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Feb 2013

Volume 20, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Phys. Plasmas 20, 022303 (2013); http://dx.doi.org/10.1063/1.4790639 (12 pages)

Julio J. Martinell and Diego del-Castillo-Negrete
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back to top Basic Plasma Phenomena, Waves, Instabilities

Ion temperature gradient instability at sub-Larmor radius scales with non-zero ballooning angle

P. Migliano, Y. Camenen, F. J. Casson, W. A. Hornsby, and A. G. Peeters

Phys. Plasmas 20, 022101 (2013); http://dx.doi.org/10.1063/1.4789856 (6 pages) | Cited 1 time

Online Publication Date: 1 February 2013

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Linear gyro-kinetic stability calculations predict unstable toroidal ion temperature gradient modes (ITGs) with normalised poloidal wave vectors well above one (kθρi>1) for standard tokamak parameters with adiabatic electron response. These modes have a maximum amplitude at a poloidal angle θ that is shifted away from the low field side (θ ≠ 0). The physical mechanism is clarified through the use of a fluid model. It is shown that the shift of the mode away from the low field side reduces the effective drift frequency which allows for the instability to develop. Numerical tests using the gyro-kinetic model confirm this physical mechanism. Furthermore, it is shown that modes localized away from the low field side can be important also for kθρi<1 close to the threshold of the ITG. In fact, modes with maximum amplitude at θ ≠ 0 can exist for normalised temperature gradient lengths below the threshold of the ITG obtained for the case with the maximum at θ = 0.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Fa Tokamaks, spherical tokamaks
02.60.-x Numerical approximation and analysis
52.25.Fi Transport properties
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)

Wakefields generated by collisional neutrinos in neutral-electron-positron plasma

Nouara Tinakiche

Phys. Plasmas 20, 022102 (2013); http://dx.doi.org/10.1063/1.4789862 (4 pages)

Online Publication Date: 1 February 2013

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A classical fluid description is adopted to investigate nonlinear interaction between an electron-type neutrino beam and a relativistic collisionless unmagnetized neutral-electron-positron plasma. In this work, we consider the collisions of the neutrinos with neutrals in the plasma and study their effect on the generation of wakefields in this plasma.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.27.Ny Relativistic plasmas

General formulation for magnetohydrodynamic wave propagation, fire-hose, and mirror instabilities in Harris-type current sheets

L.-N. Hau and Y.-T. Lai

Phys. Plasmas 20, 022103 (2013); http://dx.doi.org/10.1063/1.4789383 (6 pages)

Online Publication Date: 5 February 2013

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Harris-type current sheets with the magnetic field model of math = Bx(z)math+By(z)math have many important applications to space, astrophysical, and laboratory plasmas for which the temperature or pressure usually exhibits the gyrotropic form of math = p∥mathmath+p⊥(math−mathmath). Here, p∥ and p⊥ are, respectively, to be the pressure component along and perpendicular to the local magnetic field, math = math/B. This study presents the general formulation for magnetohydrodynamic (MHD) wave propagation, fire-hose, and mirror instabilities in general Harris-type current sheets. The wave equations are expressed in terms of the four MHD characteristic speeds of fast, intermediate, slow, and cusp waves, and in the local (k∥,k⊥,z) coordinates. Here, k∥ and k⊥ are, respectively, to be the wave vector along and perpendicular to the local magnetic field. The parameter regimes for the existence of discrete and resonant modes are identified, which may become unstable at the local fire-hose and mirror instability thresholds. Numerical solutions for discrete eigenmodes are shown for stable and unstable cases. The results have important implications for the anomalous heating and stability of thin current sheets.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
95.30.Qd Magnetohydrodynamics and plasmas
02.10.Ud Linear algebra
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.25.Fi Transport properties

Investigation of charge transfer and ionization in He-like systems (Li+, Be2+, B3+, C4+, N5+, O6+)-hydrogen atom collisions in Debye plasmas

M. K. Pandey, Y.-C. Lin, and Y. K. Ho

Phys. Plasmas 20, 022104 (2013); http://dx.doi.org/10.1063/1.4790663 (13 pages)

Online Publication Date: 8 February 2013

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The charge transfer and ionization cross sections have been calculated for He-like system (Li+, Be2+, B3+, C4+, N5+, O6+) and hydrogen atom collisions in Debye plasmas for energies ranging from 1 to 500 keV using the classical trajectory Monte Carlo method. Interactions of the active electrons with the projectile ions have been described by model potentials. Cross sections are determined in both screening and unscreening environments, and a comparative study between both environments has been carried out. In particular, an interesting feature of sudden increase in the ionization cross sections at lower velocities is also observed in all the systems like pandey et al. [M. K. Pandey et al., Phys. Plasmas 19, 062104 (2012)] calculations for O8+ + H collision. The feature of sudden increase in ionization cross sections at lower velocities and the effect of plasmas condition on it are explained in terms of the classical trajectory framework. We have found the cross sections for both capture and ionization are dependence on Debye screening lengths throughout the collision energies range, but are particularly pronounced at low projectile collisions energies. The calculated cross sections for the unscreened case are found in reasonable agreement with available experimental and theoretical results.
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52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Jm Ionization of plasmas
52.65.Pp Monte Carlo methods
02.50.Ng Distribution theory and Monte Carlo studies
FREE

Representation of ideal magnetohydrodynamic modes

R. B. White

Phys. Plasmas 20, 022105 (2013); http://dx.doi.org/10.1063/1.4791661 (4 pages) | Cited 1 time

Online Publication Date: 8 February 2013

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One of the most fundamental properties of ideal magnetohydrodynamics is the condition that plasma motion cannot change magnetic topology. The conventional representation of ideal magnetohydrodynamic modes by perturbing a toroidal equilibrium field through δmath = ∇×(math×math) ensures that δmath·∇ψ = 0 at a resonance, with ψ labelling an equilibrium flux surface. Also useful for the analysis of guiding center orbits in a perturbed field is the representation δmath = ∇×αmath. These two representations are equivalent, but the vanishing of δmath·∇ψ at a resonance is necessary but not sufficient for the preservation of field line topology, and a indiscriminate use of either perturbation in fact destroys the original equilibrium flux topology. It is necessary to find the perturbed field to all orders in math to conserve the original topology. The effect of using linearized perturbations on stability and growth rate calculations is discussed.
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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.)

Propagation and dispersion of whistler waves generated by fast reconnection onset

Nagendra Singh

Phys. Plasmas 20, 022106 (2013); http://dx.doi.org/10.1063/1.4791650 (9 pages)

Online Publication Date: 13 February 2013

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The role of whistler mode during the onset of magnetic reconnection (MR) has been widely suggested, but the manifestations of its highly dispersive and anisotropic propagation properties in reconnection events remain largely unclear. Comparing results from a recently developed theoretical model for reconnection in terms of whistler's dispersive behavior with those reported from laboratory experiments on fast spontaneous magnetic reconnection, we demonstrate that the onset of fast reconnection in electron current layers (ECLs) emits whistler wave packets. The time scale of the explosively fast reconnection events are inversely related to the whistler mode frequencies at the lower end of the whistler frequency band. The wave packets in this frequency band have a characteristic angular dispersion, which marks the initial opening of the reconnection exhaust angle. The multidimensional propagation of the whistler for the reconnection with a strong guide magnetic field is investigated, showing that the measured propagation velocities of the reconnection electric field along the guide field in the Versatile Toroidal Facility at MIT quantitatively compare with the group velocities of the whistler wave packets. The whistler mode dispersive properties measured in laboratory experiments without a guide magnetic field in the magnetic reconnection experiments at Princeton also compare well with the theoretically predicted dispersion of the wave packets depending on the ECL width. Fast normalized reconnection rates extending to ∼0.35 at the MR onset in thin ECLs imply whistler wave propagation away from the onset location. We also present evidences for the whistler wave packets being emitted from reconnection diffusion region as seen in simulations and satellite observations.
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52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.35.Vd Magnetic reconnection
52.65.-y Plasma simulation
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Shukla-Nambu-Salimullah potential with multi electron species in magnetoplasmas

Arroj A. Khan, M. Jamil, A. Rasheed, and G. Murtaza

Phys. Plasmas 20, 022107 (2013); http://dx.doi.org/10.1063/1.4792162 (5 pages)

Online Publication Date: 14 February 2013

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The phenomenon of shielding of test charge in the presence of an external magnetic field (Shukla-Nambu-Salimullah potential) is investigated in electron ion plasmas using the approach of two temperature electrons. The modified dispersion relations of ion acoustic waves under different conditions are derived. We get different profiles of potential for different parameters and observe that the potentials fall very slowly than the standard Shukla-Nambu-Salimullah potential given in the reference.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
02.10.-v Logic, set theory, and algebra
52.25.-b Plasma properties

Aspects of linear Landau damping in discretized systems

Vasil Bratanov, Frank Jenko, David Hatch, and Stephan Brunner

Phys. Plasmas 20, 022108 (2013); http://dx.doi.org/10.1063/1.4792163 (11 pages)

Online Publication Date: 14 February 2013

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Basic linear eigenmode spectra for electrostatic Langmuir waves and drift-kinetic slab ion temperature gradient modes are examined in a series of scenarios. Collisions are modeled via a Lenard-Bernstein collision operator which fundamentally alters the linear spectrum even for infinitesimal collisionality [Ng et al., Phys. Rev. Lett. 83, 1974 (1999)]. A comparison between different discretization schemes reveals that a Hermite representation is superior for accurately resolving the spectra compared to a finite differences scheme using an equidistant velocity grid. Additionally, it is shown analytically that any even power of velocity space hyperdiffusion also produces a Case-Van Kampen spectrum which, in the limit of zero hyperdiffusivity, matches the collisionless Landau solutions.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Kt Drift waves
52.25.Dg Plasma kinetic equations
52.25.Fi Transport properties

Renormalized dynamic charge shielding on the electron-atom collision: Eikonal analysis

Young-Dae Jung and Woo-Pyo Hong

Phys. Plasmas 20, 022109 (2013); http://dx.doi.org/10.1063/1.4792248 (6 pages)

Online Publication Date: 14 February 2013

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The influence of the dynamic renormalization plasma shielding on the electron-atom collision is investigated in a dense strongly coupled electron system. The semiclassical eikonal method and effective interaction potential are employed to obtain the eikonal scattering phase shift and eikonal collision cross section as functions of the Debye length, impact parameter, projectile energy, and thermal energy. It is found that the renormalized dynamic charge shielding effect enhances the eikonal collision cross section. The variation of the dynamic renormalization shielding on the electron-atom collision is also discussed.
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52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.20.Fs Electron collisions
52.25.Fi Transport properties
02.30.Jr Partial differential equations

Kinetic models of two-dimensional plane and axially symmetric current sheets: Group theory approach

I. Y. Vasko, A. V. Artemyev, V. Y. Popov, and H. V. Malova

Phys. Plasmas 20, 022110 (2013); http://dx.doi.org/10.1063/1.4792263 (9 pages) | Cited 1 time

Online Publication Date: 15 February 2013

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In this paper, we present new class of solutions of Grad-Shafranov-like (GS-like) equations, describing kinetic plane and axially symmetric 2D current sheets. We show that these equations admit symmetry groups only for Maxwellian and κ-distributions of charged particles. The admissible symmetry groups are used to reduce GS-like equations to ordinary differential equations for invariant solutions. We derive asymptotes of invariant solutions, while invariant solutions are found analytically for the κ-distribution with κ = 7/2. We discuss the difference of obtained solutions from equilibria widely used in other studies. We show that κ regulates the decrease rate of plasma characteristics along the current sheet and determines the spatial distribution of magnetic field components. The presented class of plane and axially symmetric (disk-like) current sheets includes solutions with the inclined neutral plane.
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52.25.Fi Transport properties
02.20.-a Group theory
02.30.Hq Ordinary differential equations

Bifurcations of dust ion acoustic travelling waves in a magnetized dusty plasma with a q-nonextensive electron velocity distribution

Utpal Kumar Samanta, Asit Saha, and Prasanta Chatterjee

Phys. Plasmas 20, 022111 (2013); http://dx.doi.org/10.1063/1.4791660 (5 pages) | Cited 1 time

Online Publication Date: 20 February 2013

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Nonlinear ion acoustic waves in the magnetized dusty plasma in the presence of superthermal electron have been studied. We have used the reductive perturbation method to derive a Kadomtsev-Petviashili equation for dust ion acoustic waves in a magnetized dusty plasma with q-nonextensive velocity distributed electrons. By applying the bifurcation theory of planar dynamical systems to this equation, the existence of solitary wave solutions and periodic travelling wave solutions is proved. Two exact solutions of the above waves are obtained.
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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
52.25.Xz Magnetized plasmas
52.27.Lw Dusty or complex plasmas; plasma crystals

Generalized shock conditions and the contact discontinuity in the Hall-magnetohydrodynamics model

Eliezer Hameiri

Phys. Plasmas 20, 022112 (2013); http://dx.doi.org/10.1063/1.4792258 (20 pages)

Online Publication Date: 20 February 2013

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It is shown that shocks and contact discontinuities in the Hall-magnetohydrodynamics (HMHD) model must satisfy solvability conditions that replace some of the familiar Rankine-Hugoniot jump conditions when the latter do not apply due to singular behavior of fluxes of conserved quantities. Some of these conditions depend on the larger topology of the plasma and magnetic field and are not merely “local.” The contact discontinuity which separates two adjoining plasma regions or plasma and vacuum regions is the simplest case where the new jump conditions are applicable and is discussed for a toroidal plasma with sheared magnetic field such as the tokamak, but with no initial mass flow. It is proven that a static discontinuous tokamak-like equilibrium is linearly stable in the HMHD model if it is linearly stable within the ideal magnetohydrodynamics model, provided that the electron pressure depends only on the density, and some other restrictions on the ratio of pressure to density gradients also apply. When the electron pressure does depend on two thermodynamic variables, a sufficient condition for Hall-MHD plasma stability is derived as well.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Tc Shock waves and discontinuities
52.55.Fa Tokamaks, spherical tokamaks

Electrostatic “bounce” instability in a magnetotail configuration

G. Fruit, P. Louarn, and A. Tur

Phys. Plasmas 20, 022113 (2013); http://dx.doi.org/10.1063/1.4793442 (11 pages)

Online Publication Date: 21 February 2013

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To understand the possible destabilization of two-dimensional current sheets, a kinetic model is proposed to describe the resonant interaction between electrostatic modes and trapped particles that bounce within the sheet. This work follows the initial investigation by Tur et al. [Phys. Plasmas 17, 102905 (2010)] that is revised and extended. Using a quasi-parabolic equilibrium state, the linearized gyro-kinetic Vlasov equation is solved for electrostatic fluctuations with period of the order of the electron bounce period. Using an appropriated Fourier expansion of the particle motion along the magnetic field, the complete time integration of the non-local perturbed distribution functions is performed. The dispersion relation for electrostatic modes is then obtained through the quasineutrality condition. It is found that strongly unstable electrostatic modes may develop provided that the current sheet is moderately stretched and, more important, that the proportion of passing particle remains small (less than typically 10%). This strong but finely tuned instability may offer opportunities to explain features of magnetospheric substorms.
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94.30.cl Magnetotail
94.30.cs Plasma motion; plasma convection
94.30.Lr Magnetic storms, substorms
52.25.Fi Transport properties
52.25.Gj Fluctuation and chaos phenomena
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)

Eigenmode characteristics of the double tearing mode in the presence of shear flows

Aohua Mao, Jiquan Li, Y. Kishimoto, and Jinyuan Liu

Phys. Plasmas 20, 022114 (2013); http://dx.doi.org/10.1063/1.4793445 (11 pages)

Online Publication Date: 21 February 2013

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The double tearing mode (DTM) is characterized by two eigen states with antisymmetric or symmetric magnetic island structure, referred to as the even or odd DTM. In this work, we systematically revisit the DTM instabilities in the presence of an antisymmetric shear flow with a focus on eigenmode characteristics as well as the stabilization or destabilization mechanism in a wide parameter region. Both initial value simulation and eigenvalue analysis are performed based on reduced resistive MHD model in slab geometry. A degenerated eigen state is found at a critical flow amplitude vc. The even (or odd) DTM is stabilized (or destabilized) by weak shear flow below vc through the distortion of magnetic islands mainly due to the global effect of shear flow rather than the local flow shear. The distortion can be quantified by the phase angles of the perturbed flux, showing a perfect correspondence to the growth rates. As the shear flow increases above vc, the degenerated eigen state bifurcates into two eigen modes with the same growth rate but opposite propagating direction, resulting in an oscillatory growth of fluctuation energy. It is identified that two eigen modes show the single tearing mode structure due to the Alfvén resonance (AR) occurring on one current sheet. Most importantly, the AR can destabilize the DTMs through enhancing the plasma flow exerting on the remaining island. Meanwhile, the local flow shear plays a remarkable stabilizing role in this region. In addition, the eigenmode characteristic of the electromagnetic Kelvin-Helmholtz instability is also discussed.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.65.Kj Magnetohydrodynamic and fluid equation
02.10.Ud Linear algebra
52.25.Gj Fluctuation and chaos phenomena
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)

Large amplitude solitary waves in a warm magnetoplasma with kappa distributed electrons

S. A. El-Tantawy, N. A. El-Bedwehy, H. N. Abd El-Razek, and S. Mahmood

Phys. Plasmas 20, 022115 (2013); http://dx.doi.org/10.1063/1.4793446 (5 pages)

Online Publication Date: 21 February 2013

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The large amplitude nonlinear ion acoustic solitary wave propagating obliquely to an external magnetic field in a magnetized plasma with kappa distributed electrons and warm ions is investigated through deriving energy-balance-like expression involving a Sagdeev potential. Analytical and numerical calculations of the values of Mach number reveal that both of subsonic and supersonic electrostatic solitary structures can exist in this system. The influence on the soliton characteristics of relevant physical parameters such as the Mach number, the superthermal parameter, the directional cosine, the ratio of ion-to-electron temperature, and the ion gyrofrequency has been investigated.
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52.35.Sb Solitons; BGK modes
94.20.Fg Plasma temperature and density
52.25.Kn Thermodynamics of plasmas
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
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.)

High-frequency electromagnetic surface waves in a semi-bounded weakly ionized plasma

M. Moaied, Yu. Tyshetskiy, and S. V. Vladimirov

Phys. Plasmas 20, 022116 (2013); http://dx.doi.org/10.1063/1.4793456 (9 pages)

Online Publication Date: 26 February 2013

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High-frequency electromagnetic surface waves (SWs) in a weakly ionized plasma half-space with Maxwellian electrons are studied taking into account elastic electron-neutral collisions. The SWs spectrum and damping rate are obtained numerically for a wide range of wavelengths, and the asymptotes of damping rate are analytically calculated in some limits. It is shown that the high-frequency SWs become strongly damped at wavelengths λ<λMin, where λMin significantly depends on plasma parameters (e.g., electron temperature and electron and neutral atom density). The relative importance of collisional and Cherenkov (collisionless) damping of SWs is investigated and is graphically shown for a range of plasma parameters and SW wavelengths. The behavior of weakly ionized plasma with respect to the SW propagation has been recovered for the collisional parameter η.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
02.60.-x Numerical approximation and analysis
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Jm Ionization of plasmas
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
FREE

Rotating copper plasmoid in external magnetic field

Pramod K. Pandey and Raj K. Thareja

Phys. Plasmas 20, 022117 (2013); http://dx.doi.org/10.1063/1.4793729 (8 pages)

Online Publication Date: 28 February 2013

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Effect of nonuniform magnetic field on the expanding copper plasmoid in helium and argon gases using optical emission spectroscopy and fast imaging is presented. We report a peculiar oscillatory rotation of plasmoid in magnetic field and argon ambient. The temporal variation and appearance of the dip in the electron temperature show a direct evidence of the threading and expulsion of the magnetic field lines from the plasmoid. Rayleigh Taylor instability produced at the interface separating magnetic field and plasma is discussed.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
back to top Nonlinear Phenomena, Turbulence, Transport

Study of nonlinear oscillations in a glow discharge plasma using empirical mode decomposition and Hilbert Huang transform

A. M. Wharton, A. N. Sekar Iyengar, and M. S. Janaki

Phys. Plasmas 20, 022301 (2013); http://dx.doi.org/10.1063/1.4789853 (8 pages)

Online Publication Date: 1 February 2013

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Hilbert Huang transform (HHT) based time series analysis was carried out on nonlinear floating potential fluctuations obtained from hollow cathode glow discharge plasma in the presence of anode glow. HHT was used to obtain contour plots and the presence of nonlinearity was studied. Frequency shift with time, which is a typical nonlinear behaviour, was detected from the contour plots. Various plasma parameters were measured and the concepts of correlation coefficients and the physical contribution of each intrinsic mode function have been discussed. Physically important quantities such as instantaneous energy and their uses in studying physical phenomena such as intermittency and non-stationary data have also been discussed.
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52.80.Hc Glow; corona
02.30.Uu Integral transforms
52.25.Gj Fluctuation and chaos phenomena
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.)

On numerical turbulence generation for test-particle simulations

R. C. Tautz and A. Dosch

Phys. Plasmas 20, 022302 (2013); http://dx.doi.org/10.1063/1.4789861 (8 pages)

Online Publication Date: 4 February 2013

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A modified method is presented to generate artificial magnetic turbulence that is used for test-particle simulations. Such turbulent fields are obtained from the superposition of a set of wave modes with random polarizations and random directions of propagation. First, it is shown that the new method simultaneously fulfils requirements of isotropy, equal mean amplitude and variance for all field components, and vanishing divergence. Second, the number of wave modes required for a stochastic particle behavior is investigated by using a Lyapunov approach. For the special case of slab turbulence, it is shown that already for 16 wave modes the particle behavior agrees with that shown for considerably larger numbers of wave modes.
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52.35.Ra Plasma turbulence
52.65.-y Plasma simulation
02.30.Yy Control theory
02.50.Ey Stochastic processes
02.60.-x Numerical approximation and analysis
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Gyroaverage effects on chaotic transport by drift waves in zonal flows

Julio J. Martinell and Diego del-Castillo-Negrete

Phys. Plasmas 20, 022303 (2013); http://dx.doi.org/10.1063/1.4790639 (12 pages)

Online Publication Date: 8 February 2013

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Finite Larmor radius (FLR) effects on E × B test particle chaotic transport in the presence of zonal flows is studied. The FLR effects are introduced by the gyro-average of a simplified E × B guiding center model consisting of the linear superposition of a non-monotonic zonal flow and drift waves. Non-monotonic zonal flows play a critical role on transport because they exhibit robust barriers to chaotic transport in the region(s) where the shear vanishes. In addition, the non-monotonicity gives rise to nontrivial changes in the topology of the orbits of the E × B Hamiltonian due to separatrix reconnection. The present study focuses on the role of FLR effects on these two signatures of non-monotonic zonal flows: shearless transport barriers and separatrix reconnection. It is shown that, as the Larmor radius increases, the effective zonal flow profile bifurcates and multiple shearless regions are created. As a result, the topology of the gyro-averaged Hamiltonian exhibits very complex separatrix reconnection bifurcations. It is also shown that FLR effects tend to reduce chaotic transport. In particular, the restoration of destroyed transport barriers is observed as the Larmor radius increases. A detailed numerical study is presented on the onset of global chaotic transport as function of the amplitude of the drift waves and the Larmor radius. For a given amplitude, the threshold for the destruction of the shearless transport barrier, as function of the Larmor radius, exhibits a fractal-like structure. The FLR effects on a thermal distribution of test particles are also studied. In particular, the fraction of confined particles with a Maxwellian distribution of gyroradii is computed, and an effective transport suppression is found for high enough temperatures.
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52.35.Kt Drift waves
52.35.Vd Magnetic reconnection
02.60.-x Numerical approximation and analysis
52.25.Fi Transport properties
52.25.Gj Fluctuation and chaos phenomena
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Ion-acoustic K-dV and mK-dV solitons in a degenerate electron-ion dense plasma

L. Nahar, M. S. Zobaer, N. Roy, and A. A. Mamun

Phys. Plasmas 20, 022304 (2013); http://dx.doi.org/10.1063/1.4790519 (5 pages)

Online Publication Date: 11 February 2013

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A theoretical investigation has been made of the nonlinear propagation of ion-acoustic waves associated with a dense plasma system consisting degenerate electron and ion fluids. This fluid model, which is valid for both the non-relativistic and ultra-relativistic limits, has been employed with the reductive perturbation method. The K-dV and modified K-dV (mK-dV) equations have been derived and numerically analyzed. The basic features of solitons have been observed. It has been shown that the plasma system under consideration supports the propagation of solitons (electrostatic solitary structures) obtained from the solutions of K-dV and mK-dV equations. The implications of our results obtained from this investigation in compact astrophysical objects have been briefly discussed.
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52.35.Sb Solitons; BGK modes
95.30.Qd Magnetohydrodynamics and plasmas
02.30.Hq Ordinary differential equations
02.60.Lj Ordinary and partial differential equations; boundary value problems
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.)

Comparing linear ion-temperature-gradient-driven mode stability of the National Compact Stellarator Experiment and a shaped tokamak

J. A. Baumgaertel, G. W. Hammett, and D. R. Mikkelsen

Phys. Plasmas 20, 022305 (2013); http://dx.doi.org/10.1063/1.4791657 (8 pages)

Online Publication Date: 11 February 2013

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One metric for comparing confinement properties of different magnetic fusion energy configurations is the linear critical gradient of drift wave modes. The critical gradient scale length determines the ratio of the core to pedestal temperature when a plasma is limited to marginal stability in the plasma core. The gyrokinetic turbulence code GS2 was used to calculate critical temperature gradients for the linear, collisionless ion temperature gradient (ITG) mode in the National Compact Stellarator Experiment (NCSX) and a prototypical shaped tokamak, based on the profiles of a JET H-mode shot and the stronger shaping of ARIES-AT. While a concern was that the narrow cross section of NCSX at some toroidal locations would result in steep gradients that drive instabilities more easily, it is found that other stabilizing effects of the stellarator configuration offset this so that the normalized critical gradients for NCSX are competitive with or even better than for the tokamak. For the adiabatic ITG mode, NCSX and the tokamak had similar adiabatic ITG mode critical gradients, although beyond marginal stability, NCSX had larger growth rates. However, for the kinetic ITG mode, NCSX had a higher critical gradient and lower growth rates until a/LT ≈ 1.5 a/LT,crit, when it surpassed the tokamak's. A discussion of the results presented with respect to a/LT vs. R/LT is included.
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52.55.Fa Tokamaks, spherical tokamaks
52.55.Jd Magnetic mirrors, gas dynamic traps
52.65.Tt Gyrofluid and gyrokinetic simulations
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Kt Drift waves
52.35.Ra Plasma turbulence

Strong nonlinear electron multiplication without impact ionization in dielectric nanoparticles embedded in optical materials

Guillaume Duchateau

Phys. Plasmas 20, 022306 (2013); http://dx.doi.org/10.1063/1.4791662 (12 pages)

Online Publication Date: 13 February 2013

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The interaction of a dielectric nano-particle or nano-defect, embedded in the bulk of an optical material, with an intense and short laser pulse is addressed. Due to the finite size of the target and the possible large production of electrons in the conduction band, large electric field enhancement or surintensity may be induced inside the particle. Since ionization rates also depend on the instantaneous electric field, a strong time-dependent connection between electron production and surintensity may take place. Such a connection is shown to possibly lead to a nonlinear temporal increase in the free electron density relevant from an avalanche process, called optical avalanche, similar to the one induced by electron impact ionization. However, the present build-up in the electron density clearly exhibits more nonlinear features than traditional collisional avalanche, which is shown to induce an exponential growth of the density: when the optical avalanche is engaged, the temporal electron evolution exhibits an explosive behavior. That leads to a nanometric plasma at solid density whose subsequent laser heating may lead locally to matter under extreme conditions. Furthermore, we show that the defect induces a change in the ionization mechanism in the course of interaction: a transition from multiphoton to tunnel ionization may take place.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.-b Plasma properties
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Transport of radial heat flux and second sound in fusion plasmas

Ö. D. Gürcan, P. H. Diamond, X. Garbet, V. Berionni, G. Dif-Pradalier, P. Hennequin, P. Morel, Y. Kosuga, and L. Vermare

Phys. Plasmas 20, 022307 (2013); http://dx.doi.org/10.1063/1.4792161 (8 pages) | Cited 2 times

Online Publication Date: 15 February 2013

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Simple flux-gradient relations that involve time delay and radial coupling are discussed. Such a formulation leads to a rather simple description of avalanches and may explain breaking of gyroBohm transport scaling. The generalization of the flux-gradient relation (i.e., constitutive relation), which involve both time delay and spatial coupling, is derived from drift-kinetic equation, leading to kinetic definitions of constitutive elements such as the flux of radial heat flux. This allows numerical simulations to compute these cubic quantities directly. The formulation introduced here can be viewed as an extension of turbulence spreading to include the effect of spreading of cross-phase as well as turbulence intensity, combined in such a way to give the flux. The link between turbulence spreading and entropy production is highlighted. An extension of this formulation to general quasi-linear theory for the distribution function in the phase space of radial position and parallel velocity is also discussed.
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52.25.Fi Transport properties
52.35.Ra Plasma turbulence
02.60.Cb Numerical simulation; solution of equations
52.25.Dg Plasma kinetic equations

Self-generated magnetic fields in q-distributed plasmas

Ding-Guo Li, San-Qiu Liu, and Xiao-Qing Li

Phys. Plasmas 20, 022308 (2013); http://dx.doi.org/10.1063/1.4793455 (11 pages)

Online Publication Date: 22 February 2013

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A quasi-steady magnetic field can be generated with high-frequency electromagnetic radiation through wave–wave and wave–particle interactions in astrophysical plasmas and laser-produced plasmas. Nonlinear coupling equations of self-generated magnetic fields are obtained in nonextensive distribution frame, as a generalization for the standard Maxwellian distribution frame. The numerical results show that self-generated magnetic fields may collapse and lead to various turbulent patterns with different index q.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Ra Plasma turbulence
95.30.Qd Magnetohydrodynamics and plasmas
02.60.-x Numerical approximation and analysis
52.25.Fi Transport properties
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