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Apr 1988

Volume 31, Issue 4, pp. 709-951

Page 1 of 2 Pages Next Page | Jump to Page

Reynolds number scaling of turbulent diffusivity in wall flows

Victor Yakhot

Phys. Fluids 31, 709 (1988); http://dx.doi.org/10.1063/1.866805 (2 pages) | Cited 1 time

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The quantitative interpretation of the recent experiments on turbulent diffusivity in high‐Reynolds‐number Couette–Taylor flow by Tam and Swinney [Phys. Rev. A 36, 1374 (1987)], is presented.
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47.27.T- Turbulent transport processes
47.32.Ef Rotating and swirling flows
47.60.-i Flow phenomena in quasi-one-dimensional systems

An improvement of the nonlocal heat flux formula

A. Bendib, J. F. Luciani, and J. P. Matte

Phys. Fluids 31, 711 (1988); http://dx.doi.org/10.1063/1.866806 (3 pages) | Cited 36 times

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A new heat flux formula valid in strong inhomogeneous laser‐produced plasmas has been derived from the Fokker–Planck equation. The nonlocal treatment of Luciani et al. [Phys. Rev. Lett. 51, 1664 (1983); Phys. Fluids 28, 835 (1985)] is improved by taking into account the electric potential effect. A simple and reliable phenomenological formula is proposed, which is in good agreement with numerical Fokker–Planck computations.
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52.25.Fi Transport properties
44.10.+i Heat conduction
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Interchange stabilization of a mirror plasma using radio‐frequency waves below the ion cyclotron frequency

J. J. Browning, R. Majeski, T. Intrator, N. Hershkowitz, and S. Meassick

Phys. Fluids 31, 714 (1988); http://dx.doi.org/10.1063/1.866807 (3 pages) | Cited 14 times

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It is demonstrated that radio‐frequency (rf) waves applied below the ion cyclotron frequency (ω/Ωi≊0.75) can stabilize a mirror plasma against the interchange instability. A set of phased antennas in the Phaedrus‐B tandem mirror central cell [Phys. Rev. Lett. 59, 206 (1987)] is used to select the rf azimuthal mode number (m). When the m=−1 mode is selected, the ponderomotive force from the left‐hand polarized wave fields is sufficient to stabilize the plasma. Measurements of the rf mode number and of the wave polarization indicate strong excitation of m=−1 modes with much of the wave having a left‐hand polarization.
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28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

The sedimentation rate of disordered suspensions

John F. Brady and Louis J. Durlofsky

Phys. Fluids 31, 717 (1988); http://dx.doi.org/10.1063/1.866808 (11 pages) | Cited 29 times

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An explicit expression for the sedimentation velocity at low particle Reynolds number in a concentrated suspension is derived and evaluated for two different approximations to the hydrodynamic interactions: a strict pairwise additive approximation and a far‐field, or Rotne–Prager, approximation. It is shown that the simple Rotne–Prager approximation gives a very accurate prediction for the sedimentation velocity of random suspensions from the dilute limit all the way up to close packing. The pairwise additive approximation, however, fails completely, predicting an aphysical negative sedimentation velocity above a volume fraction ϕ≊0.23. The explanation for these different behaviors is shown to be linked to the ‘‘effective medium’’ behavior of the suspensions. It is shown analytically and by Stokesian dynamics simulation that a suspension of neutrally buoyant particles may be modeled as a homogeneous fluid with an effective viscosity, but a sedimenting suspension cannot. As a result, the Rotne–Prager approximation actually captures the correct features of the many‐body interactions in sedimentation. An analytical expression for the sedimentation rate, which is in good agreement with experiment, is obtained using the Percus–Yevick hard‐sphere distribution function.
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47.55.Kf Particle-laden flows
82.70.Kj Emulsions and suspensions

The effect of hydrodynamic interactions on the orientation of axisymmetric particles flowing through a fixed bed of spheres or fibers

E. S. G. Shaqfeh and Donald L. Koch

Phys. Fluids 31, 728 (1988); http://dx.doi.org/10.1063/1.866809 (16 pages) | Cited 25 times

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Averaged equations describing the evolution of the orientation distribution in a dilute suspension of axisymmetric ‘‘tracer’’ particles flowing through a fixed bed of spheres or fibers are derived. The orientations of the freely suspended ‘‘tracer’’ particles change because of the stochastically fluctuating velocity field induced by the randomly distributed fixed‐bed particles. In the limit of small fixed‐bed volume fraction the orientation distribution satisfies a local orientational advective‐diffusion equation with an effective rotary diffusivity and ‘‘drift’’ velocity, which are functions of the orientation of the particle relative to the direction of the average flow. Solutions of this equation show that the tracer particles tend to align with their ‘‘thin side’’ toward the direction of the bulk flow and that the degree of this alignment depends on the aspect ratio of the particle.
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47.56.+r Flows through porous media
47.55.Kf Particle-laden flows
82.70.Kj Emulsions and suspensions
47.10.-g General theory in fluid dynamics

Bubble characteristics and trajectories in a microbubble boundary layer

S. Pal, C. L. Merkle, and S. Deutsch

Phys. Fluids 31, 744 (1988); http://dx.doi.org/10.1063/1.866810 (8 pages) | Cited 8 times

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Optical and photographic surveys of microbubble boundary layers are presented. The results show that the outer edge of the bubble cloud diffuses away from the wall as the bubbles are swept downstream. The plate‐on‐bottom orientation contains a bubble‐free region near the wall that cannot be discerned for the plate‐on‐top configuration. Skin friction measurements made when the bubble‐free region extends to y+=200 show there is no longer any Cf reduction present suggesting bubbles are not effective when they are outside the near‐wall region of the boundary layer. Bubble sizes, which increase with airflow and distance from the injection section and decrease with free‐stream velocity, were measured to be between 150 and 1100 μm.
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47.15.Cb Laminar boundary layers
47.27.N- Wall-bounded shear flow turbulence
47.55.Kf Particle-laden flows
47.60.-i Flow phenomena in quasi-one-dimensional systems

A model of bubble dynamics in a Hele–Shaw cell

Alain Pumir and Hassan Aref

Phys. Fluids 31, 752 (1988); http://dx.doi.org/10.1063/1.866811 (12 pages) | Cited 3 times

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A model of the interaction of small, well‐separated bubbles of one fluid propagating through another ‘‘resident’’ fluid in a Hele–Shaw cell is introduced and studied. In the model each bubble acts on the others by setting up a velocity field of the dipole type. A system of ordinary differential equations is developed for the bubble positions. The system is solved completely for the two‐bubble problem. The three‐bubble problem is addressed by numerical simulations. A set of self‐similar motions are also found analytically. The dynamics of rows of bubbles is investigated analytically and via numerical simulations. Although clearly an extreme idealization, the model appears to shed considerable light on what to expect in laboratory experiments.
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47.56.+r Flows through porous media
47.55.Kf Particle-laden flows

Evolution of bioconvection patterns in a culture of motile flagellates

Akira Harashima, Masataka Watanabe, and Issei Fujishiro

Phys. Fluids 31, 764 (1988); http://dx.doi.org/10.1063/1.866812 (12 pages) | Cited 21 times

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Numerical experiments were carried out on the pattern formation of bioconvection that is observed in cultures of motile aquatic microorganisms. New features were revealed on how the bioconvective system evolves and how the number of falling fingers is selected at each stage of evolution. At the onset of convection, the relevant dynamical regime is that of the Rayleigh–Taylor instability. Then, readjustment of the wavenumber occurs as the adjacent convection cells combine with each other. The trajectory in (total kinetic energy, total potential energy) space shows that evolution of the system proceeds in the direction of intensifying the downward advection of microorganisms and reducing the total potential energy of the system. Finally the system reaches a stationary state, where the aspect ratio of the convection cells resembles that of Bénard–Rayleigh convection and is optimum for the efficient downward advection of microorganisms. Furthermore, it is demonstrated that trajectories of the two cases deviate from this major evolution. In the case where the diffusion time of the system is large, the system shows remarkable oscillation and repeats the Rayleigh–Taylor instability intermittently. In the case where the viscous effect is large, the system ceases to evolve before reaching the optimum mode.
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87.19.-j Properties of higher organisms
47.20.-k Flow instabilities

Primary instabilities and bicriticality in flow between counter‐rotating cylinders

W. F. Langford, Randall Tagg, Eric J. Kostelich, Harry L. Swinney, and Martin Golubitsky

Phys. Fluids 31, 776 (1988); http://dx.doi.org/10.1063/1.866813 (10 pages) | Cited 61 times

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The primary instabilities and bicritical curves for flow between counter‐rotating cylinders have been computed numerically from the Navier–Stokes equations assuming axial periodicity. The computations provide values of the Reynolds numbers, wavenumbers, and wave speeds at the primary transition from Couette flow for radius ratios from 0.40–0.98. Particular attention has been focused on the bicritical curves that separate (as the magnitude of counter‐rotation is increased) the transitions from Couette flow to flows with different azimuthal wavenumbers m and m+1. This lays the foundation for further analysis of nonlinear mode interactions and pattern formation occurring along the bicritical curves and serves as a benchmark for experimental studies. Preliminary experimental measurements of transition Reynolds numbers and wave speeds presented here agree well with the computations from the mathematical model.
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47.20.-k Flow instabilities
47.32.Ef Rotating and swirling flows

Instability and transition of a three‐dimensional boundary layer on a swept flat plate

P. Nitschke‐Kowsky and H. Bippes

Phys. Fluids 31, 786 (1988); http://dx.doi.org/10.1063/1.866814 (10 pages) | Cited 11 times

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Stability features are studied experimentally for the unstable three dimensional boundary layer flow on a swept‐back flat plate. A pressure gradient on the flat plate is induced by a displacement body. Infinite sweep conditions are approximated by means of contoured endplates. For the measurements, hot‐wire and surface hot‐film anemometry as well as flow visualization techniques are used. In addition to stationary waves, traveling waves are also traced. The cross‐flow Reynolds numbers for the first appearance of either instability mode are of approximately the same magnitude. Wavelength and the direction of stationary vortices, as well as the frequencies of the most amplified traveling waves, are measured for different Reynolds numbers. The data obtained by the measurements are compared with the results of linear stability theory. The location of the final transition on the swept flat plate has proved to be fairly well predicted by the empirical transition criterion of Coustols (Thèse de Docteur Ingénieur, Ecole Nationale Supérieur de l’Aéronautique et de l’Espace, Toulouse, 1983).
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47.20.-k Flow instabilities
47.15.Cb Laminar boundary layers

Effect of bulges on the stability of boundary layers

Ali H. Nayfeh, Saad A. Ragab, and Ayman A. Al‐Maaitah

Phys. Fluids 31, 796 (1988); http://dx.doi.org/10.1063/1.866815 (11 pages) | Cited 13 times

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The instability of flows around hump and dip imperfections is investigated. The mean flow is calculated using interacting boundary layers, thereby accounting for viscous/inviscid interaction and separation bubbles. Then, the two‐dimensional linear stability of this flow is analyzed, and the amplification factors are computed. Results are obtained for several height/width ratios and locations. The theoretical results have been used to correlate the experimental results of Walker and Greening (British Aeronautical Research Council 5950, 1942). The observed transition locations are found to correspond to amplification factors varying between 7.4 and 10.0, consistent with previous results for flat plates. The method accounts for both viscous and shear‐layer instabilities. Separation is found to increase significantly the amplification factor.
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47.15.Cb Laminar boundary layers
47.27.Cn Transition to turbulence
47.20.Ft Instability of shear flows (e.g., Kelvin-Helmholtz)

Shock induced Rayleigh–Taylor instability in the presence of a boundary layer

L. Houas, A. Farhat, and R. Brun

Phys. Fluids 31, 807 (1988); http://dx.doi.org/10.1063/1.866816 (6 pages) | Cited 5 times

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The aim of this work is an experimental study of the development of perturbations of a gaseous interface impulsively accelerated by a plane shock wave. The experiments are performed in a double diaphragm shock tube, where the second diaphragm is a very thin Mylar film which can be initially bulged because of a pressure difference between the two gases. The shape of the leading front of the contact zone is measured at three locations along the tube using a transversal array of heat transfer gauges. After the shock passage, the evolution of the interface is sensitive to vorticity production and boundary layer effects so that the impulsive Rayleigh–Taylor theory is inadequate for the description of this evolution. In particular, the predicted perturbation reversal when the shock wave passes from the heavy gas to the light one may not occur because of the boundary layer effect.
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68.03.Kn Dynamics (capillary waves)
68.05.-n Liquid-liquid interfaces
47.40.Nm Shock wave interactions and shock effects

Radiative instabilities in a sheared magnetic field

J. F. Drake, L. Sparks, and G. Van Hoven

Phys. Fluids 31, 813 (1988); http://dx.doi.org/10.1063/1.866817 (10 pages) | Cited 37 times

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The structure and growth rate of the radiative instability in a sheared magnetic field B have been calculated analytically using the Braginskii fluid equations. In a shear layer, temperature and density perturbations are linked by the propagation of sound waves parallel to the local magnetic field. As a consequence, density clumping or condensation plays an important role in driving the instability. Parallel thermal conduction localizes the mode to a narrow layer where k∥ =k⋅B/‖B‖ is small and stabilizes short wavelengths k>kc, where kc depends on the local radiation and conduction rates. Thermal coupling to ions also limits the width of the unstable spectrum. It is shown that a broad spectrum of modes is typically unstable in tokamak edge plasmas and it is argued that this instability is sufficiently robust to drive the large‐amplitude density fluctuations often measured there.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.55.Fa Tokamaks, spherical tokamaks

Kinetic theory for electrostatic waves due to transverse velocity shears

G. Ganguli, Y. C. Lee, and P. J. Palmadesso

Phys. Fluids 31, 823 (1988); http://dx.doi.org/10.1063/1.866818 (16 pages) | Cited 86 times

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A kinetic theory in the form of an integral equation is provided to study the electrostatic oscillations in a collisionless plasma immersed in a uniform magnetic field and a nonuniform transverse electric field. In the low temperature limit (kyρi ≪1, where ky is the wave vector in the y direction and ρi is the ion gyroradius) the dispersion differential equation is recovered for the transverse Kelvin–Helmholtz modes for arbitrary values of k∥, where k∥ is the component of the wave vector in the direction of the external magnetic field assumed in the z direction. For higher temperatures (kyρi>1) the ion‐cyclotron‐like modes described earlier in the literature by Ganguli, Lee, and Palmadesso [Phys. Fluids 28, 761 (1985)] are recovered. In this article the integral equation is reduced to a second‐order differential equation and a study is made of the kinetic Kelvin–Helmholtz and the ion‐cyclotron‐like modes that constitute the two branches of oscillation in a magnetized plasma including a transverse inhomogeneous dc electric field.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.25.Mq Dielectric properties

Relativistic magnetosonic solitons with reflected particles in electron–positron plasmas

David Alsop and Jonathan Arons

Phys. Fluids 31, 839 (1988); http://dx.doi.org/10.1063/1.866765 (9 pages) | Cited 19 times

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The presence of magnetically reflected particles is shown to allow the existence of large amplitude magnetosonic solitary waves in relativistic electron–positron plasmas. If the flow is assumed to contain a single loop of gyrating particles, self‐consistent structures are found with peak field amplitudes (B/B∞)max<(11)1/2, where B∞ is the magnitude of the upstream magnetic field. In contrast, without reflected particles, the amplitude of a relativistic magnetosonic soliton is restricted to (B/B∞) −1<2/γ∞, where γ∞ is the upstream Lorentz factor. Therefore, if γ∞≫1, reflected particles greatly increase the allowable amplitudes of these nonlinear waves. It is also shown that when γ∞≫1, the wave properties are independent of γ∞, and are completely parametrized by the ratio of the Poynting flux to the kinetic energy flux in the upstream flow. Some new features of solitary waves without reflected particles are also derived, and a heuristic model is presented which gives a simple physical interpretation of many of these results.
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52.35.Sb Solitons; BGK modes
52.35.Tc Shock waves and discontinuities
52.27.Ny Relativistic plasmas
95.30.Qd Magnetohydrodynamics and plasmas

Dynamics of nonlinearly excited plasma waves

Giovanni Miano

Phys. Fluids 31, 848 (1988); http://dx.doi.org/10.1063/1.866766 (9 pages) | Cited 5 times

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In an underdense plasma a large‐amplitude plasma oscillation may be produced by the beating of two electromagnetic waves with a frequency difference approximately equal to the plasma frequency. In the spatially one‐dimensional, cold, and collisionless plasma the large‐amplitude plasma oscillation is limited by the nonlinearity caused by relativistic effects. In this paper a simple nonlinear equation, resembling the original equation of Rosenbluth and Liu [Phys. Rev. Lett. 29, 701 (1972)], is derived in the weak beat power limit from the fully relativistic fluid model proposed by Sprangle, Sudan, and Tang [Appl. Phys. Lett. 45, 375 (1984); Phys. Fluids 28, 1974 (1985)]. This equation also contains the effects of the relativistic transverse motion. Its analytical solution, describing the plasma oscillation dynamics, is given in a closed form by using Jacobian elliptic functions. The analytical computations are compared with numerical computations. Finally the fully relativistic equation, describing free plasma oscillations, is studied analytically.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.50.Gj Plasma heating by particle beams

The electrostatic two‐stream instability driven by slab‐shaped and cylindrical beams injected into plasmas

Miguel Galvez and Joseph E. Borovsky

Phys. Fluids 31, 857 (1988); http://dx.doi.org/10.1063/1.866767 (6 pages) | Cited 4 times

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An electrostatic linear analysis is performed for a finite‐width electron or ion beam streaming along a strong magnetic field in the presence of a homogeneous background plasma. The linear fluid equations have been solved as a boundary value problem for planar and cylindrical beam shapes, and the dispersion which results as an eigenvalue problem is solved numerically without approximation as a function of the electron beam width. The solution gives unstable modes for any beam width and the dispersion relation shows different branches. There is a branch in both configurations that represents the most unstable mode, and the wavelength of this unstable mode for the cylindrical beam is larger than the corresponding wavelength for the most unstable mode of the slab‐shaped beam.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.40.Mj Particle beam interactions in plasmas
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Two‐dimensional electrostatic simulations of plasma propagation perpendicular to a magnetic field

Miguel Galvez and Christopher Barnes

Phys. Fluids 31, 863 (1988); http://dx.doi.org/10.1063/1.866768 (6 pages) | Cited 15 times

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A two‐dimensional electrostatic particle‐in‐cell code is used to simulate a finite‐width plasma streaming across a uniform magnetic field. The simulations show that the plasma polarizes, and non‐neutral charge layers develop along its edges. In an electron–ion plasma, the charge layers are asymmetric and the electron layer is unstable to the diocotron mode. The simulations show that this instability has smaller growth rate for plasma streams that are relatively less dense and wider. For a positive/negative ion plasma with equal mass ions the charge layers are symmetric and the plasma is stable to the diocotron mode. The results show that the diocotron instability leads to vortex structure when the plasma width is greater than the ion gyroradius, but this instability disrupts the entire plasma when the plasma width is of the order of or smaller than the ion gyroradius.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.65.-y Plasma simulation
52.27.Jt Nonneutral plasmas

Magnetic fluctuations can contribute to plasma transport, ‘‘self‐consistency constraints’’ notwithstanding

John A. Krommes and Chang‐Bae Kim

Phys. Fluids 31, 869 (1988); http://dx.doi.org/10.1063/1.866769 (18 pages) | Cited 22 times

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The recent conclusion of Terry, Diamond, and Hahm (TDH) [Phys. Rev. Lett. 57, 1899 (1986)] that in a turbulent, collisionless plasma ‘‘magnetic transport including quasilinear magnetic flutter transport  . . .  does not contribute to the relaxation of 〈f〉, and thus is not responsible for electron energy or momentum transport’’ is argued to be irrelevant or incorrect for a variety of situations of physical interest, including saturation by quasilinear plateau formation, induced scattering, and, most important, conventional mode coupling. The well‐established theory of the mean infinitesimal response function and the spectral balance equation provides a unifying framework for understanding the work of TDH. In particular, the cancellations which lead to the TDH conclusion are special cases of well‐known relationships between the response functionparticle propagator, and dielectric function. A more general, concise, and manifestly gauge‐invariant algebraic derivation of the cancellations is given. Although the cancellations occur in a certain limit, the conclusions of TDH do not follow in general: The TDH picture of steady‐state turbulence as consisting of small‐scale ‘‘incoherent’’ ballistic ‘‘clumps’’ shielded by long‐wavelength ‘‘coherent’’ dielectric response is misleading physically and incomplete mathematically since it does not describe correctly the often dominant process of renormalized n‐wave coupling, particularly important for the ions. Although ion ballistic response is negligible, ions are important nevertheless: Their nonlinear contribution to the saturated potential can drive parallel electron currents, hence magnetic fluctuations, through linear mechanisms. Thus, when ion nonlinearities are considered, formulas for the magnetic contribution to transport emerge which are quite similar to the quasilinear formula.
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52.35.Ra Plasma turbulence
52.25.Gj Fluctuation and chaos phenomena
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.25.Fi Transport properties

Exact solutions of magnetohydrodynamic equations for fluids in a circular magnetic field

Tomikazu Namikawa and Hiromitsu Hamabata

Phys. Fluids 31, 887 (1988); http://dx.doi.org/10.1063/1.866770 (3 pages) | Cited 17 times

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Exact solutions of the nonlinear magnetohydrodynamic equations for a highly conducting fluid within an axisymmetric container are obtained. Attention is focused on fluids in which the unperturbed velocity and magnetic field are axially symmetric and purely zonal. It is shown that there are exact solutions with large amplitude but restricted form, indicating that an arbitrary disturbing force produces other motions as well as Alfvén waves propagating along an azimuthal magnetic field whose strength varies with radius.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Flux coordinates, self‐consistent equilibria, and variational principle

K. S. Riedel

Phys. Fluids 31, 890 (1988); http://dx.doi.org/10.1063/1.866771 (4 pages) | Cited 4 times

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The magnetohydrodynamic (MHD) equations are presented in an invariant form in flux variables and variational principles are formulated for these variables. These equations are then solved in Boozer coordinates in the small curvature expansion.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.-s Magnetic confinement and equilibrium

Particle simulation on radio frequency stabilization of flute modes in a tandem mirror. I. Parallel antenna

Yutaka Kadoya and Hirotada Abe

Phys. Fluids 31, 894 (1988); http://dx.doi.org/10.1063/1.866772 (8 pages) | Cited 4 times

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A two‐ and one‐half‐dimensional electromagnetic particle code (PS2M) [H. Abe and S. Nakajima, J. Phys. Soc. Jpn. 53, xxx (1987)] is used to study how an electric field applied parallel to the magnetic field affects the radio frequency stabilization of flute modes in a tandem mirror plasma. The parallel electric field E∥ perturbs the electron velocity v∥ parallel to the magnetic field and also induces a perpendicular magnetic field perturbation B⊥. The unstable growth of the flute mode in the absence of such a radio frequency electric field is first studied as a basis for comparison. The ponderomotive force originating from the time‐averaged product 〈v∥B⊥〉 is then shown to stabilize the flute modes. The stabilizing wave power threshold, the frequency dependency, and the dependence on ∇‖E∥‖ all agree with the theoretical predictions.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.65.-y Plasma simulation

Experimental study of nonlinear M=1 modes in the Tara tandem mirror

J. H. Irby, B. G. Lane, J. A. Casey, K. Brau, S. N. Golovato, W. C. Guss, S. F. Horne, J. Kesner, R. S. Post, E. Sevillano, J. D. Sullivan, and D. K. Smith

Phys. Fluids 31, 902 (1988); http://dx.doi.org/10.1063/1.866773 (6 pages) | Cited 11 times

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The nature of a rigid, flutelike M=1 instability as seen in the Tara tandem mirror [Nucl. Fusion 22, 549 (1982); Plasma Physics and Controlled Nuclear Fusion 1984 (IAEA, Vienna, 1985), Vol. 2, p. 285] is discussed. Radial density and light emission profiles obtained by inverting chord measurements are compared to end loss radial profiles during the evolution of the mode to its nonlinear saturated state. This final state is characterized by a coherent, flutelike motion of the plasma as a whole about the machine axis.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Particle simulations of plasma and dielectric Čerenkov masers

T. D. Pointon and J. S. De Groot

Phys. Fluids 31, 908 (1988); http://dx.doi.org/10.1063/1.866774 (8 pages) | Cited 12 times

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A new particle simulation model has been developed to investigate Čerenkov masers. The novel aspects of the code are briefly described, and results of simulations of two types of Čerenkov masers are presented. The first device uses a conventional dielectric lining as its slow‐wave structure. The second is a new type of Čerenkov maser in which a circular waveguide is partially filled with a dense annular plasma instead of a dielectric layer. Both simulations agree well with experimental results and linear theory calculations. Saturation of the instability is shown to be due to trapping of the beam electrons. The relative merits of each system are discussed.
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52.40.Mj Particle beam interactions in plasmas
52.65.-y Plasma simulation
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)

Injection, trapping, and acceleration of an electron beam in a stellatron accelerator

B. Mandelbaum, H. Ishizuka, A. Fisher, and N. Rostoker

Phys. Fluids 31, 916 (1988); http://dx.doi.org/10.1063/1.866775 (8 pages) | Cited 4 times

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The UCI modified betatron [Phys. Rev. Lett. 53, 266 (1984)] was converted into a stellatron accelerator by the addition of helical quadrupole coils to the betatron configuration. An experimental study of the injection, trapping, acceleration, and disruption of a beam in this apparatus has been conducted. The stellarator field applied was of up to 10 kG and with a rotational transform of ι≃0.1– 0.15. Electrons were injected from a thermionic emitter typically operated by applying 20 kV, 2– 4 μsec pulses to the hot cathode, which emitted ∼3 A. A beam of ∼200 A was trapped in the torus and accelerated by the betatron field applied immediately after the injection. The beam life was extended by increasing the toroidal field. The beam current suffered a partial disruption after it reached its peak value. After that the beam lost electrons gradually, accompanied by generation of x rays, until the entire beam was lost close to the peak of the accelerating betatron field. Electron energies of up to ∼4 MeV were reached. The dependence of the beam current and its lifetime, upon the applied fields and injection conditions, was explored.
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52.75.Di Ion and plasma propulsion
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  5. The effect of surface tension on the shape of a Hele–Shaw cell bubble
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