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Mar 2009

Volume 16, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Phys. Plasmas 16, 033101 (2009); http://dx.doi.org/10.1063/1.3076207 (7 pages)

E. Brambrink, H. G. Wei, B. Barbrel, P. Audebert, A. Benuzzi-Mounaix, T. Boehly, T. Endo, C. Gregory, T. Kimura, R. Kodama, N. Ozaki, H.-S. Park, M. Rabec le Gloahec, and M. Koenig
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Model of a magnetic field in poloidal divertor tokamaks affected by resonant magnetic perturbations

S. S. Abdullaev

Phys. Plasmas 16, 030701 (2009); http://dx.doi.org/10.1063/1.3083293 (4 pages) | Cited 5 times

Online Publication Date: 3 March 2009

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A generic analytical model for the description of magnetic field lines in poloidal divertor tokamaks in the presence of external resonant magnetic perturbations is proposed. It is based on the Hamiltonian description of magnetic field lines in tokamaks. The safety factor and the spectra of magnetic perturbations are chosen by the requirement to satisfy their generic behavior near the magnetic separatrix and at the magnetic axis. The field line equations of the model are integrated using symplectic efficient mappings of field lines. The analytical formulas for the quasilinear diffusion and convection coefficients of field lines are obtained. The latter describes the outwardly directed transport of field lines at the plasma edge. It was shown that they are in a good agreement with the corresponding numerically calculated coefficients.
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52.55.Dy General theory and basic studies of plasma lifetime, particle and heat loss, energy balance, field structure, etc.
52.55.Fa Tokamaks, spherical tokamaks
05.45.Ac Low-dimensional chaos
45.20.Jj Lagrangian and Hamiltonian mechanics

Excitation of low-n toroidicity induced Alfvén eigenmodes by energetic particles in global gyrokinetic tokamak plasmas

Y. Nishimura

Phys. Plasmas 16, 030702 (2009); http://dx.doi.org/10.1063/1.3088028 (4 pages) | Cited 12 times

Online Publication Date: 6 March 2009

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The first linear global electromagnetic gyrokinetic particle simulation on the excitation of toroidicity induced Alfvén eigenmode (TAE) by energetic particles is reported. It is shown that the long wavelength magnetohydrodynamic instabilities can be studied by the gyrokinetic particle simulation. With an increase in the energetic particle pressure, the TAE frequency moves down into the lower continuum together with an increase in the linear growth rate.
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52.55.Fa Tokamaks, spherical tokamaks
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.65.Tt Gyrofluid and gyrokinetic simulations

Transient growth in stable collisionless plasma

Enrico Camporeale, David Burgess, and Thierry Passot

Phys. Plasmas 16, 030703 (2009); http://dx.doi.org/10.1063/1.3094759 (4 pages) | Cited 5 times

Online Publication Date: 10 March 2009

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The first kinetic study of transient growth for a collisionless homogeneous Maxwellian plasma in a uniform magnetic field is presented. A system which is linearly stable may display transient growth if the linear operator describing its evolution is non-normal so that its eigenvectors are nonorthogonal. In order to include plasma kinetic effects, a Landau fluid model is employed. The linear operator of the model is shown to be non-normal and the results suggest that the non-normality of a collisionless plasma is intrinsically related to its kinetic nature, with the transient growth being more accentuated for smaller scales and higher plasma beta. The results based on linear spectral theory have been confirmed with nonlinear simulations.
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52.25.Dg Plasma kinetic equations
52.65.-y Plasma simulation
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
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back to top Basic Plasma Phenomena, Waves, Instabilities

Effect of current corrugations on the stability of the tearing mode

F. Militello, M. Romanelli, R. J. Hastie, and N. F. Loureiro

Phys. Plasmas 16, 032101 (2009); http://dx.doi.org/10.1063/1.3079077 (8 pages) | Cited 4 times

Online Publication Date: 3 March 2009

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The generation of zonal magnetic fields in laboratory fusion plasmas is predicted by theoretical and numerical models and was recently observed experimentally. It is shown that the modification of the current density gradient associated with such corrugations can significantly affect the stability of the tearing mode. A simple scaling law is derived that predicts the impact of small stationary current corrugations on the stability parameter Δ′. The described destabilization mechanism can provide an explanation for the trigger of the neoclassical tearing mode in plasmas without significant magnetohydrodynamic activity.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Effect of nonisothermal electrons on dressed soliton in ion beam plasma system

R. S. Tiwari

Phys. Plasmas 16, 032102 (2009); http://dx.doi.org/10.1063/1.3080740 (13 pages) | Cited 3 times

Online Publication Date: 9 March 2009

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Using the reductive perturbation method (RPM) evolution equations, governing the first and second order potentials for ion acoustic wave in an ion beam plasma system with nonisothermal electrons, are derived. Adopting renormalization procedure of Kodama and Taniuti [ J. Phys. Soc. Jpn. 45, 298 (1978) ] nonsecular dressed soliton solution of these coupled equations is determined. An alternative approach is also used to obtain large amplitude soliton solution, retaining higher order nonlinearities in the expansion of the Sagdeev potential and integrating the resulting energy equation for the system. For small amplitude approximation, this solution reduces to dressed soliton solution obtained for the system using the renormalization in the RPM. Variation of the amplitude (A), velocity (λ), width (W), and the product amplitude×width4 (AW4) are numerically studied for the Korteweg–de Vries, dressed and large amplitude soliton for different values of parameters of the beam-plasma system, and results are summarized.
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52.35.Sb Solitons; BGK modes
52.35.Dm Sound waves

Ballistic and snowplow regimes in J×B plasma acceleration

C. Thoma, D. R. Welch, and T. P. Hughes

Phys. Plasmas 16, 032103 (2009); http://dx.doi.org/10.1063/1.3081550 (12 pages) | Cited 1 time

Online Publication Date: 10 March 2009

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The J×B acceleration of a one-dimensional uniform plasma slab is analyzed using fully electromagnetic particle-in-cell simulations. Two different regimes of ion dynamics are observed. At relatively high magnetic field values, the ions are accelerated nearly ballistically in a thin sheath at the plasma-vacuum interface and then form a beam which propagates through the downstream bulk plasma. This behavior can be explained by a simple collisionless thin-sheath model. At lower field values the sheath becomes thicker and the ions are collisional at the interface. This leads to “snowplowing” of ion density at the interface. From the electron transport equations for a simple magnetized plasma we can estimate the temperature and effective collisionality in the sheath as a function of magnetic field strength. From this theory we can qualitatively explain the existence of the two regimes. In the simulations the plasma sheath thickness is found to scale somewhat more weakly with magnetic field strength than is predicted by the simple transport theory. We propose that a high Mach number plasma slab may be obtained by the combination of a short accelerator and a strong magnetic field in the collisionless regime.
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52.25.Fi Transport properties
52.40.Kh Plasma sheaths
52.25.Xz Magnetized plasmas
52.65.Rr Particle-in-cell method
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Dispersion of waves in relativistic plasmas with isotropic particle distributions

Roman V. Shcherbakov

Phys. Plasmas 16, 032104 (2009); http://dx.doi.org/10.1063/1.3080748 (7 pages) | Cited 1 time

Online Publication Date: 13 March 2009

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The dispersion laws of Langmuir and transverse waves are calculated in the relativistic nonmagnetized formalism for several isotropic particle distributions: thermal, power law, relativistic Lorentzian κ, and hybrid β. For Langmuir waves the parameters of superluminal undamped, subluminal damped principal, and higher modes are determined for a range of distribution parameters. The undamped and principal damped modes are found to match smoothly. Principal damped and second damped modes are found not to match smoothly. The presence of maximum wavenumber is discovered above that no longitudinal modes formally exist. The higher damped modes are discovered to be qualitatively different for thermal and certain nonthermal distributions. Consistently with the known results, the Landau damping is calculated to be stronger for nonthermal power-law-like distributions. The dispersion law is obtained for the single undamped transverse mode. The analytic results for the simplest distributions are provided.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Quantum correction to Landau damping of electron plasma waves

Jun Zhu, Peiyong Ji, and Nan Lu

Phys. Plasmas 16, 032105 (2009); http://dx.doi.org/10.1063/1.3091935 (6 pages) | Cited 8 times

Online Publication Date: 17 March 2009

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It is often assumed that quantum effects will be significant only in the low temperature and high density plasmas. In this paper this assumption is challenged by considering the quantum contribution to the Landau damping of electron plasma waves in normal temperature and high density plasmas. Starting from the linearized Vlasov equation which contains the Bohm quantum potential, the dispersion relation of electron plasma waves propagating in a quantum plasma is derived. A linear Landau damping rate and equations for this process are also deduced. Result indicates that quantum effects enlarge effective frequency of plasmas, which is attributed to an increase in charge or number density of plasma electrons. As a result, Debye length is reduced, and the Debye screening effect becomes obvious. So the quantum behavior appears screening effect here. Landau damping rate is reduced by quantum effects and the exchange of energy between particles and waves is retarded.
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52.25.Fi Transport properties
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
03.65.-w Quantum mechanics

The Rayleigh–Taylor instability in quantum magnetized plasma with para- and ferromagnetic properties

Mikhail Modestov, Vitaly Bychkov, and Mattias Marklund

Phys. Plasmas 16, 032106 (2009); http://dx.doi.org/10.1063/1.3085796 (11 pages) | Cited 7 times

Online Publication Date: 18 March 2009

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We investigate influence of magnetic field on the Rayleigh–Taylor instability in quantum plasmas with para- and ferromagnetic properties. Magnetization of quantum plasma happens due to the collective electron spin behavior at low temperature and high plasma density. In the classical case, without magnetization, magnetic field tends to stabilize plasma perturbations with wave numbers parallel to the field and with sufficiently short wavelengths. Paramagnetic effects in quantum plasma make this stabilization weaker. The stabilization disappears completely for short wavelength perturbations in the ferromagnetic limit, when the magnetic field is produced by intrinsic plasma magnetization only. Still, for perturbations of long and moderate wavelength, certain stabilization always takes place due to the nonlinear character of quantum plasma magnetization.
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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.-s Magnetic confinement and equilibrium

Evolution of a relativistic electron beam–plasma return current system

X. Kong, J. Park, C. Ren, Z. M. Sheng, and J. W. Tonge

Phys. Plasmas 16, 032107 (2009); http://dx.doi.org/10.1063/1.3088056 (6 pages) | Cited 13 times

Online Publication Date: 18 March 2009

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Evolution of a relativistic electron beam-plasma return current system has been studied using particle-in-cell simulations. The mode number-resolved linear growth rates of the oblique instabilities that the system suffers generally agree with the existing theory [ A. Bret et al., Phys. Rev. E 72, 016403 (2005) ]. The comparison of in- and out-of-plane simulations shows that two-stream type of instabilities dominates the early stage of energy transfer from the beam drift energy to the beam and plasma thermal energy. The end stage of the nonlinear evolution is dominated Weibel/filament type of instabilities, resulting a beam with a moderately increased angular spread, reduced drift energy, and no reduction in the initial cross section.
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52.40.Mj Particle beam interactions in plasmas
52.27.Ny Relativistic plasmas
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.65.Rr Particle-in-cell method
41.75.Fr Electron and positron beams

Effect of trapped electrons on soliton propagation in a plasma having a density gradient

Farah Aziz and Ulrich Stroth

Phys. Plasmas 16, 032108 (2009); http://dx.doi.org/10.1063/1.3091934 (7 pages) | Cited 7 times

Online Publication Date: 20 March 2009

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A Korteweg–deVries equation with an additional term due to the density gradient is obtained using reductive perturbation technique in an unmagnetized plasma having a density gradient, finite temperature ions, and two-temperature nonisothermal (trapped) electrons. This equation is solved to get the solitary wave solution using sine-cosine method. The phase velocity, soliton amplitude, and width are examined under the effect of electron and ion temperatures and their concentrations. The effect of ion (electron) temperature is found to be more significant in the presence of larger (smaller) number of trapped electrons in the plasma.
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52.35.Sb Solitons; BGK modes

A Hamiltonian electromagnetic gyrofluid model

F. L. Waelbroeck, R. D. Hazeltine, and P. J. Morrison

Phys. Plasmas 16, 032109 (2009); http://dx.doi.org/10.1063/1.3087972 (8 pages) | Cited 13 times

Online Publication Date: 20 March 2009

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An isothermal truncation of the electromagnetic gyrofluid model of Snyder and Hammett [Phys. Plasmas 8, 3199 (2001) ] is shown to be Hamiltonian. The corresponding noncanonical Lie–Poisson bracket and its Casimir invariants are presented. The invariants are used to obtain a set of coupled Grad–Shafranov equations describing equilibria and propagating coherent structures.
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52.30.Ex Two-fluid and multi-fluid plasmas
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
94.30.cq MHD waves, plasma waves, and instabilities

Using numerical simulations to extract parameters of toroidal electron plasmas from experimental data

B. N. Ha, M. R. Stoneking, and J. P. Marler

Phys. Plasmas 16, 032110 (2009); http://dx.doi.org/10.1063/1.3091924 (6 pages) | Cited 2 times

Online Publication Date: 23 March 2009

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Measurements of the image charge induced on electrodes provide the primary means of diagnosing plasmas in the Lawrence Non-neutral Torus II (LNT II) [ Phys. Rev. Lett. 100, 155001 (2008) ]. Therefore, it is necessary to develop techniques that determine characteristics of the electron plasma from features of the induced image charge signal. This paper presents a numerical study which finds that the frequency of the image charge signal due to the toroidal version of the m = 1 diocotron mode is proportional to the total trapped charge and inversely proportional to magnetic field strength, as in the cylindrical case. In the toroidal case, additional information about the m = 1 motion of the plasma can be obtained by analysis of the image charge signal amplitude and shape. Finally, results from the numerical simulations are compared to experimental data from the LNT II and plasma characteristics are reported.
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52.27.Jt Nonneutral plasmas
52.65.Cc Particle orbit and trajectory
52.70.Ds Electric and magnetic measurements
52.55.Jd Magnetic mirrors, gas dynamic traps
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Two-dimensional envelope electron-acoustic waves under transverse perturbations

Tarsem Singh Gill, Chanchal Bedi, and Amandeep Singh Bains

Phys. Plasmas 16, 032111 (2009); http://dx.doi.org/10.1063/1.3091913 (8 pages) | Cited 5 times

Online Publication Date: 24 March 2009

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As is well known, the envelope electron-acoustic (EA) nonlinear waves in one dimension are governed by the nonlinear Schrödinger equation. If transverse perturbations are considered, then this type of nonlinear wave can be described by the general form of the Davey–Stewartson equation. In this work, modulational properties of EA wave and its stability regions in two-dimensional plasma have been studied.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
back to top Nonlinear Phenomena, Turbulence, Transport

Suppression of stimulated Raman scattering due to localization of electron plasma wave in laser beam filaments

Prerana Sharma and R. P. Sharma

Phys. Plasmas 16, 032301 (2009); http://dx.doi.org/10.1063/1.3077670 (8 pages) | Cited 4 times

Online Publication Date: 3 March 2009

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The filamentation of the high power laser beam by taking off-axial contribution is investigated when ponderomotive nonlinearity is taken into account. The splitted profile of the laser beam is obtained due to uneven focusing of the off-axial rays. It is observed that the weak electron plasma wave (EPW) propagating in the z direction is nonlinearly coupled in the modified filamentary regions of the laser beam. The semianalytical solution of the nonlinear coupled EPW equation in the presence of laser beam filaments has been found and it is observed that the nonlinear coupling between these two waves leads to localization of the EPW. Stimulated Raman scattering (SRS) of this EPW is studied and backreflectivity has been calculated. Further, the localization of EPW affects the eigenfrequency and damping of plasma wave. As a result of this, mismatch and modified enhanced Landau damping lead to the disruption of SRS process and a substantial reduction in the backreflectivity. For the typical laser beam and plasma parameters with wavelength (λ = 1064 nm), power flux ( ≈ 1016 W cm−2), and plasma density (n/ncr) = 0.2; the backreflectivity was found to be suppressed by a factor of around 20%.
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52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Fully nonlinear ion-acoustic solitary waves in a plasma with positive-negative ions and nonthermal electrons

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

Phys. Plasmas 16, 032302 (2009); http://dx.doi.org/10.1063/1.3088005 (8 pages) | Cited 22 times

Online Publication Date: 3 March 2009

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Properties of fully nonlinear ion-acoustic solitary waves in a plasma with positive-negative ions and nonthermal electrons are investigated. For this purpose, the hydrodynamic equations for the positive-negative ions, nonthermal electron density distribution, and the Poisson equation are used to derive the energy integral equation with a new Sagdeev potential. The latter is analyzed to examine the existence regions of the solitary pulses. It is found that the solitary excitations strongly depend on the mass and density ratios of the positive and negative ions as well as the nonthermal electron parameter. Numerical solution of the energy integral equation clears that both positive and negative potentials exist together. It is found that faster solitary pulses are taller and narrower. Furthermore, increasing the electron nonthermality parameter (negative-to-positive ions density ratio) decreases (increases) the localized excitation amplitude but increases (decreases) the pulse width. The present model is used to investigate the solitary excitations in the (H+,O2−) and (H+,H−) plasmas, where they are presented in the D- and F-regions of the Earth’s ionosphere. This investigation should be helpful in understanding the salient features of the fully nonlinear ion-acoustic solitary waves in space and in laboratory plasmas where two distinct groups of ions and non-Boltzmann distributed electrons are present.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
94.05.Fg Solitons and solitary waves
52.35.Sb Solitons; BGK modes

Effect of compressibility on the Rayleigh–Taylor and Richtmyer–Meshkov instability induced nonlinear structure at two fluid interface

M. R. Gupta, Sourav Roy, Manoranjan Khan, H. C. Pant, Susmita Sarkar, and M. K. Srivastava

Phys. Plasmas 16, 032303 (2009); http://dx.doi.org/10.1063/1.3074789 (12 pages) | Cited 7 times

Online Publication Date: 5 March 2009

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The effect of compressibility and of density variation on Rayleigh–Taylor and Richtmyer–Meshkov instability of the temporal development of two fluid interfacial structures such as bubbles and spikes have been investigated. It is seen that the velocity of the tip of the bubble or spike increases (destabilization) if the local Atwood number increases due to density variation of either of the fluids. The opposite is the result, i.e., the bubble or spike tip velocity decreases (stabilization) if the density variation leads to lowering of the value of the local Atwood number. The magnitude of stabilization or destabilization is an increasing function of the product of the wave number k and interfacial pressure p0. The effect of compressibility is quite varied. If the heavier (upper) fluid alone is incompressible (γh→∞), but the lighter fluid is compressible the growth rate is higher (destabilization) than when both the fluids are incompressible. Moreover the heavier fluid remaining incompressible the growth rate decreases (stabilization) as γl (finite) increases and ultimately tends to the incompressible limit value as γl→∞. With γl→∞ but γh finite the growth increases (destabilization) as γh increases. When both γh and γl are finite (density ρh>density ρl) the growth is reduced when γh<γl compared to that when both fluids are incompressible and enhanced when γh>γl. The set of nonlinear equations describing the dynamics of bubbles and spikes in the presence of fluid density variations are not analytically integrable in closed form. The results derived by numerical solution methods are represented and interpreted in corresponding figures.
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47.20.Ma Interfacial instabilities (e.g., Rayleigh-Taylor)
47.40.-x Compressible flows; shock waves
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
47.55.D- Drops and bubbles
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Nonlinear electron-acoustic waves in quantum plasma

O. P. Sah and J. Manta

Phys. Plasmas 16, 032304 (2009); http://dx.doi.org/10.1063/1.3080741 (8 pages) | Cited 6 times

Online Publication Date: 9 March 2009

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The nonlinear wave structure of electron-acoustic waves (EAWs) is investigated in a three component unmagnetized dense quantum plasma consisting of two distinct groups of electrons (one inertial cold electron, and other inertialess hot electrons) and immobile ions. By employing one dimensional quantum hydrodynamic model and standard reductive perturbation technique, a Korteweg–de-Vries equation governing the dynamics of EAWs is derived. Both compressive and rarefactive solitons along with periodical potential structures are found to exist for various ranges of dimensionless quantum parameter H. The quantum mechanical effects are also examined numerically on the profiles of the amplitude and the width of electron-acoustic solitary waves. It is observed that both the amplitude and the width of electron-acoustic solitary waves are significantly affected by the parameter H. The relevance of the present investigation to the astrophysical ultradense plasmas is also discussed.
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52.25.Gj Fluctuation and chaos phenomena

The disparate impact of the ion temperature gradient and the density gradient on edge transport and the low-high transition in tokamaks

Robert G. Kleva and Parvez N. Guzdar

Phys. Plasmas 16, 032305 (2009); http://dx.doi.org/10.1063/1.3086862 (5 pages) | Cited 1 time

Online Publication Date: 10 March 2009

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Steepening of the ion temperature gradient in nonlinear fluid simulations of the edge region of a tokamak plasma causes a rapid degradation in confinement. As the density gradient steepens, there is a continuous improvement in confinement analogous to the low (L) to high (H) transition observed in tokamaks. In contrast, as the ion temperature gradient steepens, there is a rapid increase in the particle and energy fluxes and no L-H transition. For a given pressure gradient, confinement always improves when more of the pressure gradient arises from the density gradient, and less of the pressure gradient arises from the ion temperature gradient.
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52.35.Ra Plasma turbulence
52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties
52.65.Kj Magnetohydrodynamic and fluid equation

Turbulent and neoclassical impurity transport in tokamak plasmas

T. Fülöp and H. Nordman

Phys. Plasmas 16, 032306 (2009); http://dx.doi.org/10.1063/1.3083299 (8 pages) | Cited 13 times

Online Publication Date: 12 March 2009

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Impurity particle transport in tokamaks is studied using an electrostatic fluid model for main ion and impurity temperature gradient (ITG) mode and trapped electron (TE) mode turbulence in the collisionless limit and neoclassical theory. The impurity flux and impurity density peaking factor obtained from a self-consistent treatment of impurity transport are compared and contrasted with the results of the often used trace impurity approximation. Comparisons between trace and self-consistent turbulent impurity transport are performed for ITER-like profiles. It is shown that for small impurity concentrations the trace impurity limit is adequate if the plasma is dominated by ITG turbulence. However, in case of TE mode dominated plasmas the contribution from impurity modes may be significant, and therefore a self-consistent treatment may be needed.
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52.25.Fi Transport properties
52.55.Fa Tokamaks, spherical tokamaks
28.52.Av Theory, design, and computerized simulation
52.35.Ra Plasma turbulence
52.25.Vy Impurities in plasmas

Ion acoustic waves in pair-ion plasma: Linear and nonlinear analyses

R. Saeed and A. Mushtaq

Phys. Plasmas 16, 032307 (2009); http://dx.doi.org/10.1063/1.3087986 (6 pages) | Cited 6 times

Online Publication Date: 13 March 2009

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Linear and nonlinear properties of low frequency ion acoustic wave (IAW) in pair-ion plasma in the presence of electrons are investigated. The dispersion relation and Kadomtsev–Petviashvili equation for linear/nonlinear IAW are derived from sets of hydrodynamic equations where the ion pairs are inertial while electrons are Boltzmannian. The dispersion curves for various concentrations of electrons are discussed and compared with experimental results. The predicted linear IAW propagates at the same frequencies as those of the experimentally observed IAW if ne0 ∼ 104 cm−3. It is found that nonlinear profile of the ion acoustic solitary waves is significantly affected by the percentage ratio of electron number density and temperature. It is also determined that rarefactive solitary waves can propagate in this system. It is hoped that the results presented in this study would be helpful in understanding the salient features of the finite amplitude localized ion acoustic solitary pulses in a laboratory fullerene plasma.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Dm Sound waves
52.35.Sb Solitons; BGK modes

Clarifications to the limitations of the s-α equilibrium model for gyrokinetic computations of turbulence

X. Lapillonne, S. Brunner, T. Dannert, S. Jolliet, A. Marinoni, L. Villard, T. Görler, F. Jenko, and F. Merz

Phys. Plasmas 16, 032308 (2009); http://dx.doi.org/10.1063/1.3096710 (9 pages) | Cited 6 times

Online Publication Date: 26 March 2009

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In the context of gyrokinetic flux-tube simulations of microturbulence in magnetized toroidal plasmas, different treatments of the magnetic equilibrium are examined. Considering the Cyclone DIII-D base case parameter set [ Dimits et al., Phys. Plasmas 7, 969 (2000) ], significant differences in the linear growth rates, the linear and nonlinear critical temperature gradients, and the nonlinear ion heat diffusivities are observed between results obtained using either an s-α or a magnetohydrodynamic (MHD) equilibrium. Similar disagreements have been reported previously [ Redd et al., Phys. Plasmas 6, 1162 (1999) ]. In this paper it is shown that these differences result primarily from the approximation made in the standard implementation of the s-α model, in which the straight field line angle is identified to the poloidal angle, leading to inconsistencies of order ε (ε = a/R is the inverse aspect ratio, a the minor radius and R the major radius). An equilibrium model with concentric, circular flux surfaces and a correct treatment of the straight field line angle gives results very close to those using a finite ε, low β MHD equilibrium. Such detailed investigation of the equilibrium implementation is of particular interest when comparing flux tube and global codes. It is indeed shown here that previously reported agreements between local and global simulations in fact result from the order ε inconsistencies in the s-α model, coincidentally compensating finite ρ∗ effects in the global calculations, where ρ∗ = ρs/a with ρs the ion sound Larmor radius. True convergence between local and global simulations is finally obtained by correct treatment of the geometry in both cases, and considering the appropriate ρ∗→0 limit in the latter case.
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52.35.Ra Plasma turbulence
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.25.Dg Plasma kinetic equations
52.55.Jd Magnetic mirrors, gas dynamic traps
52.65.Kj Magnetohydrodynamic and fluid equation

Basis operator bispectral analysis

D. A. Baver, P. W. Terry, and C. Holland

Phys. Plasmas 16, 032309 (2009); http://dx.doi.org/10.1063/1.3093844 (10 pages)

Online Publication Date: 30 March 2009

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A new procedure for calculating model coefficients from fluctuation data for fully developed turbulence is derived. This procedure differs from previous related methods in that it is constructed in a spatial rather than spectral representation. This has a number of advantages, such as reduced data set requirements, ability to represent spatially inhomogeneous systems such as the ones with curvature or zonal flows, and ability to use data from experimental diagnostics with limited spatial resolution. In this method, the model equation is represented as a linear superposition of linear and nonlinear differential operators. The coefficients of this superposition are calculated using a least-squares method. This method has been tested on simulations of fully developed two dimensional turbulence and compared to previous methods.
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47.11.Fg Finite element methods
02.60.Lj Ordinary and partial differential equations; boundary value problems
47.27.er Spectral methods

Kinetic dissipation and anisotropic heating in a turbulent collisionless plasma

T. N. Parashar, M. A. Shay, P. A. Cassak, and W. H. Matthaeus

Phys. Plasmas 16, 032310 (2009); http://dx.doi.org/10.1063/1.3094062 (7 pages) | Cited 18 times

Online Publication Date: 30 March 2009

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The kinetic evolution of the Orszag–Tang vortex is studied using collisionless hybrid simulations. In magnetohydrodynamics (MHD) this configuration leads rapidly to broadband turbulence. At large length scales, the evolution of the hybrid simulations is very similar to MHD, with magnetic power spectra displaying scaling similar to a Kolmogorov scaling of −5/3. At small scales, differences from MHD arise, as energy dissipates into heat almost exclusively through the magnetic field. The magnetic energy spectrum of the hybrid simulation shows a break where linear theory predicts that the Hall term in Ohm’s law becomes significant, leading to dispersive kinetic Alfvén waves. A key result is that protons are heated preferentially in the plane perpendicular to the mean magnetic field, creating a proton temperature anisotropy of the type observed in the corona and solar wind.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.Dg Plasma kinetic equations
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Ra Plasma turbulence
52.50.Lp Plasma production and heating by shock waves and compression
52.65.Ww Hybrid methods
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.80.Hc Glow; corona
back to top Magnetically Confined Plasmas, Heating, Confinement

Plasma current position measurements in the Korea Superconducting Tokamak Advanced Research device

Seong-Heon Seo

Phys. Plasmas 16, 032501 (2009); http://dx.doi.org/10.1063/1.3079781 (6 pages) | Cited 15 times

Online Publication Date: 3 March 2009

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The plasma current position is measured based on the current multipole moment method in the Korea Superconducting Tokamak Advanced Research (KSTAR) device [ G. S. Lee et al., Nucl. Fusion 41, 1515 (2001) ]. Since a limited number of magnetic probes and flux loops were installed for the first campaign, an iteration method is used to interpolate the magnetic field in the area absent of probes. A numerical technique is developed which automatically compensates for the linear drift of the integrator. The measured plasma position is cross checked with the charge coupled device images. In KSTAR, the plasma current is displaced toward the lower outboard direction during the current initiation phase. This displacement is expected due to eddy currents but the exact amount and direction needs more study.
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52.55.Fa Tokamaks, spherical tokamaks
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