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Mar 1999

Volume 6, Issue 3, pp. 637-1040

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Resistive wall mode stabilization in toroidal geometry

A. Bondeson, C. G. Gimblett, and R. J. Hastie

Phys. Plasmas 6, 637 (1999); http://dx.doi.org/10.1063/1.873346 (4 pages) | Cited 12 times

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The possibility of stabilizing ideal magnetohydrodynamical (MHD) instabilities by resistive walls and slow plasma rotation (rotation frequencies comparable to resistive tearing growth rates) was proposed recently by Finn [Phys. Plasmas 2, 3782 (1995)] on the basis of cylindrical theory. In the present paper we analyze toroidal effects (pressure gradients and favorable averaged curvature) [Glasser et al., Phys. Fluids 18, 875 (1975)] on this “resistive window.” It is found that in toroidal geometry the resistive window for the distance of the wall from the plasma scales as S−1/3 (S is the ratio of resistive to Alfvénic time scales) and thus becomes very small in large tokamaks. Other differences between toroidal and cylindrical theories of resistive wall mode stability are discussed. © 1999 American Institute of Physics.
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52.30.-q Plasma dynamics and flow
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Fa Tokamaks, spherical tokamaks

On electron acceleration by intense laser pulses in the presence of a stochastic field

J. Meyer-ter-Vehn and Z. M. Sheng

Phys. Plasmas 6, 641 (1999); http://dx.doi.org/10.1063/1.873347 (4 pages) | Cited 29 times

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Electron acceleration by intense laser pulses is studied in the presence of a stochastic field representing a background plasma. Electron distributions are generated peaked in the direction of laser propagation and having a quasi-thermal energy spectrum. Effective temperatures are obtained above the ponderomotive energy. They scale with laser intensity I0 and interaction time t0 proportional to I01/2t0α with α ≈ 0.5−1.0. © 1999 American Institute of Physics.
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29.20.-c Accelerators
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
02.50.Ey Stochastic processes

Quasiaxially symmetric stellarators with three field periods

Paul Garabedian and Long-Poe Ku

Phys. Plasmas 6, 645 (1999); http://dx.doi.org/10.1063/1.873348 (4 pages) | Cited 9 times

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Compact hybrid configurations with two field periods have been studied recently as candidates for a proof of principle experiment at the Princeton Plasma Physics Laboratory. This project has led us to the discovery of a family of quasiaxially symmetric stellarators with three field periods that have significant advantages, although their aspect ratios are a little larger. They have reversed shear and perform better in a local analysis of ballooning modes. Nonlinear equilibrium and stability calculations predict that the average beta limit will be at least as high as 4% if the bootstrap current turns out to be as big as that expected in comparable tokamaks. The concept relies on a combination of helical fields and bootstrap current to achieve adequate rotational transform at low aspect ratio. © 1999 American Institute of Physics.
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52.55.Jd Magnetic mirrors, gas dynamic traps
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
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back to top Basic Plasma Phenomena, Waves, Instabilities

Structure of driven Alfvén waves with oblique magnetic field and dissipation

M. S. Ruderman and A. N. Wright

Phys. Plasmas 6, 649 (1999); http://dx.doi.org/10.1063/1.873300 (11 pages) | Cited 1 time

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The quasi-resonant behavior of linear Alfvén waves in one-dimensional magnetized weakly resistive plasmas with the slightly inclined equilibrium magnetic field is studied. The analysis concentrates on the behavior of the y-component of the velocity, v, which is the component perpendicular both to the inhomogeneity direction and to the equilibrium magnetic field, and the z-component of the velocity, w, which is the component along the inhomogeneity direction. It is shown that the behavior of v and w is described by the functions F(σ;Λ) and G(σ;Λ), where σ is the dimensionless distance along the inhomogeneity direction and the parameter Λ characterizes the relative importance of resistivity and the magnetic field inclination near the quasi-resonant position. The functions F(σ;Λ) and G(σ;Λ) are generalizations of the F and G functions introduced by Goossens, Ruderman, and Hollweg [Sol. Phys. 157, 75 (1995)] and coincide with them for Λ = 0. The behavior of F(σ;Λ) and G(σ;Λ) is studied numerically for different values of Λ. It changes from monotonic to oscillatory when Λ is increased. It is shown that the connection formulas giving the jumps of w and the perturbation of the total pressure across the quasi-resonant layer and the rate of energy dissipation in the quasi-resonant layer are independent of the inclination angle. © 1999 American Institute of Physics.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.30.-q Plasma dynamics and flow

Hot plasma effects on the polarization of electron cyclotron waves

R. Dumont and G. Giruzzi

Phys. Plasmas 6, 660 (1999); http://dx.doi.org/10.1063/1.873301 (6 pages) | Cited 9 times

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The evolution of the wave polarization during the propagation of electron cyclotron waves in hot plasmas is investigated. The coupled mode equations are solved in slab geometry, including the relativistic corrections to the dielectric tensor. This formalism is applied to purely ordinary or extraordinary modes, propagating obliquely with respect to the magnetic field in tokamak plasmas, in order to determine the rate of change of the mode purity due to finite temperature effects. It is found that such an alteration of the mode purity can be one to three orders of magnitude larger than in a cold plasma. However, the overall effect remains tolerable for most applications and typical parameters of magnetically confined plasmas. © 1999 American Institute of Physics.
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52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
52.25.Kn Thermodynamics of plasmas
52.55.-s Magnetic confinement and equilibrium
52.55.Fa Tokamaks, spherical tokamaks
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

First principles justification of a “single wave model” for electrostatic instabilities

John David Crawford and Anandhan Jayaraman

Phys. Plasmas 6, 666 (1999); http://dx.doi.org/10.1063/1.873302 (8 pages) | Cited 5 times

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The nonlinear evolution of a unstable electrostatic wave is considered for a multispecies Vlasov plasma. From the singularity structure of the associated amplitude expansions, the asymptotic features of the electric field and distribution functions are studied in the limit of weak instability, i.e., γ→0+ where γ is the linear growth rate. The asymptotic electric field is monochromatic at the wavelength of the linear mode with a nonlinear time dependence. The structure of the distributions outside the resonant region is given by the linear eigenfunction but in the resonant region the distribution is nonlinear. The details depend on whether the ions are fixed or mobile; in either case this generally derived physical picture corresponds to the single wave model originally proposed by O’Neil, Winfrey, and Malmberg [Phys. Fluids 14, 1204 (1971)] for the special case of a cold weak beam instability in a plasma of fixed ions. © 1999 American Institute of Physics.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Ballooning modes on open magnetic field lines

Eliezer Hameiri

Phys. Plasmas 6, 674 (1999); http://dx.doi.org/10.1063/1.873303 (12 pages) | Cited 7 times

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The ballooning instability on open magnetic field lines is given a thorough mathematical analysis. It is shown that resistive bounding ends (endplates) induce the same stability properties as insulating ends. When unstable, the maximal growth rate increases monotonically with boundary resistivity. An interchange instability may be present, and one necessary condition for its stability is that ∫ dl/B be constant on pressure surfaces. (This is an equilibrium existence condition for systems with closed magnetic field lines.) Another necessary condition for interchange stability has the same form as in the closed line case. Precise necessary and sufficient stability criteria are given for various types of bounding ends, including insulating, resistive, and perfectly conducting. © 1999 American Institute of Physics.
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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.Fi Transport properties

On the stability of self-gravitating magnetized dusty plasmas

M. Salimullah and P. K. Shukla

Phys. Plasmas 6, 686 (1999); http://dx.doi.org/10.1063/1.873304 (6 pages) | Cited 12 times

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The effects of a homogeneous magnetic field and the plasma nonuniformity on the dispersion relations of various electrostatic waves in self-gravitating magnetized dusty plasmas have been investigated. For this purpose, the kinetic dielectric response functions for the electrons and ions distributions have been used and the dielectric response function for the magnetized dust grains has been derived from the hydrodynamic equations that include the self-gravitational potential. Thus, extremely massive charged dust grains are subjected to both the electromagnetic and gravitational forces. Analytical studies of the dispersion relations in various frequency and wave number regimes reveal that both the magnetic fields and plasma inhomogeneities contribute to the stability of a self-gravitating dusty plasma system. The results of this investigation should be useful in understanding the stability of dusty proto-stars and dusty dark molecular clouds, which are held in strong magnetic fields and equilibrium density gradients. © 1999 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.25.Vy Impurities in plasmas
52.25.Dg Plasma kinetic equations
52.25.Mq Dielectric properties
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.30.-q Plasma dynamics and flow
95.30.Qd Magnetohydrodynamics and plasmas
98.35.Ac Origin, formation, evolution, age, and star formation
98.58.Db Molecular clouds, H2 clouds, dense clouds, and dark clouds
98.38.Dq Molecular clouds, H2 clouds, dense clouds, and dark clouds

Beam-plasma instability in inhomogeneous magnetic field and second order cyclotron resonance effects

V. Y. Trakhtengerts, Y. Hobara, A. G. Demekhov, and M. Hayakawa

Phys. Plasmas 6, 692 (1999); http://dx.doi.org/10.1063/1.873305 (7 pages) | Cited 9 times

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A new analytical approach to cyclotron instability of electron beams with sharp gradients in velocity space (step-like distribution function) is developed taking into account magnetic field inhomogeneity and nonstationary behavior of the electron beam velocity. Under these conditions, the conventional hydrodynamic instability of such beams is drastically modified and second order resonance effects become important. It is shown that the optimal conditions for the instability occur for nonstationary quasimonochromatic wavelets whose frequency changes in time. The theory developed permits one to estimate the wave amplification and spatio-temporal characteristics of these wavelets. © 1999 American Institute of Physics.
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52.40.Mj Particle beam interactions in plasmas
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.30.-q Plasma dynamics and flow

Static model for dusts in a plasma

Yan-Ping Chen, Huaqiang Luo, Mao-Fu Ye, and M. Y. Yu

Phys. Plasmas 6, 699 (1999); http://dx.doi.org/10.1063/1.873306 (4 pages) | Cited 18 times

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A simple model for charged dusts in plasmas is considered. The interaction of the dusts with the electron–ion plasma background yields a dust–dust interaction force that is attractive. The latter can hold the dust grains in various stable and metastable cluster configurations. The predicted few-dust configurations agree well with the results from an experiment and a molecular dynamics simulation. © 1999 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.25.Vy Impurities in plasmas
52.65.-y Plasma simulation
02.70.Ns Molecular dynamics and particle methods

Measurements and code comparison of wave dispersion and antenna radiation resistance for helicon waves in a high density cylindrical plasma source

D. A. Schneider, G. G. Borg, and I. V. Kamenski

Phys. Plasmas 6, 703 (1999); http://dx.doi.org/10.1063/1.873307 (10 pages) | Cited 16 times

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Helicon wave dispersion and radiation resistance measurements in a high density (ne ≈ 1019−1020 m−3) and magnetic field (B<0.2 T) cylindrical plasma source are compared to the results of a recently developed numerical plasma wave code [I. V. Kamenski and G. G. Borg, Phys. Plasmas 3, 4396 (1996)]. Results are compared for plasmas formed by a double saddle coil antenna and a helical antenna. In both cases, measurements reveal a dominance of the m = +1 azimuthal mode to the exclusion of most other modes; in particular, no significant m = −1 mode was observed. The helical antenna, designed to launch m<0 and m>0 modes in opposite directions along the field, resulted in an axially asymmetric discharge with very little plasma on the m<0 side of the antenna. For both antennas, good agreement of the antenna radiation resistance and wave dispersion with the model was obtained. It is concluded that unshielded antennas formed from current loops with an important ∣m∣ = 1 component for the conditions of our experiment, couple most of their power to the m = +1 helicon mode and thus have negligible parasitic, nonhelicon plasma loading. This result greatly simplifies calculations of power balance in these sources by identifying the helicon as the mode by which energy is transferred to the plasma. © 1999 American Institute of Physics.
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52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.50.Dg Plasma sources
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides

Drift-Alfvén vortices with finite ion gyroradius and electron inertia effects

B. N. Kuvshinov, F. Pegoraro, J. Rem, and T. J. Schep

Phys. Plasmas 6, 713 (1999); http://dx.doi.org/10.1063/1.873308 (16 pages) | Cited 12 times

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A two-fluid plasma model is used to analyze drift-Alfvén vortices in a magnetized, inhomogeneous, warm plasma. This low-β model retains the effects of finite electron mass and of finite ion gyroradii. The vortices are described by two potentials: the electrostatic potential and one component of the vector potential. The background plasma is assumed to have locally a linear density profile. Solutions in the form of dipoles, which propagate with constant velocity across a strong, uniform magnetic field, are analyzed. A general dispersion relation between the eigenvalues inside and outside the separatrix is derived. The analysis of this dispersion relation and of the spatial vortex structure leads to a general classification of two-potential vortices. Explicit solutions are presented for dipole vortices in the limit of zero electron inertia where finite gyroradius effects are retained and in the limit of cold ions where finite electron mass is taken into account. © 1999 American Institute of Physics.
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52.30.-q Plasma dynamics and flow

Viscous instability in a non-neutral plasma

Priyanka Goswami, S. N. Bhattacharyya, A. Sen, and K. P. Maheshwari

Phys. Plasmas 6, 729 (1999); http://dx.doi.org/10.1063/1.873309 (8 pages)

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The effect of viscosity on the stability of a non-neutral plasma is studied. Stability boundaries are obtained for two-dimensional electrostatic perturbations of long wavelengths. It is shown that a configuration with a monotone decreasing number density profile can be unstable when the plasma has viscosity. © 1999 American Institute of Physics.
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52.27.Jt Nonneutral plasmas
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

On the realization of the current-driven dust ion-acoustic instability

K. N. Ostrikov, M. Y. Yu, S. V. Vladimirov, and O. Ishihara

Phys. Plasmas 6, 737 (1999); http://dx.doi.org/10.1063/1.873310 (4 pages) | Cited 44 times

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The current-driven dust ion-acoustic instability in a collisional dusty plasma is studied. The effects of dust-charge variation, electron and ion capture by the dust grains, as well as various dissipative mechanisms leading to the changes of the particles momenta, are taken into account. It is shown that the threshold for the excitation of the dust ion-acoustic waves can be high because of the large dissipation rate induced by the dusts. © 1999 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.35.Dm Sound waves
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Fi Transport properties
52.25.Vy Impurities in plasmas

Acoustic modes in a collisional dusty plasma

A. V. Ivlev, D. Samsonov, J. Goree, G. Morfill, and V. E. Fortov

Phys. Plasmas 6, 741 (1999); http://dx.doi.org/10.1063/1.873311 (10 pages) | Cited 56 times

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The acoustic modes in a collisional dusty plasma are studied, taking into account the influence of ion–neutral collisions, ion drag, and neutral friction. It is assumed that the frequency of ion–neutral collisions is greater than the frequency of ion–dust collisions. Two limiting cases of short-wavelength and long-wavelength modes are considered separately, depending on the ratio of the dust–ion acoustic frequency to the frequency of ion–neutral collisions. It is shown that for the long wavelengths coupling between the modes becomes strong, causing the appearance of the hybrid long-wavelength mode. It is also found that in the long-wavelength case there are two types of instability caused by ionization. The theoretical results are compared with the data obtained in experiments with growing particles. © 1999 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.35.Dm Sound waves
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
back to top Nonlinear Phenomena, Turbulence, Transport
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Electron magnetohydrodynamic turbulence

D. Biskamp, E. Schwarz, A. Zeiler, A. Celani, and J. F. Drake

Phys. Plasmas 6, 751 (1999); http://dx.doi.org/10.1063/1.873312 (8 pages) | Cited 77 times

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Electron magnetohydrodynamic (EMHD) turbulence is studied in two- and three-dimensional (2D and 3D) systems. Results in 2D are particularly noteworthy. Energy dissipation rates are found to be independent of the diffusion coefficients. The energy spectrum follows a k−5/3 law for kde>1 and k−7/3 for kde<1, which is consistent with a local spectral energy transfer independent of the linear wave properties, contrary to magnetohydrodynamic (MHD) turbulence, where the Alfvén effect dominates the transfer dynamics. In 3D spectral properties are similar to those in 2D. © 1999 American Institute of Physics.
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52.30.-q Plasma dynamics and flow
52.35.Ra Plasma turbulence
52.25.Fi Transport properties
52.20.-j Elementary processes in plasmas

Nonlinear solutions of the Vlasov–Poisson equations

A. R. Karimov and H. Ralph Lewis

Phys. Plasmas 6, 759 (1999); http://dx.doi.org/10.1063/1.873313 (3 pages) | Cited 2 times

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Based on the kinetic description, properties of collisionless unmagnetized plasma are studied. Time-dependent solutions of the nonlinear Vlasov–Poisson equations are found. Several dynamical structures of a Maxwellian type are presented. © 1999 American Institute of Physics.
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52.25.Dg Plasma kinetic equations
02.30.Jr Partial differential equations
02.60.Lj Ordinary and partial differential equations; boundary value problems

Nonlinear interaction of a high-power electromagnetic beam in a dusty plasma: Two-dimensional effects

G. Sambandan, V. K. Tripathi, J. Parashar, and R. Bharuthram

Phys. Plasmas 6, 762 (1999); http://dx.doi.org/10.1063/1.873314 (5 pages) | Cited 7 times

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A large-amplitude Gaussian electromagnetic beam, propagating through a dusty plasma, heats the electrons nonuniformly. As the electron temperature rises, the rate of electron attachment to dust particles changes, modifying dust charge and free electron density. Further, the ambipolar diffusion of the plasma under thermal pressure gradient creates a plasma channel that guides the electromagnetic beam. At powers exceeding a threshold value, the beam becomes self-focused. © 1999 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
52.25.Fi Transport properties
52.50.Gj Plasma heating by particle beams
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.25.-b Plasma properties

Periodic equilibria of the Vlasov–Maxwell system

N. Attico and F. Pegoraro

Phys. Plasmas 6, 767 (1999); http://dx.doi.org/10.1063/1.873315 (4 pages) | Cited 20 times

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A general method is presented for deriving one-dimensional equilibrium solutions of the Vlasov-Maxwell system that extend the well-known Harris solution. In particular, spatially periodic solutions are constructed. These are needed in kinetic simulations of collisionless nonlinear reconnection processes when periodic boundary conditions are used. © 1999 American Institute of Physics.
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52.65.-y Plasma simulation
52.25.Dg Plasma kinetic equations

Dynamo efficiency and Beltrami flows in rectangular cells

Akira Kageyama and Tetsuya Sato

Phys. Plasmas 6, 771 (1999); http://dx.doi.org/10.1063/1.873316 (6 pages) | Cited 3 times

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Numerical simulations are performed for a kinematic dynamo problem in a rectangular cell geometry having dynamo laboratory experiments in mind. It is shown that the maximum growth rate of the magnetic field is given by a Beltrami flow with extremum flow helicity. This relation is so accurate that a slight change of the flow always gives a lower growth rate, at least in the low magnetic Reynolds number limit. It is also pointed out that two Beltrami flows with exactly the same kinetic energy and the helicity give very different dynamo growth rates. This indicates that the helicity extremum or the Beltrami condition alone is not sufficient to tell the most efficient dynamo flow. © 1999 American Institute of Physics.
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52.30.-q Plasma dynamics and flow
52.65.Kj Magnetohydrodynamic and fluid equation

Dipole and octapole field reversals in a rotating spherical shell: Magnetohydrodynamic dynamo simulation

Márcia M. Ochi, Akira Kageyama, and Tetsuya Sato

Phys. Plasmas 6, 777 (1999); http://dx.doi.org/10.1063/1.873317 (11 pages) | Cited 8 times

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Computer simulation results of a compressible magnetohydrodynamic (MHD) dynamo in a rotating spherical shell are presented. The reversal of either the dipole or the octapole field polarity is observed accompanying flip–flop magnetic energy transitions. Three energy transitions are observed. The dipole reversal occurs in the first transition. In the initial stage of the dipole reversal, the magnetic energy is about five times larger than the kinetic energy, and the convection pattern consists essentially of six straight cyclonic and anticyclonic vortex column pairs aligned to the rotation axis. In the intermediate stage, the magnetic energy decreases and the field is observed to change direction in some regions. This is accompanied by reorganization of the vortex columns and a transition to a new energy level. In the final stage, the field is completely reversed, the number of convection columns is increased and the magnetic energy is lower than in the second stage. In the other two magnetic energy transitions, the octapole component reverses polarity. © 1999 American Institute of Physics.
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52.30.-q Plasma dynamics and flow
95.30.Qd Magnetohydrodynamics and plasmas
52.65.Kj Magnetohydrodynamic and fluid equation

Experimental study of the dynamics of conditionally averaged structures in weakly developed electrostatic turbulence

O. Grulke, T. Klinger, and A. Piel

Phys. Plasmas 6, 788 (1999); http://dx.doi.org/10.1063/1.873318 (9 pages) | Cited 36 times

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An experimental study of coherent structures in the electrostatic turbulence observed in a steady-state operated, magnetized, cylindrical low-β argon plasma is presented. The conditional averaging technique is used to detect and to characterize large-scale conditional structures. The results of conditional averaging of a single drift wave mode are consistent with theoretical predictions and the data obtained by an azimuthal array of 64 Langmuir probes. In the turbulent regime, large monopole structures in the density fluctuations are identified, which develop by particle trapping due to associated potential structures. These structures lead to transport of particles across magnetic field lines, as evident from the trajectory of the structures. The comparison of the dynamics of conditional structures and unaveraged spatiotemporal structures suggests that they are of the same origin. © 1999 American Institute of Physics.
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52.35.Ra Plasma turbulence
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.70.Ds Electric and magnetic measurements
52.25.Gj Fluctuation and chaos phenomena
52.65.-y Plasma simulation

Influence of particle trapping on the penetration of high-frequency electromagnetic field into a semibounded plasma

M. R. Rouhani, N. L. Tsintsadze, and D. D. Tskhakaya

Phys. Plasmas 6, 797 (1999); http://dx.doi.org/10.1063/1.873319 (5 pages) | Cited 1 time

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Penetration of a high-frequency (hf) electromagnetic field into a semibounded plasma in the presence of trapped particles is considered. It is shown that the trapping of particles by the hf field considerably changes the condition for its propagation. In the stationary case, with increasing the hf field amplitude at the boundary, the frequency above which the plasma is transparent continually decreases. But the trapping of particles was found to give a lower limit for this critical frequency, i.e., this lower limit goes to zero when there is no trapping continually as the incident field amplitude increases, meanwhile the length of penetration increases and approaches a finite limit, in contrast to the untrapped case, where it increases monotonically. Moreover, when the hf field amplitude at the boundary exceeds some critical value, the plasma will become transparent and the localized structure of the hf field will change to an oscillatory structure. © 1999 American Institute of Physics.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.55.-s Magnetic confinement and equilibrium
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

On the structural stability of magnetic configurations with two null lines

S. V. Bulanov, E. Yn. Echkina, I. N. Inovenkov, F. Pegoraro, and V. V. Pichushkin

Phys. Plasmas 6, 802 (1999); http://dx.doi.org/10.1063/1.873320 (14 pages) | Cited 4 times

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The nonlinear dynamics of magnetoacoustic and Alfvén-type magnetohydrodynamic (MHD) perturbations in structurally unstable magnetic configurations is studied analytically and numerically. The nonlinear evolution of the perturbed electric current turns structurally unstable configurations into structurally stable ones. This transformation is forbidden in the framework of the ideal MHD equations, but can occur in the process of magnetic field line reconnection. MHD simulations of the transformation of configurations with two null lines (X-lines) under perturbations imposed from the boundaries show that the change in the magnetic field topology due to the magnetoacoustic perturbations is accompanied by the redistribution of the electric current curried by the Alfvén perturbations.© 1999 American Institute of Physics.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.-s Magnetic confinement and equilibrium
52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering

Momentum and heat conduction in highly ionizable plasmas

K. G. Whitney

Phys. Plasmas 6, 816 (1999); http://dx.doi.org/10.1063/1.873321 (15 pages) | Cited 7 times

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Calculations of the pressure tensor and heat conductivity for highly ionizable plasmas are presented that differ in three main respects from Braginskii’s calculation [Reviews of Plasma Physics, edited by M. A. Leontovich (Consultants Bureau, New York, 1965), Vol. 1, pp. 205–311]. One, the atomic number dependence of the classical viscosity is explicitly calculated and used to demonstrate, for ionization states of 12 or more, that the magnitude of the electron viscosity can greatly exceed that of the ion viscosity. Two, additional nonlinear contributions to the electron pressure tensor, dependent on gradients in temperature and density, are calculated, which can become comparable to and larger than the classical viscosity when these (physically realizable) gradients are sufficiently large. Three, these calculations interrelate the transport of energy and momentum by electrons in a plasma. As a consequence, flux limits on local heat transport suggest similar limits on local momentum transport. A model calculation of both transported quantities shows that they increase nonlinearly in size before the flux limit is reached. This behavior, in turn, suggests that flux limiting onsets earlier than linear transport theory implies and that the fluid equations for a plasma with severe temperature and density gradients must be closed, in general, by employing a nonlocal treatment of energy and momentum transport by electrons. © 1999 American Institute of Physics.
Show PACS
52.65.Kj Magnetohydrodynamic and fluid equation
52.55.Ez Theta pinch
52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
52.25.Fi Transport properties
52.57.-z Laser inertial confinement
52.58.Hm Heavy-ion inertial confinement
52.58.Ei Light-ion inertial confinement
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