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May 2006

Volume 13, Issue 5, Articles (05xxxx)

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Larmor radius size density holes discovered in the solar wind upstream of Earth’s bow shock

G. K. Parks, E. Lee, F. Mozer, M. Wilber, E. Lucek, I. Dandouras, H. Rème, C. Mazelle, J. B. Cao, K. Meziane, M. L. Goldstein, and P. Escoubet

Phys. Plasmas 13, 050701 (2006); http://dx.doi.org/10.1063/1.2201056 (4 pages) | Cited 12 times

Online Publication Date: 22 May 2006

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The Cluster and Double Star satellites recently observed plasma density holes upstream of Earth’s collisionless bow shock to apogee distances of ∼ 19 and 13 earth radii, respectively. A survey of 147 isolated density holes using 4 s time resolution data shows they have a mean duration of ∼ 17.9±10.4 s, but holes as short as 4 s are observed. The average fractional density depletion (δn/n) inside the holes is ∼ 0.68±0.14. The upstream edge of density holes can have enhanced densities that are five or more times the solar wind density. Particle distributions show the steepened edge can behave like a shock. Multispacecraft analyses show the density holes move with the solar wind, can have an ion gyroradius scale, and could be expanding. A small normal electric field points outward. Similarly shaped magnetic holes accompany the density holes indicating strong coupling between fields and particles. The density holes are only observed with upstream particles, suggesting that backstreaming particles interacting with the solar wind are important.
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96.20.Br Origin and evolution
96.20.Dt Features, landmarks, mineralogy, and petrology
52.35.Tc Shock waves and discontinuities
52.25.Fi Transport properties
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
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back to top Basic Plasma Phenomena, Waves, Instabilities

Bounded dust-acoustic waves in a cylindrically bounded collisional dusty plasma with dust charge variation

Nan-Xia Wei and Ju-Kui Xue

Phys. Plasmas 13, 052101 (2006); http://dx.doi.org/10.1063/1.2196387 (5 pages) | Cited 8 times

Online Publication Date: 4 May 2006

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Taking into account the boundary, particle collisions, and dust charging effects, dust-acoustic waves in a uniform cylindrically bounded dusty plasma is investigated analytically, and the dispersion relation for the dust-acoustic wave is obtained. The effects of boundary, dust charge variation, particle collision, and dust size on the dust-acoustic wave are discussed in detail. Due to the bounded cylindrical boundary effects, the radial wave number is discrete, i.e., the spectrum is discrete. It is shown that the discrete spectrum, the adiabatic dust charge variation, dust grain size, and the particle collision have significant effects on the dust-acoustic wave.
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52.35.Dm Sound waves
52.27.Lw Dusty or complex plasmas; plasma crystals
52.40.Hf Plasma-material interactions; boundary layer effects
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.20.Fs Electron collisions

Generation of filamentary structures by beam-plasma interaction

X. Y. Wang and Y. Lin

Phys. Plasmas 13, 052102 (2006); http://dx.doi.org/10.1063/1.2197797 (8 pages) | Cited 5 times

Online Publication Date: 4 May 2006

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The previous simulations by Wang and Lin [Phys. Plasmas. 10, 3528, (2003) ] showed that filaments, frequently observed in space plasmas, can form via the interaction between an ion beam and a background plasma. In this study, the physical mechanism for the generation of the filaments is investigated by a two-dimensional hybrid simulation, in which a field-aligned ion beam with relative beam density nb = 0.1 and beam velocity Vb = 10VA is initiated in a uniform plasma. Right-hand nonresonant ion beam modes, consistent with the linear theory, are found to be dominant in the linear stage of the beam-plasma interaction. In the later nonlinear stage, the nonresonant modes decay and the resonant modes grow through a nonlinear wave coupling. The interaction among the resonant modes leads to the formation of filamentary structures, which are the field-aligned structures (k⊥B) of magnetic field B, density, and temperature in the final stage. The filaments are nonlinearly generated in a prey-predator fashion by the parallel and oblique resonant ion beam modes, which meanwhile evolve into two types of shear Alfvén modes, with one mainly propagating along the background field B0 and the other obliquely propagating. The filamentary structures are found to be phase standing in the plasma frame, but their amplitude oscillates with time. In the dominant filament mode, fluctuations in the background ion density, background ion temperature, and beam density are in phase with the fluctuations in B, whereas the significantly enhanced beam temperature is antiphase with B. It is found that the filaments are produced by the interaction of at least two ion beam modes with comparable amplitudes, not by only one single mode, thus their generation mechanism is different from other mechanisms such as the stimulated excitation by the decay of an Alfvén wave.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.40.Mj Particle beam interactions in plasmas
52.65.Ww Hybrid methods
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.25.Gj Fluctuation and chaos phenomena

Properties of the acoustic mode in partially ionized and dusty plasmas

J. Vranjes and S. Poedts

Phys. Plasmas 13, 052103 (2006); http://dx.doi.org/10.1063/1.2197800 (4 pages) | Cited 12 times

Online Publication Date: 4 May 2006

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The properties of current-driven ion-acoustic (IA) and dust-acoustic (DA) modes in partially ionized plasmas are investigated. The current is oriented along the magnetic field lines and the mode is assumed to propagate at an angle with respect to the current. For highly collisional light plasma components, the fluid equations in the parallel direction are used. In the case of unmagnetized heavy species, which provide the mode inertia (ions for the IA mode and grains for the DA mode), the oblique perturbations will have an acoustic nature. For an arbitrary collision frequency of heavy species with neutrals, a kinetic description is used for the heavy species. For the DA mode, the dispersion equation is solved first in the limits of an electron-depleted plasma, showing that the mode has a minimum instability threshold at a large angle of propagation. This feature is primarily due to the collisions. For higher values of the charge on the grains, this minimum vanishes but the threshold becomes considerably lower. The full dispersion equation, with electrons having a current with an opposite sign compared to ions, is solved numerically yielding both a lower frequency and a smaller increment. A similar angle-dependent threshold and increment are found for the IA mode as well.
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52.35.Dm Sound waves
52.27.Lw Dusty or complex plasmas; plasma crystals
52.25.Fi Transport properties
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.20.Fs Electron collisions
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Lower hybrid turbulence driven by parallel currents and associated electron energization

Ben F. McMillan and Iver H. Cairns

Phys. Plasmas 13, 052104 (2006); http://dx.doi.org/10.1063/1.2198212 (13 pages) | Cited 10 times

Online Publication Date: 5 May 2006

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Parallel currents are usually in the form of field-aligned electron drifts in collisionless plasmas. The field-aligned drifts often drive instabilities. For instance, Drake et al. [Science, 299, 873 (2003)] found growth of parallel propagating turbulence initially and strong levels of oblique lower hybrid (LH) waves at later times; substantial parallel electron acceleration was also found. We use collisionless linear theory and quasilinear simulations to study wave growth and parallel electron dynamics in similar systems. In low-β plasmas with intense parallel currents and both with or without parallel E fields, LH waves are shown to grow even for electron distributions stable to the parallel Buneman instability and to accelerate electrons parallel to B very rapidly. This instability may be seen as the oblique limit of the ion acoustic and Buneman instabilities. The quasilinear diffusion via LH waves may release almost all of the available drift energy, and produce stronger electron acceleration and heating than the parallel Buneman instability alone.
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Transport processes of a non-neutral plasma coupled to an external rotating wave

Y. Soga, Y. Kiwamoto, and N. Hashizume

Phys. Plasmas 13, 052105 (2006); http://dx.doi.org/10.1063/1.2193911 (7 pages) | Cited 7 times

Online Publication Date: 4 May 2006

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Experimental investigations are carried out on radial transport phenomena of a pure electron plasma under the application of an external rotating wave that belongs to Trivelpiece-Gould (T-G) modes. Substantial radial compression of the density distribution is achieved by application of a properly controlled rotating electric field to one side of the plasma. Analyses of the observed plasma wave indicate that the efficient increase of the on-axis density entails the substantial damping of the T-G wave propagating in the plasma. The radial particle flux observed during the density compression is consistent with that of the theoretical model based on the drift-kinetic Vlasov equation [ Y. Kiwamoto et al., Phys. Plasmas 12, 094501 (2005) ]. This result implies that the radial compression of the plasma density distribution consists of the transverse E×B drift of particles subject to resonant wave-particle interaction in the axial dynamics.
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52.27.Jt Nonneutral plasmas

Effect of self-gravitation on the energy loss of pair of projectiles in dusty plasma

Arshad M. Mirza, M. Adnan Sarwar, and M. S. Qaisar

Phys. Plasmas 13, 052106 (2006); http://dx.doi.org/10.1063/1.2196877 (6 pages) | Cited 3 times

Online Publication Date: 10 May 2006

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The effect of self-gravitation of massive dust grains is investigated on the shielded potential and the energy loss of pair of charged projectiles passing through a dust-contaminated plasma. Analytical general expressions are derived for the shielded potential and for the energy loss by incorporating two-body correlation effects. An interference contribution of these projectiles to the shielded potential and energy loss is observed that depends upon their orientation and separation distance. It is found that for two collinear projectiles the potential is enhanced by increasing dust Jeans frequency for separation less than Debye length and the energy loss versus projectile velocity decreases with the increase of Jeans frequency for arbitrary separation. The effect of inclination of two noncollinear projectiles on energy loss is also investigated for a fixed value of Jeans frequency ωjd = 4×10−4ωpd. The contribution to the energy loss due to the interference term has been separately calculated for a typical Jeans frequency. The present investigation would be useful to explain the coagulation of dust particles in the molecular clouds and in the ion-beam-driven inertial confinement fusion approach.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.20.Fs Electron collisions
52.25.Fi Transport properties

Magnetohydrodynamics of fractal media

Vasily E. Tarasov

Phys. Plasmas 13, 052107 (2006); http://dx.doi.org/10.1063/1.2197801 (12 pages) | Cited 12 times

Online Publication Date: 10 May 2006

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The fractal distribution of charged particles is considered. An example of this distribution is the charged particles that are distributed over the fractal. The fractional integrals are used to describe fractal distribution. These integrals are considered as approximations of integrals on fractals. Typical turbulent media could be of a fractal structure and the corresponding equations should be changed to include the fractal features of the media. The magnetohydrodynamics equations for fractal media are derived from the fractional generalization of integral Maxwell equations and integral hydrodynamics (balance) equations. Possible equilibrium states for these equations are considered.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Ra Plasma turbulence
05.45.Df Fractals
02.30.Rz Integral equations

Green’s function of compressible Petschek-type magnetic reconnection

Thomas Penz, V. S. Semenov, V. V. Ivanova, M. F. Heyn, I. B. Ivanov, and H. K. Biernat

Phys. Plasmas 13, 052108 (2006); http://dx.doi.org/10.1063/1.2193088 (9 pages) | Cited 1 time

Online Publication Date: 10 May 2006

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We present a method to analyze the wave and shock structures arising from Petschek-type magnetic reconnection. Based on a time-dependent analytical approach developed by Heyn and Semenov [Phys. Plasmas 3, 2725 (1996) ] and Semenov et al. [Phys. Plasmas 11, 62 (2004) ], we calculate the perturbations caused by a delta function-shaped reconnection electric field, which allows us to achieve a representation of the plasma variables in the form of Green’s functions. Different configurations for the initial conditions are considered. In the case of symmetric, antiparallel magnetic fields and symmetric plasma density, the well-known structure of an Alfvén discontinuity, a fast body wave, a slow shock, a slow wave, and a tube wave occurs. In the case of asymmetric, antiparallel magnetic fields, additionally surface waves are found. We also discuss the case of symmetric, antiparallel magnetic fields and asymmetric densities, which leads to a faster propagation in the lower half plane, causing side waves forming a Mach cone in the upper half plane. Complex effects like anisotropic propagation characteristics, intrinsic wave coupling, and the generation of different nonlinear and linear wave modes in a finite β plasma are retained. The temporal evolution of these wave and shock structures is shown.
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52.35.Vd Magnetic reconnection
52.35.Tc Shock waves and discontinuities
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.25.Fi Transport properties
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
02.30.Sa Functional analysis

Differential equation model of an Alfvén wave maser

G. J. Morales and J. E. Maggs

Phys. Plasmas 13, 052109 (2006); http://dx.doi.org/10.1063/1.2200629 (13 pages) | Cited 3 times

Online Publication Date: 12 May 2006

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A mathematical model describing the operation of an Alfvén wave maser in a laboratory environment is constructed from a continuous differential equation. The model incorporates the essential features of maser operation, namely, a resonator with a semitransparent boundary, a unidirectional amplification region, and a nonuniform magnetic field that provides frequency filtering. The spectral features and the parameter scaling predicted by the model are in agreement with laboratory measurements of an Alfvén wave maser [ J. E. Maggs and G. J. Morales, Phys. Rev Lett. 91, 035004 (2003) ]. The model provides a useful tool to explore a variety of operational scenarios for users of this novel wave source, including studies of Alfvénic interactions of relevance to space and fusion plasmas.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.72.+v Laboratory studies of space- and astrophysical-plasma processes

Simulation of disk- and band-like voids in dusty plasma systems

Y. H. Liu, Z. Y. Chen, F. Huang, M. Y. Yu, L. Wang, and A. Bogaerts

Phys. Plasmas 13, 052110 (2006); http://dx.doi.org/10.1063/1.2201058 (6 pages) | Cited 14 times

Online Publication Date: 12 May 2006

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The minimum-energy configurations of systems of multispecies charged grains of different mass and charge with an interaction potential including long-range repulsive as well as short-range attractive components are studied by molecular dynamics simulation. The grains are also subject to a radial drag force and a quadratic confining potential. It is found that central as well as band-like void regions separating grains of different species can exist as well as coexist, depending on the species parameters. The results are consistent with the horizontal cross-sections of the structures found in a recent experiment on self-organization of chemically synthesizing grains [Huang et al. Chin. Phys. Lett. 21, 121 (2004)] .
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61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
36.40.Wa Charged clusters
61.43.Bn Structural modeling: serial-addition models, computer simulation
52.27.Lw Dusty or complex plasmas; plasma crystals

Dynamics of potential surface modes in a nonuniform plasma waveguide with finite electron temperature

E. A. Fedutenko, V. P. Olefir, and A. Sporov

Phys. Plasmas 13, 052111 (2006); http://dx.doi.org/10.1063/1.2197840 (13 pages) | Cited 1 time

Online Publication Date: 16 May 2006

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In this paper we study the mechanisms of wave-energy transformation in nonuniform waveguide plasmas maintained by surface modes in the presence of local upper-hybrid resonance. The dispersion equation is derived for such waves in the potential case with the following effects taken into account: the finite magnetic field, the finite electron temperature, and electron-neutral collisions. Numerical and analytical solutions for the dispersion and for eigenfield distributions of the waves are presented. The thermal conversion of the surface wave into the upper-hybrid volume modes at a finite electron temperature is shown to completely change the structure of the wave field distribution and to make the surface wave wavelength and the spatial damping rate very sensitive to slight shifts of the surface wave frequency.
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52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Fi Transport properties
02.60.Cb Numerical simulation; solution of equations

Unstable longitudinal plasma oscillations in a magnetic field: Nonrelativistic and relativistic considerations

R. C. Tautz, I. Lerche, and R. Schlickeiser

Phys. Plasmas 13, 052112 (2006); http://dx.doi.org/10.1063/1.2201533 (11 pages) | Cited 5 times

Online Publication Date: 16 May 2006

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The nonrelativistic and relativistic stability properties are investigated of longitudinal waves propagating in a plasma embedded in an ambient magnetic field, when the wave propagation direction is not necessarily either parallel or perpendicular to the ambient magnetic field. The analysis is based on the concept introduced by Harris [Phys. Rev. Lett. 2, 34 (1959) ] of neutral points in wavenumber space to determine plasma instability to one side or the other of such neutral points. The critical need is to determine whether a particular plasma distribution function permits the existence of a neutral point. Relativistic considerations, although necessary to include for many astrophysical plasmas, complicate significantly the determination of instability conditions. In this paper it is shown how one can provide a general argument for such neutral point determination and for determining instability rates in the neighborhood of such neutral points. Only waves independent of resonant wave-particle effects are considered.
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52.25.Mq Dielectric properties
52.27.−h
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)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
95.30.Qd Magnetohydrodynamics and plasmas

Dispersion properties of compressional electromagnetic waves in quantum dusty magnetoplasmas

S. Ali and P. K. Shukla

Phys. Plasmas 13, 052113 (2006); http://dx.doi.org/10.1063/1.2201535 (5 pages) | Cited 12 times

Online Publication Date: 19 May 2006

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A new dispersion relation for low-frequency compressional electromagnetic waves is derived by employing quantum magnetohydrodynamic model and Maxwell equations in cold quantum dusty magnetoplasmas. The latter is composed of inertialess electrons, mobile ions, and immobile charged dust particulates. The dispersion relation for the low-frequency compressional electromagnetic modes is further analyzed for the waves propagating parallel, perpendicular, and oblique to the external magnetic field direction. It is found theoretically and numerically that the quantum parameter αq = (ni0/ne0)ℏ2/(4memi) affects the real angular frequencies and the phase speeds of the compressional electromagnetic modes. Here, ni0 (ne0) is the equilibrium number density of the ions (electrons), me (mi) is the electron (ion) mass, and ℏ is the Plank constant divided by 2π.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.27.Lw Dusty or complex plasmas; plasma crystals
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.27.Cm Multicomponent and negative-ion plasmas
52.25.Fi Transport properties

Charging properties of a dust grain in collisional plasmas

S. A. Khrapak, G. E. Morfill, A. G. Khrapak, and L. G. D’yachkov

Phys. Plasmas 13, 052114 (2006); http://dx.doi.org/10.1063/1.2201538 (5 pages) | Cited 32 times

Online Publication Date: 22 May 2006

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Charging related properties of a small spherical grain immersed in a collisional plasma are investigated. Asymptotic expressions for charging fluxes, grain surface potential, long range electrostatic potential, and the properties of grain charge fluctuations due to the discrete nature of the charging process are obtained. These analytical results are in reasonable agreement with the available results of numerical modeling.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Electron parallel-flow shear driven low-frequency electromagnetic modes in collisionless magnetoplasma

P. K. Shukla, B. Eliasson, and M. Koepke

Phys. Plasmas 13, 052115 (2006); http://dx.doi.org/10.1063/1.2203605 (6 pages) | Cited 8 times

Online Publication Date: 22 May 2006

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The free energy associated with shear in the equilibrium parallel electron velocity is shown to be responsible for the excitation of low-frequency electromagnetic waves in collisionless magnetoplasma. New dispersion relations are derived by using the hydrodynamic equations for the electron fluid, the magnetic-field-aligned (parallel) drift of which varies in one of the perpendicular directions, and by using a kinetic ion model, together with Ampère’s law and Poisson’s equation. The dispersion relations are analyzed both analytically and numerically for a set of parameters representative of a laboratory experiment. New filamentary instabilities are predicted.
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52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.35.Tc Shock waves and discontinuities
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

The excitation of extraordinary and ordinary waves in a magnetized plasma medium by a rotating electron beam

B. Shokri and S. M. Khorashadizadeh

Phys. Plasmas 13, 052116 (2006); http://dx.doi.org/10.1063/1.2203603 (6 pages) | Cited 2 times

Online Publication Date: 24 May 2006

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The possibility of the excitation of extraordinary and ordinary cyclotron waves by interaction of a rotating electron beam propagating parallel to the external magnetic field with a cold plasma medium is investigated. By obtaining the growth rates, the influence of dissipation on the development of extraordinary and ordinary cyclotron waves are studied. By comparing the development of the cyclotron instability with the dissipative instability in extraordinary and ordinary cyclotron waves excitation in the beam-plasma system, the dependency of the growth rates of these instabilities on the physical parameters is discussed.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.40.Mj Particle beam interactions in plasmas
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.25.Xz Magnetized plasmas

Modulated electrostatic modes in pair plasmas: Modulational stability profile and envelope excitations

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

Phys. Plasmas 13, 052117 (2006); http://dx.doi.org/10.1063/1.2203951 (9 pages) | Cited 40 times

Online Publication Date: 24 May 2006

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A pair plasma consisting of two types of ions, possessing equal masses and opposite charges, is considered. The nonlinear propagation of modulated electrostatic wave packets is studied by employing a two-fluid plasma model. Considering propagation parallel to the external magnetic field, two distinct electrostatic modes are obtained, namely a quasiacoustic lower moddfe and a Langmuir-like, as optic-type upper one, in agreement with experimental observations and theoretical predictions. Considering small yet weakly nonlinear deviations from equilibrium, and adopting a multiple-scale technique, the basic set of model equations is reduced to a nonlinear Schrödinger equation for the slowly varying electric field perturbation amplitude. The analysis reveals that the lower (acoustic) mode is stable and may propagate in the form of a dark-type envelope soliton (a void) modulating a carrier wave packet, while the upper linear mode is intrinsically unstable, and may favor the formation of bright-type envelope soliton (pulse) modulated wave packets. These results are relevant to recent observations of electrostatic waves in pair-ion (fullerene) plasmas, and also with respect to electron-positron plasma emission in pulsar magnetospheres.
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52.30.Ex Two-fluid and multi-fluid plasmas
52.27.Ep Electron-positron plasmas
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.)

Charging of dust grains in a plasma with negative ions

Su-Hyun Kim and Robert L. Merlino

Phys. Plasmas 13, 052118 (2006); http://dx.doi.org/10.1063/1.2204830 (7 pages) | Cited 42 times

Online Publication Date: 26 May 2006

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The effect of negative ions on the charging of dust particles in a plasma is investigated experimentally. A plasma containing a very low percentage of electrons is formed in a single-ended Q machine when SF6 is admitted into the vacuum system. The relatively cold Q machine electrons (Te ≈ 0.2 eV) readily attach to SF6 molecules to form SF6− negative ions. Calculations of the dust charge indicate that for electrons, negative ions, and positive ions of comparable temperatures, the charge (or surface potential) of the dust can be positive if the positive ion mass is smaller than the negative ion mass and if ϵ, the ratio of the electron to positive ion density, is sufficiently small. The Q machine plasma is operated with K+ positive ions (mass 39 amu) and SF6− negative ions (mass 146 amu), and also utilizes a rotating cylinder to dispense dust into the plasma column. Analysis of the current-voltage characteristics of a Langmuir probe in the dusty plasma shows evidence for the reduction in the (magnitude) of the negative dust charge and the transition to positively charged dust as the relative concentration of the residual electrons is reduced. Some remarks are offered concerning experiments that could become possible in a dusty plasma with positive grains.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.27.Cm Multicomponent and negative-ion plasmas
52.50.Dg Plasma sources
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.70.Ds Electric and magnetic measurements

Experimental study of two-fluid effects on magnetic reconnection in a laboratory plasma with variable collisionality

Masaaki Yamada, Yang Ren, Hantao Ji, Joshua Breslau, Stefan Gerhardt, Russell Kulsrud, and Aleksey Kuritsyn

Phys. Plasmas 13, 052119 (2006); http://dx.doi.org/10.1063/1.2203950 (13 pages) | Cited 52 times

Online Publication Date: 26 May 2006

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This article describes the recent findings on two-fluid effects on magnetic reconnection in plasmas with variable collisionality in the magnetic reconnection experiment (MRX) [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)] . The MRX device has been upgraded to accommodate a variety of reconnection operation modes and high energy density experiments by increasing its capacitor bank energy and extending the discharge duration. As our experimental operation regime has moved from the collisional to the collision-free, two-fluid effects have become more evident. It is observed that the two-dimensional profile of the neutral sheet is changed significantly from the rectangular shape of the familiar Sweet-Parker type to a double wedge shape as the collisionality is reduced and the reconnection rate increases. The recent evolution of our experimental research from the magnetohydrodynamics (MHD) to the two-fluid analysis is presented to illuminate the physics of Hall MHD in a collision-free reconnection layer. In particular, a clear experimental verification of an out-of-plane quadrupole field, a characteristic signature of the Hall MHD, has been made in the MRX neutral sheet, where the sheet width is comparable to the ion skin depth. It is important to note that the Hall effect, which occurs due to two-dimensional laminar flows of electrons in the reconnection plane, is observed together with the presence of low and high frequency magnetic turbulence, which often has three-dimensional structures. These observations in MRX have striking similarities to the recent magnetospheric measurements of reconnection region, in which the quadrupole component has been detected together with magnetic fluctuations.
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52.35.Vd Magnetic reconnection
52.30.Ex Two-fluid and multi-fluid plasmas
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.20.Fs Electron collisions
52.35.Ra Plasma turbulence
52.25.Gj Fluctuation and chaos phenomena
back to top Nonlinear Phenomena, Turbulence, Transport

Gyrokinetic simulations of off-axis minimum-q profile corrugations

R. E. Waltz, M. E. Austin, K. H. Burrell, and J. Candy

Phys. Plasmas 13, 052301 (2006); http://dx.doi.org/10.1063/1.2195418 (6 pages) | Cited 7 times

Online Publication Date: 4 May 2006

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Quasiequilibrium radial “profile corrugations” in the electron temperature gradient are found at lowest-order singular surfaces in global gyrokinetic code simulations of both monotonic-q and off-axis minimum-q discharges. The profile corrugations in the temperature and density gradients are time-averaged components of zonal flows. The m/n = 2/1 electron temperature gradient corrugation is measurably large and appears to trigger an internal transport barrier as the off-axis minimum-q = 2 surfaces enter the plasma.
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52.25.Fi Transport properties
52.65.Tt Gyrofluid and gyrokinetic simulations
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)

Bernstein mode coupling to cyclotron harmonic radiation in a plasma

Asheel Kumar and V. K. Tripathi

Phys. Plasmas 13, 052302 (2006); http://dx.doi.org/10.1063/1.2179007 (6 pages) | Cited 3 times

Online Publication Date: 4 May 2006

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An electron Bernstein wave in the presence of an ion-acoustic wave of suitable wave number converts itself into cyclotron harmonic electromagnetic radiation in a plasma. The Bernstein wave imparts oscillatory velocity to electrons that couples with the density perturbation associated with the sound wave to produce a nonlinear current, driving the electromagnetic wave at sum (or difference) frequency. Conversely a large amplitude electromagnetic wave at a cyclotron harmonic can parametrically excite an electron Bernstein wave that may effectively heat the electrons.
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52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Dm Sound waves
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.Fi Transport properties

Excitation of nonlinear electron acoustic waves

Francesco Valentini, Thomas M. O’Neil, and Daniel H. E. Dubin

Phys. Plasmas 13, 052303 (2006); http://dx.doi.org/10.1063/1.2198467 (7 pages) | Cited 15 times

Online Publication Date: 10 May 2006

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A particle in cell (PIC) simulation is used to investigate the excitation of electron acoustic waves (EAWs) and the stability of the EAWs against decay. An EAW is a nonlinear wave with a carefully tailored trapped particle population, and the excitation process must create the trapped particle population. For a collisionless plasma, successful excitation occurs when a relatively low amplitude driver that is spatially and temporally resonant with the EAW is applied for a sufficiently long time (many trapping periods). The excited EAW rings at a nearly constant amplitude long after the driver is turned off, provided the EAW has the largest wavelength that fits in the simulation domain. Otherwise, the excited EAW decays to a longer wavelength EAW. In phase space, this decay to longer wavelength appears as a tendency of the vortex-like trapped particle populations to merge. In a collisional plasma, successful excitation of an EAW requires the driver amplitude to exceed a threshold value. The period for a trapped particle oscillation must be short compared to the time for collisions to smooth out the trapped particle plateau.
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52.65.Ff Fokker-Planck and Vlasov equation
52.65.Rr Particle-in-cell method
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Sb Solitons; BGK modes

On the definition of a kinetic equilibrium in global gyrokinetic simulations

P. Angelino, A. Bottino, R. Hatzky, S. Jolliet, O. Sauter, T. M. Tran, and L. Villard

Phys. Plasmas 13, 052304 (2006); http://dx.doi.org/10.1063/1.2193947 (8 pages) | Cited 22 times

Online Publication Date: 12 May 2006

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Nonlinear electrostatic global gyrokinetic simulations of collisionless ion temperature gradient (ITG) turbulence and E×B zonal flows in axisymmetric toroidal plasmas are examined for different choices of the initial distribution function. Using a local Maxwellian leads to the generation of axisymmetric E×B flows that can be so strong as to prevent ITG mode growth. A method using a canonical Maxwellian is shown to avoid this spurious generation of E×B flows. In addition, a revised δf scheme is introduced and compared to the standard δf method.
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52.35.Ra Plasma turbulence
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.65.Tt Gyrofluid and gyrokinetic simulations
52.25.Dg Plasma kinetic equations
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.)

Rigorous approach to the nonlinear saturation of the tearing mode in cylindrical and slab geometry

N. Arcis, D. F. Escande, and M. Ottaviani

Phys. Plasmas 13, 052305 (2006); http://dx.doi.org/10.1063/1.2199208 (12 pages) | Cited 16 times

Online Publication Date: 16 May 2006

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The saturation of the tearing mode instability is described within the standard framework of reduced magnetohydrodynamics in the case of an r-dependent or uniform resistivity profile. Using the technique of matched asymptotic expansions, where the perturbation parameter is the island width w, the problem can be solved in two ways: with the so-called flux coordinate method, which is based on the fact that the current profile is a flux function, and with a new perturbative method that does not use this property. The latter is applicable to more general situations where an external forcing or a sheared velocity profile are involved. The calculation provides a new relationship between the saturated island width and the Δ′ stability parameter that involves a ln w/w0 term, where w0 is a nonlinear scaling length that was missing in previous work. It also yields the modification of the equilibrium magnetic-flux function.
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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.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Fi Transport properties
52.25.Xz Magnetized plasmas
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