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Jul 2008

Volume 15, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Phys. Plasmas 15, 072513 (2008); http://dx.doi.org/10.1063/1.2959128 (10 pages)

E. F. Jaeger, L. A. Berry, E. F. D’Azevedo, R. F. Barrett, S. D. Ahern, D. W. Swain, D. B. Batchelor, R. W. Harvey, J. R. Myra, D. A. D’Ippolito, C. K. Phillips, E. Valeo, D. N. Smithe, P. T. Bonoli, J. C. Wright, et al.
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back to top Basic Plasma Phenomena, Waves, Instabilities

Drift instabilities in current sheets with guide field

P. H. Yoon and A. T. Y. Lui

Phys. Plasmas 15, 072101 (2008); http://dx.doi.org/10.1063/1.2938386 (7 pages) | Cited 3 times

Online Publication Date: 1 July 2008

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Drift instabilities in current sheets with or without the guide field are investigated with a newly developed improved electrostatic dispersion relation. Traditional (local) theories of lower-hybrid drift instability typically assumes small electron drift speed, and expand the electron distribution function in Taylor series. This approximate treatment is removed in this paper. The resulting formalism is uniformly valid for an arbitrary magnitude of relative ion and electron drift speeds, and is valid for an arbitrary strength of the guide field.
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52.35.Kt Drift waves

Anomalous transport of particles in plasma flow with strong inhomogeneous velocity shear

V. S. Mikhailenko, V. V. Mikhailenko, K. N. Stepanov, and N. A. Azarenkov

Phys. Plasmas 15, 072102 (2008); http://dx.doi.org/10.1063/1.2943703 (5 pages) | Cited 2 times

Online Publication Date: 2 July 2008

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The temporal evolution of the drift modes and resulting anomalous transport are considered under the conditions of strong inhomogeneous flow shear [flow shear parameter dv0(r)/dr is greater or comparable to the drift frequency] on the ground of the nonmodal approach with application to boundary regions of tokamaks. The nonmodal linear analysis of the effect of flow shear nonuniformity on the temporal evolution of the drift modes, performed on the base of the Hasegava–Wakatani model, has shown, that terms reflecting velocity profile curvature decay more rapidly with time, as compared with those containing only velocity shearing rate. Therefore, the linear effect of the flow shear nonuniformity appears to be subdominant and the long-time evolution of the drift modes is determined by more slowly damped shear rate contained terms. The anomalous transport of particles in shear flow due to nonmodal drift perturbations exhibits a subdiffusive behavior with the diffusion coefficient reducing in time as t−3.
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52.35.Kt Drift waves
52.25.Fi Transport properties
52.30.-q Plasma dynamics and flow

A particle simulation of current sheet instabilities under finite guide field

X. Y. Wang, Y. Lin, L. Chen, and Z. Lin

Phys. Plasmas 15, 072103 (2008); http://dx.doi.org/10.1063/1.2938732 (13 pages) | Cited 6 times

Online Publication Date: 3 July 2008

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The instability of a Harris current sheet under a broad range of finite guide field (BG) is investigated using a linearized (δf) gyrokinetic electron and fully kinetic ion particle simulation code. The simulation is carried out in the two-dimensional plane containing the guide field along y and the current sheet normal along z. In this particle model, the rapid electron cyclotron motion is removed, while the realistic mass ratio mi/me, finite electron Larmor radii, and wave-particle interactions are kept. It is found that for a finite BG/Bx0 ⩽ 1, where Bx0 is the asymptotic antiparallel component of magnetic field, three unstable modes, i.e., modes A, B, and C, can be excited in the current sheet. Modes A and C, appearing to be quasielectrostatic modified two-stream instability/whistler mode, are located mainly on the edge of the current sheet. Mode B, on the other hand, is confined in the current sheet center and carries a compressional magnetic field (δBy) perturbation along the direction of electron drift velocity. Our new finding suggests that mode B may contribute directly to the electron anomalous resistivity in magnetic reconnection. In the cases with extremely large BG/Bx0⪢1, the wave modes evolve to a globally propagating instability. The simulation shows that the presence of finite BG modifies the physics of the current sheet significantly.
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52.35.Tc Shock waves and discontinuities
52.65.-y Plasma simulation
52.65.Tt Gyrofluid and gyrokinetic simulations
02.70.-c Computational techniques; simulations
04.30.Db Wave generation and sources

Electrostatic modes in multi-ion and pair-ion collisional plasmas

J. Vranjes, D. Petrovic, B. P. Pandey, and S. Poedts

Phys. Plasmas 15, 072104 (2008); http://dx.doi.org/10.1063/1.2949696 (8 pages) | Cited 17 times

Online Publication Date: 8 July 2008

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The physics of plasmas containing positive and negative ions is discussed with special attention to the recently produced pair-ion plasma containing ions of equal mass and opposite charge. The effects of the density gradient in the direction perpendicular to the ambient magnetic field vector are discussed. The possible presence of electrons is discussed in the context of plasma modes propagating at an angle with respect to the magnetic field vector. It is shown that the electron plasma mode may become a backward mode in the presence of a density gradient, and this behavior may be controlled either by the electron number density or the mode number in the perpendicular direction. In plasmas with hot electrons an instability may develop, driven by the combination of electron collisions and the density gradient, and in the regime of a sound ions’ response. In the case of a pure pair-ion plasma, for lower frequencies and for parameters close to those used in the recent experiments, the perturbed ions may feel the effects of the magnetic field. In this case the plasma mode also becomes backward, resembling features of an experimentally observed but yet unexplained backward mode.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.20.Fs Electron collisions
52.25.-b Plasma properties
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Soliton reflection in magnetized plasma: Effect of ion temperature and nonisothermal electrons

Hitendra K. Malik

Phys. Plasmas 15, 072105 (2008); http://dx.doi.org/10.1063/1.2947108 (8 pages) | Cited 10 times

Online Publication Date: 9 July 2008

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Reflection of solitons in magnetized inhomogeneous plasma is studied theoretically under the effect of ion temperature and low temperature nonisothermal electrons. The effect of ion temperature is to enhance (reduce) the amplitude (width) of the incident and reflected solitons, and this effect is more prominent in the case of a large number of nonisothermal electrons. The solitons are downshifted after the reflection and the stronger reflection is achieved when the ions of lower temperature and nonisothermal electrons with larger concentration are present in the plasma. The solitons shift more after the reflection for higher ion and electron temperatures, large concentration of the electrons, but the shift becomes smaller in the presence of stronger magnetic field. Both the incident and reflected solitons evolve with higher amplitudes if the temperature of nonisothermal electrons is raised, but the solitons are reflected weakly under this situation. The effect of magnetic field is to reduce the amplitudes of both the solitons, and the reduction in the amplitude of reflected soliton is at a faster rate, due to which the soliton reflection gets weaker. The magnetic field affects soliton reflection more significantly when it is applied at a larger angle with the direction of wave propagation.
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47.35.Fg Solitary waves
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Ion acoustic shock waves in electron-positron-ion quantum plasma

W. Masood, Arshad M. Mirza, and M. Hanif

Phys. Plasmas 15, 072106 (2008); http://dx.doi.org/10.1063/1.2949702 (5 pages) | Cited 12 times

Online Publication Date: 9 July 2008

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Ion acoustic shock waves (IASWs) are studied in an unmagnetized quantum plasma consisting of electrons, positrons, and ions employing the quantum hydrodynamic (QHD) model. Nonlinear quantum IASWs are investigated by deriving the Korteweg–deVries–Burger equation under the small amplitude perturbation expansion method. The dissipation is introduced by taking into account the kinematic viscosity among the plasma constituents. It is found that the strength of the ion acoustic shock wave is maximum for spherical, intermediate for cylindrical, and minimum for planar geometry. The temporal evolution of the shock for a quantum e-p-i plasma in a spherical geometry is also investigated. It is found that the strength and the steepness of the quantum ion acoustic shock wave increases with decreasing stretched time coordinate (representing slow time scale) ∣τ∣. It is also found that an increase in the quantum Bohm potential decreases the strength as well as the steepness of the shock. The temporal evolution of the quantum ion acoustic solitons in an e-p-i plasma for cylindrical and spherical geometries is also explored by substituting the dissipative coefficient C equal to zero. The relevance of the present study with regard to the dense astrophysical environments is also pointed out.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Tc Shock waves and discontinuities
52.25.Fi Transport properties
95.30.Qd Magnetohydrodynamics and plasmas

A novel method to construct stationary solutions of the Vlasov-Maxwell system: The relativistic case

Akihiro Suzuki

Phys. Plasmas 15, 072107 (2008); http://dx.doi.org/10.1063/1.2950302 (7 pages) | Cited 4 times

Online Publication Date: 9 July 2008

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A method to derive stationary solutions of the relativistic Vlasov-Maxwell system is explored. In the nonrelativistic case, a method using the Hermite polynomial series to describe the deviation from the Maxwell-Boltzmann distribution is found to be successful in deriving a few stationary solutions, including a two-dimensional one. Instead of the Hermite polynomial series, two special orthogonal polynomial series, which are appropriate to expand the deviation from the Maxwell-Jüttner distribution, are introduced in this paper. By applying this method, a new two-dimensional equilibrium is derived, which may provide an initial setup for investigations of three-dimensional relativistic collisionless reconnection of magnetic fields.
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52.27.Ny Relativistic plasmas
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
02.10.De Algebraic structures and number theory

Double layer created by electron cyclotron resonance heating in an inhomogeneously magnetized plasma with high-speed ion flow

K. Takahashi, T. Kaneko, and R. Hatakeyama

Phys. Plasmas 15, 072108 (2008); http://dx.doi.org/10.1063/1.2951997 (5 pages) | Cited 5 times

Online Publication Date: 9 July 2008

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A potential jump, i.e., an electric double layer (DL) is formed near an electron cyclotron resonance (ECR) point when an electron cyclotron wave is injected into an inhomogeneously magnetized plasma with high-speed ion flow. A charge separation is caused by an electron reflection due to −μ∇Bz force enhanced by ECR heating and ion inertia. It is clearly demonstrated in the experiment that the potential height of the DL is almost proportional to the field-aligned ion flow energy; the DL is found to be self-consistently formed for maintaining charge neutrality by reflecting a part of the flowing ions.
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52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.50.Sw Plasma heating by microwaves; ECR, LH, collisional heating
52.30.-q Plasma dynamics and flow

Quantum Trivelpiece–Gould waves in a magnetized dense plasma

H. Terças, J. T. Mendonça, and P. K. Shukla

Phys. Plasmas 15, 072109 (2008); http://dx.doi.org/10.1063/1.2947235 (3 pages) | Cited 3 times

Online Publication Date: 10 July 2008

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The dispersion relation for the electrostatic waves below the electron plasma frequency in a dense quantum plasma is derived by using the magnetohydrodynamic model. It is shown that in the classical case the dispersion relation reduces to the expression obtained for the well-known Trivelpiece–Gould (TG) modes. Attention is also devoted to the case of solitary waves associated with the nonlinear TG modes.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Sb Solitons; BGK modes
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Nonthermal power dissipation and nonlinear wave dynamics in a plasma penetrated by a momentum-scattered relativistic electron stream

J. Guillory, D. V. Rose, and J. H. Beall

Phys. Plasmas 15, 072110 (2008); http://dx.doi.org/10.1063/1.2950304 (13 pages)

Online Publication Date: 10 July 2008

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A previous analysis of the nonlinear dissipative equilibrium of a beam-penetrated plasma with nonthermal electron “tails” [ D. V. Rose, J. Guillory, and J. H. Beall, Phys. Plasmas 9, 1000 (2002) ] is extended to the case of a relativistic, momentum-angle-scattered electron beam (with or without accompanying ions) penetrating a fully ionized low-density nearly collisionless plasma, and to include the energy balance of the nonthermal plasma tail electron population on electron collisional timescales long compared with the primary instability growth time. Quasistationary nonlinear “dissipative equilibrium” states are quantified for various ranges of relativistic beam parameters and various tail-enhanced Landau damping rates for shorter-wavelength space-charge waves. Conditions for quasisteady wave populations are found, and for energy balance between beam energy input to and dynamic friction cooling of the nonthermal “tail electrons.” Finally, some potentially incorrect inferences based on a thermal interpretation of bremsstrahlung from such a plasma are quantified. All of these microphysical processes evolve on timescales inaccessible to conventional magnetohydrodynamic modeling of astrophysical jets, and may lead to energetics corrections to such fluid models.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams

Thermodynamics of strongly coupled repulsive Yukawa particles in ambient neutralizing plasma: Thermodynamic instability and the possibility of observation in fine particle plasmas

Hiroo Totsuji

Phys. Plasmas 15, 072111 (2008); http://dx.doi.org/10.1063/1.2953803 (14 pages) | Cited 7 times

Online Publication Date: 11 July 2008

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The thermodynamics is analyzed for a system composed of particles with hard cores, interacting via the repulsive Yukawa potential (Yukawa particulates), and neutralizing ambient (background) plasma. An approximate equation of state is given with proper account of the contribution of ambient plasma and it is shown that there exists a possibility for the total isothermal compressibility of Yukawa particulates and ambient plasma to diverge when the coupling between Yukawa particulates is sufficiently strong. In this case, the system undergoes a transition into separated phases with different densities and we have a critical point for this phase separation. Examples of approximate phase diagrams related to this transition are given. It is emphasized that the critical point can be in the solid phase and we have the possibility to observe a solid-solid phase separation. The applicability of these results to fine particle plasmas is investigated. It is shown that, though the values of the characteristic parameters are semiquantitative due to the effects not described by this model, these phenomena are expected to be observed in fine particle plasmas, when approximately isotropic bulk systems are realized with a very strong coupling between fine particles.
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52.25.Kn Thermodynamics of plasmas
52.25.-b Plasma properties

Theory and simulations of electrostatic field error transport

Daniel H. E. Dubin

Phys. Plasmas 15, 072112 (2008); http://dx.doi.org/10.1063/1.2936874 (26 pages) | Cited 4 times

Online Publication Date: 16 July 2008

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Asymmetries in applied electromagnetic fields cause plasma loss (or compression) in stellarators, tokamaks, and non-neutral plasmas. Here, this transport is studied using idealized simulations that follow guiding centers in given fields, neglecting collective effects on the plasma evolution, but including collisions at rate ν. For simplicity the magnetic field is assumed to be uniform; transport is due to asymmetries in applied electrostatic fields. Also, the Fokker–Planck equation describing the particle distribution is solved, and the predicted transport is found to agree with the simulations. Banana, plateau, and fluid regimes are identified and observed in the simulations. When separate trapped particle populations are created by application of an axisymmetric squeeze potential, enhanced transport regimes are observed, scaling as math when ν<ω0<ωB and as 1/ν when ω0<ν<ωB (where ω0 and ωB are the rotation and axial bounce frequencies, respectively). These regimes are similar to those predicted for neoclassical transport in stellarators.
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52.25.Fi Transport properties
52.65.Ff Fokker-Planck and Vlasov equation
52.55.Jd Magnetic mirrors, gas dynamic traps
52.55.Fa Tokamaks, spherical tokamaks

Critical Δ′ for stability of viscoresistive tearing modes

D. Grasso, R. J. Hastie, F. Porcelli, and C. Tebaldi

Phys. Plasmas 15, 072113 (2008); http://dx.doi.org/10.1063/1.2957916 (5 pages) | Cited 1 time

Online Publication Date: 21 July 2008

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An analytic expression for the stability threshold of linear tearing modes is derived. The magnetized plasma is described in terms of a standard viscoresistive magnetohydrodynamic model. The analytic derivation requires an extension of the standard layer equation that represents an approximation of the full model in the vicinity of the reconnecting layer. The analytic result is checked against numerical simulations, showing excellent agreement.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Quasielectrostatic whistler wave radiation from the hot electron emission of a laser-produced plasma

Stephen Vincena, Walter Gekelman, M. A. Van Zeeland, James Maggs, and Andrew Collette

Phys. Plasmas 15, 072114 (2008); http://dx.doi.org/10.1063/1.2956994 (14 pages) | Cited 2 times

Online Publication Date: 21 July 2008

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Measurements are presented of radiated wave electric fields which result from the creation of a dense, laser-produced plasma within a large, uniform background magnetoplasma. The radiated field patterns are consistent for waves propagating along the quasielectrostatic branch of the whistler wave dispersion curve calculated from the background plasma parameters. The energy source of these waves coincides with an observed energetic tail electron population escaping the laser-produced plasma. A prominent feature of the radiated electric fields is a bipolar spike in both time and space, with a cross-field size near that of the initial escaping electron burst and a duration equivalent to one oscillation at the lower hybrid frequency within the background plasma. Additionally, time-windowed snapshots of the whistler wave radiation patterns are shown to provide a remote diagnostic of the cross-field speed of the laser-produced plasma.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.-m Plasma diagnostic techniques and instrumentation
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Observations of neutral depletion and plasma acceleration in a flowing high-power argon helicon plasma

C. Mark Denning, Matt Wiebold, and John E. Scharer

Phys. Plasmas 15, 072115 (2008); http://dx.doi.org/10.1063/1.2950301 (12 pages) | Cited 10 times

Online Publication Date: 22 July 2008

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Neutral depletion effects are observed in a steady-state flowing argon helicon plasma with a magnetic nozzle for high rf input powers (up to 3 kW). Noninvasive diagnostics including 105 GHz microwave interferometry and optical spectroscopy with collisional-radiative modeling are used to measure the electron density (ne), electron temperature (Te), and neutral density (nn). A region of weak neutral depletion is observed upstream of the antenna where increasing rf power leads to increased electron density (up to ne = 1.6×1013 cm−3) while Te remains essentially constant and low (1.7–2.0 eV). The downstream region exhibits profound neutral depletion (maximum 92% line-averaged ionization), where Te rises linearly with increasing rf power (up to 4.9 eV) and ne remains constrained (below 6.5×1012 cm−3). Flux considerations indicate accelerated plasma flow (Mach 0.24) through the antenna region due to an axial pressure gradient with reduced collisional drag from neutral depletion.
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52.25.Ya Neutrals in plasmas
52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.70.Gw Radio-frequency and microwave measurements
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides

Modified Jeans instability criteria for magnetized systems

J. Lundin, M. Marklund, and G. Brodin

Phys. Plasmas 15, 072116 (2008); http://dx.doi.org/10.1063/1.2956641 (6 pages) | Cited 9 times

Online Publication Date: 25 July 2008

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The Jeans instability is analyzed for dense magnetohydrodynamic plasmas with intrinsic magnetization, the latter due to collective electron spin effects. Furthermore, the effects of electron tunneling as well as the Fermi pressure are included. It is found that the intrinsic magnetization of the plasma will enhance the Jeans instability, and can significantly modify the structure of the instability spectra. Implications and limitations of our results are discussed, as well as possible generalizations.
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52.25.Xz Magnetized plasmas
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
51.60.+a Magnetic properties

Role of nonadiabatic untrapped electrons in global electrostatic ion temperature gradient driven modes in a tokamak

J. Chowdhury, R. Ganesh, P. Angelino, J. Vaclavik, L. Villard, and S. Brunner

Phys. Plasmas 15, 072117 (2008); http://dx.doi.org/10.1063/1.2957917 (10 pages) | Cited 5 times

Online Publication Date: 25 July 2008

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In this work, role of nonadiabatic untrapped electrons in the context of a global ion temperature gradient driven mode has been investigated. In past studies, untrapped electrons have been assumed to be able to respond “instantaneously” to a disturbance. It is proposed that such adiabatic electron models should be reexamined for two important reasons: (i) It is known that global modes with n in the range of 3 ⩽ n ⩽ 15 (n is the toroidal mode number) have eigenmode widths spanning several mode-rational surfaces. It is being argued that close to these mode-rational surfaces, adiabatic electron models fail and a consistent treatment of nonadiabatic electrons is crucial for global modes. (ii) Electromagnetic effects depend on passing nonadiabatic electron dynamics. A minimal nontrivial model for the benchmarking of global linear and nonlinear gyrokinetic codes in the future becomes necessary, which can treat both passing ions and electrons on the same physics footing. As a first step, a study of the effect of nonadiabatic passing electrons in global electrostatic ion temperature gradients is presented. Interesting results include a demonstration of multiscale structure, downshift in critical ηi with increasing ηe, and a reduction in mixing-length based transport.
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52.55.Fa Tokamaks, spherical tokamaks
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Tn Ideal and resistive MHD modes; kinetic modes

Equilibrium of non-neutral plasmas in a Malmberg–Penning trap with a weakly tilted magnetic field

Igor Kotelnikov and Massimiliano Romé

Phys. Plasmas 15, 072118 (2008); http://dx.doi.org/10.1063/1.2961074 (23 pages) | Cited 2 times

Online Publication Date: 31 July 2008

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The effect of small asymmetric magnetic perturbations on the equilibrium of a non-neutral plasma confined in a Malmberg–Penning trap is analyzed. A constraint, known in the theory of tandem mirrors as the condition of current closure, is derived for non-neutral plasmas. Together with Poisson’s equation, this constraint provides a set of equations for determining self-consistent asymmetric equilibria of non-neutral plasmas in Malmberg–Penning traps. As an example of this approach, the non-neutral plasma equilibrium in the presence of a weak magnetic tilt is analyzed. Analytical and semianalytical solutions for the electric potential variations inside the trap are found in a paraxial limit for various radial density profiles of the plasma, including the case of global thermal equilibrium. The numerical procedure aimed to obtain self-consistent plasma equilibria for a magnetic field with a large asymmetry is also discussed. The newly developed method can be straightforwardly applied to determine plasma equilibria under the effect of the magnetic perturbations of higher multipolarity (such as, quadrupole or octupole fields).
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52.55.-s Magnetic confinement and equilibrium
back to top Nonlinear Phenomena, Turbulence, Transport

Fluid model of the boundary of a one-dimensional plasma under the influence of an oblique magnetic field for a wide range of collisionality

T. M. G. Zimmermann, M. Coppins, and J. E. Allen

Phys. Plasmas 15, 072301 (2008); http://dx.doi.org/10.1063/1.2946436 (8 pages) | Cited 7 times

Online Publication Date: 8 July 2008

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The effect of a magnetic field on the boundary of a plasma is studied using a one-dimensional fluid model based on the work of K.-U. Riemann [Contrib. Plasma. Phys. 34, 127 (1994) ]. The model takes into account the effects of both collisions and ionization. Two limiting regimes are identified: the collisional presheath and the (highly) magnetized presheath. Results from this model demonstrate that a highly magnetized presheath may be treated in terms of two regions: The B-aligned presheath and a Chodura layer [ R. Chodura, Phys. Fluids 25, 1628 (1982) ]. The properties of this Chodura layer are explored in some detail and it is found that the size of this layer, for example, follows a simple expression in the highly magnetized regime. Finally, an attempt is made to recover the singular behavior of the Chodura layer as the magnetic field becomes very strong and use a pseudo two-scale approach to resolve both scale lengths of the magnetized presheath.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.40.Kh Plasma sheaths
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Tn Ideal and resistive MHD modes; kinetic modes
52.65.Kj Magnetohydrodynamic and fluid equation
52.80.-s Electric discharges

Generation of electromagnetic structures via modulational instability of drift waves

A. I. Smolyakov and S. I. Krasheninnikov

Phys. Plasmas 15, 072302 (2008); http://dx.doi.org/10.1063/1.2937463 (6 pages) | Cited 4 times

Online Publication Date: 15 July 2008

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Generation mechanism for large scale electromagnetic structures (blobs) is considered by employing the technique of four-wave interactions (modulational instability). It is shown that primary electrostatic turbulence may generate elongated electromagnetic structures with poloidal modulations. Such structures are principally related to drift-Alfvén waves. The analysis fully takes into account finite ion temperature effects and associated diamagnetic contributions to Reynolds stress. The turbulent generation of blobs has instability growth rates which scale similar to the zonal flow instabilities, γ ∼ 〈qmath〉, where q is a characteristic wave vector of large scale modes, and math is a characteristic amplitude of the velocity of turbulent fluctuations. This analysis is shown to be fully consistent with results of an earlier analysis by using the wave kinetic equation.
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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.Ra Plasma turbulence
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Kt Drift waves

Exact solutions for nonlinear propagation of slow ion acoustic monotonic double layers and a solitary hole in a semirelativistic plasma

O. H. El-Kalaawy and R. S. Ibrahim

Phys. Plasmas 15, 072303 (2008); http://dx.doi.org/10.1063/1.2956336 (5 pages) | Cited 6 times

Online Publication Date: 16 July 2008

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A small-amplitude slow ion acoustic monotonic double layer in an unmagnetized plasma consisting of relativistic drifting cold electrons and nonrelativistic drifting thermal ions is investigated. By using the reductive perturbation method, Schamel–Korteweg–de Vries (SKdV) and Schamel equations are derived. We used the linearization transformation to obtained the solutions of the SKdV and Schamel equations. The method is based upon a linearization principle that can be applied on nonlinearities which have a polynomial form. We illustrate the potential of the method by finding solutions of the SKdV and Schamel equations. Furthermore, we show that the monotonic double-layer solution is a nonlinear extension of the slow ion acoustic solitary hole having a negative trapping parameter in a semi relativistic plasma.
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52.27.Ny Relativistic plasmas
52.35.Sb Solitons; BGK modes
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.)
52.40.Kh Plasma sheaths

Compression of trapped positrons in a single particle regime by a rotating electric field

R. G. Greaves and J. M. Moxom

Phys. Plasmas 15, 072304 (2008); http://dx.doi.org/10.1063/1.2956335 (6 pages) | Cited 5 times

Online Publication Date: 18 July 2008

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Positrons confined in a cylindrical Penning trap are compressed radially by applying a rotating electric field. Previous experiments were conducted with large numbers of positrons in the plasma state. Compression of small numbers of positrons in the single particle regime is reported for the first time. For low values of applied rf amplitude, the compression occurs in a narrow band of frequencies centered on the axial bounce frequency. For larger amplitudes, the compression extends to a broad range of frequencies below the bounce frequency. Under certain conditions, very rapid compression can be obtained and central density doubling times of only a few milliseconds have been observed. Possible models for the effect are discussed. Potential application to the production of brightness enhanced positron beams is described.
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52.58.Qv Electrostatic and high-frequency confinement

The role of coherent vorticity in turbulent transport in resistive drift-wave turbulence

W. J. T. Bos, S. Futatani, S. Benkadda, M. Farge, and K. Schneider

Phys. Plasmas 15, 072305 (2008); http://dx.doi.org/10.1063/1.2956640 (6 pages) | Cited 8 times

Online Publication Date: 22 July 2008

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The coherent vortex extraction method, a wavelet technique for extracting coherent vortices out of turbulent flows, is applied to simulations of resistive drift-wave turbulence in magnetized plasma (Hasegawa–Wakatani system). The aim is to retain only the essential degrees of freedom, responsible for the transport. It is shown that the radial density flux is carried by these coherent modes. In the quasi-hydrodynamic regime, coherent vortices exhibit depletion of the polarization-drift nonlinearity and vorticity strongly dominates strain, in contrast to the quasiadiabatic regime.
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52.55.Fa Tokamaks, spherical tokamaks
52.35.Ra Plasma turbulence
52.25.Fi Transport properties

Localized dynamic subgrid closure for simulation of magnetohydrodynamic turbulence

Kenji Miki and Suresh Menon

Phys. Plasmas 15, 072306 (2008); http://dx.doi.org/10.1063/1.2947312 (15 pages) | Cited 1 time

Online Publication Date: 29 July 2008

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A local dynamic kinetic energy model (LDKM) for large-eddy simulation (LES) of magnetohydrodynamic (MHD) turbulence is proposed. The proposed MHD turbulence model evaluates all model coefficients locally and dynamically without any ad hoc averaging. This model also does not assume low magnetic Reynolds numbers. The turbulent residual-helicity effect (α-effect) appearing in the magnetic induction equation is successfully modeled. For validation, high-Re decaying isotropic decay turbulence with and without a mean magnetic field are studied using LES. The effect of rotation is also studied. For the case without rotation, it is observed that the energy spectrum follows a k−5/3 law. For the case with rotation, it is shown that two mechanisms, phase scrambling due to frame rotation and Joule dissipation, are competing, and two distinct regimes with respect to rotation rate are observed. There is a critical rotation rate at which the energy decays most in MHD turbulence. It is also shown that this MHD-LDKM model is applicable to wide variety of high/low magnetic Reynolds number applications.
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52.35.Ra Plasma turbulence

Two-dimensional dynamics of relativistic solitons in cold plasmas

G. Lehmann, E. W. Laedke, and K. H. Spatschek

Phys. Plasmas 15, 072307 (2008); http://dx.doi.org/10.1063/1.2963098 (7 pages) | Cited 8 times

Online Publication Date: 30 July 2008

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The two-dimensional dynamics of solitons appearing during relativistic laser-plasma interaction is investigated. The analysis starts from known soliton models in one space-dimension (1D). Some of the soliton solutions are already unstable in 1D, and all suffer from transverse instability in two dimensions (2D). The most unstable modes are calculated. They give a hint to the 2D structures which appear because of transversal effects. The linear stability considerations are supplemented by full 2D nonlinear simulations.
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52.35.Sb Solitons; BGK modes
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.38.-r Laser-plasma interactions
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