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Dec 2006

Volume 13, Issue 12, Articles (12xxxx)

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Wire dynamics model of the implosion of nested and planar wire arrays

A. A. Esaulov, A. L. Velikovich, V. L. Kantsyrev, T. A. Mehlhorn, and M. E. Cuneo

Phys. Plasmas 13, 120701 (2006); http://dx.doi.org/10.1063/1.2402147 (4 pages) | Cited 8 times

Online Publication Date: 8 December 2006

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This paper presents the wire dynamics model (WDM), which can effectively replace the generic 0D (zero-dimensional) model in simulation of the implosions of arbitrary shaped wire arrays, including high-wire-number nested and planar array loads at multi-MA generators. Fast and inexpensive WDM modeling can predict the array implosion time and the rate of thermalization of the kinetic energy, and can estimate the timing of the x-ray pulse. Besides serving the purposes of the design and optimization of the wire array loads of complex configurations, the WDM reproduces the specific features of the wire array implosion dynamics due to the inductive current transfer, which makes the WDM a valuable amplification of the magnetohydrodynamic models.
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52.59.Qy Wire array Z-pinches
52.59.Px Hard X-ray sources
52.50.Lp Plasma production and heating by shock waves and compression

Large density variation predicted along the magnetic axis for cold electron plasmas in the Columbia Nonneutral Torus (CNT)

Remi G. Lefrancois and Thomas Sunn Pedersen

Phys. Plasmas 13, 120702 (2006); http://dx.doi.org/10.1063/1.2405341 (4 pages) | Cited 3 times

Online Publication Date: 13 December 2006

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Cold pure electron plasmas confined in Penning-Malmberg traps with mirror fields are known to exhibit density variations along field lines, such that the density is roughly proportional to the magnetic field strength, n ∼ B. The Columbia Nonneutral Torus (CNT) is the first stellarator designed to study pure electron plasmas, and exhibits substantial mirroring, with Bmax ≈ 1.8Bmin. However, results of a three-dimensional equilibrium solver, presented in this Letter, predict a factor of 5.3 increase in density from the minimum-field cross section to the maximum-field cross section along the magnetic axis, for a 1.5 cm Debye length plasma (a ≈ 15 cm for CNT). In this Letter, it is shown that the density variation of electron plasmas in mirror traps can be significantly enhanced in a device that has a cross section that varies from cylinder-like to slab-like, such as the CNT. A simple analytic expression is derived that describes the axial density variation in such a device, and it is found to agree well with the computational predictions for CNT.
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52.27.Jt Nonneutral plasmas
52.55.−s
52.65.−y
52.27.Cm Multicomponent and negative-ion plasmas
52.27.Aj Single-component, electron-positive-ion plasmas

(3+1)-dimensional generalized Johnson model for cosmic dust-ion-acoustic nebulons with symbolic computation

Yi-Tian Gao and Bo Tian

Phys. Plasmas 13, 120703 (2006); http://dx.doi.org/10.1063/1.2402916 (4 pages) | Cited 61 times

Online Publication Date: 26 December 2006

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In a cosmic dusty plasma, both azimuthal and height perturbations of a nonplanar cylindrical geometry are considered. For dust-ion-acoustic waves and with symbolic computation, (3+1)-dimensional generalized Johnson [(3+1)DGJ] model is derived and analytic solutions are constructed. Supernova-shell-typed expanding bright (3+1)DGJ nebulons and Saturn-F-ring-type expanding dark (3+1)DGJ nebulons are both pictured and discussed. Essential difference of this letter from the existing literature is pointed out, with the relevant, possibly observable (3+1)DGJ-nebulonic structures for the future cosmic experiments proposed.
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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.Sb Solitons; BGK modes
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
02.70.Wz Symbolic computation (computer algebra)
05.45.Yv Solitons
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back to top Basic Plasma Phenomena, Waves, Instabilities

Experiments and theory of an upstream ionization instability excited by an accelerated electron beam through a current-free double layer

A. Aanesland, M. A. Lieberman, C. Charles, and R. W. Boswell

Phys. Plasmas 13, 122101 (2006); http://dx.doi.org/10.1063/1.2398929 (10 pages) | Cited 4 times

Online Publication Date: 6 December 2006

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A low-frequency instability varying from 10 to 20 kHz has been discovered in the presence of a current-free double layer (DL) in a low-pressure expanding helicon plasma. The instability is observed using various electrostatic probes, such as Langmuir probes floating or biased to ion saturation and emissive probes measuring the plasma potential. A retarding field energy analyzer measuring the ion energy distribution function downstream of the double layer is used together with the LP to simultaneously observe the DL and the instability, confirming their coexistence. The frequency of the instability decreases with increasing neutral pressure, increases with increasing magnetic field in the source and increases with increasing rf power. A theory for an upstream ionization instability has been developed, in which electrons accelerated through the DL increase the ionization upstream and are responsible for the observed instability. The theory is in good agreement with the experimental results and shows that the frequency increases with the potential drop of the double layer and with decreasing chamber radius.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.40.Mj Particle beam interactions in plasmas
52.40.Kh Plasma sheaths
52.50.Dg Plasma sources
52.70.Ds Electric and magnetic measurements
52.25.Jm Ionization of plasmas

Electromagnetic dust-lower-hybrid and dust-magnetosonic waves and their instabilities in a dusty magnetoplasma

M. Salimullah, M. M. Rahman, I. Zeba, H. A. Shah, G. Murtaza, and P. K. Shukla

Phys. Plasmas 13, 122102 (2006); http://dx.doi.org/10.1063/1.2400846 (5 pages) | Cited 6 times

Online Publication Date: 6 December 2006

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The electromagnetic waves below the ion-cyclotron frequency have been examined in a collisionless and homogeneous dusty plasma in the presence of a dust beam parallel to the direction of the external magnetic field. The low-frequency mixed electromagnetic dust-lower-hybrid and purely transverse magnetosonic waves become unstable for the sheared flow of dust grains and grow in amplitude when the drift velocity of the dust grains exceeds the parallel phase velocity of the waves. The growth rate depends dominantly upon the thermal velocity and density of the electrons.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.35.Dm Sound waves
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Fi Transport properties

Fluid modeling of the electron flow driven ion acoustic mode in a collisional plasma with magnetized electrons

J. Vranjes, M. Y. Tanaka, and S. Poedts

Phys. Plasmas 13, 122103 (2006); http://dx.doi.org/10.1063/1.2397040 (9 pages) | Cited 8 times

Online Publication Date: 7 December 2006

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A fluid analysis is presented of the ion sound mode in a weakly ionized collisional plasma. The ion-neutral collision frequency exceeds the ion gyrofrequency while the electrons remain magnetized. Under these conditions, an ion sound wave can propagate at arbitrary angles with respect to the direction of the magnetic field. In the presence of an electron flow along the magnetic lines the sound mode can grow. Due to the electron collisions the mode is unstable while ion collisions cause an angle dependent instability threshold which is such that the mode is most easily excited at very large angles. Hot ion effects are included in the study by means of an effective viscosity which effectively describes the ion Landau damping effect. In the presence of an additional light ion specie, the mode frequency and increment in a certain parameter range are increased.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Dm Sound waves
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Fi Transport properties

Properties of linear and nonlinear ion thermal waves in a pair ion plasma containing charged dust impurities

W. M. Moslem and P. K. Shukla

Phys. Plasmas 13, 122104 (2006); http://dx.doi.org/10.1063/1.2397585 (6 pages) | Cited 13 times

Online Publication Date: 8 December 2006

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Properties of linear and nonlinear ion thermal waves (ITWs) in pair ion plasmas containing a fraction of stationary charged (positive or negative) dust grains are investigated. For this purpose, a linear dispersion relation, a Korteweg-de Vries equation and (an energy integral of a classical potential) for linear (nonlinear) ITWs are derived from the ion continuity and momentum equations together with the Poisson equation. It is found that both the ITW frequency and the profile of the ion thermal solitary waves are significantly affected by the presence of positively/negatively charged dust grains. The present results should be useful in understanding the salient features of finite amplitude localized ion thermal solitary pulses in a pair ion plasma containing charged dust impurities.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.27.Lw Dusty or complex plasmas; plasma crystals
52.25.Vy Impurities in plasmas
52.25.Dg Plasma kinetic equations
52.25.Fi Transport properties
52.35.Sb Solitons; BGK modes

Hall assisted forced magnetic reconnection

G. Vekstein and N. H. Bian

Phys. Plasmas 13, 122105 (2006); http://dx.doi.org/10.1063/1.2398933 (8 pages) | Cited 9 times

Online Publication Date: 8 December 2006

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The role of the Hall effect in forced magnetic reconnection is investigated analytically for the so-called Taylor problem. In the latter, a tearing stable slab plasma equilibrium, which is chosen here to be a simple magnetic field reversal, is subjected to a small-amplitude boundary deformation that drives magnetic reconnection (hence the adjective “forced” ) at the neutral surface within the plasma. It is shown that such reconnection becomes substantially accelerated by the Hall effect when the nondimensional parameter di = (c/ωpi)/a exceeds S−1/5. Here, c/ωpi is the ion inertial skin depth, a is the width of the plasma slab, and S≫1 is the Lundquist number of a highly conducting plasma. Two different types of external perturbation are considered. In the case of continuous quasistatic driving, with a frequency ω such that ωτA≪1, τA being the Alfvén transit time, various reconnection regimes are identified. The corresponding heating rates, which are determined by the parameters di, S, and ωτA, are derived. In the case of a “one-off” reconnection event, we demonstrate when and how the transition from the Hall regime to the magnetohydrodynamic regime occurs in the course of the reconnection process. It is found that the peak instantaneous reconnection rate scales as dψ1(0)/dt ∼ di1/2S−1/2(B0δ0/τA), where ψ1(0) is the reconnected magnetic flux, B0 is the magnetic field strength, and δ0 is the amplitude of the boundary deformation.
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52.35.Vd Magnetic reconnection
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
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.40.Hf Plasma-material interactions; boundary layer effects

Physics of the dusty Hall plasmas

B. P. Pandey and J. Vranjes

Phys. Plasmas 13, 122106 (2006); http://dx.doi.org/10.1063/1.2402148 (6 pages) | Cited 6 times

Online Publication Date: 13 December 2006

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The presence of the immobile charged dust in the plasma modifies the scale over which the Hall effect becomes important. For a positively charged dusty background this scale can become arbitrarily large. It is shown that the emergence of the Hall effect in an immobile charged background is related to the presence of an electric field that operates over the plasma gyration period. The generalized flux, which is a combination of the magnetic and fluid vortex flux, can decay due to the presence of the charge or the density inhomogeneities. The normal mode behavior of such a dusty plasma could be very different for positively and negatively charged grains. Whereas for negatively charged grains the usual magnetohydrodynamic (MHD) modes are present in the system, for positively charged grains, the Alfvén mode may not exist if Znd ∼ ne, where Z is the charge of the dust and nd(ne) are the dust (electron) number densities. In the presence of the inhomogeneities, inertialess dusty plasma is subject to the Hall instability. It is shown that the growth rate of the Hall instability is proportional to the whistler frequency. Since Hall drift is nondissipative in nature, this instability can play important role in redistributing the magnetic energy from the large to small scales.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.We Plasma vorticity
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.25.Fi Transport properties
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Dissipation in magnetic reconnection with a guide magnetic field

Michael Hesse

Phys. Plasmas 13, 122107 (2006); http://dx.doi.org/10.1063/1.2403784 (6 pages) | Cited 10 times

Online Publication Date: 29 December 2006

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A combination of numerical simulation results and analytical theory is applied to the problem of magnetic reconnection in a guide magnetic field. An investigation of electron distribution functions within the electron diffusion region leads to a picture of mixing of particles with different acceleration histories on electron Larmor scales. Based on an apparent average loss of accelerated particles by field-aligned and E×B transport, it is proposed that the role of the reconnection electric field is to replenish this loss by acceleration of particles that enter the electron diffusion region. Analytic theory is employed to verify this model, and an equation is derived, which balances the average electric field force density by a diffusion term applied to the electron momentum density. The diffusion coefficient contains explicitly the electron Larmor spatial scale and a poloidal transport time scale.
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52.35.Vd Magnetic reconnection
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Fi Transport properties
52.25.Dg Plasma kinetic equations
02.60.Cb Numerical simulation; solution of equations
back to top Nonlinear Phenomena, Turbulence, Transport

Stabilization of the fan instability: Electron flux relaxation

C. Krafft and A. Volokitin

Phys. Plasmas 13, 122301 (2006); http://dx.doi.org/10.1063/1.2372464 (11 pages) | Cited 2 times

Online Publication Date: 4 December 2006

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This paper presents some relevant simulation results on the interaction between electrostatic waves and suprathermal electron fluxes at anomalous cyclotron and Landau resonances. In particular, the case of a dense and continuous wave spectrum is studied. It is shown that, after the waves excited by the fan instability at anomalous cyclotron resonances have reached a first saturation stage due to particle trapping, the process of “dynamical resonance merging” takes place, which leads to a strong amplification of the waves’ amplitudes. The Landau resonances do not play an essential role in the total energy exchange between the particles and the waves, as they mainly help to smooth the peaks rising during the evolution of the electron parallel velocity distribution and contribute to damping. Moreover, the paper shows that at the asymptotic stage of the interaction, when the waves’ amplitudes are saturated and the electron flux is relaxed, some physical features clearly do not fit the predictions of the well-known quasilinear theory. The careful examination of a huge number of trajectories of particles moving in the effective field of the wave packet allows to state that most of the particles involved in the resonant interactions are trapped by several waves simultaneously. In this so-called “multitrapping” process, the particles perform complex oscillatory motions which are far from what is expected from the quasilinear theory, where the diffusive behavior of the particles in the velocity space results from small successive random steps.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.40.Mj Particle beam interactions in plasmas
52.65.Cc Particle orbit and trajectory
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.25.Fi Transport properties

Equilibrium statistical mechanics for single waves and wave spectra in Langmuir wave-particle interaction

M.-C. Firpo, F. Leyvraz, and G. Attuel

Phys. Plasmas 13, 122302 (2006); http://dx.doi.org/10.1063/1.2397039 (10 pages) | Cited 4 times

Online Publication Date: 7 December 2006

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Under the conditions of weak Langmuir turbulence, a self-consistent wave-particle Hamiltonian models the effective nonlinear interaction of a spectrum of M waves with N resonant out-of-equilibrium tail electrons. In order to address its intrinsically nonlinear time-asymptotic behavior, a Monte Carlo code was built to estimate its equilibrium statistical mechanics in both the canonical and microcanonical ensembles. First, the single wave model is considered in the cold beam-plasma instability and in the O’Neil setting for nonlinear Landau damping. O’Neil’s threshold, which separates nonzero time-asymptotic wave amplitude states from zero ones, is associated with a second-order phase transition. These two studies provide both a testbed for the Monte Carlo canonical and microcanonical codes, with the comparison with exact canonical results, and an opportunity to propose quantitative results to longstanding issues in basic nonlinear plasma physics. Then, the properly speaking weak turbulence framework is considered through the case of a large spectrum of waves. Focusing on the small coupling limit as a benchmark for the statistical mechanics of weak Langmuir turbulence, it is shown that Monte Carlo microcanonical results fully agree with an exact microcanonical derivation. The wave spectrum is predicted to collapse towards small wavelengths together with the escape of initially resonant particles towards low bulk plasma thermal speeds. This study reveals the fundamental discrepancy between the long-time dynamics of single waves, which can support finite amplitude steady states, and of wave spectra, which cannot.
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52.40.Mj Particle beam interactions in plasmas
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Ra Plasma turbulence
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.65.Pp Monte Carlo methods
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Radial propagation of structures in drift wave turbulence

T. Windisch, O. Grulke, and T. Klinger

Phys. Plasmas 13, 122303 (2006); http://dx.doi.org/10.1063/1.2400845 (7 pages) | Cited 34 times

Online Publication Date: 8 December 2006

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The formation and propagation of spatiotemporal fluctuation structures in weakly developed drift-wave turbulence in a linearly magnetized helicon device is investigated. Turbulent density fluctuations in the far edge plasma display an intermittent character with large-amplitude positive density bursts. Their peak amplitudes correspond to the time-averaged density in the maximum radial plasma pressure gradient. The conditional average technique is applied to reconstruct the dynamics of turbulent coherent structures in the azimuthal plane. The formation of turbulent structures is closely linked to a quasicoherent m = 1 drift wave mode, which is generally observed in the radial density gradient region in the weakly developed turbulent state. It is demonstrated that every positive high amplitude density burst in the plasma edge is due to the radial propagation of a turbulent structure. The typical scale size of the turbulent structures is 4ρs and their lifetime exceeds the eddy turnover time by orders of magnitude, thereby characterizing them as coherent structures. Although the turbulent structures propagate mainly azimuthally in the direction of the E×B drift they are observed to have a radial velocity, which is typically 10% of the ion sound speed.
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52.35.Ra Plasma turbulence
52.35.Kt Drift waves
52.25.Gj Fluctuation and chaos phenomena
52.40.Hf Plasma-material interactions; boundary layer effects
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.25.Fi Transport properties

Nonlinear modulated dust lattice wave packets in two-dimensional hexagonal dust crystals

B. Farokhi, I. Kourakis, and P. K. Shukla

Phys. Plasmas 13, 122304 (2006); http://dx.doi.org/10.1063/1.2400594 (10 pages) | Cited 12 times

Online Publication Date: 13 December 2006

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The amplitude modulation of dust lattice waves (DLWs) propagating in a two-dimensional hexagonal dust crystal is investigated in a continuum approximation, accounting for the effect of dust charge polarization (dressed interactions). A dusty plasma crystalline configuration with constant dust grain charge and mass is considered. The dispersion relation and the group velocity for DLWs are determined for wave propagation in both longitudinal and transverse directions. The reductive perturbation method is used to derive a (2+1)-dimensional nonlinear Schrödinger equation (NLSE). New expressions for the coefficients of the NLSE are derived and compared, for a Yukawa-type potential energy and for a “dressed” potential energy, taking into account interaction and geometric nonlinearities.
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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)
52.27.Lw Dusty or complex plasmas; plasma crystals
02.30.Hq Ordinary differential equations

Experimental evidence of mode coupling in drift wave intermittent turbulence using a wave number bicoherence analysis

F. Brochard, T. Windisch, O. Grulke, and T. Klinger

Phys. Plasmas 13, 122305 (2006); http://dx.doi.org/10.1063/1.2402131 (6 pages) | Cited 16 times

Online Publication Date: 15 December 2006

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Spatiotemporal mode coupling is studied experimentally in a cylindrical plasma device. For that purpose, a bicoherence analysis is applied to spatially resolved measurements of drift wave fluctuations in order to study nonlinear coupling in the wave number spectrum. The use of the k bicoherence is shown to be much more accurate and straightforward than one of the ω bicoherence, revealing bicoherence bursts with a characteristic duration shorter than the characteristic period of the signals. It is demonstrated that intermittent structures can be produced during these events.
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52.35.Ra Plasma turbulence
52.35.Kt Drift waves
52.25.Gj Fluctuation and chaos phenomena
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.70.Ds Electric and magnetic measurements

Characterizing electron temperature gradient turbulence via numerical simulation

W. M. Nevins, J. Candy, S. Cowley, T. Dannert, A. Dimits, W. Dorland, C. Estrada-Mila, G. W. Hammett, F. Jenko, M. J. Pueschel, and D. E. Shumaker

Phys. Plasmas 13, 122306 (2006); http://dx.doi.org/10.1063/1.2402510 (13 pages) | Cited 40 times

Online Publication Date: 20 December 2006

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Numerical simulations of electron temperature gradient (ETG) turbulence are presented that characterize the ETG fluctuation spectrum, establish limits to the validity of the adiabatic ion model often employed in studying ETG turbulence, and support the tentative conclusion that plasma-operating regimes exist in which ETG turbulence produces sufficient electron heat transport to be experimentally relevant. We resolve prior controversies regarding simulation techniques and convergence by benchmarking simulations of ETG turbulence from four microturbulence codes, demonstrating agreement on the electron heat flux, correlation functions, fluctuation intensity, and rms flow shear at fixed simulation cross section and resolution in the plane perpendicular to the magnetic field. Excellent convergence of both continuum and particle-in-cell codes with time step and velocity-space resolution is demonstrated, while numerical issues relating to perpendicular (to the magnetic field) simulation dimensions and resolution are discussed. A parameter scan in the magnetic shear, s, demonstrates that the adiabatic ion model is valid at small values of s (s<0.4 for the parameters used in this scan) but breaks down at higher magnetic shear. A proper treatment employing gyrokinetic ions reveals a steady increase in the electron heat transport with increasing magnetic shear, reaching electron heat transport rates consistent with analyses of experimental tokamak discharges.
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52.35.Ra Plasma turbulence
52.65.Rr Particle-in-cell method
52.25.Gj Fluctuation and chaos phenomena
52.25.Fi Transport properties
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.55.Fa Tokamaks, spherical tokamaks

The dynamics of an isolated plasma filament at the edge of a toroidal device

D. D. Ryutov

Phys. Plasmas 13, 122307 (2006); http://dx.doi.org/10.1063/1.2403092 (9 pages) | Cited 15 times

Online Publication Date: 20 December 2006

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The dynamics of an isolated plasma filament (an isolated blob) in the far scrape-off layer (SOL) of a toroidal device is described, with a proper averaging of the geometrical parameters as well as plasma parameters along the filament. The analysis is limited to the magnetohydrodynamic description. The effects of the electrical contact of the filament end with the limiter and of the finite plasma resistivity are also discussed.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Fi Transport properties
52.55.Fa Tokamaks, spherical tokamaks

Coupled fluid-flow and magnetic-field simulation of the Riga dynamo experiment

S. Kenjereš, K. Hanjalić, S. Renaudier, F. Stefani, G. Gerbeth, and A. Gailitis

Phys. Plasmas 13, 122308 (2006); http://dx.doi.org/10.1063/1.2404930 (14 pages) | Cited 9 times

Online Publication Date: 26 December 2006

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Magnetic fields of planets, stars, and galaxies result from self-excitation in moving electroconducting fluids, also known as the dynamo effect. This phenomenon was recently experimentally confirmed in the Riga dynamo experiment [ A. Gailitis et al., Phys. Rev. Lett. 84, 4365 (2000) ; A. Gailitis et al., Physics of Plasmas 11, 2838 (2004) ], consisting of a helical motion of sodium in a long pipe followed by a straight backflow in a surrounding annular passage, which provided adequate conditions for magnetic-field self-excitation. In this paper, a first attempt to simulate computationally the Riga experiment is reported. The velocity and turbulence fields are modeled by a finite-volume Navier-Stokes solver using a Reynolds-averaged-Navier-Stokes turbulence model. The magnetic field is computed by an Adams-Bashforth finite-difference solver. The coupling of the two computational codes, although performed sequentially, provides an improved understanding of the interaction between the fluid velocity and magnetic fields in the saturation regime of the Riga dynamo experiment under realistic working conditions.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.Fi Transport properties
52.35.Ra Plasma turbulence
02.70.Bf Finite-difference methods

Estimation of higher-order contribution to viscosity of hydrogen plasmas including electronically excited states

Gurpreet Singh and Kuldip Singh

Phys. Plasmas 13, 122309 (2006); http://dx.doi.org/10.1063/1.2405342 (4 pages) | Cited 5 times

Online Publication Date: 27 December 2006

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Within the framework of the Chapman-Enskog method, the influence of electronically excited states on viscosity and its higher-order contributions has been investigated for a partially ionized thermal hydrogen plasma. A strong dependence of viscosity and its higher-order contributions on the presence of electronically excited states (especially at high pressure) has been observed. In the present work, a simplified relationship has been suggested for estimating higher-order contribution to viscosity, which avoids the cumbersome computational procedure involved in its exact evaluation. The results thus obtained agree with the exact contributions satisfactorily.
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52.25.Fi Transport properties
52.25.Jm Ionization of plasmas

Oblique modulation of electrostatic modes and envelope excitations in pair-ion and electron-positron plasmas

A. Esfandyari-Kalejahi, I. Kourakis, and P. K. Shukla

Phys. Plasmas 13, 122310 (2006); http://dx.doi.org/10.1063/1.2405328 (9 pages) | Cited 20 times

Online Publication Date: 29 December 2006

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The nonlinear amplitude modulation of electrostatic waves propagating in a collisionless two-component plasma consisting of negative and positive species of equal mass and absolute charge is investigated. Pair-ion (e.g., fullerene) and electron-positron (e-p) plasmas (neglecting recombination) are covered by this description. Amplitude perturbation oblique to the direction of propagation of the wave has been considered. Two distinct linear electrostatic modes exist, namely an acoustic lower mode and Langmuir-type optic-type upper one. The behavior of each of these modes is examined from the modulational stability point of view. The stability criteria are investigated, depending on the electrostatic carrier wave number, the angle θ between the modulation and propagation directions, and the positron-to-electron temperature ratio σ. The analysis shows that modulated electrostatic wavepackets associated to the lower (acoustic) mode are unstable, for small values of carrier wave number k (i.e., for large wavelength λ) and for finite (small) values of the angle θ (yet stable for higher θ), while those related to the upper (optic-like) mode are stable for large values of the angle θ only, in the same limit, yet nearly for all values of σ. These results are of relevance in astrophysical contexts (e.g., in pulsar environments), where e-p plasmas are encountered, or in pair fullerene-ion plasmas, in laboratory.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Dm Sound waves
52.27.Ep Electron-positron plasmas
52.25.Fi Transport properties
back to top Magnetically Confined Plasmas, Heating, Confinement

On nonexistence of tokamak equilibria with purely poloidal flow

G. N. Throumoulopoulos, H. Weitzner, and H. Tasso

Phys. Plasmas 13, 122501 (2006); http://dx.doi.org/10.1063/1.2397042 (5 pages) | Cited 11 times

Online Publication Date: 4 December 2006

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It is proved that irrespective of compressibility, tokamak steady states with purely poloidal mass flow cannot exist in the framework of either magnetohydrodynamics (MHD) or Hall MHD models. Nonexistence persists within single-fluid plasma models with pressure anisotropy and incompressible flows.
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52.55.Fa Tokamaks, spherical tokamaks
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Erosion/redeposition analysis of the ITER first wall with convective and non-convective plasma transport

J. N. Brooks, J. P. Allain, and T. D. Rognlien

Phys. Plasmas 13, 122502 (2006); http://dx.doi.org/10.1063/1.2401610 (8 pages) | Cited 11 times

Online Publication Date: 12 December 2006

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Sputtering erosion/redeposition is analyzed for IAEA [ Report GA10FDR1-01-07-13 (2001) ] plasma facing components, with scrape-off layer (SOL) plasma convective radial transport and nonconvective (diffusion-only) transport. The analysis uses the UEDGE code [ T .D. Rognlien et al., J. Nucl. Mater. 196, 347 (1992) ] and DEGAS code [ D. P. Stotler et al., Contrib. Plasma Phys. 40, 221 (2000) ] to compute plasma SOL profiles and ion and neutral fluxes to the wall, TRIM-SP code [ J. P. Biersack, W. Eckstein, J. Appl. Phys. A34, 73 (1984) ] to compute sputter yields, and the REDEP/WBC code package [ J. N. Brooks, Fusion Eng. Des. 60, 515 (2002) ] for three-dimensional kinetic modeling of sputtered particle transport. Convective transport is modeled for the background plasma by a radially varying outward-flow component of the fluid velocity, and for the impurity ions by three models designed to bracket existing models/data. Results are reported here for the first wall with the reference beryllium coating and an alternative tungsten coating. The analysis shows: (1) sputtering erosion for convective flow is 20–40 times higher than for diffusion-only but acceptably low ( ∼ 0.3 nm/s) for beryllium, and very low ( ∼ 0.002 nm/s) for tungsten; (2) plasma contamination by wall sputtering, with convective flow, is of order 1% for beryllium and negligible for tungsten; (3) wall-to-divertor beryllium transport may be significant ( ∼ 10%–60% of the sputtered Be current); (4) tritium co-deposition in redeposited beryllium may be high ( ∼ 1–6 gT/400 s pulse).
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52.40.Hf Plasma-material interactions; boundary layer effects
52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties
52.25.Dg Plasma kinetic equations
52.25.Vy Impurities in plasmas
52.25.Ya Neutrals in plasmas

High-frequency shear Alfvén instability driven by circulating energetic ions in NSTX

Ya. I. Kolesnichenko, R. B. White, and Yu. V. Yakovenko

Phys. Plasmas 13, 122503 (2006); http://dx.doi.org/10.1063/1.2402129 (3 pages) | Cited 2 times

Online Publication Date: 12 December 2006

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It is shown that a number of features of an instability with the frequency comparable to the ion gyrofrequency observed in the National Spherical Torus Experiment [E. D. Fredrickson et al., “Observation of hole-clump pair generation by global or compressional Alfvén eigenmodes,” Contributed Papers, 33rd European Physical Society Conference on Plasma Physics, Rome, 2006, Europhysics Conference Abstracts (European Physical Society, Petit-Lancy, 2006), Report P5.058 (unpublished)] is consistent with the features of the Alfvén instability with large, about the inverse, Larmor radius of the energetic ions (ρb−1) longitudinal wavenumbers. The conclusions drawn are based on an analysis of the resonant interaction of the energetic circulating ions and the waves, as well as on the calculation of the instability growth rate taking into account effects of the finite Larmor radius, ρb.
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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.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.40.Mj Particle beam interactions in plasmas
52.55.Fa Tokamaks, spherical tokamaks

Finite β correction to the magnetic flux tube ellipticity of the straight field line mirror

N. Savenko and O. Ågren

Phys. Plasmas 13, 122504 (2006); http://dx.doi.org/10.1063/1.2401153 (9 pages) | Cited 2 times

Online Publication Date: 14 December 2006

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A marginal minimum B mirror magnetic field has been proposed as an external plasma confining magnetic field for a single cell open magnetic mirror trap. An analytical expression for the flux tube ellipticity of this magnetic field has in a previous study been derived with a zero plasma β approximation. This mirror field, which consists of straight nonparallel field lines in the confinement region, has a particular interest since it is likely to correspond to the smallest possible ellipticity for a magnetohydrodynamic stable mirror confinement. The plasma current is in this paper taken into account to the first order in β and the influence of the plasma magnetic field on the magnetic flux surface geometry is studied.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
52.55.Tn Ideal and resistive MHD modes; kinetic modes
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.25.Fi Transport properties

Experimental profile evolution of a high-density field-reversed configuration

E. L. Ruden, Shouyin Zhang, T. P. Intrator, and G. A. Wurden

Phys. Plasmas 13, 122505 (2006); http://dx.doi.org/10.1063/1.2402130 (12 pages) | Cited 3 times

Online Publication Date: 18 December 2006

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A field-reversed configuration (FRC) gains angular momentum over time, eventually resulting in an n = 2 rotational instability (invariant under rotation by π) terminating confinement. To study this, a laser interferometer probes the time history of line integrated plasma density along eight chords of the high-density ( ∼ 1017 cm−3) field-reversed configuration experiment with a liner. Abel and tomographic inversions provide density profiles during the FRC’s azimuthally symmetric phase, and over a period when the rotational mode has saturated and rotates with a roughly fixed profile, respectively. During the latter part of the symmetric phase, the FRC approximates a magnetohydrodynamic (MHD) equilibrium, allowing the axial magnetic-field profile to be calculated from pressure balance. Basic FRC properties such as temperature and poloidal flux are then inferred. The subsequent two-dimensional n = 2 density profiles provide angular momentum information needed to set bounds on prior values of the stability relevant parameter α (rotational to ion diamagnetic drift frequency ratio), in addition to a view of plasma kinematics useful for benchmarking plasma models of higher order than MHD.
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52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps
52.55.Ez Theta pinch
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Fi Transport properties
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