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Jun 2010

Volume 17, Issue 6, Articles (06xxxx)

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Phys. Plasmas 17, 062505 (2010); http://dx.doi.org/10.1063/1.3449301 (16 pages)

L. E. Sugiyama and H. R. Strauss
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Fundamental role of ion viscosity on fast magnetic reconnection in large-guide-field regimes

Andrei N. Simakov, L. Chacón, and A. Zocco

Phys. Plasmas 17, 060701 (2010); http://dx.doi.org/10.1063/1.3449589 (4 pages) | Cited 2 times

Online Publication Date: 10 June 2010

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Nonlinear analytical theory of magnetic reconnection with a large guide field is presented for the first time. We confirm that two distinct steady-state reconnection regimes are possible depending on the relative size of the diffusion region thickness δ versus the sound gyroradius ρs. The reconnection is slow (Sweet–Parker-like) for δ≳ρs, and fast otherwise. However, unlike earlier work, we find that ion viscosity μ plays a fundamental role in the fast regime. In particular, for δ<ρs we obtain δ∝Ha−1, with Ha∝1/math as the Hartmann number, and the reconnection rate Ez∝Pr−1/2, with Pr = μ/η as the Prandtl number and η as the resistivity. If the perpendicular ion viscosity is employed for μ, the reconnection rate becomes independent of plasma β and collision frequencies, and therefore potentially fast.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Fi Transport properties
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.20.-j Elementary processes in plasmas
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Rotation dependence of a phase delay between plasma edge electron density and temperature fields due to a fast rotating, resonant magnetic perturbation field

H. Stoschus, O. Schmitz, H. Frerichs, M. W. Jakubowski, B. Unterberg, S. S. Abdullaev, M. Clever, J. W. Coenen, U. Kruezi, D. Schega, and U. Samm

Phys. Plasmas 17, 060702 (2010); http://dx.doi.org/10.1063/1.3436614 (4 pages) | Cited 4 times

Online Publication Date: 15 June 2010

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Measurements of the plasma edge electron density ne and temperature Te fields during application of a fast rotating, resonant magnetic perturbation (RMP) field show a characteristic modulation of both, ne and Te coherent to the rotation frequency of the RMP field. A phase delay Φ between the ne(t) and Te(t) waveforms is observed and it is demonstrated that this phase delay Φ is a function of the radius with Φ(r) depending on the relative rotation of the RMP field and the toroidal plasma rotation. This provides for the first time direct experimental evidence for a rotation dependent damping of the external RMP field in the edge layer of a resistive high-temperature plasma which breaks down at low rotation and high resonant field amplitudes.
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28.52.−s
52.55.Fa Tokamaks, spherical tokamaks
52.55.Rk Power exhaust; divertors

Hall magnetohydrodynamic effects for current sheet flapping oscillations related to the magnetic double gradient mechanism

N. V. Erkaev, V. S. Semenov, and H. K. Biernat

Phys. Plasmas 17, 060703 (2010); http://dx.doi.org/10.1063/1.3439687 (4 pages) | Cited 1 time

Online Publication Date: 16 June 2010

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Hall magnetohydrodynamic model is investigated for current sheet flapping oscillations, which implies a gradient of the normal magnetic field component. For the initial undisturbed current sheet structure, the normal magnetic field component is assumed to have a weak linear variation. The profile of the electric current velocity is described by hyperbolic functions with a maximum at the center of the current sheet. In the framework of this model, eigenfrequencies are calculated as functions of the wave number for the “kink” and “sausage” flapping wave modes. Because of the Hall effects, the flapping eigenfrequency is larger for the waves propagating along the electric current, and it is smaller for the opposite wave propagation with respect to the current. The asymmetry of the flapping wave propagation, caused by Hall effects, is pronounced stronger for thinner current sheets. This is due to the Doppler effect related to the electric current velocity.
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94.30.ct Plasma sheet

Transport study of intense-laser-produced fast electrons in solid targets with a preplasma created by a long pulse laser

T. Yabuuchi, B. S. Paradkar, M. S. Wei, J. A. King, F. N. Beg, R. B. Stephens, N. Nakanii, M. Hatakeyama, H. Habara, K. Mima, K. A. Tanaka, and J. T. Larsen

Phys. Plasmas 17, 060704 (2010); http://dx.doi.org/10.1063/1.3447878 (4 pages) | Cited 5 times

Online Publication Date: 29 June 2010

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The effect of preplasma on fast electron generation and transport has been studied using an intense-laser pulse (I = 2×1018 W/cm2) at the Osaka University. An external long pulse laser beam (E<1.5 J) was used to create various levels of preplasmas in front of a planar target for a systematic study. Kα x-ray emission from a fluorescence layer (copper) was absolutely counted and its spatial distribution was monitored. Experimental data show Kα x-ray signal reduction (up to 60%) with an increase in the preplasma level. In addition, a ring structure of Kα x rays was observed with a large preplasma. The underlying physics of the ring structure production was studied by integrating the modeling using a radiation hydrodynamics code and a hybrid particle-in-cell code. Modeling shows that the ring structure is due to the thermoelectric magnetic field excited by the long pulse laser irradiation and an electrostatic field due to the fast electrons in the preplasma.
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52.25.Fi Transport properties
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.65.Rr Particle-in-cell method
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back to top Basic Plasma Phenomena, Waves, Instabilities

Instabilities of relativistic counterstreaming proton beams in the presence of a thermal electron background

A. Yalinewich and M. Gedalin

Phys. Plasmas 17, 062101 (2010); http://dx.doi.org/10.1063/1.3432722 (10 pages) | Cited 3 times

Online Publication Date: 4 June 2010

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A linear stability analysis is performed for two counterstreaming proton beams in the presence of a thermal electron background. Growth rates and polarization properties of unstable modes are calculated for various density ratios of the proton beams. It is found that in most cases, two unstable modes grow simultaneously: an electromagnetic filamentary mode that propagates perpendicular to the beam and an electrostatic mode that propagates parallel to the beam. The growth rates of the two modes are comparable, so that one expects that the instability would result in the development of a filamentary structure with a superimposed electrostatic pattern.
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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.Ny Relativistic plasmas
52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Collisionless magnetic reconnection in the presence of a sheared velocity field

M. Faganello, F. Pegoraro, F. Califano, and L. Marradi

Phys. Plasmas 17, 062102 (2010); http://dx.doi.org/10.1063/1.3430640 (7 pages)

Online Publication Date: 4 June 2010

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The linear theory of magnetic field lines reconnection in a two-dimensional configuration in the presence of a (Kelvin–Helmholtz stable) sheared velocity field is investigated within a single fluid model, where the onset of magnetic field line reconnection is made possible by the effect of electron inertia in the so called large Δ′ regime.
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52.35.Vd Magnetic reconnection
47.20.Ft Instability of shear flows (e.g., Kelvin-Helmholtz)

Effect of ion beam on the propagation of rarefactive solitons in multicomponent plasma with negative ions

H. Bailung, S. K. Sharma, and Y. Nakamura

Phys. Plasmas 17, 062103 (2010); http://dx.doi.org/10.1063/1.3432123 (6 pages)

Online Publication Date: 4 June 2010

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Propagation characteristics of rarefactive solitons excited in a multicomponent plasma with negative ions have been studied in the presence of a positive ion beam in a double plasma device. The Korteweg–de Vries equation for ion beam-multicomponent plasma system admits rarefactive (compressive) soliton solutions when the beam velocity is below (above) a critical value. An ion beam is found to enhance the amplitude of the rarefactive solitary waves. The Mach velocities and widths of the rarefactive solitons are measured for different beam velocities and compared with the theoretical results.
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52.35.Sb Solitons; BGK modes
52.40.Mj Particle beam interactions in plasmas
52.75.-d Plasma devices

Scaling laws of resistive magnetohydrodynamic reconnection in the high-Lundquist-number, plasmoid-unstable regime

Yi-Min Huang and A. Bhattacharjee

Phys. Plasmas 17, 062104 (2010); http://dx.doi.org/10.1063/1.3420208 (8 pages) | Cited 11 times

Online Publication Date: 10 June 2010

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The Sweet–Parker layer in a system that exceeds a critical value of the Lundquist number (S) is unstable to the plasmoid instability. In this paper, a numerical scaling study has been done with an island coalescing system driven by a low level of random noise. In the early stage, a primary Sweet–Parker layer forms between the two coalescing islands. The primary Sweet–Parker layer breaks into multiple plasmoids and even thinner current sheets through multiple levels of cascading if the Lundquist number is greater than a critical value Sc ≃ 4×104. As a result of the plasmoid instability, the system realizes a fast nonlinear reconnection rate that is nearly independent of S, and is only weakly dependent on the level of noise. The number of plasmoids in the linear regime is found to scales as S3/8, as predicted by an earlier asymptotic analysis [ N. F. Loureiro et al., Phys. Plasmas 14, 100703 (2007) ]. In the nonlinear regime, the number of plasmoids follows a steeper scaling, and is proportional to S. The thickness and length of current sheets are found to scale as S−1, and the local current densities of current sheets scale as S−1. Heuristic arguments are given in support of theses scaling relations.
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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.)
52.25.Fi Transport properties
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A saddle-node bifurcation model of magnetic reconnection onset

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

Phys. Plasmas 17, 062105 (2010); http://dx.doi.org/10.1063/1.3435269 (7 pages) | Cited 3 times

Online Publication Date: 11 June 2010

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It was recently shown that magnetic reconnection exhibits bistability, where the Sweet–Parker (collisional) and Hall (collisionless) reconnection solutions are both attainable for the same set of system parameters. Here, a dynamical model based on saddle-node bifurcations is presented which reproduces the slow to fast transition. It is argued that the properties of the dynamical model are a result of the Hall effect and the dispersive physics associated with it. Evidence from resistive two-fluid and Hall magnetohydrodynamics simulations are presented that show that the time evolution agrees with the dynamical model, the outflow speed is correlated with the dispersive physics due to the Hall effect, and bistability persists in the absence of electron inertia.
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52.65.Kj Magnetohydrodynamic and fluid equation
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Vd Magnetic reconnection

The effect of plasma flow on line-tied magnetohydrodynamic modes

Francesco Arcudi, Gian Luca Delzanno, and John M. Finn

Phys. Plasmas 17, 062106 (2010); http://dx.doi.org/10.1063/1.3418317 (14 pages) | Cited 2 times

Online Publication Date: 14 June 2010

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The linear stability of a linear pinch to kink modes with line-tying boundary conditions and equilibrium axial flow is studied. Numerical results in visco-resistive magnetohydrodynamics show that for long plasmas, in which the line-tying stabilization effect is weak, plasma flow is stabilizing. For shorter plasmas, near the length at which line-tying stabilizes the mode for zero flow, the flow can be destabilizing. A simple model using reduced ideal magnetohydrodynamics with a step-function current density and an even simpler one-dimensional sound wave model with equilibrium flow elucidate these effects. It is concluded that: (1) The stabilization in long plasmas is due to convective stabilization; (2) the destabilization for short plasmas can be explained using a picture involving the coupling of two stable waves, one propagating in the forward direction and one in the backward direction; and (3) strong magnetic shear suppresses the flow destabilization for short plasmas.
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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
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Tn Ideal and resistive MHD modes; kinetic modes

Kinetic Alfvén wave instability driven by electron temperature anisotropy in high-β plasmas

L. Chen and D. J. Wu

Phys. Plasmas 17, 062107 (2010); http://dx.doi.org/10.1063/1.3439680 (7 pages) | Cited 2 times

Online Publication Date: 16 June 2010

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Based on the kinetic dispersion equation in the low-frequency condition of ω<Ωi (the ion cyclotron frequency), the instability driven by the electron temperature anisotropy in high-β plasmas, which is associated with kinetic Alfvén waves in the wave vector range of k∥λI⪡1 and k⊥ρi⪡1 (where λI and ρi are the ion inertial length and gyroradius, respectively), is investigated. The results show that the structures of both the growth rate and the real frequency are different from those driven by the ion temperature anisotropy. The growth rate is larger than that driven by the ion anisotropy. The critical instability condition is modified dramatically, in which the electron driven growth rate does not vanish at the classical critical point and its deviation from zero increases with the kinetic effect due to the short-wavelength modification.
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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
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Plasma tubes becoming collimated as a result of magnetohydrodynamic pumping

Gunsu S. Yun and Paul M. Bellan

Phys. Plasmas 17, 062108 (2010); http://dx.doi.org/10.1063/1.3437075 (12 pages) | Cited 2 times

Online Publication Date: 17 June 2010

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Collimated magnetized plasma structures are commonly observed on galactic, stellar, and laboratory scales. The Caltech plasma gun produces magnetically driven plasma jets bearing a striking resemblance to astrophysical jets and solar coronal loops by imposing boundary conditions analogous to those plasmas. This paper presents experimental observations of gun-produced plasma jets that support a previously proposed magnetohydrodynamic (MHD) pumping model [ P. M. Bellan, Phys. Plasmas 10, 1999 (2003) ] as a universal collimation mechanism. For any initially flared, magnetized plasma tube with a finite axial current, the model predicts (i) magnetic pumping of plasma particles from a constricted region into a bulged region and (ii) tube collimation if the flow slows down at the bulged region leading to accumulation of mass and thus concentrating the azimuthal magnetic flux frozen in the mass flow (i.e., increasing the pinch force). Time- and space-resolved spectroscopic measurements of gun-produced plasmas have confirmed the highly dynamic nature of the process leading to a collimated state, namely, (i) suprathermal Alfvénic flow (30–50 km/s), (ii) large density amplification from ∼ 1017 to ∼ 1022 m−3 in an Alfvénic time scale (5–10 μs), and (iii) flow slowing down and mass accumulation at the flow front, the place where the tube collimation occurs according to high-speed camera imaging. These observations are consistent with the predictions of the MHD pumping model, and offer valuable insight into the formation mechanism of laboratory, solar, and astrophysical plasma structures.
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95.30.Qd Magnetohydrodynamics and plasmas
52.30.−q
52.72.+v Laboratory studies of space- and astrophysical-plasma processes
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

High frequency instability of a magnetized spherical electron sheath

R. L. Stenzel

Phys. Plasmas 17, 062109 (2010); http://dx.doi.org/10.1063/1.3437398 (10 pages)

Online Publication Date: 17 June 2010

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A positively biased spherical electrode in a magnetized plasma exhibits a ring of energetic electrons in the equatorial plane where the sheath electric field is normal to the magnetic field. High frequency waves are excited which propagate with the average E×B drift and form toroidal eigenmodes. Up to 20 harmonic eigenmodes are observed in the spectrum. Injected test waves are amplified. The drift wave can excite whistler modes. Electron inertia produces the instability.
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52.40.Kh Plasma sheaths
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
94.05.Jq Spacecraft sheaths, wakes, and charging

Nonstationary statistical theory for multipactor

S. Anza, C. Vicente, J. Gil, V. E. Boria, B. Gimeno, and D. Raboso

Phys. Plasmas 17, 062110 (2010); http://dx.doi.org/10.1063/1.3443128 (11 pages) | Cited 3 times

Online Publication Date: 28 June 2010

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This work presents a new and general approach to the real dynamics of the multipactor process: the nonstationary statistical multipactor theory. The nonstationary theory removes the stationarity assumption of the classical theory and, as a consequence, it is able to adequately model electron exponential growth as well as absorption processes, above and below the multipactor breakdown level. In addition, it considers both double-surface and single-surface interactions constituting a full framework for nonresonant polyphase multipactor analysis. This work formulates the new theory and validates it with numerical and experimental results with excellent agreement.
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52.20.Fs Electron collisions
52.40.Hf Plasma-material interactions; boundary layer effects
52.80.-s Electric discharges

Ionization instability of ion-acoustic waves

Sergey A. Khrapak and Gregor E. Morfill

Phys. Plasmas 17, 062111 (2010); http://dx.doi.org/10.1063/1.3447883 (4 pages)

Online Publication Date: 28 June 2010

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Stability of ion-acoustic waves in weakly ionized unmagnetized plasmas is investigated using fluid equations, assuming an arbitrary dependence of ion production and loss rates on electron and ion densities. The linear dispersion relation is derived and the condition for the positive growth rate is identified. Some examples corresponding to different plasma regimes are given to illustrate the application of the obtained results.
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52.35.−g
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.27.Lw Dusty or complex plasmas; plasma crystals

Is the Weibel instability enhanced by the suprathermal populations or not?

M. Lazar, R. Schlickeiser, and S. Poedts

Phys. Plasmas 17, 062112 (2010); http://dx.doi.org/10.1063/1.3446827 (5 pages) | Cited 4 times

Online Publication Date: 28 June 2010

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The kinetic instabilities of the Weibel type are presently invoked in a large variety of astrophysical scenarios because anisotropic plasma structures are ubiquitous in space. The Weibel instability is driven by a temperature anisotropy which is commonly modeled by a bi-axis distribution function, such as a bi-Maxwellian or a generalized bi-Kappa. Previous studies have been limited to a bi-Kappa distribution and found a suppression of this instability in the presence of suprathermal tails. In the present paper it is shown that the Weibel growth rate is rather more sensitive to the shape of the anisotropic distribution function. In order to illustrate the distinguishing properties of this instability a product-bi-Kappa distribution is introduced, with the advantage that this distribution function enables the use of different values of the spectral index in the two directions, κ∥ ≠ κ⊥. The growth rates and the instability threshold are derived and contrasted with those for a simple bi-Kappa and a bi-Maxwellian. Thus, while the maximum growth rates reached at the saturation are found to be higher, and the threshold is drastically reduced making the anisotropic product bi-Kappa (with small Kappas) highly susceptible to the Weibel instability. This effect could also raise questions on the temperature or the temperature anisotropy that seems to be not an exclusive source of free energy for this instability, and definition of these notions for such Kappa distributions must probably be reconsidered.
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52.25.Dg Plasma kinetic equations
52.27.Aj Single-component, electron-positive-ion plasmas
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
back to top Nonlinear Phenomena, Turbulence, Transport

Dipolar vortex formation in electromagnetic ion-temperature-gradient driven waves in a dust-contaminated magnetoplasma

Anisa Qamar, M. Yaqub Khan, Arshad M. Mirza, and Zulfiqar Ahmad

Phys. Plasmas 17, 062301 (2010); http://dx.doi.org/10.1063/1.3430631 (10 pages) | Cited 1 time

Online Publication Date: 11 June 2010

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We investigated linear and nonlinear properties of electromagnetic ion-temperature-gradient driven mode for a dissipative, nonuniform dust-contaminated electron-ion plasma with sheared ion flows. In the linear limit, a new dispersion relation has been derived and several interesting limiting cases are also discussed. On the other hand, in the nonlinear case, by ignoring dissipative effects, the nonlinear set of equations admits a dipolar vortex type solution. The results of the present investigation should be helpful to understand some linear as well as nonlinear properties of magnetically confined dust-contaminated tokamak edge plasmas.
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52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.We Plasma vorticity
52.40.Hf Plasma-material interactions; boundary layer effects
52.27.Lw Dusty or complex plasmas; plasma crystals
52.55.Fa Tokamaks, spherical tokamaks

Nonlinear acoustic waves in nonthermal dusty or pair plasmas

Frank Verheest

Phys. Plasmas 17, 062302 (2010); http://dx.doi.org/10.1063/1.3435275 (10 pages) | Cited 9 times

Online Publication Date: 14 June 2010

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Using a Sagdeev pseudopotential formalism where nonlinear structures are stationary in a comoving frame, large dust-acoustic solitary waves and double layers have been studied in plasmas with negative cold dust or heavier ions, in the presence of nonthermal electrons and protons/positrons. The existence domain of negative solitary waves is limited by infinite compression of the negative dust or heavy ion species, that of positive solitary waves by the occurrence of positive double layers. These double layers require a sufficient degree of nonthermality of the hot species. There are parameter ranges where both negative and positive solitary structures can occur; sometimes both of the solitary wave type or sometimes one solitary wave and the other a double layer. Great emphasis is placed on the determination of the existence domains in compositional parameter space, with the help of strong analytical results, before typical Sagdeev pseudopotentials and solitary wave profiles are presented. Subject to simple adjustments, these results apply equally to a conjugate plasma model of positive dust or heavy ions, together with nonthermal electrons and protons/positrons.
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52.27.Ep Electron-positron plasmas
52.27.Lw Dusty or complex plasmas; plasma crystals
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.)
52.35.Sb Solitons; BGK modes

Linear and nonlinear quantum ion acoustic waves in a plasma with positive, negative ions and Fermi electron gas

Saeed-ur-Rehman

Phys. Plasmas 17, 062303 (2010); http://dx.doi.org/10.1063/1.3431633 (5 pages) | Cited 4 times

Online Publication Date: 15 June 2010

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Linear and nonlinear propagations of quantum ion acoustic waves in positive, negative ions and electron plasma have been vetted via the dispersion relation and Korteweg–de Vries equation, where the ions are inertial and electrons are inertialess. The quantum mechanical effects arising due to the quantum diffraction and Fermi–Dirac statistics for this system are taken into account. The existence, as well as the type (compressive/rarefactive) of solitary wave propagating in the system, is strongly dependent on the numerical value of dimensionless quantum parameter He. It is observed that negative ion population and ion mass ratio have emphatic influence on the phase velocity of ion acoustic wave and the propagation of localized coherent solitary structures at quantum scale in the system.
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52.35.Dm Sound waves
05.30.Fk Fermion systems and electron gas
52.35.Sb Solitons; BGK modes

Nonlinear Langmuir structures: Soliton and shock in a rotating weakly relativistic electron-positron magnetoplasma with stationary positive ions

S. K. El-Labany, W. M. Moslem, and E. I. El-Awady

Phys. Plasmas 17, 062304 (2010); http://dx.doi.org/10.1063/1.3439683 (8 pages) | Cited 1 time

Online Publication Date: 16 June 2010

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Theoretical and numerical studies are performed for nonlinear Langmuir structures (soliton and shock) in a rotating weakly relativistic electron-positron magnetoplasma with background stationary positive ions. For this purpose, the reductive perturbation technique is employed to the weakly relativistic hydrodynamical electrons/positrons fluid equations and Poisson equation, obtaining extended Zakharov–Kuznetsov equation. The latter has been solved analytically. The features of the nonlinear excitations and their propagation conditions are investigated numerically. Our finding could elucidate the nonlinear electrostatic structures that propagate in astrophysical plasma situations where rotating, magnetized plasma can exist; such as polar cups region of pulsars, around active galactic nuclei, neutron stars, and white dwarfs.
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52.35.Sb Solitons; BGK modes
52.35.Tc Shock waves and discontinuities
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.27.Ny Relativistic plasmas

Effects of time-varying E×B flow on slab ion-temperature-gradient turbulence

S. Maeyama, A. Ishizawa, T.-H. Watanabe, M. M. Škorić, N. Nakajima, S. Tsuji-Iio, and H. Tsutsui

Phys. Plasmas 17, 062305 (2010); http://dx.doi.org/10.1063/1.3432121 (9 pages) | Cited 1 time

Online Publication Date: 17 June 2010

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Effects of time-varying sheared E×B flow on turbulence driven by slab ion temperature gradient instabilities are investigated by means of Landau fluid simulation. Here, the E×B flow, which consists of stationary and time-periodic oscillatory parts, is externally imposed to the turbulence. The dependence on the amplitude and frequency of E×B flow is examined in the case that the amplitude of oscillatory part is the same or less than that of stationary part. The ion heat transport caused by turbulence oscillates with the same period as the E×B flow and the time-averaged transport coefficient is larger than the coefficient which is evaluated without the oscillatory part. The time-averaged coefficient is maximized when the amplitude of oscillatory part is equal to that of stationary part. As the frequency of E×B flow increases, the time-averaged coefficient decreases and is close to the coefficient which is evaluated without the oscillatory part. This mechanism is explained by introducing a kind of the logistic equation which describes the time evolution of transport coefficient as a response of turbulence to the amplitude of E×B flow.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Ra Plasma turbulence
52.65.Kj Magnetohydrodynamic and fluid equation

Ion temperature gradient driven transport in tokamaks with square shaping

N. Joiner and W. Dorland

Phys. Plasmas 17, 062306 (2010); http://dx.doi.org/10.1063/1.3432120 (6 pages)

Online Publication Date: 18 June 2010

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Advanced tokamak schemes which may offer significant improvement to plasma confinement on the usual large aspect ratio Dee-shaped flux surface configuration are of great interest to the fusion community. One possibility is to introduce square shaping to the flux surfaces. The gyrokinetic code GS2 [ Kotschenreuther et al., Comput. Phys. Commun. 88, 128 (1996) ] is used to study linear stability and the resulting nonlinear thermal transport of the ion temperature gradient driven (ITG) mode in tokamak equilibria with square shaping. The maximum linear growth rate of ITG modes is increased by negative squareness (diamond shaping) and reduced by positive values (square shaping). The dependence of thermal transport produced by saturated ITG instabilities on squareness is not as clear. The overall trend follows that of the linear instability, heat and particle fluxes increase with negative squareness and decrease with positive squareness. This is contradictory to recent experimental results [ Holcomb et al., Phys. Plasmas 16, 056116 (2009) ] which show a reduction in transport with negative squareness. This may be reconciled as a reduction in transport (consistent with the experiment) is observed at small negative values of the squareness parameter.
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52.25.Fi Transport properties
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.55.-s Magnetic confinement and equilibrium
52.55.Fa Tokamaks, spherical tokamaks

Transport properties of finite-β microturbulence

M. J. Pueschel and F. Jenko

Phys. Plasmas 17, 062307 (2010); http://dx.doi.org/10.1063/1.3435280 (10 pages) | Cited 5 times

Online Publication Date: 22 June 2010

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Via nonlinear gyrokinetic simulations, microturbulent transport is investigated for electromagnetic trapped electron mode (TEM) and ion temperature gradient (ITG) tokamak core turbulence with β up to and beyond the kinetic ballooning mode threshold. Deviations from linear expectations are explained by zonal flow activity in the TEM case. For the ITG scenario, β-induced changes are observed in the nonlinear critical gradient upshift—from a certain β, a strong increase is observed in the Dimits shift. Additionally, a Rechester–Rosenbluth-type model for magnetic transport is applied, and the amplitudes of magnetic field fluctuations are quantified for different types of turbulence.
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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
52.55.Fa Tokamaks, spherical tokamaks
52.55.Tn Ideal and resistive MHD modes; kinetic modes
52.65.Kj Magnetohydrodynamic and fluid equation

A gyrofluid description of Alfvénic turbulence and its parallel electric field

N. H. Bian and E. P. Kontar

Phys. Plasmas 17, 062308 (2010); http://dx.doi.org/10.1063/1.3439682 (5 pages) | Cited 2 times

Online Publication Date: 28 June 2010

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Anisotropic Alfvénic fluctuations with k∥/k⊥⪡1 remain at frequencies much smaller than the ion cyclotron frequency in the presence of a strong background magnetic field. Based on the simplest truncation of the electromagnetic gyrofluid equations in a homogeneous plasma, a model for the energy cascade produced by Alfvénic turbulence is constructed, which smoothly connects the large magnetohydrodynamics scales and the small “kinetic” scales. Scaling relations are obtained for the electromagnetic fluctuations, as a function of k⊥ and k∥. Moreover, a particular attention is paid to the spectral structure of the parallel electric field which is produced by Alfvénic turbulence. The reason is the potential implication of this parallel electric field in turbulent acceleration and transport of particles. For electromagnetic turbulence, this issue was raised some time ago in Hasegawa and Mima [J. Geophys. Res. 83, 1117 (1978)] .
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Ra Plasma turbulence
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.Tt Gyrofluid and gyrokinetic simulations
52.25.Fi Transport properties
52.25.Gj Fluctuation and chaos phenomena
back to top Magnetically Confined Plasmas, Heating, Confinement

Impurity transport driven by ion temperature gradient turbulence in tokamak plasmas

T. Fülöp, S. Braun, and I. Pusztai

Phys. Plasmas 17, 062501 (2010); http://dx.doi.org/10.1063/1.3430639 (9 pages) | Cited 4 times

Online Publication Date: 8 June 2010

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Impurity transport driven by electrostatic turbulence is analyzed in weakly collisional tokamak plasmas using a semianalytical model based on a boundary layer solution of the gyrokinetic equation. Analytical expressions for the perturbed density responses are derived and used to determine the stability boundaries and the quasilinear particle fluxes. For moderate impurity charge number Z, the stability boundaries are very weakly affected by the increasing impurity charge for constant effective charge, while for lower impurity charge the influence of impurities is larger, if the amount of impurities is not too small. Scalings of the mode frequencies and quasilinear fluxes with charge number, effective charge, impurity density scale length, and collisionality are determined and compared to quasilinear gyrokinetic simulations with GYRO [ J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003) ] resulting in very good agreement. Collisions do not affect the mode frequencies, growth rates, and impurity fluxes significantly. The eigenfrequencies and growth rates depend only weakly on Z and Zeff but they are sensitive to the impurity density gradient scale length. An analytical approximate expression of the zero-flux impurity density gradient is derived and used to discuss its parametric dependencies.
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52.25.Vy Impurities in plasmas
52.35.Ra Plasma turbulence
52.40.Hf Plasma-material interactions; boundary layer effects
52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties
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