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May 2003

Volume 10, Issue 5, pp. 1183-2175

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Hysteresis-like effects in gyrotron oscillators

O. Dumbrajs, T. Idehara, Y. Iwata, S. Mitsudo, I. Ogawa, and B. Piosczyk

Phys. Plasmas 10, 1183 (2003); http://dx.doi.org/10.1063/1.1561277 (4 pages) | Cited 9 times

Online Publication Date: 22 April 2003

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Special experiments devoted to studying hysteresis in gyrotron oscillators have been performed for the first time. Clear hysteresis-like effects with respect to variation of the cathode voltage have been observed in the mode competition scenario of the Forschungszentrum Karlsruhe coaxial gyrotron [B. Piosczyk et al., IEEE Trans. Plasma Sci. 30, 818 (2002)] and with respect to variation of the magnetic field and voltage in a single-mode operation of the Fukui IV gyrotron [T. Idehara et al., Int. J. Infrared Millim. Waves 19, 793 (1998)]. The observed phenomena are explained theoretically. © 2003 American Institute of Physics.
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84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)
84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)

Unexpected axial asymmetry in radiated power from high-temperature dynamic-hohlraum x-ray sources

T. W. L. Sanford, R. C. Mock, R. J. Leeper, D. L. Peterson, R. C. Watt, R. E. Chrien, G. C. Idzorek, B. V. Oliver, N. F. Roderick, and M. G. Haines

Phys. Plasmas 10, 1187 (2003); http://dx.doi.org/10.1063/1.1562630 (4 pages) | Cited 19 times

Online Publication Date: 22 April 2003

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Radiation from the interior of a dynamic hohlraum within a wire-array Z pinch is used to generate high-power x-ray pulses in both the up and down axial directions through radiation exit holes (REHs) in the anode and cathode, respectively. Despite a concerted effort to ensure a symmetrical up-down configuration, the measured peak top radiated power remained about twice that of the bottom (with similar total radiated energies from each REH), as compared to current simulations that predict equal powers. This large asymmetry suggests the need for improved physics models and simulation capabilities. © 2003 American Institute of Physics.
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52.55.Ez Theta pinch
52.57.-z Laser inertial confinement

Observations of low frequency oscillations due to transverse sheared flows

Edward Thomas, Jon David Jackson, Edwynn A. Wallace, and Gurudas Ganguli

Phys. Plasmas 10, 1191 (2003); http://dx.doi.org/10.1063/1.1567287 (4 pages) | Cited 9 times

Online Publication Date: 22 April 2003

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This Letter details observations of low frequency (i.e., ω ⩽ Ωi, where Ωi is the ion cyclotron frequency), coherent instabilities in the Auburn Linear Experiment for Instability Studies (ALEXIS). In the ALEXIS device, which is a 1.8-m long magnetized plasma column, the observed instabilities are excited by the presence of sheared flows in the plasma that are transverse to the axial magnetic field. The instabilities have long azimuthal wavelengths (m ⩽ 2) and are localized in the plasma to regions where the sheared flow is maximized and are anticorrelated to both density gradients and field aligned currents. © 2003 American Institute of Physics.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.75.Xx Thermionic and filament-based sources (e.g., Q machines, double- and triple-plasma devices, etc.)
52.72.+v Laboratory studies of space- and astrophysical-plasma processes

Kinetic ballooning stability of internal transport barriers in tokamaks

A. Hirose and M. Elia

Phys. Plasmas 10, 1195 (2003); http://dx.doi.org/10.1063/1.1568948 (4 pages) | Cited 2 times

Online Publication Date: 22 April 2003

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Steep plasma pressure gradient can be stably sustained in tokamaks if the magnetic shear s is weak, either positive or negative. A fully kinetic integral equation code has been developed to investigate stability of the drift and ballooning modes in tokamaks. For small shear ∣s∣≪1 where the magnetohydrodynamic ballooning mode is known to be stable, the kinetic ballooning mode is stable only if the pressure gradient exceeds a threshold.© 2003 American Institute of Physics.
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52.25.Fi Transport properties
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
52.25.Dg Plasma kinetic equations
52.25.-b Plasma properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Tn Ideal and resistive MHD modes; kinetic modes
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back to top Basic Plasma Phenomena, Waves, Instabilities

Dust-acoustic wave instability at the diffuse edge of radio frequency inductive low-pressure gas discharge plasma

V. E. Fortov, A. D. Usachev, A. V. Zobnin, V. I. Molotkov, and O. F. Petrov

Phys. Plasmas 10, 1199 (2003); http://dx.doi.org/10.1063/1.1563667 (10 pages) | Cited 26 times

Online Publication Date: 22 April 2003

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A spontaneous excitation of a grain density wave in a dusty cloud of monodisperse particles suspended at the diffuse edge of an rf inductive gas discharge has been discovered. The main physical parameters of this wave (phase velocity, wavelength, and growth rate) and of the background plasma (distributions of the electron density, electron temperature, and space potential) were measured. A theoretical model of the observable phenomenon based on the theory of dust acoustic waves in a collisional dusty plasma correlates well with the experimental data in a broad range of experimental conditions. The influence of a varying dust grain charge on the development of the observed dusty plasma instability has been analyzed. It is shown that the necessary condition for the instability excitation is the availability of a permanent electrical field (E0 ⩾3 V/cm) in the dusty cloud region. © 2003 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
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.)
52.80.Pi High-frequency and RF discharges
52.25.Kn Thermodynamics of plasmas
52.20.-j Elementary processes in plasmas

Non-neutral plasma equilibria, trapping, separatrices, and separatrix crossing in magnetic mirrors

J. Fajans

Phys. Plasmas 10, 1209 (2003); http://dx.doi.org/10.1063/1.1564820 (6 pages) | Cited 17 times

Online Publication Date: 22 April 2003

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The equilibria of non-neutral plasmas confined in Penning–Malmberg traps with axial varying (mirror) magnetic fields exhibit numerous unusual features, including potential differences along field lines, plasma density variations, trapped particles in both the high and low field regions, and unusual separatrices between trapped and untrapped particles. Mirror fields play prominent roles in a number of recent experiments, and overly simplistic models of the equilibria can lead to errors in the interpretation of experimental results. © 2003 American Institute of Physics.
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52.27.Jt Nonneutral plasmas
28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams

Nonthermal effects on occurrence scattering time in generalized Lorentzian distribution plasmas

Young-Dae Jung

Phys. Plasmas 10, 1215 (2003); http://dx.doi.org/10.1063/1.1565338 (5 pages) | Cited 5 times

Online Publication Date: 22 April 2003

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Nonthermal effects on the occurrence time advance for the elastic electron–ion collisions in generalized Lorentzian (kappa) distribution plasmas are investigated using the first-order eikonal analysis. The electron–ion interaction potential in the Lorentzian plasmas is obtained by the introduction of the plasma dielectric function (εκ). The semiclassical straight-line trajectory method is applied to the path of the projectile electron in order to obtain the eikonal phase and the scattering amplitude as functions of the impact parameter, Debye length, and spectral index (κ), and collision energy. The occurrence time advance is found to be increased with the increasing scattering angle. It is found that the occurrence time advance has the maximum value for the case of the thermal Maxwellian distribution plasmas. It is also found that the occurrence time advance decreases with the decreasing spectral index, i.e., increasing the nonthermal character of the plasma. © 2003 American Institute of Physics.
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52.20.-j Elementary processes in plasmas
52.25.Mq Dielectric properties

Equilibrium molecular dynamics simulations of the transport coefficients of the Yukawa one component plasma

Gwenaël Salin and Jean-Michel Caillol

Phys. Plasmas 10, 1220 (2003); http://dx.doi.org/10.1063/1.1566749 (11 pages) | Cited 12 times

Online Publication Date: 22 April 2003

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Equilibrium molecular-dynamics simulations in the microcanonical ensemble have been performed to obtain the thermal conductivity and the two viscosities of the Yukawa one-component plasma from the Kubo formulas. The expressions of the Kubo currents (pressure tensor and energy current) which enter these formulas are derived in terms of Ewald sums. The simulation results for the transport coefficients are compared with the predictions of the Chapman–Enskog theory which has been solved numerically. © 2003 American Institute of Physics.
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52.27.Gr Strongly-coupled plasmas
52.27.Lw Dusty or complex plasmas; plasma crystals
52.25.Fi Transport properties

Decay of trapped-particle asymmetry modes in non-neutral plasmas in a Malmberg–Penning trap

Grant W. Mason

Phys. Plasmas 10, 1231 (2003); http://dx.doi.org/10.1063/1.1566959 (8 pages) | Cited 5 times

Online Publication Date: 22 April 2003

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The mechanism for the strong damping of diocotron-like azimuthal trapped-particle asymmetry modes in a Malmberg–Penning trap is investigated with a detailed three-dimensional particle-in-cell computer simulation. The m = 1,kz ≠ 0 modes are created by a voltage squeeze from a mid-detector ring followed by a displacement of trapped particles in opposite directions on either side of the ring. The voltage squeeze creates a population of particles confined to half the trap length (trapped) and a population of particles that move longitudinally along the full length of the cylinder (untrapped). The damping of the modes is found to be the result of radial transport relative to the m = 1 mode (charge) center caused by transitions of particles from untrapped-to-trapped states induced by diffusion of the particles in velocity space. The transport is the immediate consequence of a difference in dynamical orbits for trapped and untrapped particles. The random walk in velocity space results in particles repeatedly changing state from trapped to untrapped and back. The dependence of the mode frequency and the exponential decay constant are explored as a function of squeeze voltage, magnetic field, and temperature in order to establish scaling behavior. © 2003 American Institute of Physics.
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52.27.Jt Nonneutral plasmas
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Simple modes of thin oblate non-neutral plasmas

Sh. Amiranashvili, M. Y. Yu, and L. Stenflo

Phys. Plasmas 10, 1239 (2003); http://dx.doi.org/10.1063/1.1569488 (4 pages) | Cited 3 times

Online Publication Date: 22 April 2003

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Lagrangian variables are used to describe linear and nonlinear oscillations of a magnetized non-neutral plasma slab in a harmonic trap, for slab width larger or comparable to the Debye length. The plasma particles move along the magnetic field lines, so that the oscillations are one-dimensional. The oscillation spectrum is found analytically, and the thermal corrections to the frequencies are calculated in a nonperturbative manner. Simple exact nonlinear solutions for the low-order modes are also obtained. © 2003 American Institute of Physics.
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52.27.Jt Nonneutral plasmas
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.50.-b Plasma production and heating
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.)

Currents and shear Alfvén wave radiation generated by an exploding laser-produced plasma: Perpendicular incidence

M. VanZeeland, W. Gekelman, S. Vincena, and J. Maggs

Phys. Plasmas 10, 1243 (2003); http://dx.doi.org/10.1063/1.1564598 (10 pages) | Cited 9 times

Online Publication Date: 22 April 2003

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Examples of one plasma expanding into another and the consequent radiation of wave energy are abundant in both nature and the laboratory. This work is an experimental study of the expansion of a dense laser-produced plasma (initially, nlpp/n0≫1) into a magnetized background plasma (n0 = 2×1012 cm−3) capable of supporting Alfvén waves. The experiments are carried out on the upgraded Large Plasma Device (LAPD) at UCLA [W. Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)]. It has been observed that the presence of a background plasma allows laser-plasma charge separation to occur that would otherwise be limited by large ambipolar fields. This charge separation results in the creation of current structures which radiate shear Alfvén waves. The waves propagate away from the target and are observed to become plasma column resonances. Conditions for increased current amplitude and wave coupling are investigated. © 2003 American Institute of Physics.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.38.Mf Laser ablation
94.20.Bb Wave propagation

Quasi-perpendicular magnetosonic waves in a multi-ion-species plasma

Shinsuke Irie and Yukiharu Ohsawa

Phys. Plasmas 10, 1253 (2003); http://dx.doi.org/10.1063/1.1568947 (9 pages) | Cited 18 times

Online Publication Date: 22 April 2003

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Propagation of oblique magnetosonic waves in a multi-ion-species plasma is studied with theory and three-fluid simulations. First, the linear dispersion relation of the high-frequency mode, the upper branch of magnetosonic waves, is examined in detail. Next, nonlinear evolution equation for this mode is derived. This mode can propagate as compressive or rarefactive solitary pulses, depending on the propagation angle. Ion acceleration due to these pulses and resultant pulse damping are analytically discussed. These processes are then demonstrated by fluid simulations for a plasma consisting of H, He, and electrons; either rarefactive or compressive pulses are gradually damped owing to the slight ion acceleration. © 2003 American Institute of Physics.
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52.35.Dm Sound waves
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.65.Kj Magnetohydrodynamic and fluid equation
52.27.Cm Multicomponent and negative-ion plasmas
52.35.Sb Solitons; BGK modes
52.25.Fi Transport properties

Stability analysis of hollow electron columns including compressional and thermal effects: Initial value treatment

V. I. Pariev and G. L. Delzanno

Phys. Plasmas 10, 1262 (2003); http://dx.doi.org/10.1063/1.1569269 (16 pages) | Cited 2 times

Online Publication Date: 22 April 2003

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The diocotron spectrum for a simplified fluid model of Malmberg–Penning traps that includes compressional effects due to end curvature with finite temperature is investigated analytically. The general initial value treatment of the l = 1 mode is performed and the algebraic growth proportional to math is recovered when the plasma length profile is the integrable one as introduced by Delzanno et al. [Phys. Plasmas 9, 4863 (2002)]. Then, nonintegrable length profiles slightly different from the integrable one are considered (the difference being characterized by ε). It is shown that complex discrete eigenfrequencies appear near the edge of the continuous spectrum of the l = 1 mode. Depending on the sign of ε, these discrete eigenfrequencies may or may not lead to exponential instability. The discrete eigenfrequency scales as ε2/3 with respect to the upper edge of the continuum. This confirms and explains the numerical observations of Finn et al. [Phys. Plasmas 6, 3744 (1999)] and Delzanno et al. [Phys. Plasmas 9, 4863 (2002)] and proves that the ε2/3 scaling law is a generic property of the modified drift-Poisson model near the edge of the continuum. The same general treatment is also applied to the l = 1 diocotron spectrum in a cylindrical Malmberg–Penning trap with an additional coaxial inner conductor of radius a. © 2003 American Institute of Physics.
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52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.27.Jt Nonneutral plasmas
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
02.10.Ud Linear algebra
52.25.-b Plasma properties

Measurement of the ion drag force on falling dust particles and its relation to the void formation in complex (dusty) plasmas

C. Zafiu, A. Melzer, and A. Piel

Phys. Plasmas 10, 1278 (2003); http://dx.doi.org/10.1063/1.1569486 (5 pages) | Cited 45 times

Online Publication Date: 22 April 2003

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Experiments on the quantitative determination of the weaker forces (ion drag, thermophoresis, and electric field force) on free-falling dust particles in a rf discharge tube are presented. The strongest force, gravity, is balanced by gas friction and the weaker forces are investigated in the radial (horizontal) plane. Under most discharge conditions, the particles are found to be expelled from the central plasma region. A transition to a situation where the falling particles are focused into the plasma center is observed at low gas pressures using small particles. These investigations allow a quantitative understanding of the mechanism of unwanted dust-free areas (so-called voids) in dusty plasmas under microgravity. Good quantitative agreement with standard models of the ion drag is found. © 2003 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.25.Fi Transport properties
52.25.Tx Emission, absorption, and scattering of particles
52.80.-s Electric discharges
52.35.Kt Drift waves
back to top Nonlinear Phenomena, Turbulence, Transport

Periodic driving of plasma turbulence

M. S. Baptista, I. L. Caldas, M. V. A. P. Heller, and A. A. Ferreira

Phys. Plasmas 10, 1283 (2003); http://dx.doi.org/10.1063/1.1561612 (8 pages) | Cited 6 times

Online Publication Date: 22 April 2003

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Tools to characterize three important characteristics of turbulence are proposed: Structures-within-structures, intermittent amplitude bursting, and turbulence complexity. These tools are applied to show that the injection of a rf wave into the plasma confined on the Tokamak Chauffage Alfvén Bresilién (TCABR) [R. M. O. Galvao, V. Bellintani, Jr., R. D. Bengtson et al., Plasma Phys. Controlled Fusion 43, A299 (2001)] decreases plasma edge turbulence, although not completely destroy it, by destroying the only two types of time structures found in the data. Both structures present multiscaling spectra, with infinitely many possible scalings. So, according to this analysis, complexity of this turbulence is mainly due to the multiscaling character of the oscillations. © 2003 American Institute of Physics.
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52.35.Ra Plasma turbulence
52.55.Fa Tokamaks, spherical tokamaks
52.40.Hf Plasma-material interactions; boundary layer effects

Global extended magnetohydrodynamic studies of fast magnetic reconnection

J. A. Breslau and S. C. Jardin

Phys. Plasmas 10, 1291 (2003); http://dx.doi.org/10.1063/1.1566026 (8 pages) | Cited 20 times

Online Publication Date: 22 April 2003

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Recent experimental and theoretical results have led to two lines of thought regarding the physical processes underlying fast magnetic reconnection. One is based on the traditional Sweet–Parker model but replaces the Spitzer resistivity with an enhanced resistivity caused by electron scattering by ion acoustic turbulence. The other includes the finite gyroradius effects that enter Ohm’s law through the Hall and electron pressure gradient terms. A two-dimensional numerical study, conducted with a new implicit parallel two-fluid code, has helped to clarify the similarities and differences in predictions between these two models. The former yields resistivity-dependent reconnection with a thick, moderate-aspect-ratio current sheet. If the sheet thickness is less than or comparable to the ion skin depth, it is verified that the Hall effect will predominate [Shay et al., Geophys. Res. Lett. 26, 2163 (1999)], producing true fast reconnection with a microscopic current sheet of unit aspect ratio and a distorted out-of-plane magnetic field [Mandt et al., Geophys. Res. Lett. 21, 73 (1994)]. © 2003 American Institute of Physics.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.Fi Transport properties

Kinetic instabilities of thin current sheets: Results of two-and-one-half-dimensional Vlasov code simulations

I. Silin and J. Büchner

Phys. Plasmas 10, 1299 (2003); http://dx.doi.org/10.1063/1.1561275 (9 pages) | Cited 12 times

Online Publication Date: 22 April 2003

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Nonlinear triggering of the instability of thin current sheets is investigated by two-and-one-half- dimensional Vlasov code simulations. A global drift-resonant instability (DRI) is found, which results from the lower-hybrid-drift waves penetrating from the current sheet edges to the center where they resonantly interact with unmagnetized ions. This resonant nonlinear instability grows faster than a Kelvin–Helmholtz instability obtained in previous studies. The DRI is either asymmetric or symmetric mode or a combination of the two, depending on the relative phase of the lower-hybrid-drift waves at the edges of the current sheet. With increasing particle mass ratio the wavenumber of the fastest-growing mode increases as kLz ∼ (mi/me)1/2/2 and the growth rate of the DRI saturates at a finite level. © 2003 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.)
52.65.-y Plasma simulation
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)

Frequency dependence of asymmetry-induced transport in a non-neutral plasma trap

D. L. Eggleston and B. Carrillo

Phys. Plasmas 10, 1308 (2003); http://dx.doi.org/10.1063/1.1561276 (7 pages) | Cited 12 times

Online Publication Date: 22 April 2003

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A key prediction of the theory of asymmetry-induced transport is that the particle flux will be dominated by particles that move in resonance with the asymmetry. For the case of a time-varying asymmetry, the resonance condition is ω−lωR−nπv/L = 0, where v is the axial velocity, L is the plasma length, ωR is the E×B rotation frequency, and ω, l, and n are the asymmetry frequency, azimuthal wavenumber, and axial wavenumber, respectively. Data are presented from experiments on a low density trap in which ω, ωR, and n are varied and the resulting radial particle flux is measured. The experiments show a resonance in the flux similar to that predicted by theory. The peak frequency of this resonance increases with ωR and varies with n, in qualitative agreement with theory, but quantitative comparisons between experiment and theory show serious discrepancies. © 2003 American Institute of Physics.
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52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps
52.25.Fi Transport properties

Simulations and theories of relativistic ion cyclotron instabilities driven by MeV alpha particles in thermal deuterium plasmas

K. R. Chen

Phys. Plasmas 10, 1315 (2003); http://dx.doi.org/10.1063/1.1561611 (10 pages) | Cited 8 times

Online Publication Date: 22 April 2003

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The harmonic relativistic ion cyclotron instabilities driven by MeV alpha particles in magnetized thermal deuterium plasmas are studied with a perturbation theory, a kinetic theory, and particle-in-cell simulations. Due to the mass deficit of alphas, the resonant harmonic cyclotron frequency of the alphas is not smaller than that of the deuterons such that the low harmonics are linearly stabilized by the deuterons. However, the thermal deuterons behave as a cold-gyro-stream plasma at high harmonics so that, by including relativistic streaming in gyro-phase, the alpha particles can drive the high harmonic electrostatic ion cyclotron instability, that is in a quadratic form, although their Lorentz factor is very close to unity (e.g., γ = 1.000 94 for 3.5 MeV alphas). The dielectric of the first deuteron cyclotron harmonic determines the alpha harmonic number threshold for instability; the quadratic instability occurs in the lower-hybrid frequency regime. As in a sharp contrast to the nonresistive thermalization of MeV protons due to the two-gyro-stream instability dominating at low harmonics, the high harmonic interaction between the unstable waves and the alphas becomes selective; only alpha particles with its perpendicular momentum above a threshold are involved and the interaction stops when they are slowed down to the threshold. The resultant energy spectrum is in a shape close to the profile of the theoretical interaction strength between the alpha particles and the dominating wave mode; the alpha particles almost loss no net energy. New-born alpha particles experience a similar selective gyro-broadening process in a shorter time scale. A simple explanation for the selective gyro-broadening based on the wave–alpha interaction calculated from the perturbation theory is given. © 2003 American Institute of Physics.
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52.55.Pi Fusion products effects (e.g., alpha-particles, etc.), fast particle effects
52.65.-y Plasma simulation
52.25.Xz Magnetized plasmas
03.30.+p Special relativity

Hamiltonian canonical formulation of Hall-magnetohydrodynamics: Toward an application to weak turbulence theory

F. Sahraoui, G. Belmont, and L. Rezeau

Phys. Plasmas 10, 1325 (2003); http://dx.doi.org/10.1063/1.1564086 (13 pages) | Cited 9 times

Online Publication Date: 22 April 2003

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The different levels of description of fluid media [e.g., magnetohydrodynamics (MHD), Hall-magnetohydrodynamics, bi-fluid,…] are commonly known under the form of Newtonian systems of equations. Nevertheless, this form proves to be ill-suited to derive a fully analytical weak turbulence theory of these media, due to the well-known complexity of the calculations implied. For such studies, therefore, a more appropriate mathematical frame needs to be found and this is shown to be the Hamiltonian formalism, even though it can often appear difficult to handle. The goal of this paper is to look for Hamiltonian formulations for the different levels of the fluid description of a plasma using the variational principle. Starting from the bi-fluid system, it is shown that such a formulation can be obtained by combining the Lagrangians already used for describing: (i) the motion of a charged particle in an electromagnetic field; (ii) the evolution of an electromagnetic field in presence of sources; (iii) the motion of a neutral fluid (Clebsch variables). The equivalence of the obtained description in terms of the generalized-Clebsch variables to the familiar Newtonian formulation is discussed. It is shown that each solution of the Hamiltonian system is also a solution for the Newtonian one, but that the converse is not true. The origin and the implication of this restriction are discussed. Reducing the Hamiltonian formulation obtained for the bi-fluid system to lower orders of the fluid approximations is then shown to be mandatory when one tries to obtain analytical results for linear waves and nonlinear wave–wave couplings. It is shown that this goal can be reached in two steps. The first one leads to a “reduced bi-fluid” system, which is identical to the bi-fluid one when the displacement current is neglected but the electron inertia is still working. The number of linear modes then goes down from six to three. The second step, leading to the Hall-MHD system, consists in neglecting the electron mass. It is demonstrated that the only four generalized Clebsch variables are sufficient to describe the full Hall-MHD dynamics. Some future applications of such a powerful formalism are outlined. © 2003 American Institute of Physics.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.Kj Magnetohydrodynamic and fluid equation
52.35.Ra Plasma turbulence
52.20.-j Elementary processes in plasmas
47.65.-d Magnetohydrodynamics and electrohydrodynamics
47.27.-i Turbulent flows
47.11.-j Computational methods in fluid dynamics

Collisional diffusion in a two-dimensional point vortex gas or a two-dimensional plasma

Daniel H. E. Dubin

Phys. Plasmas 10, 1338 (2003); http://dx.doi.org/10.1063/1.1564596 (13 pages) | Cited 11 times

Online Publication Date: 22 April 2003

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This paper analyzes collisional diffusion of a multispecies two-dimensional (2D) point vortex gas, or a 2D plasma, in the presence of retrograde shear. Diffusion both along and across the shear flow is calculated using Boltzmann, Kubo, Klimontovitch and resonance-broadening theories. It is shown that diffusion is reduced in the presence of shear, just as for the shear reduction of transport observed in fusion plasmas. Here, however, fluctuations are thermal rather than turbulent, allowing a rigorous calculation of the transport. When there are several species of point vortices, Onsager relations require that the diffusive flux conserves the total vorticity ρ(r), which is proportional to charge density in the plasma analogue. Surprisingly, the diffusive flux concentrates vortices with large positive (or negative) circulations at maxima (or minima) of the mean vorticity profile. © 2003 American Institute of Physics.
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52.25.Fi Transport properties
52.20.-j Elementary processes in plasmas
52.25.Gj Fluctuation and chaos phenomena
52.35.We Plasma vorticity
52.25.Dg Plasma kinetic equations
52.30.-q Plasma dynamics and flow

The electron–electron instability in a spherical plasma structure with an intermediate double layer

V. Lapuerta and E. Ahedo

Phys. Plasmas 10, 1351 (2003); http://dx.doi.org/10.1063/1.1564597 (13 pages)

Online Publication Date: 22 April 2003

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A linear dynamic model of a spherical plasma structure with an intermediate double layer is analyzed in the high-frequency range. The two ion populations tend to stay frozen in their stationary response and this prevents the displacement of the double layer. Different electron modes dominate the plasma dynamics in each quasineutral region. The electrostatic potential and the electron current are the magnitudes most perturbed. The structure develops a reactive electron–electron instability, which is made up of a countable family of eigenmodes. Space-charge effects must be included in the quasineutral regions to determine the eigenmode carrying the maximum growth rate. Except for very small Debye lengths, the fundamental eigenmode governs the instability. The growth rate for the higher harmonics approaches that of an infinite plasma. The instability modes develop mainly on the plasma at the high-potential side of the double layer. The influence of the parameters defining the stationary solution on the instability growth rate is investigated, and the parametric regions of stability are found. The comparison with a couple of experiments on plasma contactors is satisfactory. © 2003 American Institute of Physics.
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52.20.-j Elementary processes in plasmas
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
52.40.Hf Plasma-material interactions; boundary layer effects

Dissipative solitary kinetic Alfvén wave and electron acceleration

D. J. Wu

Phys. Plasmas 10, 1364 (2003); http://dx.doi.org/10.1063/1.1564821 (7 pages) | Cited 16 times

Online Publication Date: 22 April 2003

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Some recent studies of observations in situ by space satellites show that low frequency electromagnetic fluctuations in the auroral ionosphere and magnetosphere can often be identified as soliatry kinetic Alfvén waves (SKAWs), and further analyses of the data reveal clearly that electron collisional dissipation can considerably affect the structure and evolution of SKAWs. In this paper, a model of nonlinear kinetic Alfvén waves, called a dissipative SKAW (DSKAW), is presented, in which the effect of electron collisional dissipation has been taken into account. The results show that DSKAW can produce a local shock-like structure with a net parallel electric potential drop, in which the associated parallel electric field is primarily caused by nonlinear electron inertia. In particular, it is argued that DSKAW can accelerate electrons efficiently to the order of the local Alfvén velocity. This suggests that DSKAW can provide an efficient acceleration mechanism for energetic electrons, which can frequently be encountered in various space and cosmic plasma environments. © 2003 American Institute of Physics.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Sb Solitons; BGK modes
94.20.Qq Particle precipitation
96.60.P- Corona

Analysis of turbulent-transport suppression in non-neutral plasmas by turbulence theory based on mass-weighted averaging

Akira Yoshizawa and Nobumitsu Yokoi

Phys. Plasmas 10, 1371 (2003); http://dx.doi.org/10.1063/1.1566030 (11 pages) | Cited 2 times

Online Publication Date: 22 April 2003

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Turbulent-transport suppression is investigated on the basis of the turbulence theory founded on the mass-weighted averaging. Effects of plasma non-neutrality occur twofold. One is a direct electric-field effect, and the other is an indirect effect through the E×B flow. The results are discussed in light of transport barriers in tokamaks. Specifically, it is shown that the electric-field curvature and the bulk poloidal flow generating a centripetal force contribute to the suppression of turbulence and heat transport, but that the shear part of the flow leads to the enhancement of turbulence. © 2003 American Institute of Physics.
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52.35.Ra Plasma turbulence
52.25.Fi Transport properties

The quasilinear behavior of convective turbulence with sheared flows

N. Bian, S. Benkadda, O. E. Garcia, J.-V. Paulsen, and X. Garbet

Phys. Plasmas 10, 1382 (2003); http://dx.doi.org/10.1063/1.1566442 (7 pages) | Cited 13 times

Online Publication Date: 22 April 2003

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In the present contribution, the quasilinear dynamics of convective turbulence is studied. In essence, and contrary to the “frozen gradient” assumption, the quasilinear approach takes into account the back-reaction of the convective flux on the mean gradient driving the instability. The dynamical regulation of convective transport by a sheared mean flows is also included. Close to the instability threshold it naturally gives rise to a transition from low to high confinement modes. Further away, regular relaxation oscillations are sustained. In this time-dependent state, each transient maximum of the convective flux activity triggers a ballistic transport event observed on the mean profile. The period of the oscillations is not controlled by the nonlinearity but by the dissipation on the mean flow. A “Dimits-shift” regime is thus identified in the limit of zero damping on the mean flow. This infinite period cycle corresponds to a single ballistic transport event triggered before the system settles into its diffusive state. Far away from the threshold, relaxation oscillations are still sustained in the presence of mean flow dissipation, but are superimposed on high-frequency fluctuations. This particular behavior makes the convective transport to follow exponential statistics when measured at a local probe. © 2003 American Institute of Physics.
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52.25.Fi Transport properties
52.35.Ra Plasma turbulence
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
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