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Jun 2006

Volume 13, Issue 6, Articles (06xxxx)

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Excitation of the geodesic acoustic mode during ion cyclotron resonance heating

V. S. Marchenko

Phys. Plasmas 13, 060701 (2006); http://dx.doi.org/10.1063/1.2212828 (4 pages) | Cited 2 times

Online Publication Date: 14 June 2006

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It is shown that poloidal polarization of the plasma during ion cyclotron resonance heating (ICRH) can provide the source of free energy for excitation of the geodesic acoustic mode (GAM). A rough estimate for the threshold rf electric field amplitude necessary for GAM instability is given by νQL/νi>q−3, where νQL is the rate of ICRH-induced quasilinear diffusion in velocity space, νi is the ion collision rate, and q is the safety factor.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Dm Sound waves
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.25.Fi Transport properties
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Scalings of steady state Hall magnetohydrodynamic reconnection in high-beta plasmas

Xiaogang Wang, Hong-Ang Yang, and Shu-Ping Jin

Phys. Plasmas 13, 060702 (2006); http://dx.doi.org/10.1063/1.2218815 (4 pages) | Cited 9 times

Online Publication Date: 28 June 2006

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Scalings of Hall magnetohydrodynamics reconnection in high-β plasmas has been studied in steady states. It again confirms previous temporal evolution reconnection results that while the width of the reconnection layer is scaled by ωA/Ωci = di/Lc, where ωA is the Alfvén frequency, Ωci is the ion gyrofrequency, Lc is the typical system length scale, and di = c/ωpi is the ion inertial length, the length of the layer should be scaled by (ωA/Ωci)1/2Lc = (diLc)1/2 [X. Wang and A. Bhattacharjee, Phys. Rev. Lett. 70, 1627 (1993)], to yield the fast reconnection rate of (di/Lc)1/2VA with VA as the Alfvén velocity [X. Wang, A. Bhattacharjee, and Z. Ma, Phys. Rev. Lett. 87, 265003 (2001)]. It is also shown that the reconnection rate is proportional to the perturbed boundary flow. Furthermore it is found that in the high-β plasmas, the reconnection keeps constant in the regime β<2, and decays as β−1/2 for β ≥ 2.
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52.35.Vd Magnetic reconnection
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.25.Fi Transport properties
52.40.Hf Plasma-material interactions; boundary layer effects
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back to top Basic Plasma Phenomena, Waves, Instabilities

Transition scale at quasiperpendicular collisionless shocks: Full particle electromagnetic simulations

Manfred Scholer and David Burgess

Phys. Plasmas 13, 062101 (2006); http://dx.doi.org/10.1063/1.2207126 (5 pages) | Cited 2 times

Online Publication Date: 7 June 2006

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One-dimensional full particle simulations of almost perpendicular supercritical collisionless shocks over a wide Alfvén Mach number range are presented. The physical ion to electron mass ratio has been used; however, due to computer time limitations a value of the ratio of the electron plasma frequency to the electron gyrofrequency of 4 has been assumed. The shock structure in the density and magnetic field consists of a foot, formed by reflected ions, and a steeper ramp leading to an overshoot. It is shown that the shock ramp scale in units of the upstream ion inertial length is more or less constant and close to 1 over the Mach number regime investigated, i.e., up to MA ≈ 14. Further, the convective ion gyroradius in units of the upstream ion inertial length is also constant with the Mach number when the gyroradius is evaluated with the magnetic field strength in the overshoot. Thus the shock transition also scales with the convected gyroradius. When a hyperbolic tangent function is fitted to the density profile the neglect of the overshoot essentially results, for high Mach number shocks, in a fit of the foot and not of the ramp, i.e., the shock transition scale is grossly overestimated. The simulations suggest that in a regime above the critical Mach number the nonlinear steepening is balanced by gyroviscosity of the reflected ions as the shock ramp scale is given by the convected gyroradius in the overshoot. At higher Mach numbers the shock becomes unsteady the ramp scale can become as small as several electron inertial length during a part of the reformation cycle. At still higher Mach number microinstabilities in the foot may have growth times much shorter than the inverse ion gyrofrequency so that they can lead to ion heating, and a steady resistive shock will result.
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52.35.Tc Shock waves and discontinuities
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.25.Fi Transport properties
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Gyrokinetic linear theory of the entropy mode in a Z pinch

Paolo Ricci, B. N. Rogers, W. Dorland, and M. Barnes

Phys. Plasmas 13, 062102 (2006); http://dx.doi.org/10.1063/1.2205830 (10 pages) | Cited 10 times

Online Publication Date: 12 June 2006

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The linear gyrokinetic theory of the entropy mode is presented in a Z-pinch configuration in the regime of plasma β⪡1, focusing primarily on the parameter regime in which the ideal interchange mode is stable. The entropy mode is a small-scale, nonmagnetohydrodynamic mode that typically has peak growth rates at kρs ∼ 1[ρs2 = (T0e+T0i)/(miΩci2)], with magnitudes comparable to those of ideal modes. The properties of this mode are studied as a function of the density and temperature gradients, plasma collisionality, and electron to ion temperature ratio.
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52.25.Dg Plasma kinetic equations
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.58.Lq Z-pinches, plasma focus, and other pinch devices
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

Laser-induced-fluorescence observation of ion velocity distribution functions in a plasma sheath

N. Claire, G. Bachet, U. Stroth, and F. Doveil

Phys. Plasmas 13, 062103 (2006); http://dx.doi.org/10.1063/1.2206786 (8 pages) | Cited 9 times

Online Publication Date: 12 June 2006

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Experimental results obtained by laser-induced-fluorescence on metastable ion velocity distribution functions (MIVDF) in electrostatic presheaths and sheaths in argon plasmas produced by the thermoionic effect in a multipolar dc discharge are presented. The shape of the measured MIVDF are in qualitative agreement, for the presheath, with Emmert’s model and exhibit: (1) a Maxwellian profile at the center of the device where the potential is zero; (2) a distribution function’s shape made of three distinct parts at the entrance of the presheath. Inside the sheath the recorded MIVDF recovers a Maxwellian profile with a width unexpectedly related to the background neutral pressure. The velocity and potential profiles that can be deduced from the measured MIVDF show a strong influence of the primary electrons emitted by the filaments.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Fi Transport properties
52.40.Kh Plasma sheaths
52.50.Dg Plasma sources
52.80.-s Electric discharges
52.25.Ya Neutrals in plasmas

Simulations of Kelvin-Helmholtz modes in partially ionized dusty plasmas comparing different charge numbers, charge polarities, and masses of the dust

Heinz M. Wiechen

Phys. Plasmas 13, 062104 (2006); http://dx.doi.org/10.1063/1.2208309 (7 pages) | Cited 6 times

Online Publication Date: 12 June 2006

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Results of multifluid simulations of Kelvin-Helmholtz modes in partially ionized, dusty plasmas are presented assuming different masses and charges of the dust. The results show a stabilizing effect for more massive dust grains and indicate a destabilizing effect for higher charge numbers. No significant dependence on the charge polarity of the dust was found.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.27.Lw Dusty or complex plasmas; plasma crystals
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.Jm Ionization of plasmas

Equilibrium, multistability, and chiral asymmetry in rotated mirror plasmas

P. M. Valanju, S. M. Mahajan, and H. J. Quevedo

Phys. Plasmas 13, 062105 (2006); http://dx.doi.org/10.1063/1.2209967 (5 pages) | Cited 3 times

Online Publication Date: 14 June 2006

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The Hall term in two-fluid magnetohydrodynamics is shown to be necessary to balance the curl of the ion inertial force in a rotating plasma with spatially nonuniform crossed electric and magnetic fields. Two-fluid solutions are obtained that qualitatively explain the multistable rotational response observed in magneto-Bernoulli experiment, imply chiral symmetry breaking, i.e., handedness, and yield new dynamo-like electromotive terms in the effective circuit equation for externally rotated mirror plasma equilibria.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.30.Ex Two-fluid and multi-fluid plasmas
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
52.25.Fi Transport properties

Speed and shape of dust acoustic solitary waves with variable dust charge and two temperature ions

Brindaban Das and Prasanta Chatterjee

Phys. Plasmas 13, 062106 (2006); http://dx.doi.org/10.1063/1.2210469 (5 pages) | Cited 1 time

Online Publication Date: 21 June 2006

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Dust acoustic solitary waves are investigated on the nonlinear, unmagnetized homogeneous dust ion electron plasma with variable dust charge and two temperature ions. The Sagdeev’s pseudopotential is determined in terms of ud, the dust ion speed. It is found that there exists a critical value of ud, beyond which the solitary waves cease to exist. This critical value of ud depends on other plasma parameters also.
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52.35.Sb Solitons; BGK modes
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Dm Sound waves
52.27.Lw Dusty or complex plasmas; plasma crystals
52.27.Cm Multicomponent and negative-ion plasmas
52.25.Fi Transport properties

Propagation of radially localized helicon waves in longitudinally nonuniform plasmas

Alexey V. Arefiev and Boris N. Breizman

Phys. Plasmas 13, 062107 (2006); http://dx.doi.org/10.1063/1.2212367 (7 pages) | Cited 2 times

Online Publication Date: 21 June 2006

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A gradient in the plasma density across the guiding magnetic field can support a low-frequency radially localized helicon (RLH) wave in a plasma column. If the radial density gradient changes along the magnetic field, this wave can undergo reflection and also excite conventional whistlers. This paper presents calculations of the corresponding reflection coefficient, including the effect of whistler radiation. It is shown that a sharp longitudinal density drop causes a nearly complete reflection of the RLH wave. The longitudinal wavelength of the excited whistlers is much greater than that of the RLH wave, and, as a result, only a small fraction of the RLH wave energy is transferred to the whistlers.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)

Two-stream instability for a longitudinally compressing charged particle beam

Edward A. Startsev and Ronald C. Davidson

Phys. Plasmas 13, 062108 (2006); http://dx.doi.org/10.1063/1.2212807 (8 pages) | Cited 8 times

Online Publication Date: 21 June 2006

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The electrostatic two-stream instability for a cold, longitudinally compressing charged particle beam propagating through a background plasma has been investigated both analytically and numerically. Small-signal coupled equations describing the evolution of the perturbations are derived, and the asymptotic solutions are obtained. The results are confirmed by direct numerical solution of the linearized fluid equations. It is found that the longitudinal beam compression strongly modifies the space-time development of the instability. In particular, the dynamic compression leads to a significant reduction in the growth rate of the two-stream instability compared to the case without an initial velocity tilt.
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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)
02.60.Cb Numerical simulation; solution of equations

Perpendicularly propagating electromagnetic modes in a strongly magnetized hot plasma with non-Maxwellian distribution function

S. Zaheer, G. Murtaza, and H. A. Shah

Phys. Plasmas 13, 062109 (2006); http://dx.doi.org/10.1063/1.2212830 (10 pages) | Cited 5 times

Online Publication Date: 21 June 2006

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Electromagnetic modes (ordinary and extraordinary) for strongly magnetized plasma are studied and their damping factors γor and γex are calculated using non-Maxwellian velocity distribution function. It is observed that for moderate values of the spectral indices r and q [used in (r, q) distribution functions], both the damping decrements show substantial change. As the value of the spectral index r increases for a fixed value of q, the damping increases for the O mode but decreases for the X mode. In the limiting case of r = 0, q→∞, the damping factors reduce to the standard Maxwellian values.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.25.Xz Magnetized plasmas

Study of two-dimensional Debye clusters using Brownian motion

T. E. Sheridan and W. L. Theisen

Phys. Plasmas 13, 062110 (2006); http://dx.doi.org/10.1063/1.2215475 (8 pages) | Cited 10 times

Online Publication Date: 27 June 2006

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A two-dimensional Debye cluster is a system of n identical particles confined in a parabolic well and interacting through a screened Coulomb (i.e., a Debye-Hückel or Yukawa) potential with a Debye length λ. Experiments were performed for 27 clusters with n = 3–63 particles (9 μm diam) in a capacitively coupled 9 W rf discharge at a neutral argon pressure of 13.6 mTorr. In the strong-coupling regime each particle exhibits small amplitude Brownian motion about its equilibrium position. These motions were projected onto the center-of-mass and breathing modes and Fourier analyzed to give resonance curves from which the mode frequencies, amplitudes, and damping rates were determined. The ratio of the breathing frequency to the center-of-mass frequency was compared with theory to self-consistently determine the Debye shielding parameter κ, Debye length λ, particle charge q, and mode temperatures. It is found that 1≲κ≲2, and κ decreases weakly with n. The particle charge averaged over all measurements is −14 200±200 e, and q decreases slightly with n. The two center-of-mass modes and the breathing mode are found to have the same temperature, indicating that the clusters are in thermal equilibrium with the neutral gas. The average cluster temperature is 399±5 K.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.27.Gr Strongly-coupled plasmas
52.25.Fi Transport properties
52.80.Pi High-frequency and RF discharges
52.58.Qv Electrostatic and high-frequency confinement
52.25.Kn Thermodynamics of plasmas

Low-noise electromagnetic δf particle-in-cell simulation of electron Bernstein waves

Nong Xiang, John R. Cary, Daniel C. Barnes, and John Carlsson

Phys. Plasmas 13, 062111 (2006); http://dx.doi.org/10.1063/1.2215460 (13 pages) | Cited 4 times

Online Publication Date: 28 June 2006

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The conversion of the extraordinary (X) mode to an electron Bernstein wave (EBW) is one way to get rf energy into an overdense plasma. Analysis of this is complex, as the EBW is a fully kinetic wave, and so its linear propagation is described by an intractable integro-differential equation. Nonlinear effects cannot be calculated within this rubric at all. Full particle-in-cell (PIC) simulations cannot be used for these analyses, as the noise levels for reasonable simulation parameters are much greater than the typical rf amplitudes. It is shown that the delta-f computations are effective for this analysis. In particular, the accuracy of those computations has been verified by comparison with full PIC, cold plasma theory, and small gyroradius theory. This computational method is then used to analyze mode conversion in different frequency regimes. In particular, reasonable agreement with the theoretical predictions of Ram and Schultz [Phys. Plasmas 7, 4084 (2000)] in the linear regime is found, where 100% X−B mode conversion has been obtained when the driving frequency is less than twice the electron gyrofrequency. The results show that cold-plasma theory well predicts the mode conversion efficiency, as is consistent with the phase-space picture of mode conversion. From this it can be shown that nearly 100% X−B mode conversion cannot be obtained when the frequency is higher than the electron second harmonic cyclotron frequency.
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52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.65.Rr Particle-in-cell method
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.25.Dg Plasma kinetic equations
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons

Ion-acoustic dressed solitons in a dusty plasma

R. S. Tiwari and M. K. Mishra

Phys. Plasmas 13, 062112 (2006); http://dx.doi.org/10.1063/1.2216936 (8 pages) | Cited 10 times

Online Publication Date: 30 June 2006

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Using the reductive perturbation method, equations for ion-acoustic waves governing the evolution of first- and second-order potentials in a dusty plasma including the dynamics of charged dust grains have been derived. The renormalization procedure of Kodama and Taniuti is used to obtain a steady state nonsecular solution of these equations. The variation of velocity and width of the Korteweg-de Vries (KdV) as well as dressed solitons with amplitude have been studied for different concentrations and charge multiplicity of dust grains. The higher-order perturbation corrections to the KdV soliton description significantly affect the characteristics of the solitons in dusty plasma. It is found that in the presence of positively charged dust grains the system supports only compressive solitons. However, the plasma with negatively charged dust grains can support compressive solitons only up to a certain concentration of dust. Above this critical concentration of negative charge, the dusty plasma can support rarefactive solitons. An expression for the critical concentration of negatively charged dust in terms of charge and mass ratio of dust grains with plasma ions is also derived.
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back to top Nonlinear Phenomena, Turbulence, Transport

On the use of critical gradient models in fusion plasma transport studies

B. A. Carreras, V. E. Lynch, B. Ph. van Milligen, and R. Sánchez

Phys. Plasmas 13, 062301 (2006); http://dx.doi.org/10.1063/1.2205196 (7 pages) | Cited 4 times

Online Publication Date: 7 June 2006

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Transport models for tokamak devices are often based on transport coefficients involving a critical threshold condition. In this paper, it is argued that the validation of such models against experimental data requires special care when the system profiles are close to this threshold (at some locations), due to the contribution of fluctuations to transport. The arguments presented here could have implications for the understanding and modeling of heat transport in tokamaks, since the large stiffness of the temperature profile observed in experimental points to a near-critical situation over much of the radius. The difficulties are illustrated by means of a simplified transport model, and a possible way to ameliorate this issue is proposed.
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52.25.Fi Transport properties
52.55.Fa Tokamaks, spherical tokamaks
52.25.Gj Fluctuation and chaos phenomena

Modulational instability of dust acoustic waves in dusty plasmas: Modulation obliqueness, background ion nonthermality, and dust charging effects

W. F. El-Taibany and I. Kourakis

Phys. Plasmas 13, 062302 (2006); http://dx.doi.org/10.1063/1.2205197 (11 pages) | Cited 17 times

Online Publication Date: 12 June 2006

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The oblique modulational instability of dust acoustic (DA) waves in an unmagnetized warm dusty plasma with nonthermal ions, taking into account dust grain charge variation (charging), is investigated. A nonlinear Schrödinger-type equation governing the slow modulation of the wave amplitude is derived. The effects of dust temperature, dust charge variation, ion deviation from Maxwellian equilibrium (nonthermality) and constituent species’ concentration on the modulational instability of DA waves are examined. It is found that these parameters modify significantly the oblique modulational instability domain in the k-θ plane. Explicit expressions for the instability rate and threshold have been obtained in terms of the dispersion laws of the system. The possibility and conditions for the existence of different types of localized excitations are also discussed. The findings of this investigation may be useful in understanding the stable electrostatic wave packet acceleration mechanisms close to the Moon, and also enhances our knowledge on the occurrence of instability associated to pickup ions around unmagnetized bodies, such as comets, Mars, and Venus.
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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.Dm Sound waves
52.27.Lw Dusty or complex plasmas; plasma crystals
52.25.Gj Fluctuation and chaos phenomena
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
02.30.Hq Ordinary differential equations

Self-consistent nonlinear transverse waves in relativistic plasmas

U. Schaefer-Rolffs and I. Lerche

Phys. Plasmas 13, 062303 (2006); http://dx.doi.org/10.1063/1.2207123 (14 pages) | Cited 11 times

Online Publication Date: 12 June 2006

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Previous investigations of the relativistic Weibel instability provide motivation to consider the nonlinear domain because, for asymmetric particle distributions, there is only an isolated unstable Weibel mode—reminiscent of nonlinear wave-types of behavior. From the collisionless Boltzmann equation together with Maxwell’s equations, a nonlinear, self-consistent wave equation is derived that is solvable for a broad range of distribution functions. For monochromatic electrons the nonlinear equation can be solved exactly, but results in an unphysical behavior of the magnetic field due to the compact support required of the distribution function. The general equation can be solved by asymptotic representation producing physically correct nonlinear wave solutions over bounded domains with varying internal structure of the electric and magnetic fields that range from nearly Gaussian to “sawtooth” in shape. A lower limit on the nonlinear wave amplitude is required in order that the nonlinear wave be of limited extent and so not represent a sinusoidal disturbance with no bounding domain. Limits for the nonlinear wave maximum magnetic field, and particle number density within the nonlinear wave, are given by considering the constraints on the nonlinear wave due to radiation processes, electron collision effects, and electron degeneracy pressure. The basic physical scale results are depicted mostly conducive for astrophysical applications involving relativistic flows and γ-ray emission, for which detailed investigations will be given elsewhere.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.27.Ny Relativistic plasmas
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.25.Dg Plasma kinetic equations
52.25.Fi Transport properties
52.20.Fs Electron collisions

Self-sustaining vortex perturbations in smooth shear flows

J.-H. Kim, J. C. Perez, W. Horton, G. D. Chagelishvili, R. G. Changishvili, J. G. Lominadze, and John C. Bowman

Phys. Plasmas 13, 062304 (2006); http://dx.doi.org/10.1063/1.2209229 (8 pages) | Cited 4 times

Online Publication Date: 12 June 2006

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The nonlinear dynamics of coherent circular/elliptical cyclonic and anticyclonic vortices in plane flow with constant shear is investigated numerically using a dealiased Fourier pseudospectral code. The flow is asymptotically linearly stable, but is highly non-normal, allowing perturbations to gain energy transiently from the background shear flow. This linear transient growth interplays with nonlinear processes. In certain cases it is shown that the nonlinear feedback is positive, leading to self-sustaining coherent vortices. Self-sustaining coherent vortices exist where the vorticity is parallel to the mean flow vorticity (cyclonic rotation). The required nonlinear feedback is absent for small amplitude anticyclonic vortices. However, elliptical anticyclonic vortices become self-sustaining if the amplitude exceeds a threshold value. The self-sustaining of coherent vortices is similar to the subcritical, so-called bypass, transition to turbulence in shear flows. The common features are: transient linear growth; positive nonlinear feedback; and anisotropy of the linear and nonlinear phenomena (in contrast to isotropic Kolmogorov turbulence). A plasma laboratory experiment is suggested based on the results of this investigation.
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52.35.We Plasma vorticity
52.30.-q Plasma dynamics and flow
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Ra Plasma turbulence
02.60.Cb Numerical simulation; solution of equations

Physical origin of the quadrupole out-of-plane magnetic field in Hall-magnetohydrodynamic reconnection

Dmitri A. Uzdensky and Russell M. Kulsrud

Phys. Plasmas 13, 062305 (2006); http://dx.doi.org/10.1063/1.2209627 (14 pages) | Cited 30 times

Online Publication Date: 12 June 2006

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A quadrupole pattern of the out-of-plane component of the magnetic field inside a reconnection region is seen as an important signature of the Hall-magnetohydrodynamic regime of reconnection. It has been first observed in numerical simulations and just recently confirmed in the Magnetic Reconnection Experiment [ Y. Ren, M. Yamada, S. Gerhardt, H. Ji, R. Kulsrud, and A. Kuritsin, Phys. Rev. Lett. 95, 055003 (2005) ] and also seen in spacecraft observations of Earth’s magnetosphere. In this study, the physical origin of the quadrupole field is analyzed and traced to a current of electrons that flows along the lines in and out of the inner reconnection region to maintain charge neutrality. The role of the quadrupole magnetic field in the overall dynamics of the reconnection process is discussed. In addition, the bipolar poloidal electric field is estimated and its effect on ion motions is emphasized.
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52.35.Vd Magnetic reconnection
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.Fi Transport properties
94.30.cp Magnetic reconnection
94.30.cs Plasma motion; plasma convection
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Modeling of the turbulent magnetohydrodynamic residual-energy equation using a statistical theory

Nobumitsu Yokoi

Phys. Plasmas 13, 062306 (2006); http://dx.doi.org/10.1063/1.2209232 (17 pages) | Cited 7 times

Online Publication Date: 19 June 2006

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The difference between the kinetic and magnetic energies in a conducting fluid is investigated in the framework of magnetohydrodynamics. The deviation from equipartition is measured by the turbulent residual energy KR. With the aid of the two-scale direct-interaction approximation, a statistical analytical theory for inhomogeneous turbulence, expressions for the correlation tensors appearing in the evolution equation for the residual energy are derived. Using these results, we propose a model equation for KR evolution. Examination of the structure of this equation shows that the evolution of the scaled residual energy is related to the cross helicity (velocity-magnetic-field correlation) of turbulence coupled with the mean-field shears. An application to the solar wind shows that the scaled ∣KR∣ can be increased near the outside of the Alfvén point in the inner heliosphere whereas the almost stationary behavior of ∣KR∣ is suggested in the outer heliosphere. These results are consistent with observations of solar-wind turbulence.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Ra Plasma turbulence
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
96.20.Br Origin and evolution
96.50.Tf MHD waves; plasma waves, turbulence
96.50.Xy Heliosphere/interstellar medium interactions

Dust-acoustic solitary waves in an inhomogeneous magnetized hot dusty plasma with dust charge fluctuations

Amar P. Misra and A. Roy Chowdhury

Phys. Plasmas 13, 062307 (2006); http://dx.doi.org/10.1063/1.2210928 (8 pages) | Cited 18 times

Online Publication Date: 19 June 2006

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Using a standard reductive perturbation theory, a Zakharov-Kuznnetsov (ZK) equation is derived in an inhomogeneous dusty plasma comprised of negatively charged dust grains of equal radii, Boltzmann distributed electrons and positive ions. The effects of dust thermal pressure, dust charge variation, dust-neutral collision, and the external magnetic field are taken into account. Either compressive or rarefective solitons are shown to exist depending on the critical value of the phase velocity which in turn, depends on the dust temperature and pressure. An analytic soliton solution is obtained and discussed. The behaviors of the soliton amplitude, width, and the Mach number are investigated numerically for different plasma parameters.
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52.35.Sb Solitons; BGK modes
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Dm Sound waves
52.27.Lw Dusty or complex plasmas; plasma crystals
52.25.Gj Fluctuation and chaos phenomena
52.25.Xz Magnetized plasmas

Chaotic behavior of nonlinearly coupled electrostatic and electromagnetic modes in electron-positron-ion magnetoplasma with equilibrium flows

M. Azeem and Arshad M. Mirza

Phys. Plasmas 13, 062308 (2006); http://dx.doi.org/10.1063/1.2209629 (7 pages) | Cited 1 time

Online Publication Date: 21 June 2006

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A new set of nonlinear equations has been derived to study the temporal behavior of low frequency electrostatic and electromagnetic ion-temperature-gradient driven modes in an electron-positron-ion (e-p-i) magnetoplasma. The temporal behavior of the nonlinear mode coupling equations, under certain conditions, are governed by the coupled equations, which are the generalization of Lorenz and Stenflo type equations, admitting chaotic behavior. The linear stability of the generalized Lorenz-Stenflo system of equations is also presented for electrostatic and electromagnetic cases. The results of present investigation should be useful to understand the nonlinear properties of electromagnetic/electrostatic waves in an e-p-i magnetoplasma.
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52.25.Gj Fluctuation and chaos phenomena
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Nonlinear inward particle flux component in trapped electron mode turbulence

P. W. Terry and R. Gatto

Phys. Plasmas 13, 062309 (2006); http://dx.doi.org/10.1063/1.2212403 (9 pages) | Cited 9 times

Online Publication Date: 21 June 2006

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Trapped electron turbulence is shown to have a significant inward particle flux component associated with nonlinear deviations of the density-potential cross correlation from the quasilinear value. The cross correlation is altered because the density advection nonlinearity mixes a linearly stable eigenmode with the eigenmode of the instability. The full nonlinear flux is evaluated by solving spectrum balance equations in a complete basis spanning the fluctuation space. An ordered expansion for small collisionality, perpendicular wave number, and temperature/density-gradient instability threshold parameter enables an analytic solution for a weakly driven regime. The solution quantifies the role of zonal modes on transport via their saturation of the turbulence under intensely anisotropic transfer. The inward transport is neither diffusive nor convective, but is driven by temperature gradient and enhanced by flat density gradients. It is slightly smaller than the outwardly directed flux associated with the growing eigenmode, making the flux a small fraction of the quasilinear value.
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52.25.Fi Transport properties
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Ra Plasma turbulence
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.25.Gj Fluctuation and chaos phenomena
52.20.Fs Electron collisions

Numerical modeling of diffusive heat transport across magnetic islands and local stochastic field

Q. Yu

Phys. Plasmas 13, 062310 (2006); http://dx.doi.org/10.1063/1.2206788 (12 pages) | Cited 19 times

Online Publication Date: 23 June 2006

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The heat diffusion across magnetic islands is studied numerically and compared with analytical results. For a single island, the enhanced radial heat diffusivity, χr, due to the parallel transport along the field lines is increased over a region of about the island width w. The maximum enhanced heat conductivity at the rational surface is proportional to w2(χ‖χ⊥)1/2 for sufficiently high values of χ‖/χ⊥, where χ‖/χ⊥ is the ratio between the parallel and the perpendicular heat diffusivity. For low ratios of χ‖/χ⊥, however, the maximum value of χr is proportional to w4χ‖. In a locally stochastic magnetic field, χr is again proportional to w4χ‖ for low χ‖/χ⊥, which is in agreement with the analytical results. With increasing χ‖/χ⊥, χr is dominated first by the additive effect of individual islands and then by the field ergodicity.
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52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Fa Tokamaks, spherical tokamaks
02.60.Cb Numerical simulation; solution of equations

Forced Hall magnetic reconnection: Parametric variation of the “Newton Challenge”

J. D. Huba

Phys. Plasmas 13, 062311 (2006); http://dx.doi.org/10.1063/1.2212397 (5 pages) | Cited 2 times

Online Publication Date: 23 June 2006

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A parametric study of forced magnetic reconnection using a 2D Hall magnetohydrodynamic (MHD) code based on the “Newton Challenge” is presented. The “Newton Challenge” defined a magnetic reconnection problem in which reconnection was initiated by a spatially and temporally dependent inflow velocity on the upstream boundary. In this study the magnitude and time dependence of the inflow velocity are varied, as well as the length of the system and the boundary conditions. The general conclusion is that reconnection occurs sooner and faster for stronger impulsive drives (e.g., larger inflow velocities and longer time scales). The results are fairly insensitive to system length. Finally, the Hall MHD results are compared to results from a particle-in-cell simulation study.
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52.35.Vd Magnetic reconnection
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.Kj Magnetohydrodynamic and fluid equation
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