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May 2009

Volume 16, Issue 5, Articles (05xxxx)

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Phys. Plasmas 16, 052704 (2009); http://dx.doi.org/10.1063/1.3130263 (11 pages)

F. Girard, M. Primout, B. Villette, Ph. Stemmler, L. Jacquet, D. Babonneau, and K. B. Fournier
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Formation of a localized acceleration potential during magnetic reconnection with a guide field

J. Egedal, W. Daughton, J. F. Drake, N. Katz, and A. Lê

Phys. Plasmas 16, 050701 (2009); http://dx.doi.org/10.1063/1.3130732 (4 pages) | Cited 10 times

Online Publication Date: 1 May 2009

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Magnetic reconnection near the surface of the sun and in the Earth’s magnetotail is associated with the production of highly energetic electrons. Direct acceleration in the reconnection electric field has been proposed as a possible mechanism for energizing these electrons. Here, however, we use kinetic simulations of guide-field reconnection to show that in two-dimensional (2D) reconnection the parallel electric field, E∥ in the reconnection region is localized and its structure does not permit significant energization of the electrons. Rather, a large fraction of the electrons become trapped due to a sign reversal in E∥, imposing strict constraints on their motions and energizations. Given these new results, simple 2D models, which invoke direct acceleration for energizing electrons during a single encounter with a reconnection region, need to be revised.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Nested multilayered X pinches for generators with mega-ampere current level

T. A. Shelkovenko, S. A. Pikuz, R. D. McBride, P. F. Knapp, H. Wilhelm, D. A. Hammer, and D. B. Sinars

Phys. Plasmas 16, 050702 (2009); http://dx.doi.org/10.1063/1.3132611 (4 pages) | Cited 7 times

Online Publication Date: 12 May 2009

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A symmetric X pinch configuration that is conducive to using large numbers of wires on ≥ 1 MA pulsed power generators has been tested at 1 MA. Using an initial configuration of wires before their twisting, similar to nested cylindrical wire arrays, enables a geometrically simple, compact, multilayer wire configuration at the X pinch crossing region. Multilayer X pinches with the same or different materials in the inner and outer wire layers were tested. Optimization resulted in X pinch radiation sources with peak power comparable to the most successful single layer X pinch, but with a compact, single bright X radiation source more reliably obtained using the nested configuration.
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52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.59.Px Hard X-ray sources

Static analysis of possible emittance growth of intense charged particle beams with thermal equilibrium distribution

Takashi Kikuchi and Kazuhiko Horioka

Phys. Plasmas 16, 050703 (2009); http://dx.doi.org/10.1063/1.3130264 (4 pages)

Online Publication Date: 13 May 2009

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Possible emittance growths of intense, nonuniform beams during a transport in a focusing channel are derived as a function of nonlinear field energy and space charge tune depression factors. The nonlinear field energy of the beam with thermal equilibrium distribution is estimated by considering the particle distribution across the cross section of the beam. The results show that the possible emittance growth can be suppressed by keeping the beam particle in thermal equilibrium distribution during the beam transport.
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52.59.Sa Space-charge-dominated beams
52.59.-f Intense particle beams and radiation sources
52.59.Fn Multistage accelerated heavy-ion beams
52.58.Hm Heavy-ion inertial confinement

Electron scale structures in collisionless magnetic reconnection

Neeraj Jain and A. Surjalal Sharma

Phys. Plasmas 16, 050704 (2009); http://dx.doi.org/10.1063/1.3134045 (4 pages) | Cited 2 times

Online Publication Date: 19 May 2009

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The early time-dependent phase of collisionless reconnection, which is dominated by electron dynamics, is investigated using electron-magnetohydrodynamic simulations. Simulations initialized with multi-wavelength perturbations lead to reconnection at multiple sites and the interaction of electron flows generated at the neighboring sites leads to secondary instabilities. These electron-scale processes limit the size of the current sheet and lead to an out-of-plane magnetic field with nested quadrupoles. These structures have important implications for multi-spacecraft missions exploring Earth’s magnetotail.
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52.35.Vd Magnetic reconnection
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

A physical parametrization of coupled transverse dynamics based on generalized Courant–Snyder theory and its applications

Hong Qin and Ronald C. Davidson

Phys. Plasmas 16, 050705 (2009); http://dx.doi.org/10.1063/1.3142472 (4 pages) | Cited 4 times

Online Publication Date: 26 May 2009

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A physical parametrization of coupled transverse dynamics is developed by generalizing the Courant–Snyder (CS) theory for one degree of freedom to the case of coupled transverse dynamics with two degrees of freedom. The four basic components of the original CS theory, i.e., the envelope equation, phase advance, transfer matrix, and CS invariant, all have their counterparts with remarkably similar expressions in the generalized theory. Applications of the new theory are given. It is discovered that the stability of coupled dynamics is completely determined by the generalized phase advance.
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29.27.−a
52.20.Dq Particle orbits
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back to top Basic Plasma Phenomena, Waves, Instabilities

Effect of ion and ion-beam mass ratio on the formation of ion-acoustic solitons in magnetized plasma in the presence of electron inertia

B. C. Kalita and S. N. Barman

Phys. Plasmas 16, 052101 (2009); http://dx.doi.org/10.1063/1.3123423 (6 pages) | Cited 2 times

Online Publication Date: 4 May 2009

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The propagation of ion-acoustic solitary waves in magnetized plasma with cold ions and ion-beams together with electron inertia has been investigated theoretically through the Korteweg–de Vries equation. Subject to the drift velocity of the ion beam, the existence of compressive solitons is found to become extinct as α ( = cold ion mass/ion-beam mass) tends to 0.01 when γ = 0.985 (γ is the beam velocity/phase velocity). Interestingly, a transitional direction of propagation of solitary waves has been unearthed for change over, from compressive solitons to rarefactive solitons based on α and συ( = cosine of the angle θ made by the wave propagation direction ξ with the direction of the magnetic field) for fixed Q( = electron mass/ion mass). Further, the direction of propagation of ion-acoustic waves is found to be the deterministic factor to admit compressive or rarefactive solitons subject to beam outsource.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Sb Solitons; BGK modes

Self-excited surface plasmon-polaritons at the interface of counterstreaming plasmas

M. Lazar, W. M. Moslem, A. Smolyakov, and P. K. Shukla

Phys. Plasmas 16, 052102 (2009); http://dx.doi.org/10.1063/1.3130265 (4 pages) | Cited 2 times

Online Publication Date: 7 May 2009

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Surface plasma modes are coupled electromagnetic/electrostatic (plasmon-polariton) excitations of free electrons near the vacuum-plasma or plasma-plasma interface. The surface plasmon-polariton propagates along the surface plane and decays on both sides of the boundary. The effect of counterstreaming on the surface plasmon-polariton excitation is examined. It is shown that the two-stream instability can excite self-consistently the surface modes at the interface of two counterstreaming plasmas. The dispersion relation is derived and the exact numerical solutions are plotted for comparison to the excitations of a nonstreaming plasma-plasma interface. Such plasma models are of interest in electronic signal transmission, as well as in astrophysical applications and in beam-plasma experiments.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Tc Shock waves and discontinuities
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Investigation of spatiotemporal behavior of the plasma density during the development of the thermocurrent instability

M. M. Hatami, B. Shokri, A. R. Niknam, and A. Aliakbari

Phys. Plasmas 16, 052103 (2009); http://dx.doi.org/10.1063/1.3130724 (4 pages) | Cited 2 times

Online Publication Date: 11 May 2009

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Considering a weakly ionized, collisional, quasineutral plasma placed in an electric field under the condition of nonresonant Cerenkov radiation and using the hydrodynamic model, a nonlinear diffusionlike equation with negative diffusion coefficient is obtained, which describes the dynamics of plasma density during the development of the thermocurrent instability. This equation is solved by the Adomian decomposition method. According to this solution, the spatiotemporal behavior of the plasma density during the growth of the thermocurrent instability is investigated. It is shown that the development of the thermocurrent instability causes the initial perturbations in the plasma density to grow. Also, it is shown that the increment in these perturbations continues until the growth of the thermocurrent instability ceases due to the breakdown of the quasineutrality condition. In this case, it is seen that the profile of the plasma density does not change any more and gets to a constant limit.
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52.25.Fi Transport properties
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

On the electron whistler dispersion law in a cold plasma with light ions and heavy charged particulates

B. V. Lundin and C. Krafft

Phys. Plasmas 16, 052104 (2009); http://dx.doi.org/10.1063/1.3125310 (11 pages) | Cited 1 time

Online Publication Date: 13 May 2009

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The dispersion equation of electron whistler waves in a cold plasma with two light ions of comparable gyrofrequencies and heavy charged particulates is derived. It is valid in a very wide frequency range above the highest ion cutoff frequency when the wave frequency is essentially less than the electron plasma frequency. The derived electron whistler dispersion law is expressed through the relative contents of the two light ions and the electrons, as well as the characteristic frequencies of the magnetized plasma, as the lower hybrid resonance frequency, the two highest ion cutoff frequencies, the gyrofrequencies of the light ions, and the electron gyro- and plasma frequencies. The approximation of vanishingly small gyrofrequencies of the heavy ions permits to determine with a relevant accuracy the electron whistler dispersion law using the features of electron whistler spectrograms only. Estimates of the relative charge density of the light ions are obtained and the dispersion laws of the adjacent branches, i.e., the electron whistler waves and the so-called ion cyclotron whistlers are calculated. For the electron whistler waves, the presence of negative ions can be the origin of a manyfold increase in the lower cutoff frequency; a merging effect of the cutoff frequencies of the adjacent branches can also appear.
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52.27.Cm Multicomponent and negative-ion plasmas
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons

Warm electromagnetic lower hybrid wave dispersion relation

A. L. Verdon, Iver H. Cairns, D. B. Melrose, and P. A. Robinson

Phys. Plasmas 16, 052105 (2009); http://dx.doi.org/10.1063/1.3132628 (12 pages) | Cited 3 times

Online Publication Date: 13 May 2009

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Lower hybrid (LH) waves can interact resonantly with both electrons and ions transferring energy between the species. For this reason the properties of LH waves are of interest. Most treatments of LH waves include either electromagnetic (EM) or warm plasma effects but not both. Here a new analytic dispersion relation for LH waves, including both EM and warm plasma effects, is derived and shown to be more consistent than the previous analytic dispersion relations with numerical results. These comparisons show a very good agreement of the real part of the frequency and reasonable agreement of the imaginary part for a wide range of parameters. It is found that ion magnetization effects, which have been neglected in all previous analytic treatments of LH waves, are surprisingly important. When ion magnetization effects become important the continuous LH mode breaks up into a series of segments of ion Bernstein modes.
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52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)

Hydromagnetic waves and instabilities in kappa distribution plasma

B. Basu

Phys. Plasmas 16, 052106 (2009); http://dx.doi.org/10.1063/1.3132629 (11 pages) | Cited 4 times

Online Publication Date: 14 May 2009

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Stability properties of hydromagnetic waves (shear and compressional Alfven waves) in spatially homogeneous plasma are investigated when the equilibrium particle velocity distributions in both parallel and perpendicular directions (in reference to the ambient magnetic field) are modeled by kappa distributions. Analysis is presented for the limiting cases |ξα|⪡1 and |ξα|⪢1 for which solutions of the dispersion relations are analytically tractable. Here ξα(α = e,i) is the ratio of the wave phase speed and the electron (ion) thermal speed. Both low and high β ( = plasma pressure/magnetic pressure) plasmas are considered. The distinguishing features of the hydromagnetic waves in kappa distribution plasma are (1) both Landau damping and transit-time damping rates are larger than those in Maxwellian plasma because of the enhanced high-energy tail of the kappa distribution and (2) density and temperature perturbations in response to the electromagnetic perturbations are different from those in Maxwellian plasma when |ξα|⪡1. Moreover, frequency of the oscillatory stable modes (e.g., kinetic shear Alfven wave) and excitation condition of the nonoscillatory (zero frequency) unstable modes (e.g., mirror instability) in kappa distribution plasma are also different from those in Maxwellian plasma. Quantitative estimates of the differences depend on the specific choice of the kappa distribution. For simplicity of notations, same spectral indices κ∥ and κ⊥ have been assumed for both electron and ion population. However, the analysis can be easily generalized to allow for different values of the spectral indices for the two charged populations.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Magnetic reconnection with pressure tensor in electron magnetohydrodynamics

Huishan Cai and Ding Li

Phys. Plasmas 16, 052107 (2009); http://dx.doi.org/10.1063/1.3122050 (5 pages)

Online Publication Date: 15 May 2009

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The dissipation mechanisms of reconnection and the pressure gradient effects on tearing mode with guide magnetic field are analyzed systematically by including the electron pressure tensor in electron magnetohydrodynamics. It is found that which dissipation mechanism dominates, either pressure-based dissipation or inertia-based dissipation, has a great relation with the relative scaling orders between the electron thermal Larmor radius and electron inertia skin depth. The effects of pressure gradient also depend on the relative magnitude between parallel and perpendicular equilibrium pressure gradients. When the pressure-based dissipation is dominant, the condition that pressure drives or suppresses tearing mode instability also depends on the relative magnitude between parallel and perpendicular equilibrium pressure gradients.
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52.35.Vd Magnetic reconnection
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Fi Transport properties
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Filamentation of laser in a magnetized plasma under relativistic and ponderomotive nonlinearities

Ranjeet Singh and V. K. Tripathi

Phys. Plasmas 16, 052108 (2009); http://dx.doi.org/10.1063/1.3139258 (5 pages) | Cited 5 times

Online Publication Date: 20 May 2009

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Filamentation of a circularly polarized short pulse laser propagating along the direction of ambient magnetic field in plasma is studied. The nonlinearity arises through the combined effect of relativistic mass variation and ponderomotive force induced electron cavitation. The growth rate is maximum Γmax for an optimum filament size, qopt−1. Γmax and qopt increases with plasma density and ambient magnetic field.
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52.38.-r Laser-plasma interactions
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.27.Ny Relativistic plasmas

Linear coupling of Alfven waves and acoustic-type modes in dense quantum magnetoplasmas

S. A. Khan and H. Saleem

Phys. Plasmas 16, 052109 (2009); http://dx.doi.org/10.1063/1.3140604 (6 pages) | Cited 4 times

Online Publication Date: 27 May 2009

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A coupled dispersion relation of low frequency shear Alfven waves and electrostatic waves in a dense quantum magnetoplasma is derived by using hydrodynamic model. The dispersive contribution of electron quantum effects is discussed for dynamic as well as static ions. The dominant role of electron Fermi pressure is highlighted and its comparison with the quantum pressure arising due to quantum Bohm potential is presented. For illustrative purpose, the results are analyzed numerically. The relevance of present work with the dense astrophysical and laboratory plasmas is pointed out with possible consequences.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven 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)

Tests of collision operators using laboratory measurements of shear Alfvén wave dispersion and damping

D. J. Thuecks, C. A. Kletzing, F. Skiff, S. R. Bounds, and S. Vincena

Phys. Plasmas 16, 052110 (2009); http://dx.doi.org/10.1063/1.3140037 (11 pages) | Cited 4 times

Online Publication Date: 28 May 2009

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Measurements of shear Alfvén waves are used to test the predictions of a variety of different electron collision operators, including several Krook collision operators as well as a Lorentz collision operator. New expressions for the collisional warm-plasma dielectric tensor resulting from the use of the fully magnetized collisional Boltzmann equation are presented here. Theoretical predictions for the parallel phase velocity and damping as a function of perpendicular wave number k⊥ are derived from the dielectric tensor. Laboratory measurements of the parallel phase velocity and damping of shear Alfvén waves were made to test these theoretical predictions in both the kinetic (vte⪢vA) and inertial (vte⪡vA) parameter regimes and at several wave frequencies (ω<ωci). Results show that, in the inertial regime, the best match between measurements and theory occur when any of the Krook operators are used to describe electron collisions. In contrast, the best agreement in the kinetic regime is found when collisions are completely ignored.
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52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.20.Fs Electron collisions
52.72.+v Laboratory studies of space- and astrophysical-plasma processes

Parker problem in Hall magnetohydrodynamics

Bhimsen K. Shivamoggi

Phys. Plasmas 16, 052111 (2009); http://dx.doi.org/10.1063/1.3140055 (4 pages) | Cited 1 time

Online Publication Date: 28 May 2009

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The Parker problem in Hall magnetohydrodynamics (MHD) is considered. Poloidal shear superposed on the toroidal ion flow associated with the Hall effect is incorporated. This is found to lead to a triple deck structure for the Parker problem in Hall MHD, with the magnetic field falling off in the intermediate Hall-resistive region more steeply (like 1/x3) than that (like 1/x) in the outer ideal MHD region.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Tn Ideal and resistive MHD modes; kinetic modes
back to top Nonlinear Phenomena, Turbulence, Transport

Implementation and application of two synthetic diagnostics for validating simulations of core tokamak turbulence

C. Holland, A. E. White, G. R. McKee, M. W. Shafer, J. Candy, R. E. Waltz, L. Schmitz, and G. R. Tynan

Phys. Plasmas 16, 052301 (2009); http://dx.doi.org/10.1063/1.3085792 (15 pages) | Cited 15 times

Online Publication Date: 1 May 2009

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The deployment of multiple high-resolution, spatially localized fluctuation diagnostics on the DIII-D tokamak [ J. L. Luxon, Nucl. Fusion 42, 614 (2002) ] opens the door to a new level of core turbulence model validation. Toward this end, the implementation of synthetic diagnostics that model physical beam emission spectroscopy and correlation electron cyclotron emission diagnostics is presented. Initial results from their applications to local gyrokinetic simulations of two locations in a DIII-D L-mode discharge performed with the GYRO code [ J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003) ] are also discussed. At normalized toroidal flux ρ = 0.5, we find very good agreement between experiment and simulation in both the energy flows and fluctuation levels measured by both diagnostics. However, at ρ = 0.75, GYRO underpredicts the observed energy flows by roughly a factor of 7, with rms fluctuation levels underpredicted by a factor of 3. Interestingly, at both locations we find good agreement in the shapes of the radial and vertical density correlation functions and in the shapes of the frequency power spectra. At both locations, the attenuation of the GYRO-predicted fluctuations due to the spatial averaging imposed by the diagnostics’ spot sizes is significant, and its incorporation via the use of synthetic diagnostics is shown to be essential for quantitative comparisons such as these.
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52.35.Ra Plasma turbulence
52.25.Fi Transport properties
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.55.Fa Tokamaks, spherical tokamaks
52.65.Tt Gyrofluid and gyrokinetic simulations

A novel mechanism for exciting intrinsic toroidal rotation

C. J. McDevitt, P. H. Diamond, Ö. D. Gürcan, and T. S. Hahm

Phys. Plasmas 16, 052302 (2009); http://dx.doi.org/10.1063/1.3122048 (12 pages) | Cited 21 times

Online Publication Date: 4 May 2009

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Beginning from a phase space conserving gyrokinetic formulation, a systematic derivation of parallel momentum conservation uncovers two physically distinct mechanisms by which microturbulence may drive intrinsic rotation. The first mechanism, which emanates from E×B convection of parallel momentum, has already been analyzed [ O. D. Gurcan et al., Phys. Plasmas 14, 042306 (2007) ; R. R. Dominguez and G. M. Staebler, Phys. Fluids B 5, 3876 (1993) ] and was shown to follow from radial electric field shear induced symmetry breaking of the spectrally averaged parallel wave number. Thus, this mechanism is most likely active in regions with steep pressure gradients or strong poloidal flow shear. The second mechanism uncovered, which appears in the gyrokinetic formulation through the parallel nonlinearity, emerges due to charge separation induced by the polarization drift. This novel means of driving intrinsic rotation, while nominally higher order in an expansion of the mode frequency divided by the ion cyclotron frequency, does not depend on radial electric field shear. Thus, while the magnitude of the former mechanism is strongly reduced in regions of weak radial electric field shear, this mechanism remains unabated and is thus likely relevant in complementary regimes.
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52.30.-q Plasma dynamics and flow
52.35.Ra Plasma turbulence
52.55.Jd Magnetic mirrors, gas dynamic traps

Finite orbit width effect in ion collisional transport in TJ-II

J. L. Velasco, F. Castejón, and A. Tarancón

Phys. Plasmas 16, 052303 (2009); http://dx.doi.org/10.1063/1.3126583 (9 pages) | Cited 5 times

Online Publication Date: 7 May 2009

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The validity of the traditional local diffusive approach and of the use of monoenergetic calculations has been studied for the stellarator TJ-II [ Alejaldre et al., Fusion Technol. 17, 131 (1990) ]: it is shown to be doubtful, under some circumstances, even in a purely collisional description of transport. The diffusion in physical space starting from Dirac-delta-like initial conditions has been studied using the code Integrator of Stochastic Differential Equations for Plasmas by Castejón et al. [Plasma Phys. Controlled Fusion 49, 753 (2007) ]. Particles may experience large radial excursions from their original magnetic surfaces in a single collisional time. The contribution of these particles to the flux may make it nondiffusive; non-Gaussian density distributions, characterized by long tails, are observed. In the velocity space, there are important variations in the average particle kinetic energy after one collision time. We discuss the effect of this fact over the calculation of monoenergetic transport coefficients and their convolution. A simple analysis based on Hurst exponents has shown nevertheless that the description of transport by means of a pinch term and an effective transport coefficient is more correct than expected.
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52.25.Fi Transport properties
52.20.-j Elementary processes in plasmas
52.55.Jd Magnetic mirrors, gas dynamic traps

Probability distribution function for self-organization of shear flows

Eun-jin Kim, Han-Li Liu, and Johan Anderson

Phys. Plasmas 16, 052304 (2009); http://dx.doi.org/10.1063/1.3132631 (5 pages) | Cited 5 times

Online Publication Date: 14 May 2009

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The first prediction of the probability distribution function (PDF) of self-organized shear flows is presented in a nonlinear diffusion model where shear flows are generated by a stochastic forcing while diffused by a nonlinear eddy diffusivity. A novel nonperturbative method based on a coherent structure is utilized for the prediction of the strongly intermittent exponential PDF tails of the gradient of shear flows. Numerical simulations using Gaussian forcing not only confirm these predictions but also reveal the significant contribution from the PDF tails with a large population of supercritical gradients. The validity of the nonlinear diffusion model is then examined using a threshold model where eddy diffusivity is given by discontinuous values, elucidating an important role of relative time scales of relaxation and disturbance in the determination of the PDFs.
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52.30.-q Plasma dynamics and flow
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.Fi Transport properties
52.65.Ff Fokker-Planck and Vlasov equation
02.50.Ey Stochastic processes
02.60.Cb Numerical simulation; solution of equations

Particle-in-cell simulation with Vlasov ions and drift kinetic electrons

Yang Chen and Scott E. Parker

Phys. Plasmas 16, 052305 (2009); http://dx.doi.org/10.1063/1.3138743 (9 pages) | Cited 4 times

Online Publication Date: 20 May 2009

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There are certain limitations in using gyrokinetic ions for simulations of turbulent transport in tokamak plasmas. Applications where Vlasov ions might be more appropriate include the electron temperature gradient driven turbulence, edge turbulence with steep density gradient, and magnetic reconnection in a weak guide field. In such cases the ion gyrokinetic model presently used in simulations needs to be extended, but a satisfactory extension valid for fully electromagnetic turbulence is not presently available. Even if an accurate model is found, its numerical implementation could be very challenging. We propose a kinetic model that combines Vlasov ions with gyrokinetic electrons to avoid the difficulties with gyrokinetic ions. The field equations of this model are the Faraday’s equation and the Ampere’s equation without the displacement current. The perturbed fields B1 and E1 rather than the scalar and vector potentials are used to formulate the field equations. We have devised an implicit scheme for this model, demonstrated in three-dimensional slab for the Alfvén waves, the drift Alfvén instability and the ion acoustic waves.
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52.65.-y Plasma simulation
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Kt Drift waves
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Ra Plasma turbulence
52.55.Fa Tokamaks, spherical tokamaks

Equal energy phase space trajectories in resonant wave interactions

O. Yaakobi and L. Friedland

Phys. Plasmas 16, 052306 (2009); http://dx.doi.org/10.1063/1.3139263 (7 pages) | Cited 1 time

Online Publication Date: 26 May 2009

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Adiabatic evolution of two and three resonantly interacting wave systems with nonlinear frequency/wave vector shifts is discussed. The corresponding Hamiltonian, depending on the coupling, detuning, and nonlinear frequency shift parameters may have a variable number of fixed points, i.e., the system can experience a topological change of phase space when these parameters vary in time or space. It is shown that the oscillation periods of two equal energy trajectories in these wave systems are equal and the difference between the action integrals of such trajectories is obtained analytically as a function of the system parameters. Based on these findings, a scheme of simultaneous adiabatic variation in the parameters is designed, such that any pair of initially equal energy trajectories continues to have the same energy at later times. These results are generalizations of a previous work [ O. Polomarov and G. Shvets, Phys. Plasmas 13, 054502 (2006) ] for a single, resonantly driven wave.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Quasisteady and steady states in global gyrokinetic particle-in-cell simulations

S. Jolliet, B. F. McMillan, T. Vernay, L. Villard, A. Bottino, and P. Angelino

Phys. Plasmas 16, 052307 (2009); http://dx.doi.org/10.1063/1.3140036 (10 pages) | Cited 6 times

Online Publication Date: 26 May 2009

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Collisionless delta-f gyrokinetic particle-in-cell simulations suffer from the entropy paradox, in which the entropy grows linearly in time while low-order moments are saturated. As a consequence, these simulations do not reach a steady state and are unsuited to make quantitative predictions. A solution to this issue is the introduction of artificial dissipation. The notion of steady state in gyrokinetic simulations is studied by deriving an evolution equation for the fluctuation entropy and applying it to the global collisionless particle-in-cell code ORB5 [ S. Jolliet et al., Comput. Phys. Commun. 177, 409 (2007) ]. It is shown that a recently implemented noise-control algorithm [ B. F. McMillan et al., Phys. Plasmas 15, 052308 (2008) ] based on a W-stat provides the necessary dissipation to reach a steady state. The two interesting situations of decaying and driven turbulence are considered. In addition, it is shown that a separate heating algorithm, not based on a W-stat, does not lead to a statistical steady state.
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52.65.-y Plasma simulation
52.35.Ra Plasma turbulence

Non-Markovian renormalization of kinetic coefficients for drift-type turbulence in magnetized plasmas

A. Zagorodny and J. Weiland

Phys. Plasmas 16, 052308 (2009); http://dx.doi.org/10.1063/1.3125306 (9 pages) | Cited 1 time

Online Publication Date: 27 May 2009

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The problem of derivation of the kinetic equations for inhomogeneous plasma in an external magnetic field is considered. The Fokker–Planck-type equations with the non-Markovian kinetic coefficients are proposed. In the time-local limit (small correlation times with respect to the distribution function relaxation time) the relations obtained recover the results known from the appropriate quasilinear theory and the Dupree–Weinstock theory of plasma turbulence. Kinetic calculations of the dielectric response function are also performed with regard to the influence of turbulent fields on particle motion. The equations proposed are used to describe zonal flow generation and to estimate the diffusion coefficient for saturated turbulence.
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52.35.Ra Plasma turbulence
52.25.Dg Plasma kinetic equations
52.30.-q Plasma dynamics and flow
52.25.Mq Dielectric properties
52.55.-s Magnetic confinement and equilibrium

Effects of positron density and temperature on ion-acoustic solitary waves in a magnetized electron-positron-ion plasma: Oblique propagation

A. Esfandyari-Kalejahi, M. Mehdipoor, and M. Akbari-Moghanjoughi

Phys. Plasmas 16, 052309 (2009); http://dx.doi.org/10.1063/1.3142465 (6 pages) | Cited 12 times

Online Publication Date: 28 May 2009

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Ion-acoustic (IA) solitary waves are investigated in a magnetized three-component plasma consisting of cold ions, isothermal hot electrons, and positrons. The basic set of fluid equations is reduced to the Korteweg de Vries equation using the standard reductive perturbation (multiple-scale) technique. Theoretical and numerical analyses confirm significant effects of the presence of positrons and the dependence of the electron to positron temperature ratio on the amplitude and the width of IA solitary waves. It is shown that the rarefactive and compressive IA solitary excitations can propagate when the propagation angle θ satisfies 0 ≤ θ<π/2 and π/2<θ ≤ π, respectively. Also, it is remarked that the amplitude of the rarefactive and compressive IA solitary excitations is not affected by the magnitude of external magnetic field B0, whereas their width depends strictly on B0. The numerical analysis has been done based on the typical numerical data from a pulsar magnetosphere.
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52.25.Xz Magnetized 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.)
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