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Dec 2009

Volume 16, Issue 12, Articles (12xxxx)

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Phys. Plasmas 16, 120701 (2009); http://dx.doi.org/10.1063/1.3271410 (4 pages)

Z. Vörös, M. P. Leubner, A. Runov, V. Angelopoulos, and W. Baumjohann
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Evolution of kinklike fluctuations associated with ion pickup within reconnection outflows in the Earth’s magnetotail

Z. Vörös, M. P. Leubner, A. Runov, V. Angelopoulos, and W. Baumjohann

Phys. Plasmas 16, 120701 (2009); http://dx.doi.org/10.1063/1.3271410 (4 pages) | Cited 1 time

Online Publication Date: 4 December 2009

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Magnetic reconnection (MR) in Earth’s magnetotail is usually followed by a systemwide redistribution of explosively released kinetic and thermal energy. Recently, multispacecraft observations from the THEMIS mission were used to study localized explosions associated with MR in the magnetotail so as to understand subsequent Earthward propagation of MR outbursts during substorms. Here we investigate plasma and magnetic field fluctuations/structures associated with MR exhaust and ion-ion kink mode instability during a well-documented THEMIS MR event. Generation, evolution, and fading of kinklike oscillations are followed over a distance of ∼ 70 000 km from the reconnection site in the midmagnetotail to the more dipolar region near the Earth. We have found that the kink oscillations driven by different ion populations within the outflow region can be at least 25 000 km from the reconnection site.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
94.30.cq MHD waves, plasma waves, and instabilities

Scaling of Sweet–Parker reconnection with secondary islands

P. A. Cassak, M. A. Shay, and J. F. Drake

Phys. Plasmas 16, 120702 (2009); http://dx.doi.org/10.1063/1.3274462 (4 pages) | Cited 20 times

Online Publication Date: 9 December 2009

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Sweet–Parker (collisional) magnetic reconnection at high Lundquist number is modified by secondary islands. Daughton et al. [Phys. Rev. Lett. 103, 065004 (2009) ] suggested the Sweet–Parker model governs the fragmented current sheet segments. If true, the reconnection rate would increase by the square root of the number of secondary islands. High Lundquist number resistive magnetohydrodynamic simulations are presented which agree, in a time-averaged sense, with the predicted scaling. This result may have important implications for energy storage before a solar eruption and its subsequent release.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.-y Plasma simulation
52.80.Hc Glow; corona
52.20.-j Elementary processes in plasmas
95.30.Qd Magnetohydrodynamics and plasmas
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back to top Basic Plasma Phenomena, Waves, Instabilities

Three-dimensional null point reconnection regimes

E. R. Priest and D. I. Pontin

Phys. Plasmas 16, 122101 (2009); http://dx.doi.org/10.1063/1.3257901 (15 pages) | Cited 22 times

Online Publication Date: 3 December 2009

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Recent advances in theory and computational experiments have shown the need to refine the previous categorization of magnetic reconnection at three-dimensional null points—points at which the magnetic field vanishes. We propose here a division into three different types, depending on the nature of the flow near the spine and fan of the null. The spine is an isolated field line which approaches the null (or recedes from it), while the fan is a surface of field lines which recede from it (or approach it). So-called torsional spine reconnection occurs when field lines in the vicinity of the fan rotate, with current becoming concentrated along the spine so that nearby field lines undergo rotational slippage. In torsional fan reconnection field lines near the spine rotate and create a current that is concentrated in the fan with a rotational flux mismatch and rotational slippage. In both of these regimes, the spine and fan are perpendicular and there is no flux transfer across spine or fan. The third regime, called spine-fan reconnection, is the most common in practice and combines elements of the previous spine and fan models. In this case, in response to a generic shearing motion, the null point collapses to form a current sheet that is focused at the null itself, in a sheet that locally spans both the spine and fan. In this regime the spine and fan are no longer perpendicular and there is flux transfer across both of them.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

A detailed investigation of the properties of a Vlasov–Maxwell equilibrium for the force-free Harris sheet

T. Neukirch, F. Wilson, and M. G. Harrison

Phys. Plasmas 16, 122102 (2009); http://dx.doi.org/10.1063/1.3268771 (10 pages) | Cited 6 times

Online Publication Date: 3 December 2009

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A detailed discussion is presented of the Vlasov–Maxwell equilibrium for the force-free Harris sheet recently found by Harrison and Neukirch [Phys. Rev. Lett. 102, 135003 (2009) ]. The derivation of the distribution function and a discussion of its general properties and their dependence on the distribution function parameters will be given. In particular, the distribution function can be single-peaked or multipeaked in two of the velocity components, with possible implications for stability. The dependence of the shape of the distribution function on the values of its parameters will be investigated and the relation to macroscopic quantities such as the current sheet thickness will be discussed.
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52.20.-j Elementary processes in plasmas
52.25.Xz Magnetized plasmas
52.55.-s Magnetic confinement and equilibrium
52.65.Ff Fokker-Planck and Vlasov equation

Equilibrium of non-neutral plasmas in a Malmberg–Penning trap with quadrupole field errors

Timur Akhmetov and Igor Kotelnikov

Phys. Plasmas 16, 122103 (2009); http://dx.doi.org/10.1063/1.3265966 (10 pages)

Online Publication Date: 3 December 2009

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The effect of small quadrupole magnetic and electrostatic perturbations on the equilibrium of a non-neutral plasma confined in a Malmberg–Penning trap is analyzed on the base of the parallel current constraint derived recently [ Kotelnikov and Romé, Phys. Plasmas 15, 072118 (2008) ]. The constraint is generalized to the case of nonuniform plasma temperature. Analytical solutions for the electric potential variations inside the trap and Pfirsch–Schlüter currents are found in the paraxial limit for stepwise radial density profiles of the plasma. It is shown that the equilibrium distorted by a magnetic quadrupole is qualitatively different from that perturbed by an electric quadrupole. In particular, a magnetic quadrupole squeeze perturbs the plasma potential only within a localized region, whereas an electric quadrupole squeeze perturbs the potential in the entire plasma column. On the other hand, axially variable parts of the perturbed potential have similar radial profiles for both electric and magnetic quadrupoles.
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52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps
52.25.Fi Transport properties

Numerical studies on ultrarelativistic ion motions in an oblique magnetosonic shock wave

Shunsuke Usami, Ritoku Horiuchi, and Yukiharu Ohsawa

Phys. Plasmas 16, 122104 (2009); http://dx.doi.org/10.1063/1.3270110 (7 pages)

Online Publication Date: 4 December 2009

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The motion of ultrarelativistic ions in an oblique magnetosonic shock wave is studied analytically and numerically. The zeroth-order theory predicts that an oblique shock wave can accelerate ions in the direction nearly parallel to the magnetic field if the shock speed is vsh ∼ c cos θ, where θ is the angle between the wave normal and the magnetic field, while the perturbation is a one-dimensional oscillation nearly perpendicular to the zeroth-order motion. The perturbation frequency ω is of the order of Ωi0γ−1/2, where γ is the Lorentz factor of the zeroth-order velocity. These theoretical predictions are examined with test particle simulations, in which the test particle orbits are calculated with use of the electromagnetic fields of a shock wave obtained from an electromagnetic particle simulation. The zeroth-order and perturbed motions in the simulations are explained by the theory.
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52.35.Tc Shock waves and discontinuities
52.65.Cc Particle orbit and trajectory
52.65.Rr Particle-in-cell method
98.70.Sa Cosmic rays (including sources, origin, acceleration, and interactions)

Stationary nontearing inertial scale electron magnetohydrodynamic instability

V. S. Lukin

Phys. Plasmas 16, 122105 (2009); http://dx.doi.org/10.1063/1.3271160 (5 pages) | Cited 1 time

Online Publication Date: 7 December 2009

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Two-dimensional stationary nontearing inertial scale electron magnetohydrodynamic (EMHD) instability is described. The physical mechanism of the instability is illustrated. Analytical asymptotic estimate of the growth rate is provided and verified with a numerical calculation of the instability, also describing the characteristic structure of the eigenmode. Natural occurrence of the instability is demonstrated in a nonlinear EMHD simulation of a system undergoing magnetic reconnection, where the instability manifests itself on the outflow side of the magnetic field separatrix and may affect the self-determined length of the layer.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
02.10.Ud Linear algebra
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Vd Magnetic reconnection

Self-excited plasmon polaritons in counterstreaming quantum plasmas

W. M. Moslem, M. Lazar, R. Sabry, and P. K. Shukla

Phys. Plasmas 16, 122106 (2009); http://dx.doi.org/10.1063/1.3259958 (5 pages) | Cited 2 times

Online Publication Date: 7 December 2009

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The effect of counterstreaming on the quantum plasmon-polariton excitation is examined. For this purpose, the dispersion relation describing a counterstreaming quantum plasma system has been derived. Solutions are displayed numerically and analyzed for different values of the quantum parameters and the streaming electrons. It is found that the quantum effects and the two-stream instability are relevant for the self-consistently excited surface plasmon polaritons.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Tc Shock waves and discontinuities
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Magnetorotational instability in dissipative dusty plasmas

Haijun Ren, Zhengwei Wu, Jintao Cao, and Paul K. Chu

Phys. Plasmas 16, 122107 (2009); http://dx.doi.org/10.1063/1.3272092 (7 pages) | Cited 2 times

Online Publication Date: 7 December 2009

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The magnetorotational instability (MRI) in differential rotating dusty plasmas with dissipative effects is investigated by using local linear analysis. We assume that the dust grains are heavy enough to be immobile so that the dust effects are contained in our model only by introducing an electric field term in the one-fluid equation of plasma motion. The general local dispersion relation is derived and two limiting cases are discussed with respect to the dust-induced effect. The instability criterions in the different limiting cases are presented and the growth rate of local MRI in the last case is demonstrated.
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52.27.Lw Dusty or complex plasmas; plasma crystals
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.)
52.55.Tn Ideal and resistive MHD modes; kinetic modes

Circularly polarized wave propagation in magnetofluid dynamics for relativistic electron-positron plasmas

Felipe A. Asenjo, Víctor Muñoz, Juan Alejandro Valdivia, and Tohru Hada

Phys. Plasmas 16, 122108 (2009); http://dx.doi.org/10.1063/1.3272667 (5 pages) | Cited 5 times

Online Publication Date: 8 December 2009

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The dispersion relation for circularly polarized electromagnetic waves propagating in the direction of an external magnetic field in a relativistic electron-positron plasma with arbitrary constant drift velocities is obtained for constant temperature in the homentropic regime. This result is an exact solution of the nonlinear magnetofluid unification field formalism introduced by S. Mahajan [Phys. Rev. Lett. 90, 035001 (2003) ], where the electromagnetic and fluid fields are coupled through the relativistic enthalpy density. The behavior of electromagnetic and Alfvén branches of the dispersion relation are discussed for different temperatures.
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52.27.Ep Electron-positron plasmas
52.27.Ny Relativistic plasmas
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams

Rarefaction shock waves and Hugoniot curve in the presence of free and trapped particles

A. R. Niknam, M. Hashemzadeh, B. Shokri, and M. R. Rouhani

Phys. Plasmas 16, 122109 (2009); http://dx.doi.org/10.1063/1.3265963 (5 pages) | Cited 2 times

Online Publication Date: 10 December 2009

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The effects of the relativistic ponderomotive force and trapped particles in the presence of ponderomotive force on the rarefaction shock waves are investigated. The ponderomotive force alters the electron density distribution. This force and relativistic mass affect the plasma frequency. These physical parameters modify the total pressure and the existence condition of the rarefaction shock wave. Furthermore, the trapping of particles by the high frequency electromagnetic field considerably changes the existence condition of the rarefaction shock wave. The total pressure and Hugoniot curve are obtained by considering the relativistic ponderomotive force and trapped particles.
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52.35.Tc Shock waves and discontinuities
52.30.-q Plasma dynamics and flow
52.27.Ny Relativistic plasmas
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
47.40.Nm Shock wave interactions and shock effects
47.45.-n Rarefied gas dynamics

New construction of the magnetohydrodynamic spectrum of stationary plasma flows. I. Solution path and alternator

J. P. Goedbloed

Phys. Plasmas 16, 122110 (2009); http://dx.doi.org/10.1063/1.3271164 (14 pages) | Cited 5 times

Online Publication Date: 14 December 2009

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A new method of systematically constructing the full structure of the complex magnetohydrodynamic spectra of stationary flows is presented. It is based on the self-adjointness of the generalized force operator G and the Doppler–Coriolis shift operator U, and the associated quadratic forms for the normalized energy math and the normalized Doppler–Coriolis shift math, which may be constructed for all complex values of ω if the original eigenvalue problem is converted into a one-sided boundary value problem. This turns math into a complex expression, while math remains real. Whereas the solution path Ps of stable modes is just the real axis, the solution path Pu of unstable modes in the complex ω plane is found by requiring that the solution-averaged Doppler–Coriolis shifted real part of the frequency vanishes, σ−math[ξ(ω)] = 0, or that the energy is real, Im math[ξ(ω)] = 0. The location of the eigenvalues on these solution paths is determined by two quadratic forms, which may straightforwardly be evaluated in any of the finite element spectral codes in existence. A new oscillation theorem is proved about the monotonicity of complex eigenvalues for one-dimensional systems. Instead of counting internal nodes of the real displacement vector ξ (as in static plasmas), it is based on counting the zeros of the alternating ratio, or alternator, R ≡ ξ/Π of the boundary values of the complex functions ξ and the total pressure perturbation Π, which is real on the solution path. This finally provides the generalization of the basic structural properties of the magnetohydrodynamic spectrum of static plasmas, which has been known for a long time, to stationary plasmas.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.30.-q Plasma dynamics and flow
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
47.65.-d Magnetohydrodynamics and electrohydrodynamics

New construction of the magnetohydrodynamic spectrum of stationary plasma flows. II. Rayleigh–Taylor and Kelvin–Helmholtz instability

J. P. Goedbloed

Phys. Plasmas 16, 122111 (2009); http://dx.doi.org/10.1063/1.3271166 (13 pages) | Cited 3 times

Online Publication Date: 14 December 2009

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In a preceding paper [ J. P. Goedbloed, Phys. Plasmas 16, 122110 (2009) ] a new method was developed to compute the magnetohydrodynamic spectrum of waves and instabilities of stationary plasma flows by means of the construction of the solution paths, Ps and Pu, of stable waves and instabilities in the complex ω plane of an extended boundary value problem and the monotonicity of the alternator R ≡ ξ/Π (ratio of displacement and total pressure perturbation) along those paths to find the eigenvalues. This method is applied in this paper to explicitly construct the solution paths, and the eigenvalues on it, for a plane gravitating plasma slab with shear flow. The topology of the solution paths for Rayleigh–Taylor and Kelvin–Helmholtz instabilities that are constructed here for the first time exhibits a surprising complexity. This is not a mathematical artifact, but characteristic for the structure of the magnetohydrodynamic spectrum of plasmas with background flow. Hence, its construction is crucial for the success of magnetohydrodynamic spectroscopy, aimed at determining the internal equilibrium characteristics of astrophysical and laboratory fusion plasmas.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.30.-q Plasma dynamics and flow
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
47.65.-d Magnetohydrodynamics and electrohydrodynamics

Dressed solitons in quantum electron-positron-ion plasmas

Prasanta Chatterjee, Kaushik Roy, Ganesh Mondal, S. V. Muniandy, S. L. Yap, and C. S. Wong

Phys. Plasmas 16, 122112 (2009); http://dx.doi.org/10.1063/1.3272085 (8 pages) | Cited 7 times

Online Publication Date: 14 December 2009

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Nonlinear propagation of quantum ion acoustic waves in a dense quantum plasma whose constituents are electrons, positrons, and positive ions is investigated using a quantum hydrodynamic model. The Korteweg–de Vries equation is derived using reductive perturbation technique. The higher order inhomogeneous differential equation is obtained for the dressed soliton. The dynamical equation for dressed soliton is solved using the renormalization method. The conditions for the validity of the higher order correction are described. The effects of quantum parameter, positron concentration, electron to positron Fermi temperature ratio, and soliton velocity on the amplitude and width of the dressed soliton are studied.
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52.35.Sb Solitons; BGK modes
52.27.Jt Nonneutral plasmas
52.27.Aj Single-component, electron-positive-ion plasmas
52.27.Ep Electron-positron plasmas
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Nonlinear evolution of double tearing mode in Hall magnetohydrodynamics

C. L. Zhang (张城龙) and Z. W. Ma (马志为)

Phys. Plasmas 16, 122113 (2009); http://dx.doi.org/10.1063/1.3276534 (5 pages) | Cited 11 times

Online Publication Date: 31 December 2009

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Nonlinear evolution of a double tearing mode for different plasma resistivities (η) and ion inertial lengths (di) is investigated using Hall magnetohydrodynamics simulations. In the Hall dominant regime, the magnetic field configuration in the reconnection region evolves from Y-type to X-type geometry, which leads to fast reconnection in the nonlinear growth phase. The maximum growth rate of total kinetic energy of plasma γmax in the explosive growth phase is found to have a di2/5η1/10 scaling and the maximum total kinetic energy (Ek)max scales as di4/5. In the regime with weak Hall effect, it is found that the elongated thin current sheet formed in the early phase is broken into two X-points, forming a magnetic island in the late stage, instead of shrinking to an X-type geometry.
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52.55.Tn Ideal and resistive MHD modes; kinetic modes
52.35.Vd Magnetic reconnection
52.65.Kj Magnetohydrodynamic and fluid equation

Double layer formation in a two-region electronegative plasma

E. Kawamura, A. J. Lichtenberg, M. A. Lieberman, and J. P. Verboncoeur

Phys. Plasmas 16, 122114 (2009); http://dx.doi.org/10.1063/1.3276155 (14 pages) | Cited 6 times

Online Publication Date: 31 December 2009

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The formation of a double layer (DL) in a two-dimensional (2D) electronegative plasma with a source (heating) section connected to a larger downstream section is described. A 2D particle-in-cell (PIC) code is used to exhibit the DL, which appears near the transition between the source and downstream chambers, over a range of pressures and electronegativities. Diagnostics of the PIC code allow the calculation of various plasma parameters, not easily measured in experiments, to be compared with an analytic theory. The theory consists of a collisionless one-dimensional model of a DL connected to 2D source and downstream global models. The conditions of positive and negative ion balance upstream and downstream, and the downstream energy balance determine the DL potential, electron temperatures, and other plasma parameters. A rescaled oxygen reaction set is used both for the simulation and for the analytic comparison. The PIC simulations exhibit a Maxwellian electron distribution in the source region at temperature Th, and a bi-Maxwellian distribution downstream, with a low energy population at temperature Tc<Th and with a hotter tail also having temperature Th. At the upstream DL edge, an accelerated electron component is observed. Using these results in the model, a DL is found in reasonable agreement with that obtained in the simulation.
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52.27.Cm Multicomponent and negative-ion plasmas
52.75.Di Ion and plasma propulsion
back to top Nonlinear Phenomena, Turbulence, Transport

Parametric coupling of low frequency whistler to Alfven wave in a plasma

Nafis Ahmad, V. K. Tripathi, M. Rafat, and Mudassir M. Husain

Phys. Plasmas 16, 122301 (2009); http://dx.doi.org/10.1063/1.3270109 (7 pages)

Online Publication Date: 3 December 2009

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The parametric decay of a large amplitude electromagnetic wave in the ion cyclotron range of frequency into a compressional Alfven wave and an electromagnetic sideband wave in a magnetized plasma is investigated. The pump wave propagates in the direction of ambient magnetic field whereas the decay waves propagate at oblique angles. When the pump wave is left circularly polarized the decay is not permitted kinematically as the momentum of pump photon always exceeds the sum of momenta of the decay wave photons. For the right circularly polarized whistler mode pump the decay is permitted with sideband nearly right circularly polarized. The density perturbation associated with the Alfven wave couples with the pump driven oscillatory velocities of ions and electrons to produce a current driving the sideband. The sideband and the pump exert pondermotive force on ions and electrons that drive the Alfven wave. The frequency and growth rate of the Alfven wave increase with the normalized pump frequency. The threshold power density, determined by the collisional damping rates of the decay waves is rather modest.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.20.-j Elementary processes in plasmas
52.25.Xz Magnetized plasmas

Linear gyrokinetic calculations of toroidal momentum transport in the presence of trapped electron modes in tokamak plasmas

N. Kluy, C. Angioni, Y. Camenen, and A. G. Peeters

Phys. Plasmas 16, 122302 (2009); http://dx.doi.org/10.1063/1.3271411 (7 pages) | Cited 15 times

Online Publication Date: 3 December 2009

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The toroidal momentum transport in the presence of trapped electron mode microinstabilities in tokamak plasmas is studied by means of quasilinear gyrokinetic calculations. In particular, the role of the Coriolis drift in producing an inward convection of toroidal momentum is investigated. The Coriolis drift term has been implemented in the gyrokinetic code GS2 [ W. Dorland et al., Phys. Rev. Lett. 85, 5579 (2000) ] specifically for the completion of this work. A benchmark between the GS2 implementation of the Coriolis drift and the implementations included in two other gyrokinetic codes is presented. The numerical calculations show that in the presence of trapped electron modes, despite of a weaker symmetry breaking of the eigenfunctions with respect to the case of ion temperature gradient modes, a pinch of toroidal momentum is produced in most conditions. The toroidal momentum viscosity is also computed, and found to be small as compared with the electron heat conductivity, but significantly larger than the ion heat conductivity. In addition, interesting differences are found in the dependence of the toroidal momentum pinch as a function of collisionality between trapped electron modes and ion temperature gradient modes. The results identify also parameter domains in which the pinch is predicted to be small, which are also of interest for comparisons with the experiments.
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52.25.Fi Transport properties
52.65.Tt Gyrofluid and gyrokinetic simulations
52.55.Fa Tokamaks, spherical tokamaks

Free energy minimization approach to penetration of resonant magnetic perturbations in tokamaks

D. Reiser and M. Z. Tokar

Phys. Plasmas 16, 122303 (2009); http://dx.doi.org/10.1063/1.3267845 (9 pages)

Online Publication Date: 3 December 2009

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By applying the principle of minimum free energy an analytical model for the plasma response to externally applied resonant magnetic perturbations (RMPs) is proposed. The results are compared with ATTEMPT code calculations [ D. Reiser et al., Phys. Plasmas 16, 0042317 (2009) ] and reproduce qualitatively and quantitatively the numerical results on the collisionality dependence of RMP penetration characteristics. Strong increase in the radial electric field with reduced screening at RMPs above a certain threshold is also reproduced by the model.
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52.55.Fa Tokamaks, spherical tokamaks
52.65.Vv Perturbative methods

Saturation mechanisms for edge turbulence

D. A. Russell, J. R. Myra, and D. A. D’Ippolito

Phys. Plasmas 16, 122304 (2009); http://dx.doi.org/10.1063/1.3270051 (12 pages) | Cited 15 times

Online Publication Date: 4 December 2009

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Saturation mechanisms for two-dimensional (2D) edge turbulence are studied in a Braginskii-type fluid model using the scrape-off-layer turbulence code. The simulations study the interaction of edge and scrape-off-layer (SOL) turbulence, blob generation, momentum transport, and shear flow generation in 2D turbulence. It is shown that a key parameter is the zonal flow shear damping rate, which controls both the level of saturated turbulence and the rate of blob generation. The flow shear profile is produced by a combination of the turbulent Reynold’s stress inside the last closed surface and the sheath-induced flow in the SOL. The turbulent properties are studied as a function of zonal flow damping. The role of other edge and SOL dissipation mechanisms are also discussed.
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52.35.Ra Plasma turbulence
52.35.Kt Drift waves
52.55.Fa Tokamaks, spherical tokamaks
52.65.Kj Magnetohydrodynamic and fluid equation

Reduction of inward momentum flux by damped eigenmodes

P. W. Terry, D. A. Baver, and D. R. Hatch

Phys. Plasmas 16, 122305 (2009); http://dx.doi.org/10.1063/1.3271158 (11 pages) | Cited 6 times

Online Publication Date: 7 December 2009

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The inward momentum flux driven by the off-diagonal pressure gradient in a fluid model for ion temperature gradient turbulence with large Richardson number is significantly reduced by the excitation of stable eigenmodes. This is accomplished primarily through the amplitude autocorrelation of the damped eigenmode, which, in the flux, directly counteracts the quasilinear contribution of the unstable eigenmode. Stable eigenmode cross correlations also contribute to the flux, but the symmetry of conjugate pairing of growing and damped eigenmodes leads to significant cancellations between cross correlation terms. Conjugate symmetry is a property of unstable wavenumbers but applies to the whole of the saturated state because damped eigenmodes in the unstable range prevent the spread of energy outside that range. The heat and momentum fluxes are nearly isomorphous when expressed in terms of the eigenmode correlations. Due to this similarity of form, the thermodynamic constraint, which keeps the heat flux outward even when significantly reduced by the damped eigenmode, results in a momentum flux that remains inward, even though it is also reduced by the damped eigenmode. The isomorphism is not perfect. When the contribution of stable eigenmode cross correlations to the flux do not cancel, the momentum flux can reverse sign and become outward.
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52.30.-q Plasma dynamics and flow
52.35.Ra Plasma turbulence
52.25.Kn Thermodynamics of plasmas
02.10.Ud Linear algebra

Electrostatic shocks and solitons in pair-ion plasmas in a two-dimensional geometry

W. Masood, S. Mahmood, and N. Imtiaz

Phys. Plasmas 16, 122306 (2009); http://dx.doi.org/10.1063/1.3272666 (5 pages) | Cited 6 times

Online Publication Date: 8 December 2009

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Nonlinear electrostatic waves are studied in unmagnetized, dissipative pair-ion plasmas in the presence of weak transverse perturbations. The dissipation in the system is taken into account by incorporating the kinematic viscosity of both positive and negative ions in plasmas. The Kadomtsev–Petviashvili–Burger equation is derived using the small amplitude expansion method. The Kadomtsev–Petviashvili equation for pair-ion plasmas is also presented by ignoring the dissipative effects. Both compressive and rarefactive shocks and solitary waves are found to exist in pair-ion plasmas. The dependence of compression and rarefaction on the temperature ratios between the ion species is numerically shown. The present study may have relevance to the understanding of the formation of electrostatic shocks and solitons in laboratory produced pair-ion plasmas.
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52.50.Lp Plasma production and heating by shock waves and compression
52.35.Tc Shock waves and discontinuities
52.35.Sb Solitons; BGK modes

Electromagnetic formulation of global gyrokinetic particle simulation in toroidal geometry

I. Holod, W. L. Zhang, Y. Xiao, and Z. Lin

Phys. Plasmas 16, 122307 (2009); http://dx.doi.org/10.1063/1.3273070 (10 pages) | Cited 17 times

Online Publication Date: 9 December 2009

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The fluid-kinetic hybrid electron model for global electromagnetic gyrokinetic particle simulations has been formulated in toroidal geometry using magnetic coordinates, providing the capabilities to describe low frequency processes in electromagnetic turbulence with electron dynamics. In the limit of long wavelength and no parallel electric field our equations reduce to the ideal magnetohydrodynamic equations. The formulation has been generalized to include equilibrium flows. The equations for zonal components of electrostatic and vector potentials have been derived, demonstrating the electron screening of the zonal vector potential.
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52.55.Jd Magnetic mirrors, gas dynamic traps
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Ra Plasma turbulence
52.65.-y Plasma simulation

Square grid state in dielectric barrier discharge system

L. F. Dong, S. F. Li, W. L. Fan, and Y. Y. Pan

Phys. Plasmas 16, 122308 (2009); http://dx.doi.org/10.1063/1.3273069 (4 pages)

Online Publication Date: 9 December 2009

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A square grid state and a hexagonal grid state are observed in a dielectric barrier discharge system. They are selected by different resonance mechanisms, namely, a four-wave interaction for the square grid state and a three-wave interaction for the hexagonal grid state. The spatiotemporal dynamics of the square grid state is studied by an optical method. It is found that the square grid state is an interleaving of three different sublattices, which correspond to a harmonic mode and two subharmonic modes.
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52.80.-s Electric discharges
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams

Solitary kinetic Alfvén waves in adiabatic process

Lihui Chai and Yi Li

Phys. Plasmas 16, 122309 (2009); http://dx.doi.org/10.1063/1.3271409 (4 pages) | Cited 3 times

Online Publication Date: 17 December 2009

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Solitary kinetic Alfvén waves (SKAWs) have been an important subject in the field of space plasma physics because of their nonzero parallel electrical field and density fluctuations. Under different thermodynamic processes, SKAWs, within the limit of small amplitude, are studied analytically and numerically using the Sagdeev potential method. The results show that the width of the solitary structures is larger and the amplitude of the density humps is smaller under constant entropy than those under constant temperature with other relevant parameters being the same. The perturbed electromagnetic fields Ex, By, and Ez are also studied further.
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52.35.Sb Solitons; BGK modes
95.30.Qd Magnetohydrodynamics and plasmas
94.05.Fg Solitons and solitary waves
52.25.Gj Fluctuation and chaos phenomena
52.25.Kn Thermodynamics of plasmas
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
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