines (krLe≪1≪krLi). Theory is presented for both quasilinear and nonlinear stages of the evolution of the system for the case that the instability is electrostatic [(B2/8π) (1+β) >nmiVd2/8] and is compared with a series of computer simulation experiments. It is found that the quasilinear theory gives a fairly accurate description of spatially averaged plasma properties until the ion beams have been sufficiently modulated for ions to be trapped by the waves. In the subsequent nonlinear stage, stabilization occurs when the ion trapping period is equal to the reciprocal growth rate associated with the instability. The directed ion beam energy is mainly converted into random ion energy. The possible role of this instability in high Mach number shocks is discussed.
Resonance Cones in the Field Pattern of a Radio Frequency Probe in a Warm Anisotropic Plasma
Authors: Fisher R. K. , Gould R. W.
Published: February 2004

An experimental and theoretical investigation of the angular distribution of the electric field of a short radio frequency probe in a plasma in a magnetic field is described. The field is observed to become very large along a resonance cone whose axis is parallel to the static magnetic field and whose opening angle is observed to vary with incident probe frequency, cyclotron frequency, and plasma frequency in agreement with simple cold plasma dielectric theory. The relationship of these cones to the limiting phase- and group-velocity cones which appear in the theory of plane wave propagation is discussed. The addition of electron thermal velocities (warm plasma effects) is examined in the limit of a large static magnetic field. A fine structure appears inside the cones and is shown to result from an interference between a fast electromagnetic wave and a slow plasma wave. This interference structure is observed experimentally and measurements of the angular interference spacing are shown to agree with the warm plasma theory. The use of measurements of the resonance cones and structure as a diagnostic tool to determine the plasma density and electron temperature in a plasma in a magnetic field is discussed.
Trapping and Containment of a Cesium Plasma in a Magnetic Mirror
Authors: Kesner Jay
Published: February 2004

A study was performed of the trapping and confinement of a cesium plasma in a magnetic mirror. Time-dependent plasma behavior was observed by injecting plasma pulses, created by means of a rotating shutter, into a Q machine. Reflection of short collisionless plasma pulses from a single magnetic mirror was observed, and a comparison of the experimental results with a computer simulation was used to obtain information about the ion velocity distribution function and about the dynamics of plasma-mirror interaction. Build up and decay of plasma in a magnetic mirror well was studied by injecting dense, collisional plasma pulses into the Q machine at the mirror throat. The density of plasma at the midplane of the mirror was seen to increase significantly due to trapping and the containment times observed were about 10 msec (approximately 10 transit times). The plasma decay rate was slower than would be expected for a collisionless mirror. A model, based on Coulomb scattering for the trapping and decay processes, gives predictions in good agreement with the experimental results.