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Jun 2005

Volume 12, Issue 6, Articles (06xxxx)

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Temperature and melting of laser-shocked iron releasing into an LiF window

G. Huser, M. Koenig, A. Benuzzi-Mounaix, E. Henry, T. Vinci, B. Faral, M. Tomasini, B. Telaro, and D. Batani

Phys. Plasmas 12, 060701 (2005); http://dx.doi.org/10.1063/1.1896375 (4 pages) | Cited 12 times

Online Publication Date: 27 May 2005

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Absolute reflectivity and self-emission diagnostics are used to determine the gray-body equivalent temperature of laser-shocked iron partially releasing into a lithium fluoride window. Pressure and reflectivity are measured simultaneously by means of velocity interferometer system for any reflector interferometers. In the temperature-pressure plane, a temperature plateau in the release is observed which is attributed to iron’s melting line. Extrapolation of data leads to a melting temperature at Earth’s inner-outer core boundary of 7800±1200 K, in good agreement with previous works based on dynamic compression. Shock temperatures were calculated and found to be in the liquid phase.
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62.50.-p High-pressure effects in solids and liquids
52.50.Lp Plasma production and heating by shock waves and compression
91.60.Fe Equations of state
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back to top Basic Plasma Phenomena, Waves, Instabilities

Invariant imbedding theory of mode conversion in inhomogeneous plasmas. I. Exact calculation of the mode conversion coefficient in cold, unmagnetized plasmas

Kihong Kim and Dong-Hun Lee

Phys. Plasmas 12, 062101 (2005); http://dx.doi.org/10.1063/1.1914536 (7 pages) | Cited 11 times

Online Publication Date: 26 May 2005

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This is the first of a series of papers devoted to the development of the invariant imbedding theory of mode conversion in inhomogeneous plasmas. A new version of the invariant imbedding theory of wave propagation in inhomogeneous media allows one to solve a wide variety of coupled wave equations exactly and efficiently, even in the cases where the material parameters change discontinuously at the boundaries and inside the inhomogeneous medium. In this paper, the invariant imbedding method is applied to the mode conversion of the simplest kind, that is, the conversion of p-polarized electromagnetic waves into electrostatic modes in cold, unmagnetized plasmas. The mode conversion coefficient and the field distribution are calculated exactly for linear and parabolic plasma density profiles and compared quantitatively with previous results.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.25.-b Plasma properties
52.20.-j Elementary processes in plasmas

Exact orbital motion theory of the shielding potential around an emitting, spherical body

G. L. Delzanno, A. Bruno, G. Sorasio, and G. Lapenta

Phys. Plasmas 12, 062102 (2005); http://dx.doi.org/10.1063/1.1914546 (18 pages) | Cited 13 times

Online Publication Date: 26 May 2005

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A kinetic theory for the equilibrium of an unmagnetized plasma consisting of electrons and ions surrounding a spherical body emitting electrons (due to thermionic emission, photoemission, or secondary emission) is presented. The theory is valid for positively charged bodies, neglects collisions of the plasma particles, and is formulated for profiles of the shielding potential presenting an attractive well. Particle-in-cell simulations are shown to be in good agreement with the theory. An approximated criterion is derived to determine the presence of the potential well.
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52.25.Dg Plasma kinetic equations
52.25.Tx Emission, absorption, and scattering of particles
52.65.Rr Particle-in-cell method

Absolute and convective instabilities of parallel propagating circularly polarized Alfvén waves: Beat instability

D. Simpson and M. S. Ruderman

Phys. Plasmas 12, 062103 (2005); http://dx.doi.org/10.1063/1.1919407 (9 pages) | Cited 6 times

Online Publication Date: 26 May 2005

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Ruderman and Simpson [Phys. Plasmas 11, 4178 (2004) ] studied the absolute and convective decay instabilities of parallel propagating circularly polarized Alfvén waves in plasmas where the sound speed cS is smaller than the Alfvén speed υA. We extend their analysis for the beat instability which occurs in plasmas with cS>υA. We assume that the dimensionless amplitude of the circularly polarized Alfvén wave (pump wave), a, is small. Applying Briggs’ method we study the problem analytically using expansions in power series with respect to a. It is shown that the pump wave is absolutely unstable in a reference frame moving with the velocity U with respect to the rest plasma if Ul<U<Ur, where Ul = −υA+O(a) and Ur = υA+O(a). When U<Ul or U>Ur, the instability is convective. The signaling problem is studied in a reference frame where the pump wave is convectively unstable. It is shown that the spatially amplifying waves exist only when the signaling frequency is in two narrow symmetric frequency bands with the widths of the order of a3. These results enable us to extend for the case when cS>υA the conclusions, previously made for the case when cS<υA, that circularly polarized Alfvén waves propagating in the solar wind are convectively unstable in a reference frame of any spacecraft moving with the velocity not exceeding a few tens of km/s in the solar reference frame. The characteristic scale of spatial amplification for these waves exceeds 1 a.u.
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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)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Transition from flute modes to drift waves in a magnetized plasma column

F. Brochard, E. Gravier, and G. Bonhomme

Phys. Plasmas 12, 062104 (2005); http://dx.doi.org/10.1063/1.1921167 (7 pages) | Cited 15 times

Online Publication Date: 26 May 2005

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Recent experiments performed on the low β plasma device Mirabelle [ T. Pierre, G. Leclert, and F. Braun, Rev. Sci. Instrum. 58, 6 (1987) ] using a limiter have shown that transitions between various gradient driven instabilities occurred on increasing the magnetic field strength. New thorough measurements allow to identify unambiguously three instability regimes. At low magnetic field the strong E×B velocity shear drives a Kelvin–Helmholtz instability, whereas at high magnetic field drift waves are only observed. A centrifugal (Rayleigh–Taylor) instability is also observed in between when the E×B velocity is shearless and strong enough. A close connection is made between the ratio ρs/L⊥ of the drift parameter to the radial density gradient length and each instability regime.
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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.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Kt Drift waves
52.25.Xz Magnetized plasmas
52.75.-d Plasma devices
52.30.-q Plasma dynamics and flow

Tailoring of ion species composition in complex plasmas with charge exchange collisions

K. Ostrikov

Phys. Plasmas 12, 062105 (2005); http://dx.doi.org/10.1063/1.1925547 (8 pages) | Cited 1 time

Online Publication Date: 26 May 2005

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A generic approach towards tailoring of ion species composition in reactive plasmas used for nanofabrication of various functional nanofilms and nanoassemblies, based on a simplified model of a parallel-plate rf discharge, is proposed. The model includes an idealized reactive plasma containing two neutral and two ionic species interacting via charge exchange collisions in the presence of a microdispersed solid component. It is shown that the number densities of the desired ionic species can be efficiently managed by adjusting the dilution of the working gas in a buffer gas, rates of electron impact ionization, losses of plasma species on the discharge walls, and surfaces of fine particles, charge exchange rates, and efficiency of three-body recombination processes in the plasma bulk. The results are relevant to the plasma-aided nanomanufacturing of ordered patterns of carbon nanotip and nanopyramid microemitters.
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52.77.-j Plasma applications
52.80.Pi High-frequency and RF discharges
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Ya Neutrals in plasmas
52.40.Hf Plasma-material interactions; boundary layer effects
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

Experimental verification of the dielectric constant of a magnetized rotating plasma

C. Teodorescu, R. F. Ellis, A. Case, C. Cothran, A. Hassam, R. Lunsford, and S. Messer

Phys. Plasmas 12, 062106 (2005); http://dx.doi.org/10.1063/1.1924391 (6 pages) | Cited 3 times

Online Publication Date: 26 May 2005

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Direct measurements confirm that the magnetized plasma perpendicular dielectric constant has a linear dependence on the plasma density for fixed magnetic field, as predicted by magnetohydrodynamic (MHD) theory. In experiments performed on the Maryland Centrifugal Experiment (MCX) [ R. F. Ellis, A. B. Hassam, S. Messer, and B. R. Osborn, Phys. Plasmas, 8, 2057 (2001) ], line-averaged hydrogen plasma electron density is measured using a Mach–Zehnder interferometer. For small rotational Alfven Mach numbers, the measured size of the perpendicular plasma dielectric constant is also in agreement with MHD theory. Plasma density in the range of (1–8)×1020 m−3 and relative perpendicular plasma dielectric constant of the order of 106 are measured.
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52.25.Mq Dielectric properties
52.25.Xz Magnetized plasmas
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Dust-lattice waves: Role of charge variations and anisotropy of dust-dust interaction

R. Kompaneets, A. V. Ivlev, V. Tsytovich, and G. Morfill

Phys. Plasmas 12, 062107 (2005); http://dx.doi.org/10.1063/1.1926650 (6 pages) | Cited 14 times

Online Publication Date: 27 May 2005

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Dust-lattice waves are studied in the framework of the one-dimensional particle string model. The dust-dust interaction potential is assumed to have an arbitrary dependence on the vertical and horizontal coordinates, which allows to take into account the wake field effects. Both the vertical and horizontal charge variations are also included into the model. The model yields the coupling between the vertical and horizontal (longitudinal) modes: the coupling coefficient is the sum of six terms, each caused by a different physical mechanism. It is shown that the coupling can trigger the resonance oscillatory instability, which has been already observed in experiments. It is also shown that a nonoscillatory instability can appear at small wave numbers due to the coupling.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.27.Lw Dusty or complex plasmas; plasma crystals
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Effect of charge fluctuations and collisions on the energy loss of N×M projectiles for a generalized Lorentzian dusty plasma

M. Adnan Sarwar and Arshad M. Mirza

Phys. Plasmas 12, 062108 (2005); http://dx.doi.org/10.1063/1.1928387 (9 pages) | Cited 10 times

Online Publication Date: 6 June 2005

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The shielded potential and the energy loss by N×M projectiles passing through a collisional dust-contaminated plasma with dust-charge fluctuations and grain-size distribution are presented. Analytical general expressions are obtained for the shielded potential and for the energy loss by considering two-body correlation effects. An interference contribution of these projectiles to the potential and energy loss is observed which depends upon their orientation and separation distance. The dust-charge fluctuation produces a potential well instead of Coulomb-type potential for a slowly moving test charge with slow charge relaxation rate and energy is gained by the charged projectiles. However, fast charge relaxation enhances the energy loss and some peaks are observed showing the excitation of some electrostatic modes. On the other hand, the dust neutral collisions also enhance the energy loss for projectile velocities greater than the dust acoustic speed for a Maxwellian plasma (for a large value of the spectral index κ).
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52.25.Gj Fluctuation and chaos phenomena
52.20.-j Elementary processes in plasmas
52.27.Lw Dusty or complex plasmas; plasma crystals
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.)
52.40.Mj Particle beam interactions in plasmas
52.25.Ya Neutrals in plasmas

The effect of ion drift on the sheath, presheath, and ion-current collection for cylinders in a collisionless plasma

J. C. McMahon, G. Z. Xu, and J. G. Laframboise

Phys. Plasmas 12, 062109 (2005); http://dx.doi.org/10.1063/1.1924392 (11 pages) | Cited 7 times

Online Publication Date: 6 June 2005

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A calculation is presented of the behavior of the sheath and presheath surrounding an infinite cylindrical conducting object, representing a spacecraft or electrostatic probe, which is moving transversely through a collisionless plasma, such as is encountered in the ionosphere. The calculation is done by solving the coupled Vlasov (collisionless Boltzmann) and Poisson equations in an iterative manner. The results show that for some ratios of probe radius to electron Debye length, the ion current collected by the probe in a drifting plasma can be less than that collected in a nondrifting plasma. These changes in the current-collection behavior can be linked to changes that occur in the sheath and presheath with plasma drift, including at large enough drift speeds the disappearance or “collapse” of the presheath.
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52.40.Kh Plasma sheaths
52.70.Nc Particle measurements
52.65.Cc Particle orbit and trajectory
52.65.Ff Fokker-Planck and Vlasov equation

Nonlinear dynamic of low-frequency Buneman instability of a current-driven plasma

B. Shokri and A. R. Niknam

Phys. Plasmas 12, 062110 (2005); http://dx.doi.org/10.1063/1.1929367 (3 pages) | Cited 10 times

Online Publication Date: 8 June 2005

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Theoretical investigation of the nonlinear dynamic of the low-frequency Buneman instability of a current-driven plasma is presented. In the nonlinear stage, this instability is described by the diffusion equation with a negative nonlinear diffusion coefficient. As a result, the plasma density profile reaches a sharp peak and is accompanied by the breakdown of quasineutrality and establishment of stationary self-focusing structures.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.Fi Transport properties

Polarization evolution of radiation in hot magnetized plasma with dissipation

S. E. Segre and V. Zanza

Phys. Plasmas 12, 062111 (2005); http://dx.doi.org/10.1063/1.1931927 (6 pages) | Cited 4 times

Online Publication Date: 8 June 2005

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A formalism is presented for the analysis of polarization evolution in a magnetized plasma with dissipation due to kinetic effects. Such a plasma in addition to the Faraday and Cotton-Mouton effects also presents dichroism, namely anisotropic absorption. As expected this effect is significant near the cyclotron harmonics.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.25.Xz Magnetized plasmas

Numerical studies of driven, chirped Bernstein, Greene, and Kruskal modes

F. Peinetti, W. Bertsche, J. Fajans, J. Wurtele, and L. Friedland

Phys. Plasmas 12, 062112 (2005); http://dx.doi.org/10.1063/1.1928251 (9 pages) | Cited 7 times

Online Publication Date: 8 June 2005

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Recent experiments showed the possibility of creating long-lived, nonlinear kinetic structures in a pure-electron plasma. These structures, responsible for large-amplitude periodic density fluctuations, were induced by driving the plasma with a weak oscillating drive, whose frequency was adiabatically decreased in time [ W. Bertsche, J. Fajans, and L. Friedland, Phys. Rev. Lett. 91, 265003 (2003) ]. A one-dimensional analytical model of the system was developed [ L. Friedland, F. Peinetti, W. Bertsche, J. Fajans, and J. Wurtele, Phys. Plasmas 11, 4305 (2004) ], which pointed out the phenomenon responsible for the modifications induced by the weak drive in the phase-space distribution of the plasma (initially Maxwellian). In order to validate the theory and to perform quantitative comparisons with the experiments, a more accurate description of the system is developed and presented here. The new detailed analysis of the geometry under consideration allows for more precise simulations of the excitation process, in which important physical and geometrical parameters (such as the length of the plasma column) are evaluated accurately. The numerical investigations probe properties and features of the modes not accessible to direct measurement. Due to the presence of two distinct time scales (because of the adiabatic chirp of the drive frequency), a fully two-dimensional numerical study of the system is expected to be rather time consuming. This becomes particularly important when, as here, a large number of comparisons (covering a wide range of drive parameters) are performed. For this reason, a coupled one-dimensional, radially averaged model is derived and implemented in a particle-in-cell code.
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52.27.Jt Nonneutral plasmas
52.35.Sb Solitons; BGK modes
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Waves and instabilities in weak inhomogeneous ideal Hall-magnetohydrodynamic plasmas

Zohar Kolberg, Edward Liverts, and Michael Mond

Phys. Plasmas 12, 062113 (2005); http://dx.doi.org/10.1063/1.1933758 (8 pages) | Cited 2 times

Online Publication Date: 8 June 2005

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The two-fluid magnetohydrodynamic equations in which the Hall term is taken into account in Faraday’s law (Hall magnetohydrodynamic) for low-density magnetized inhomogeneous plasmas with finite pressure, and accounting for the inertial electron and ion dynamics responses are considered for slab geometry. Waves that propagate in the direction perpendicular to the density gradient and close to the direction of the background magnetic field are considered and linear analysis is employed in order to derive a local dispersion relation. It is shown that both the ion-cyclotron acoustic mode as well as the magnetosound mode are susceptible to an instability that is driven by the spatial inhomogeneity of the plasma density. The condition under which unstable waves appear and the growth rate of the unstable modes are obtained for collisionless plasmas. The results of this theoretical investigation can be relevant to instabilities in low-beta fusion plasma devices as well as in various space applications.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Spin waves in dusty plasmas

B. Shokri and S. Kh. Alavi

Phys. Plasmas 12, 062114 (2005); http://dx.doi.org/10.1063/1.1937425 (5 pages)

Online Publication Date: 8 June 2005

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Taking into account the spin of dust particles in a dusty plasma, the bulk and surface spin oscillations in an isotropic one are studied. The dispersion relation and frequency spectra for bulk and surface spin waves are obtained.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.27.Lw Dusty or complex plasmas; plasma crystals
52.30.-q Plasma dynamics and flow

Control of the charge and the nonlinear oscillation of dust particles by alternating current voltage superposition on the cathode in a direct current discharge

S. Park, C. R. Seon, and W. Choe

Phys. Plasmas 12, 062115 (2005); http://dx.doi.org/10.1063/1.1938127 (7 pages)

Online Publication Date: 9 June 2005

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Experimental and theoretical studies were conducted to investigate the control of charge and modification of nonlinear oscillations of externally injected dust particles in a dc discharge. The superposition of ac voltage on a dc cathode led to plasma density modulation, which brought about a drastic change of particle oscillation characteristics. Examples of the changes include disappearance of the subharmonic resonance peak and hysteresis as the ac superposition voltage was increased, which is attributed to the fact that the ac superposition made sheath structure less nonlinear and less parametrically resonant. In addition, as the ac frequency decreased from 5 kHz to 1 kHz at the same ac voltage (15 V), the subharmonic peak became weakened along with its frequency. This result demonstrates that the dust charge is the main parameter in determining occurrence of the subharmonic resonance peak. We consequently expect that modification of the oscillation dynamics of dust particles and furthermore the separate control of the charge may be possible by the ac modulation of the dc biased cathode.
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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.)
52.27.Lw Dusty or complex plasmas; plasma crystals
52.40.Kh Plasma sheaths
52.25.Fi Transport properties
52.80.Hc Glow; corona

Effect of frequency variation on electromagnetic pulse interaction with charges and plasma

A. G. Khachatryan, F. A. van Goor, J. W. J. Verschuur, and K.-J. Boller

Phys. Plasmas 12, 062116 (2005); http://dx.doi.org/10.1063/1.1938167 (8 pages) | Cited 12 times

Online Publication Date: 9 June 2005

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The effect of frequency variation (chirp) in an electromagnetic (EM) pulse on the pulse interaction with a charged particle and plasma is studied. Various types of chirp and pulse envelopes are considered. In vacuum, a charged particle receives a kick in the polarization direction after interaction with a chirped EM pulse. Interaction of a one-dimensional chirped pulse with uniform plasma is considered. We found that the amplitude of the wake wave generated in plasma by an EM pulse can be significantly higher when the pulse is chirped.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma

A magnetohydrodynamic model for quantum plasmas

F. Haas

Phys. Plasmas 12, 062117 (2005); http://dx.doi.org/10.1063/1.1939947 (9 pages) | Cited 145 times

Online Publication Date: 9 June 2005

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The quantum hydrodynamic model for charged particle systems is extended to the cases of nonzero magnetic fields. In this way, quantum corrections to magnetohydrodynamics are obtained starting from the quantum hydrodynamical model with magnetic fields. The importance of the quantum corrections is described by a parameter H which can be significant in dense astrophysical plasmas. The quantum magnetohydrodynamic model is analyzed in the infinite conductivity limit. The conditions for equilibrium in ideal quantum magnetohydrodynamics are established. Translationally invariant exact equilibrium solutions are obtained in the case of the ideal quantum magnetohydrodynamic model.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Fi Transport properties
03.65.Ge Solutions of wave equations: bound states
back to top Nonlinear Phenomena, Turbulence, Transport

Onset and saturation of guide-field magnetic reconnection

P. L. Pritchett

Phys. Plasmas 12, 062301 (2005); http://dx.doi.org/10.1063/1.1914309 (11 pages) | Cited 31 times

Online Publication Date: 26 May 2005

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The onset and saturation of collisionless magnetic reconnection in the presence of a guide field are investigated using two-dimensional particle-in-cell simulations in which the reconnection evolves out of the initial thermal noise in the current sheet and in which the resolution is sufficient to resolve the electron singular layer. The simulations show that reconnection does not abate when the island width exceeds either the electron singular layer or the initial current sheet width. Instead, reconnection proceeds through an explosive stage which appears to be limited only by the spatial size of the system. The guide-field reconnection dynamics is dominated by the formation of an asymmetric configuration with a deep density cavity along one pair of separatrix arms. In this cavity an electron beam feature is formed which excites the Buneman instability. Near the X line the reconnection electric field is supported by a combination of quasiviscous and bulk inertia effects for the electrons. Around the island perimeter, intense Debye-scale, predominantly perpendicular, electric field structures are formed.
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52.35.Vd Magnetic reconnection
52.65.Rr Particle-in-cell method
52.25.Fi Transport properties
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Nonlinear gyrokinetic turbulence simulations of E×B shear quenching of transport

J. E. Kinsey, R. E. Waltz, and J. Candy

Phys. Plasmas 12, 062302 (2005); http://dx.doi.org/10.1063/1.1920327 (9 pages) | Cited 46 times

Online Publication Date: 26 May 2005

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The effects of E×B velocity shear have been investigated in nonliner gyrokinetic turbulence simulations with and without kinetic electrons. The impact of E×B shear stabilization in electrostatic flux-tube simulations is well modeled by a simple quench rule with the turbulent diffusivity scaling like 1−αEγE/γmax, where γE is the E×B shear rate, γmax is maximum linear growth rate without E×B shear, and αE is a multiplier. The quench rule was originally deduced from adiabatic electron ion temperature gradient (ITG) simulations where it was found that αE ≈ 1. The results presented in this paper show that the quench rule also applies in the presence of kinetic electrons for long-wavelength transport down to the ion gyroradius scale. Without parallel velocity shear, the electron and ion transport is quenched near γE/γmax ≈ 2 (αE ≈ 1/2). When the destabilizing effect of parallel velocity shear is included in the simulations, consistent with purely toroidal rotation, the transport may not be completely quenched by any level of E×B shear because the Kelvin–Helmholtz drive increases γmax faster than γE increases. Both ITG turbulence with added trapped electron drive and electron-directed and curvature-driven trapped electron mode turbulence are considered.
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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.Tt Gyrofluid and gyrokinetic simulations
52.35.Kt Drift waves
52.25.Fi Transport properties
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.30.-q Plasma dynamics and flow

Coherent structure of zonal flow and onset of turbulent transport

K. Itoh, K. Hallatschek, S.-I. Itoh, P. H. Diamond, and S. Toda

Phys. Plasmas 12, 062303 (2005); http://dx.doi.org/10.1063/1.1922788 (14 pages) | Cited 26 times

Online Publication Date: 26 May 2005

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Excitation of the turbulence in the range of drift wave frequency and zonal flow in magnetized plasmas is analyzed. Nonlinear stabilization effect on zonal flow drive is introduced, and the steady state solution is obtained. The condition for the onset of turbulent transport is obtained and partition ratio of fluctuation energy into turbulence and zonal flows is derived. The turbulent transport coefficient, which includes the effect of zonal flow, is also obtained. Analytic result and direct numerical simulation show a good agreement.
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52.30.-q Plasma dynamics and flow
52.35.Ra Plasma turbulence
52.25.Fi Transport properties
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.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.Xz Magnetized plasmas

Extension of geodesic acoustic mode theory to helical systems

T. Watari, Y. Hamada, A. Fujisawa, K. Toi, and K. Itoh

Phys. Plasmas 12, 062304 (2005); http://dx.doi.org/10.1063/1.1922807 (8 pages) | Cited 33 times

Online Publication Date: 26 May 2005

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The present paper extends the theory of geodesic acoustic mode (GAM) oscillation, which so far has been applied to tokamaks, to helical systems. By using drift kinetic equations for three-dimensional equilibriums, a generalized dispersion relation is obtained including Landau damping. The oscillation frequency is obtained in terms of the squared sum of Fourier components of the magnetic field intensity expressed by means of magnetic flux coordinates. An analytic form of the collisionless damping rate of GAM is obtained by solving the dispersion relation perturbatively. It is found that the GAM frequency is higher in helical systems than in tokamaks and that damping rate is enhanced in multi-helicity magnetic configurations. However, damping rates are predicted to be small if the temperature of electrons is higher than that of ions.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Kt Drift waves
52.35.Dm Sound waves
52.25.Dg Plasma kinetic equations
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.55.Jd Magnetic mirrors, gas dynamic traps

Particle simulations with a generalized gyrokinetic solver

Alexey Mishchenko, Axel Könies, and Roman Hatzky

Phys. Plasmas 12, 062305 (2005); http://dx.doi.org/10.1063/1.1925587 (10 pages) | Cited 8 times

Online Publication Date: 26 May 2005

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This paper presents a generalized gyrokinetic solver which can be used for all perpendicular wavelengths of interest and allows to include the nonlinear gyrokinetic polarization density in the simulations. The polarization density, being an integral over the phase space is calculated using “numerical particles” (not to be confused with the marker particles which are used in the charge assignment) and finite elements. Integrals over the gyroangle are calculated using an N-point approximation. The accuracy requirements on the number of the gyropoints and numerical particles are discussed. The linear part of the solver has been implemented numerically and benchmarked with the slab dispersion relation for both the ion temperature gradient driven (ITG) mode and the electron temperature gradient driven (ETG) mode. Additionally, linear ITG and ETG modes are considered in a two-dimensional bumpy pinch configuration.
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52.65.Tt Gyrofluid and gyrokinetic simulations
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.25.-b Plasma properties

Distorted waves for the study of dispersion

Barnana Pal, Santwana Raychaudhuri, and Yoshinobu Kawai

Phys. Plasmas 12, 062306 (2005); http://dx.doi.org/10.1063/1.1915348 (4 pages)

Online Publication Date: 26 May 2005

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A Fourier transform computational method for the study of dispersion causing distortion of waves in general is presented in this paper. The method is employed for the first time to determine the propagation parameters for ion-acoustic waves produced in a double plasma device. The dispersion characteristics obtained for this system are found to be in good agreement with the theoretically predicted dispersion relation.
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52.35.Dm Sound waves
52.75.-d Plasma devices

Effect of ion ∇B drift direction on density fluctuation poloidal flow and flow shear

C. Fenzi, G. R. McKee, R. J. Fonck, K. H. Burrell, T. N. Carlstrom, and R. J. Groebner

Phys. Plasmas 12, 062307 (2005); http://dx.doi.org/10.1063/1.1915349 (9 pages) | Cited 10 times

Online Publication Date: 26 May 2005

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The divertor magnetic geometry has a significant effect on the poloidal velocity and resulting velocity shear of turbulent density fluctuations in the outer region of L-mode tokamak plasmas, as determined via two-dimensional measurements of density fluctuations with beam emission spectroscopy on DIII-D [ J. L. Luxon, Nucl. Fusion 42, 614 (2002) ]. Plasmas with similar parameters, except that in one case the ion ∇B drift points towards the divertor X point (lower-single-null, LSN), and in the other case, the ion ∇B drift points away from the divertor X point (upper-single-null, USN), are compared. Inside r/a = 0.9, the turbulence characteristics (density fluctuation amplitude, flow direction, correlation lengths) are similar in both cases, while near r/a = 0.92, a dramatic reversal of the poloidal velocity of turbulent eddies relative to the core flow direction is observed in plasmas with the ion ∇B drift pointing towards the divertor X point. No such velocity reversal is observed in plasmas with the ion ∇B drift pointing away from the divertor X point. This poloidal velocity reversal results in a significantly larger local shear in the poloidal velocity of density fluctuations in plasmas with the ion ∇B drift pointing towards the divertor X point. Additionally, these plasmas locally exhibit significant dispersion with two distinct and counterpropagating turbulence modes. Likewise, the radial correlation length of the density fluctuations is reduced in these plasmas, consistent with biorthogonal decomposition measurements of dominant turbulence structures. The naturally occurring density fluctuation poloidal velocity shear in these LSN plasmas may facilitate the L-H transition that occurs at an input power of roughly one-half to one-third that of corresponding plasmas with the ion ∇B drift pointing away from the X point.
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52.25.Gj Fluctuation and chaos phenomena
52.30.-q Plasma dynamics and flow
52.35.Ra Plasma turbulence
52.55.Fa Tokamaks, spherical tokamaks
52.55.Rk Power exhaust; divertors
52.70.Nc Particle measurements
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