bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic processes in plasma heating by resonant mode conversion of Alfvén wave
Authors: Hasegawa Akira , Chen Liu
Published: March 2003

An externally applied oscillating magnetic field (at a frequency near 1 MHz for typical tokamak parameters) resonantly mode converts to the kinetic Alfvén wave, the Alfvén wave with the perpendicular wavelength comparable to the ion gyroradius. The kinetic Alfvén wave, while it propagates into the higher density side of the plasma after the mode conversion, dissipates due to both linear and nonlinear processes and heats the plasma. If a magnetic field of 50 G effective amplitude is applied, approximately 10 MJ per cubic meter of energy can be deposited in 1 sec into the plasma. The heating rate here is faster than that in the transit time magnetic pumping by a factor of β−1.
Electron distribution function in a plasma generated by fission fragments
Authors: Hassan H. A. , Deese Jerry E.
Published: March 2003

A Boltzmann equation formulation is presented for the determination of the electron distribution function in a plasma generated by fission fragments. The formulation takes into consideration ambipolar diffusion, elastic and inelastic collisions, recombination and ionization, and allows for the fact that the primary electrons are not monoenergetic. Calculations for He in a tube coated with fissionable material shows that, over a wide pressure and neutron flux range, the distribution function is non-Maxwellian, but the electrons are essentially thermal. Moreover, about a third of the energy of the primary electrons is transferred into the inelastic levels of He. This fraction of energy transfer is almost independent of pressure and neutron flux.
Spectroscopic measurements of the plasma temperature in the ZT−1 toroidal pinch
Authors: Howell R. B. , Karr H. J.
Published: March 2003

The plasma temperature in the ZT-1 toroidal pinch as been determined using spectral line Doppler broadening measurements facilitated by the use of analog-to-digital converters and an on-line computer. The ZT-1 system has been operated in a ’’derated’’ mode with peak toroidal currents of 30 to 110 kA, initial current rise times of 0.5 to 2.5×1011 A/sec, stabilizing toroidal magnetic fields of 0.06 to 0.3 T, and filling pressures of 2 to 30 Pa. Results of the plasma temperature measurements in this mode of operation are reviewed with the objective of determining the effects of scaling the machine parameters on the ion temperature with extension to results obtained in the earlier higher current ’’fast’’ mode operation. An analysis and experimental tests of several possible sources of error in the ion temperature measurements are given in an appendix.
Equilibrium and stability of tokamak with arbitrary cross section
Authors: Okada Osami
Published: March 2003

An analytical study is made of the equilibrium and stability of tokamaks with an arbitrary cross section. The ideal hydromagnetic model is used. With inverse aspect-ratio expansion, the analytical expression of the equilibrium magnetic surface which is correct to the second order of the inverse aspect ratio is obtained as a function of the mean radius of the magnetic surface. The specific volume of the magnetic flux is obtained explicitly, and the stability against an interchange mode is discussed.
Poloidal structure of the dissipative trapped electron drift instability
Authors: Liewer Paulett C. , Manheimer Wallace M. , Tang W. M.
Published: March 2003

A study of the poloidal mode structure of the dissipative trapped electron drift mode by Fourier analysis shows that when ion inertia effects are small compared with trapped electron effects, the mode balloons out in the region of trapped particles. When ion inertia effects are large, there is no ballooning and the growth rates are correspondingly smaller.
Excitation of the ordinary electromagnetic mode in low-β plasmas
Authors: Freund H. P. , Wu C. S.
Published: March 2003

The excitation of the ordinary mode propagating perpendicular to an external magnetic field in a plasma with low β∥ is discussed. The analysis is performed for plasma in which in addition to the thermal electrons there is a hot anisotropic electron component. Relativistic effects are taken into account in the stability analysis. Both a ring distribution and a loss cone distribution are used to model the hot electron species. For the ring distribution typical growth rates are larger than that for the case of the loss cone distribution. Excitation of the ordinary mode is found at numerous harmonics of the cyclotron frequency for the ring distribution, however, the loss cone distribution is found to give instability primarily at the fundamental harmonic.
Energy lost by a relativistic electron beam due to two-stream instability
Authors: Thode Lester E.
Published: March 2003

The two-stream instability between a monoenergetic relativistic electron beam of energy γ0 mc2 and density nb and an unmagnetized, homogeneous plasma of density ne is investigated. For weak interactions, S=β20γ0(nb/2ne)1/3<0.45, the two-stream spectrum is predominantly one-dimensional, and the fractional beam energy loss is ΔE=S (1+S)−5/2. However, for strong interactions, S≳0.45, efficient coupling occurs to waves with perpendicular wavenumbers 0≳k⊥< (nb/ne)1/3 ωe/c. Independent of S ΔE≃0.18 for strong interactions. The analysis is supported by one- and two-dimensional computer simulations. In addition, it is observed that nonlinear wave particle interactions lead to rapid heating of the plasma in two-dimensional space. Symmetric bulk heating and high energy tail formation of plasma electrons is observed perpendicular to the beam direction. Plasma heating parallel to the beam is asymmetric (v≳0), since the large amplitude waves are generated as a result of beam trapping in the forward direction.
Mega-Gauss turbulence due to seeded composition fluctuations in dense plasma, and electron beam scattering
Authors: Tidman D. A.
Published: March 2003

Fine scale variations in the chemical composition of a collision-dominated plasma give rise to corresponding spatial fluctuations in the electron density, which persist until being dispersed by diffusive or turbulent mixing. In the presence of a steep background temperature gradient these density fluctuations are expected to give rise to magnetic field fluctuations that reach the mega-Gauss range for temperatures of about a kilovolt. Using a simplified static plasma model, a spectrum is derived for the field fluctuations, together with a diffusion operator for the enhanced scattering of energetic particles in such a plasma. This phenomenon may be of interest in the design of targets for electron-beam driven fusion.
Energy cross term for a quantum vortex ring
Authors: Blood Frank A.
Published: March 2003

The energy cross term Ec between an initial fluid flow v0 and the flow from a vortex ring is normally written as v0⋅P, where P is the momentum of the vortex ring. There is some uncertainty about how to calculate P. Ec is computed exactly for flow around a closed circuit (a ring) in an incompressible fluid where circulation is quantized. v0 is allowed to be a function of position. The vortex rings are assumed not to be created impulsively. The result is that Ec is equal to the circulation times the mass of fluid that v0 causes to flow through the vortex ring per second. This reduces to the usual result P=ρκπr2 when v0 is constant in the neighborhood of the vortex ring.
Spherical cap bubbles and skirt formation
Authors: Hnat J. G. , Buckmaster J. D.
Published: March 2003

Spherical cap bubbles in viscous liquids often develop trailing gas ’’skirts.’’ Fundamental arguments relating to the shape of gas caps, the formation of skirts, their length and thickness are discussed. Experimental results in mineral oil of gas cap indentation, the structure of skirted and nonskirted wakes, the length of skirts, and criteria for skirt formation and skirt instabilities are presented.
Runaway electrons in an impure plasma
Authors: Cohen Ronald H.
Published: March 2003

The electron runaway theories of Kruskal and Bernstein and Lebedev are extended to apply to multiply ionized, multiple species plasmas. The resulting expressions for electron runaway rates are compared with results obtained by Kulsrud, Sun, Winsor, and Fallon from numerical solutions of the Fokker–Planck equation.
Effects of low-frequency fluctuations on the growth or decay of high frequency modes
Authors: Escande D. F.
Published: March 2003

The problem of high-frequency modes propagating in a plasma where density fluctuations are large enough to produce plasmon reflections is investigated. The special cases of an instability and of a locally excited damped wave are considered.
Cylindrical solitons in a warm, multi-ion plasma
Authors: Maxon Stephen
Published: March 2003

The soliton problem for ion acoustic waves propagating in a warm plasma consisting of a mixture of two ion species is solved for cylindrically symmetric ingoing waves. The small amplitude approximation is made and a modified Korteweg–de Vries equation is obtained. The early time solution show that the solitons for the two ion species plasma are narrower in spatial width and propagate faster than their counterpart in the single ion plasma. Also, a given initial disturbance will break up into more solitons in the multi-ion, warm plasma than in the cold single-ion plasma.
High-frequency flute instability with loss-cone distribution function
Authors: Hirose A.
Published: March 2003

The effect of a loss-cone-shaped distribution function on the current-driven, high-frequency flute mode has been investigated. The effect becomes significant when the wavelength is of the same order as the electron Larmor radius and, in general, tends to destabilize the instability.
Shear induced growth and damping of waves
Authors: Manheimer Wallace M.
Published: March 2003

It is shown very simply with a time domain analysis that shear always stabilizes positive or negative energy waves. If the mode energy changes sign as a function of position, however, shear may destabilize the wave.
Stability limits of the ion beam excited electrostatic ion cyclotron instability
Authors: Michelsen P.
Published: March 2003

The dispersion relation for low-frequency electrostatic waves was analyzed numerically to find the region of instability for an ion beam plasma versus beam velocity vb, and versus electron to ion temperature ratio. For Vb≳1.6 a the marginal unstable mode has a perpendicular wavenumber k⊥≠0.
Some diffusion equations in plasma physics
Authors: Peyraud Jean , Coste Jean
Published: March 2003

Unstable diffusion equations of the form [∂t−∂xD (x) ∂x] f (x,t) =γ (x)  f (x,t) are studied. In the absence of the dissipation function γ (x), the Green’s function of the equation when D≈x−n (n is an even integer) is derived. Considering the propagation of unstable modes, the overall growth rate of the distribution of the modes, when γ (x) is a sharply peaked function, is evaluated. The three-dimensional propagation of unstable modes for the case D=Cte are also considered. It is shown that the diffusion may suppress the instability of the modes.
Plasma loss and associated diffusion coefficients to an isolated internal octupole ring
Authors: Cavallo Alfred J.
Published: March 2003

Measurement of particle transport is made in the magnetohydrodynamically stable region near a completely isolated internal ring in a levitated octupole by telemetering the collected plasma signal. With a toroidal field of 10% of the poloidal field and with the parameters of gun-injected plasma (Ti=20–40 eV, Te=5 eV, n=109/cc) a derived diffusion coefficient of D=60 cm2/sec results. With only the poloidal field, and thus without flux surfaces or shear, D=750 cm2/sec. Both diffusion coefficients are independent of magnetic field strength between 1.2 and 3.0 kG. This independence suggests Okuda–Dawson convective diffusion, but the observed magnitude with a toroidal field is 40 times greater than the minimum given by theory including mirroring effects. With only the poloidal field the observed result is 20 times the theoretical estimate. Transport with a toroidal field is very sensitive to levitation. Supports or potential disturbing connections must be removed from the ring or transport is an order of magnitude larger.
Magnetohydrodynamic spectrum in a class of toroidal equilibria
Authors: Spies G. O.
Published: March 2003

A normal mode analysis is performed for small amplitude magnetohydrodynamic motions about arbitrary, axially symmetric, static equilibria with purely poloidal magnetic fields. It is shown that the maximum growth rate pertaining to a fixed azimuthal mode number m increases with ‖m‖, and that the point eigenvalues become densely spaced in the limit ‖m‖→∞, thus forming an unstable continuum. For large ‖m‖, the determination of the normal modes is reduced to a problem in ordinary differential equations, and the dependence of the point eigenvalues on mode numbers is studied. As a practical consequence, it is found that the criterion derivable from the energy principle through trial functions localized at a pressure surface is necessary for gross stability (i.e., for stability of modes with small mode numbers). This conclusion does not apply to equilibria with shear.
Ion-beam excitation of electrostatic ion-cyclotron waves
Authors: Böhmer H. , Hauck J. P. , Rynn N.
Published: March 2003

Electrostatic ion-cyclotron waves are excited by a cesium ion beam injected into a cesium plasma in a Q machine. Strong interactions are observed. Spatial growth rates are measured as a function of beam and plasma parameters.
Anomalous penetration of high-frequency electromagnetic waves into a plasma
Authors: Ferrari L. A. , LaHaye R. J. , McQuade A. W.
Published: March 2003

Measurements of anomalously large effective penetration depths of high-frequency (ω≈ωce) electromagnetic waves in a plasma are reported. The penetration depth increases from 7 to 20 times the cold plasma value as the average incident power level is increased from 3 to 10 W/cm2. In this regime the electromagnetic wave energy is found to be concentrated in an annular region in the plasma.
Porous pipe flow
Authors: Van Dooren R.
Published: March 2003

A new approach to the steady laminar axisymmetric flow of a Newtonian viscous incompressible fluid through a porous circular pipe is introduced based on the assumption of a wall porosity of the exponential type and a Poiseuille inlet profile.
Extraordinary-mode electromagnetic instability with generalized distribution functions
Authors: Lai C. S.
Published: March 2003

The extraordinary-mode electromagnetic instability associated with the plasma waves propagating perpendicular to the magnetic field is studied for the class of the plasma distributions of the Dory–Guest–Harris type. For j⩾2 distributions, the instability may occur in both low-β and high-β plasmas and is very sensitive to the value of Ω2e/ω2pe. It turns out that the electrostatic instability for the k∥=0 waves is just a special case of the extraordinary-mode instability under the condition c→∞.
Electromagnetic current instabilities
Authors: Gary S. Peter , Gerwin R. A. , Forslund D. W.
Published: March 2003

Linear electromagnetic waves in an infinite, homogenous current-carrying Vlasov plasma with ion β≈1 are considered. Three instabilities emerge: a long wavelength, ’’kink-like’’ mode, and two instabilities with wavenumbers greater than the reciprocal ion Larmor radius, the ’’electromagnetic ion acoustic instability’’ and the ’’whistler current instability.’’ The linear properties of these instabilities are investigated in detail; they have substantially lower thresholds than the electrostatic ion-acoustic instability, and are generally favored by increasing ion β. In the regime of linear growth, the whistler current instability can give rise to an anomalous resistivity, and preferentially heats the ions.
Resonances of oscillating vapor bubbles
Authors: Hsieh Din-Yu
Published: March 2003

A physical explanation is presented of the second resonance of an oscillating vapor bubble due to the evaporation–condensation effect.
Observations of magnetohydrodynamic rarefaction waves
Authors: Niimura M.
Published: March 2003

Transverse magnetohydrodynamic rarefaction waves in a fully ionized deuterium plasma have been studied and measurements of the electron density as a function of time are compared with theoretical predictions. The agreement is good.
Interference structure near the resonance cone
Authors: Singh Nagendra
Published: March 2003

By comparing theoretical and experimental results, the Airy function-like behavior of the interference structure near the resonance cone has been confirmed. This leads to a rigorous method for determining the resonance cone angle.
Heat transport in a stratified two-phase fluid
Authors: Salpeter E. E. , Stevenson D. J.
Published: March 2003

A self-gravitating fluid, stratified into two phases of appreciably different densities and heated from within is considered. The heat flux, viscosity, and thermal diffusivity are assumed to be small enough to that, away from the interface between the phases, the flux is mainly carried by turbulent convection with a very small superadiabaticity. Different modes are investigated for transporting the heat flux across the interface, and both possible signs of the latent heat L are considered. A thermal boundary layer, distortion of the interface, and the nucleation, growth and motion of droplets and bubbles are included. It is shown that, under a specified range of conditions, the transition region near the interface is thin with a small change in the temperature T across it. The entropy difference between the two phases is then L/T. These considerations probably apply to the interior of Jupiter.
Compressible boundary layers over wavy walls
Authors: Lekoudis Spyridon G. , Nayfeh Ali H. , Saric William S.
Published: March 2003

An analysis is presented of compressible viscous flows past wavy walls without restricting the mean flow to be linear in the disturbance layer. Linearization of the compressible disturbance equations results in a system of six first-order differential equations for the perturbation quantities. The method of orthonormalization is used to control the error growth in the numerical solution of these equations. The present results agree more closely with experimental data than the results obtained by using Lighthill’s theory, which restricts the mean flow to be linear in the disturbance layer.
Theory of electric field correlations in a two-dimensional drift plasma
Authors: Weinstock J.
Published: March 2003

Recently, the results of numerical simulations of electric field correlations in a two-dimensional drift plasma by Okuda et al. were compared with theories of strong turbulence. Discrepancies were claimed to exist. Here, a brief re-examination is made of both theories and simulations. It is found that the ’’observed’’ time dependence of the correlation is explained by theory if the short time, inertial motion, of the particles is accounted for. This inertial motion also goes a long way toward explaining the strong magnetic field dependence of the ’’observed’’ e-folding time. It is pointed out that the parameters of the simulations only marginally satisfy a basic validity condition of the theories, and that close agreement would require a more elaborate theory, than is presently available, in which higher order cumulants of the particle orbits are calculated.
Transition from particle trapping to a quasi-linear-like beam-plasma system
Authors: Jones R. , Carr W. , Seidl M.
Published: March 2003

Experimental observations show that the beam-plasma instability generates a modified beam distribution function which can destabilize new modes. These sideband modes nonlinearly saturate, modify the beam further, and a cascade proceeds. For strong beams the cascade and attendent phase mixing lead to a quasilinear-like spectrum of waves and a nearly plateau-like beam. For absolute instability, the approach to a quasilinear system is slower than for the convective instability because the spectrum is fundamentally discrete.
Transient response from a small antenna in an anisotropic plasma
Authors: Simonutti Mario D.
Published: March 2003

The linear response of a cold anisotropic plasma to a point source under impulse excitation displays a frequency spectrum having maxima at the two frequencies determined by the resonance cone condition and at the upper hybrid frequency. A laboratory demonstration is reported.
Effect of small amplitude wall waviness upon the stability of the laminar boundary layer
Authors: Lessen Martin , Gangwani Santu T.
Published: March 2003

The effect of small amplitude wall roughness on the minimum critical Reynolds number of a laminar boundary layer is studied under the assumptions normally employed in parallel flow stability problems. The presence of a single Fourier component of roughness enhances the instability of the flow by introducing a point of inflection and increasing the profile curvature at the critical layer, and the effect becomes increasingly important as the wavelength of the roughness component decreases. Numerical calculations show a 10% reduction in minimum critical Reynolds numbers in the presence of small wavelength roughness with an amplitude of only 1% of the boundary layer thickness.
Drift wave stability of inverted gradient profiles in tokamaks
Authors: Horton Wendell
Published: March 2003

The stability theory of the drift wave and trapped electron mode is extended to include the dissipative contributions from electrons in three collisionality regimes. Application of the theory to the inverted profiles (∇n∇T<0) shows a substantial gain in stability over normal profiles (∇n∇T≳0) for ν*e<0.3 and a destabilization for ν*e≳1.0.
Multibeam instability in a Maxwellian simulation plasma
Authors: Gitomer S. J. , Adam J. C.
Published: March 2003

Two types of simulation models were used to study the multibeam instability in a plasma with a Maxwellian electron velocity distribution. Simulation results obtained are in substantial agreement with linear theory. The large instability growth rates found, γ/ωe≲0.1, suggest that ordered velocity initializations be used with caution in plasma simulation studies.
Two-temperature disparate-mass gas mixtures: A thirteen moment description
Authors: Goebel C. J. , Harris S. M. , Johnson E. A.
Published: March 2003

Thirteen moment equations for a binary mixture of Maxwell molecules are used to discuss the way in which a disparate-mass gas approaches equilibrium, the way in which a normal description may or may not emerge, and the usefulness and applicability of a number of existing treatments of two-temperature disparate-mass gases and associated temperature-difference relaxation equations. Corrections to some of the predictions in the literature are also found necessary.
Eigenvalue formulation for linear modes in the homogeneous multiple-fluid plasma
Authors: Simonutti Mario D.
Published: March 2003

The linearized equations of the multiple-fluid model, including an isotropic pressure law, of a plasma are cast into a concise form directly suited for the calculation of the full set of characteristic modes of the system. A fully ionized, homogeneous, drift-free, magnetized plasma having an arbitrary number of finite-temperature components is considered. For oscillations of the form exp[i (k⋅r−ωt)], the three separate problems of determining ω vs (k,ϑ), k vs (ω,ϑ), and kx vs (ω,kz) are treated by formulating the set of algebraic equations into matrix eigenvalue problems for which the eigenvalues are ω2, k2, and k2x, respectively. For each of the three cases, an example of the results of numerical evaluation of the eigenvalues is presented for an electron, two-ion species plasma. A method is described which may be used for calculating, directly within the eigensystem formulation, the group velocity of the characteristic modes.
Plasma turbulence in the vicinity of a magnetic neutral line
Authors: Overskei D. , Politzer P. A.
Published: March 2003

The behavior of a collisionless plasma in the vicinity of a magnetic neutral line has been investigated. An electric field externally applied along the neutral line results in a redistribution of plasma density which is consistent with E×B flows. The development of a complex spectrum of low frequency waves, ωci<ω<ωpi, is observed. These waves are spatially localized to within 3.5 cm of the neutral line and propagate antiparallel to the applied electric field. The power spectrum varies as P∝ω−5 and increases monotonically with the applied electric field, saturating just prior to electric field saturation. Heating of both the bulk and the tail of the electron energy distribution is observed and increases with increasing intensity of the density fluctuation spectrum. Typical measured values for the density, electron temperature, and electric field indicate an anomalously large resistivity. The Sagdeev and Galeev effective collision frequency for a current-driven ion acoustic mode with Vde≃Vs leads to electric fields consistent with those experimentally measured. These observations indicate the presence of a variant of the current-driven ion acoustic mode, which gives rise to significant heating of the electron distribution. Such a process may likely play an important role in the generation of energetic particles in solar flares and the geomagnetic tail neutral sheet.
Spiky turbulence generated by a propagating electrostatic wave of finite spatial extent
Authors: Morales G. J. , Lee Y. C.
Published: March 2003

The excitation of a new type of plasma turbulence consisting of a collection of neighboring localized electric fields of high intensity is investigated. The individual localized fields that constitute the spiky turbulence oscillate at frequencies close to the electron plasma frequency, and their localization is attributed to wave-trapping inside the self-consistent density cavities generated by the total ponderomotive force. Unlike previous investigations of this type of nonlinearity, which have dealt almost exclusively with the effects triggered by electromagnetic radiation, the present work studies the turbulence which is generated by a propagating electrostatic wave of finite spatial extent. This type of pump wave may arise naturally in beam-plasma experiments or in other situations which lead to a finite amplification region. The spiky turbulence is found to evolve in the nonlinear regime out of the linear parametric instabilities that can be excited by such a pump wave. A detailed linear analysis of the relevant linear instabilities is presented, and the results are found to be in good agreement with the direct numerical solution of the model equations of the problem. The nonlinear results of the present calculation show excellent agreement with the recent beam-plasma experiment of Wong and Quon in which the generation of spiky turbulence has been positively identified.
Toroidal plasma rotation in axisymmetric and slightly nonaxisymmetric systems
Authors: Tsang K. T. , Frieman E. A.
Published: March 2003

The relaxation of toroidal plasma rotation in the intermediate and collisional regimes has been calculated. The present results connect smoothly to previous results for the banana and collisional regimes. Small magnetic field ripples lead to a nonambipolar ion flux which may significantly affect toroidal rotation in all three regimes. This has also been calculated.
Field generation by a generalized ponderomotive force
Authors: Stamper J. A.
Published: March 2003

The inclusion of absorption leads to a ponderomotive force which depends explicitly on the field momentum transferred to the electrons. This generalized force implies, in contrast with the usual ponderomotive force, that time-averaged magnetic fields are generated directly by the radiative forces.
Effect of magnetic field on propagation of nonlinear ion-acoustic wave
Authors: Tagare S. G. , Sharma A. S.
Published: March 2003

The Korteweg–de Vries equations describing the propagation of slow and fast nonlinear ion-acoustic waves in a magnetic field are derived by using a perturbation method. The effect of the direction of propagation on the amplitude and width of the solitary solutions are discussed.
Nonlinear virtual ion modes
Authors: Mantei T. D. , Grésillon D. , Matthieussent G.
Published: March 2003

The nonlinear growth and saturation of the nonresonant beat oscillation driven by two ion-acoustic waves have been observed. After saturation, the beat signal relaxes into a resonant ion-acoustic wave.
Turbulent boundary layer wall-pressure fluctuations downstream from an abrupt change in surface roughness
Authors: Mulhearn P. J.
Published: March 2003

Spectra of wall-pressure fluctuations beneath a turbulent boundary layer have been investigated immediately downstream from an abrupt change in surface roughness, from slightly rough to very rough. Over the measurable frequency band (400 Hz to 7 kHz), the spectra in the first 150 mm scale on wall variables. This indicates that the motions responsible for the pressure fluctuations measured in this region are very close to the wall. Farther downstream this scaling procedure breaks down. It is suggested that the initially thin internal layer behaves independently of the flow external to it until it has grown appreciably and only then interacts with the outer boundary layer. It was found that, for all frequencies measured, the dimensional spectral level decreases initially then rises to a maximum at 250 mm from the roughness change before decreasing once more. The position of the maximum is close to where the internal layer ceases to have a distinct edge.
Plasma heating by scattered relativistic electron beams: Correlations among experiment, simulation, and theory
Authors: Thode Lester E.
Published: March 2003

The streaming instability is the primary heating mechanism in most, if not all, experiments in which the beam is injected into partially or fully ionized gas. In plasma heating experiments the relativistic beam must traverse an anode foil before interacting with the plasma. The linear theory for such a scattered beam is discussed, including a criterion for the onset of the kinetic interaction. A nonlinear model of the two-stream instability for a scattered beam is developed. Using this model, data from ten experiments are unfolded to obtain the following correlations: (i) for a fixed anode foil the dependence of the plasma heating on the beam-to-plasma density ratio is due to anode foil scattering, (ii) for a fixed beam-to-plasma density ratio the predicted change in the magnitude of plasma heating as a function of the anode foil is in agreement with experiment, and (iii) the plasma heating tentatively appears to be proportional to the beam kinetic energy density and beam pulse length.
Whistler wave propagation in a large magnetoplasma
Authors: Stenzel R. L.
Published: March 2003

The propagation of linear whistler waves is investigated in a very large quiescent collisionless discharge plasma in the parameter regime 0.05<ω /ωc<1, ωc/2π≃250 MHz, ωp/ωc≳10, where ωc and ωp are electron cyclotron and plasma frequency, respectively. Wave dispersion, damping, and polarization are determined from interferometer measurements. Group velocities are measured by propagating phase-coherent wave bursts. Low frequency wave packets disperse into nose whistlers. The phase and amplitude distribution of antenna-excited whistler waves is mapped along and across the magnetic field. The different directions of group and phase velocities are clearly demonstrated. Highly oblique whistlers are observed. In weakly nonuniform plasmas (ne/∇⊥ne≫λ∥) ray tracing is performed directly verifying the theoretical picture of ducting in density troughs. Perfectly ducted undamped whistlers are observed in field aligned troughs of width d≃λ∥. The profound effect of ray divergence from finite size antennas and of wave refraction effects on the axial amplitude decay has been neglected in most previous experiments and incorrectly interpreted as collisional or cyclotron damping.
Filamentation instability of a large amplitude whistler wave
Authors: Stenzel R. L.
Published: March 2003

A filamentation instability of a large amplitude whistler wave is observed in a laboratory experiment. The wave is launched in a large uniform magnetoplasma from antennas which produce a diverging energy flow in the linear regime. At large amplitudes (Bw/B0≃1%) the radiation pressure gives rise to a density depression originating from the antenna. The wave refracts into the density minimum which enhances the pressure and a filamentation instability develops. It saturates when a long field-aligned density trough is formed in which the wave is almost perfectly ducted. The temporal and spatial evolution of the self-ducting process are shown. The duct formed by the high power whistler wave also guides small amplitude whistlers over a wide range of frequencies.
Nonlocal analysis of the lower-hybrid-drift instability in theta-pinch plasmas
Authors: Batchelor D. B. , Davidson R. C.
Published: March 2003

A nonlocal analysis of the lower-hybrid-drift instability is presented for theta-pinch plasmas. For diffuse equilibrium profiles, nonlocal and local theories are shown to be in excellent agreement (with respect to maximum growth rate, corresponding l value, and radius of localization) for the fastest growing mode. The lower-hybrid-drift instability is also shown to provide a possible mechanism for predicting the wavelength and radius of localization of the flute perturbations observed experimentally in scylla 1-B.
Axial confinement of plasma by a magnetic trap
Authors: Niimura M. , Gross R. A.
Published: March 2003

The axial confinement of plasma by means of a magnetic trap has been studied in a coaxial electromagnetic shock tube. The propagation speed of the magnetic trap vacuum field-plasma interface, as it expanded into the plasma, was measured by magnetic field probes. The subsequent density change in the trapped plasma was determined by a Michelson He–Ne laser interferometer. Definite plasma trapping was achieved.
Constants of motion in models of two-dimensional turbulence
Authors: Hald Ole H.
Published: March 2003

It is shown by four examples, that the truncated spectral model for two-dimensional flows can have other constants of motion than energy and enstrophy. Thus, for these models the flow cannot be mixing.
Improved Korteweg–deVries type equation for cylindrical and spherical solitary wave
Authors: Panat P. V.
Published: March 2003

The Korteweg–deVries type equation describing the cylindrical and spherical solitons is derived for a mixture of warm ion fluid and hot, isothermal electrons. An approximate early time solution is discussed.
Field induced mixing across a diaphragm
Authors: Lang J. H. , Hoburg J. F. , Melcher J. R.
Published: March 2003

Electrohydrodynamic mixing, through a diaphragm separating liquids of viscosity η and permittivity ε but of differing electrical conductivities, is induced by a tangential electric field E. Mass transfer rates are shown to be controlled by a diffusion coefficient proportional to εE2/η.
Minimum drift velocity for instability in current-carrying, non-Maxwellian plasmas
Authors: Jentsch Volker
Published: March 2003

The drift velocity which separates stability from instability in current-carrying plasmas is sensitive to the specific shape of the distribution function. This result is used to interpret some features of low pressure discharge experiments.
Stability of solitary waves in shallow water
Authors: Berryman James G.
Published: March 2003

The stability properties of the solitary wave solutions of a Boussinesq equation and the Korteweg–de Vries equation are studied. In both cases the eigenfunctions of the linear equations for the perturbation are obtained directly through a series of transformations. For the Korteweg–de Vries equation, the results of Jeffrey and Kakutani are reproduced. Furthermore, it is demonstrated that localized perturbations can be expanded in terms of certain linear combinations of these eigenfunctions, contrary to the statement of Jeffrey and Kakutani. It is shown that the Korteweg–de Vries soliton is stable whereas the Boussinesq solitary wave is unstable to infinitesimal perturbations. The instability of the Boussinesq solitary wave is attributed to deficiencies of the long wavelength approximations used by Boussinesq in deriving his equation. No physical instability of water waves should be anticipated as a consequence of this result. A short discussion of a nonlinear stability analysis for the Boussinesq solitary wave is given. The evidence for nonlinear stability is inconclusive.
Electrostatic waves in an inhomogeneous collisionless plasma
Authors: Lindgren N. E. , Langdon A. Bruce , Birdsall C. K.
Published: March 2003

Small amplitude electrostatic ion-cyclotron waves are examined under a variety of conditions, with emphasis on nonuniform density plasmas, and, in particular, on the drift-cyclotron flute instability. The plasma is assumed collisionless and uniform in temperature. Rather than seeking plasma parameters which yield marginal stability, solutions of the dispersion relations for various parameter values have been obtained in such a way as to discover, for example, the frequencies and wavelengths at which the growth rate is the largest and which therefore are most likely to be seen experimentally. Perpendicular velocity distributions range from Maxwellian to an idealized (monoenergetic) loss cone. Some new features of known modes are discussed. Connections are made between branches of the solutions in various limits and other modes such as the electron drift waves.
Similarity solution of the axisymmetric Burgers equation
Authors: Sinai Yehuda
Published: March 2003

A singular perturbation analysis is utilized for determined the shape of a body which will comply with the requirements for a well-known similitude for the cylindrical form of Burgers’ equation, and the far-field shock profiles are presented.
Pressure induced by a stagnating turbulent field
Authors: Goodman L. , Massey A.
Published: March 2003

The frequency spectrum of a pressure field resulting from turbulence stagnating on a body is shown to be related to the fluctuating dynamic head through a Fourier-like transform along the mean stagnation streamline.
Korteweg–deVries equation modified by viscosity
Authors: Miles John W.
Published: March 2003

The Korteweg–deVries equation is modified to include both the dissipative and dispersive effects of viscous boundary layers.
Finite amplitude electrostatic ion cyclotron modes
Authors: Chaturvedi P. K.
Published: March 2003

Some special steady state finite amplitude nonsinusoidal solutions for an obliquely traveling electrostatic ion-cyclotron wave in a collisionless magnetoplasma are presented.
Orbit classification for spherical probes
Authors: Sherman Christopher
Published: March 2003

A correction is made to a commonly used scheme for classifying orbits in the theory of electrostatic spherical probes.
An exact solution for toroidal plasma in equilibrium
Authors: Lai C. S. , Verleun Mary
Published: March 2003

A class of exact solutions for magnetohydrodynamic toroidal equilibrium is found, which is more realistic than that discovered by Sudano.
Parametric decay of electromagnetic waves into two plasmons and its consequences
Authors: Liu C. S. , Rosenbluth Marshall N.
Published: March 2003

The parametric decay of the laser radiation into two plasma waves at the quarter critical density of an inhomogeneous plasma is analyzed. The growth rate and threshold of the absolute instability are derived. The bound on the saturation level of the plasma waves is obtained from the consideration of the pump depletion. The scattered radiation at 3/2 ω0 due to the beating of the incident wave with the backward plasma wave is calculated and compared with observations.
Radial expansion of self-focused, relativistic electron beams
Authors: Briggs R. J. , Hester R. E. , Lauer E. J. , Lee Edward P. , Spoerlein R. L.
Published: March 2003

Measurements of the radial expansion from gas scattering of a low ν/γ relativistic electron beam are presented. The measured current density profiles approach a Bennett shape, as predicted theoretically, and the rate of expansion of the beam radius with distance is in good agreement with the predictions of an envelope equation. locus has been determined. It terminates at zero temperature at
Vlasov equilibrium and nonlocal stability properties of an inhomogeneous plasma column
Authors: Davidson R. C.
Published: March 2003

A fully kinetic, nonlocal, matrix dispersion equation is derived for electrostatic perturbations about a spatially nonuniform cylindrical plasma equilibrium. The analysis is carried out for the class of radially confined rigid-rotor equilibria described by f0j(x,v) = (n̂jmj/2πTj) F (H⊥/Tj− ωjPϑ/Tj,vz), where Pϑ is the canonical angular momentum, vz is the axial velocity, H⊥ is the perpendicular energy, and n̂j, Tj, and ωj are constants. Assuming equilibrium charge neutrality and negligible spatial variation in the axial magnetic field B0êz, it is shown that the particle trajectories (in the equilibrium electric and magnetic fields) and the orbit integrals required in the stability analysis can be evaluated in closed form. Expanding the perturbed electrostatic potential in terms of the vacuum eigenfunctions {Jl(λnr) } for the conducting cylinder leads to a matrix dispersion equation of the form det[δn′,n+ Σjχjn′,n(ω)]=0, where the susceptibility χjn′,n(ω) is expressed as a phase-space integral over f0j(x,v) and known functions of ω, r λn, etc. The limiting case of strongly magnetized electrons and unmagnetized ions is considered together with a preliminary application to the lower-hyprid-drift instability.
Two-fluid theory of divertors without viscosity
Authors: Boozer Allen H.
Published: March 2003

A simple model of a divertor is studied with the classical two-fluid equations. The ion temperature is assumed zero, which has the simplifying effect of giving zero ion viscosity. The electrons are shown to leave the divertor much closer to the main body of the plasma than the ions. The divertor width is found comparable to the ion gyroradius calculated with the electron temperature, which is substantially wider than some classical estimates.
Turbulent heating in a moderate energy electron beam plasma experiment
Authors: Mross M. R. , Walsh J. E.
Published: March 2003

The excitation and dissipation of electron beam driven electrostatic turbulence has been investigated experimentally and theoretically. Optimization of the beam to wave power transfer efficiency is shown to depend on the details of the linear dispersion of plasma waves on the bounded plasma column. In addition, the time variation of the cw operated beam plasma system has been modeled by a coupled set of nonlinear rate equations for the intensity of unstable field fluctuations, the electron temperature, and the plasma density. Agreement with the experiment is excellent allowing identification of the important dynamics. In particular, the dominant dissipation mechanism is shown to be stochastic heating of (nonresonant) thermal electrons.
Parametric instabilities excited by localized pumps near the lower-hybrid frequency
Authors: Kuo Yu-Yun , Chen Liu
Published: March 2003

Parametric instabilities excited in nonuniform plasmas by spatially localized pump fields oscillating near the local lower-hybrid frequency are analytically investigated. Corresponding threshold conditions, temporal growth rates, and spatial amplification factors are obtained for the oscillating-two-stream instability and the decay instabilities due to nonlinear electron and ion Landau dampings.
Nonlinear multiphase deep-water wavetrains
Authors: Roskes G. J.
Published: March 2003

Nonlinear multiphase wavetrains on deep water are described using a nonlinear Schrödinger equation system. Instability and multiphase solitary envelope waves are considered in special cases.
Stability of hot electron plasmas
Authors: Berk H. L.
Published: March 2003

The linear theory of a flute mode in a hot electron plasma is presented when the precessional drift frequency is comparable to or larger than the ion cyclotron frequency. The mode is found to stabilize when a sufficiently large component of cold electrons is present.
Investigation of nonlinear waves on liquid jets
Authors: Taub Howard H.
Published: March 2003

The breakup of a liquid jet subject to a small sinusoidal disturbance is studied using a sensitive, high-resolution optical probe technique that generates an electrical signal proportional to the local jet diameter. This signal is resolved into its harmonic components which are measured as a function of distance along the jet axis. Measurements of the growth along the axis of the fundamental and first two harmonic components are compared with calculations based on the nonlinear analysis of Yuen. Excellent agreement is found for cases where the harmonic components lie both inside and outside the bandpass of the instability as described by the linearized theory.
Correction to the retarding torque experienced by two rotating concentric spheres
Authors: Kendall William M.
Published: March 2003

A general expression is determined for the first correction to the retarding torque experienced by two concentric spheres which slowly and steadily rotate about a common axis of symmetry and which bound an incompressible viscous fluid.
Experimental measurement of current cancellation in astron injection
Authors: Condit William C.
Published: March 2003

Recent work has shown that pulse-stacking in the astron device would not work for a charge-neutralized electron ring. Spreading of the electrons in the existing layer would offset gains resulting from adding new electrons. Experiments are described in which density spreading is consistent with theoretical predictions .
Head-on collisions between radiation-driven ionization fronts
Authors: Halverson Ward
Published: March 2003

Jump ratios for temperature, density, and absorption coefficient are calculated for head-on collisions between one-dimensional radiation fronts of equal strength. For weakly compressed incident fronts, the absorption of radiation in the collision zone causes a considerable increase of plasma temperature over that produced by shock heating alone. An experiment is suggested to study collisions between CO2 laser-driven radiation fronts in a strong longitudinal magnetic field.
Fast-ion generation in laser–plasma interactions
Authors: Valeo E. J. , Bernstein Ira B.
Published: March 2003

A model is proposed to explain the appearance of high energy ions in recent laser–solid target experiments. It is shown that the need to draw a neutralizing return current through a cold, collisional background can result in containment of laser heated electrons to the low density corona for a time long enough to appreciably accelerate the plasma ions.
Nonlinear excitation of acoustic waves in a double plasma device
Authors: Weibel E. S. , Tran M. Q.
Published: March 2003

In the double plasma device, ion acoustic waves are generated when the potential difference between the two plasmas is varied as Φ0sinωt. This perturbation at first affects only the ions since the electrons are repelled from the grid that separates the two plasmas. The analysis of the ion orbits near the grid leads to a source term in Vlasov’s equation for the ion distribution function. This source and therefore the ion acoustic wave depend nonlinearly on the exciting potential. Analytic and numerical results are given which show that the nth harmonic of the wave potential is proportional to Φn0 but is independent of ω when ω≪ωpi.