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May 2007

Volume 14, Issue 5, Articles (05xxxx)

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Editorial: Announcement of editorial policy statement on verification and validation

Ronald C. Davidson

Phys. Plasmas 14, 050401 (2007); http://dx.doi.org/10.1063/1.2744350 (1 page) | Cited 3 times

Online Publication Date: 29 May 2007

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Abstract Unavailable
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01.30.-y Physics literature and publications
01.10.Cr Announcements, news, and awards
52.00.00 Physics of plasmas and electric discharges
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Reentrant cone angle dependence of the energetic electron slope temperature in high-intensity laser-plasma interactions

M. Nakatsutsumi, R. Kodama, P. A. Norreys, S. Awano, H. Nakamura, T. Norimatsu, A. Ooya, M. Tampo, K. A. Tanaka, T. Tanimoto, T. Tsutsumi, and T. Yabuuchi

Phys. Plasmas 14, 050701 (2007); http://dx.doi.org/10.1063/1.2730490 (4 pages) | Cited 14 times

Online Publication Date: 14 May 2007

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Energy spectra of fast electrons, generated when high-intensity laser pulses irradiated hollow conical targets, have been measured experimentally. It is shown here that the slope temperature of the fast electrons is strongly dependent on the opening angle of the cone, and has a maximum value at 25°. The data confirms optical guiding of the laser pulse, by comparison of the measured electron temperature with ray-tracing calculations that include absorption in plasmas. The enhanced energy flow and intensity induced by optical guiding of the laser pulse inside the cone as a function of the opening angle as well as the f-number of the focusing optics is discussed.
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52.38.Ph X-ray, γ-ray, and particle generation
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.Nc Particle measurements
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back to top Basic Plasma Phenomena, Waves, Instabilities

On the continuous spectrum of leaky magnetohydrodynamic modes and the associated quasimodes

Jesse Andries and Marcel Goossens

Phys. Plasmas 14, 052101 (2007); http://dx.doi.org/10.1063/1.2714513 (18 pages) | Cited 4 times

Online Publication Date: 2 May 2007

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We aim to clarify the mathematical status of the leaky modes in an unbounded magnetohydrodynamic (MHD) plasma. The initial value problem of a one-dimensional unbounded MHD plasma is solved by means of a Laplace transform in time. It is shown that the MHD operator remains self-adjoint in the sense that a self-adjoint extension of the minimal MHD operator exists and that the eigenfrequencies should therefore be real. However, the classical picture of the MHD spectrum is to be extended with a slow and a fast leaky continuous spectrum when unbounded spatial domains are considered. The inversion integral for the Laplace transform is evaluated in such a way as to recast the continuum contribution in terms of a complete spectral representation. This involves the construction of the spectral measure associated with the continuous spectra. In the case of a slab structure, the spectral measure is not a monotonic function of the frequency, but peaks appear in the spectral measure around specific frequencies. These frequencies correspond to the discrete damped leaky modes described in the context of solar physics. The spectral measure can be interpreted physically in terms of the energy carried in and out by the incoming and outgoing waves.
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02.30.Tb Operator theory
02.60.Lj Ordinary and partial differential equations; boundary value problems
02.70.Hm Spectral methods
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
96.50.Tf MHD waves; plasma waves, turbulence
96.60.pf Coronal loops, streamers

Kinetic properties of magnetic merging in the coalescence process

P. L. Pritchett

Phys. Plasmas 14, 052102 (2007); http://dx.doi.org/10.1063/1.2727458 (10 pages) | Cited 5 times

Online Publication Date: 4 May 2007

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The magnetic merging process associated with pairwise magnetic island coalescence is investigated using two-dimensional particle-in-cell simulations for the case where the initial island separation ζ is in the range of 3–12c/ωpi, where c/ωpi is the ion inertia length. In this regime the coalescence process is driven by the electrons, the electron and ion bulk flows decouple on the global island scale (the electron flows are much larger than those for the ions), there is no magnetic flux pileup near the merging line, and the X-O line separation drops smoothly to zero on a time scale of the order of twice the linear e-folding time for the coalescence instability. For fixed island aspect ratio, the scaling of the merging electric field Ey as a function of ζ is rather weak; i.e., ∼ ζ−0.5. The magnitude of Ey, however, is strongly dependent on the magnitude of the current concentration at the initial O lines, suggesting that driven merging does not exhibit a universal rate. These kinetic results support the existence of a regime with merging rates faster than the linear Alfvén scaling with island size, but we were not able to observe the transition between these two regimes.
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52.35.Vd Magnetic reconnection
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
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.)
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)

Eigenfunctions and eigenvalues of the Dougherty collision operator

M. W. Anderson and T. M. O’Neil

Phys. Plasmas 14, 052103 (2007); http://dx.doi.org/10.1063/1.2727463 (4 pages) | Cited 2 times

Online Publication Date: 4 May 2007

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The Dougherty collision operator is a simplified Fokker-Planck collision operator that conserves particle number, momentum, and energy. In this paper, a complete set of orthogonal eigenfunctions of the linearized Dougherty operator is obtained. Five of the eigenfunctions have zero eigenvalue and correspond to the five conserved quantities (particle number, three components of momentum, and energy). The connection between the eigenfunctions and fluid modes in the limit of strong collisionality is demonstrated; in particular, the sound speed, thermal conductivity, and viscosity predicted by the Dougherty operator are identified.
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52.27.Jt Nonneutral plasmas

Density steepening formation in the interaction of microwave field with a plasma

A. R. Niknam and B. Shokri

Phys. Plasmas 14, 052104 (2007); http://dx.doi.org/10.1063/1.2727483 (5 pages) | Cited 2 times

Online Publication Date: 14 May 2007

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A modification of the electron density distribution of an unmagnetized plasma by the ponderomotive force of high-power microwave propagating into the plasma is studied. Using the Maxwell and fluid equations, nonlinear differential and integral equations for the electric field are obtained. The solution of these nonlinear equations shows that the profiles of the electric and magnetic field depart slightly from a sinusoidal shape, the amplitude of oscillations decreases in the plasma, and these oscillations become lengthened. Also, the period of oscillations decreases by increasing the microwave energy flux and the electron density becomes highly steepened for high microwave energy flux. Furthermore, the axial density profile shows a stationary density modulation that is phase-shifted with respect to the wave amplitude. This density modulation increases with the microwave energy flux.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
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.Dg Plasma kinetic equations
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
02.30.Hq Ordinary differential equations

Parametric instability in a collisional dusty plasma

B. P. Pandey and S. V. Vladimirov

Phys. Plasmas 14, 052105 (2007); http://dx.doi.org/10.1063/1.2730495 (8 pages) | Cited 7 times

Online Publication Date: 14 May 2007

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The present work investigates the parametric instability of parallel propagating circularly polarized Alfvén (pump) waves in a collisional dusty plasma. It is demonstrated that the relative drift between the charged dust and the electrons and ions gives rise to the Hall effect resulting in the modified pump wave characteristics. Although the linearized fluid equations with periodic coefficients are difficult to solve analytically, it is shown that a linear transformation can remove the periodic dependence. The resulting linearized equations with constant coefficients are used to derive an algebraic dispersion relation. The growth rate of the parametric instability is a sensitive function of the amplitude of the pump wave as well as to the ratio of the pump and the dust-cyclotron frequencies. The instability is insensitive to the plasma-beta parameter. The possible application of the result in the astrophysical context is discussed.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.30.Ex Two-fluid and multi-fluid plasmas
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Current sheet formation and nonideal behavior at three-dimensional magnetic null points

D. I. Pontin, A. Bhattacharjee, and K. Galsgaard

Phys. Plasmas 14, 052106 (2007); http://dx.doi.org/10.1063/1.2722300 (13 pages) | Cited 19 times

Online Publication Date: 16 May 2007

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The nature of the evolution of the magnetic field, and of current sheet formation, at three-dimensional (3D) magnetic null points is investigated. A kinematic example is presented that demonstrates that for certain evolutions of a 3D null (specifically those for which the ratios of the null point eigenvalues are time-dependent), there is no possible choice of boundary conditions that renders the evolution of the field at the null ideal. Resistive magnetohydrodynamics simulations are described that demonstrate that such evolutions are generic. A 3D null is subjected to boundary driving by shearing motions, and it is shown that a current sheet localized at the null is formed. The qualitative and quantitative properties of the current sheet are discussed. Accompanying the sheet development is the growth of a localized parallel electric field, one of the signatures of magnetic reconnection. Finally, the relevance of the results to a recent theory of turbulent reconnection is discussed.
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52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.Kj Magnetohydrodynamic and fluid equation
52.35.Vd Magnetic reconnection
52.35.Ra Plasma turbulence

Simulation studies of non-neutral plasma equilibria in an electrostatic trap with a magnetic mirror

K. Gomberoff, J. Fajans, J. Wurtele, A. Friedman, D. P. Grote, R. H. Cohen, and J.-L. Vay

Phys. Plasmas 14, 052107 (2007); http://dx.doi.org/10.1063/1.2727470 (8 pages) | Cited 6 times

Online Publication Date: 16 May 2007

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The equilibrium of an infinitely long, strongly magnetized, non-neutral plasma confined in a Penning-Malmberg trap with an additional mirror coil has been solved analytically [J. Fajans, Phys. Plasmas 10, 1209 (2003)] and shown to exhibit unusual features. Particles not only reflect near the mirror in the low field region, but also may be weakly trapped in part of the high field region. The plasma satisfies a Boltzmann distribution along field lines; however, the density and the potential vary along field lines. Some other simplifying assumptions were employed in order to analytically characterize the equilibrium; for example the interface region between the low and high field regions was not considered. The earlier results are confirmed in the present study, where two-dimensional particle-in-cell (PIC) simulations are performed with the Warp code in a more realistic configuration with an arbitrary (but physical) density profile, realistic trap geometry and magnetic field. A range of temperatures and radial plasma sizes are considered. Particle tracking is used to identify populations of trapped and untrapped particles. The present study also shows that it is possible to obtain local equilibria of non-neutral plasmas using a collisionless PIC code, by a scheme that uses the inherent numerical collisionality as a proxy for physical collisions.
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52.27.Jt Nonneutral plasmas
52.65.Rr Particle-in-cell method
28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
52.25.Xz Magnetized plasmas
52.25.Fi Transport properties
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Potential around a charged dust particle in a collisional sheath

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

Phys. Plasmas 14, 052108 (2007); http://dx.doi.org/10.1063/1.2730498 (7 pages) | Cited 24 times

Online Publication Date: 16 May 2007

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By employing a self-consistent kinetic approach, an analytical expression is derived for the potential of a test charge in a weakly ionized plasma with ion drift. The drift is assumed to be due to an external electric field, with the velocity being mobility-limited and much larger than the thermal velocity of neutrals. The derived expression is proven to be in excellent agreement with the measurements by Konopka et al. [Phys. Rev. Lett. 84, 891 (2000) ] performed in the sheath region of a rf discharge.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.40.Kh Plasma sheaths

Current sheets at three-dimensional magnetic nulls: Effect of compressibility

D. I. Pontin, A. Bhattacharjee, and K. Galsgaard

Phys. Plasmas 14, 052109 (2007); http://dx.doi.org/10.1063/1.2734949 (8 pages) | Cited 14 times

Online Publication Date: 18 May 2007

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The nature of current sheet formation in the vicinity of three-dimensional (3D) magnetic null points is investigated. The particular focus is upon the effect of the compressibility of the plasma on the qualitative and quantitative properties of the current sheet. An initially potential 3D null is subjected to shearing perturbations, as in a previous paper [Pontin et al., Phys. Plasmas 14, 052106 (2007)] . It is found that as the incompressible limit is approached, the collapse of the null point is suppressed and an approximately planar current sheet aligned to the fan plane is present instead. This is the case regardless of whether the spine or fan of the null is sheared. Both the peak current and peak reconnection rate are reduced. The results have a bearing on previous analytical solutions for steady-state reconnection in incompressible plasmas, implying that fan current sheet solutions are dynamically accessible, while spine current sheet solutions are not.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Fi Transport properties
52.35.Vd Magnetic reconnection
52.65.Kj Magnetohydrodynamic and fluid equation

Computation of three-dimensional tokamak and spherical torus equilibria

Jong-kyu Park, Allen H. Boozer, and Alan H. Glasser

Phys. Plasmas 14, 052110 (2007); http://dx.doi.org/10.1063/1.2732170 (9 pages) | Cited 40 times

Online Publication Date: 18 May 2007

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A nominally axisymmetric plasma configuration, such as a tokamak or a spherical torus, is highly sensitive to nonaxisymmetric magnetic perturbations due to currents outside of the plasma. The high sensitivity means that the primary interest is in the response of the plasma to very small perturbations, i.e., ∣math/math∣ ≈ 10−2 to 10−4, which can be calculated using the theory of perturbed equilibria. The ideal perturbed equilibrium code (IPEC) is described and applied to the study of the plasma response in a spherical torus to such external perturbations.
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52.55.Fa Tokamaks, spherical tokamaks
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Fi Transport properties
52.65.Vv Perturbative methods
back to top Nonlinear Phenomena, Turbulence, Transport

Theory and particle simulation of nonlinear double layers in a magnetized plasma

Seung-Shik Kim, Tae-Han Kim, and Ho-Yeun Kim

Phys. Plasmas 14, 052301 (2007); http://dx.doi.org/10.1063/1.2722291 (10 pages) | Cited 2 times

Online Publication Date: 1 May 2007

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Theoretical investigation and particle simulation of obliquely propagating nonlinear double layers (NDLs) of nonmonotonic type are performed in a magnetized plasma, which consists of a positively charged ion fluid and trapped, as well as free electrons. The modified Zakharov-Kuznetsov equation is derived by the usual reductive perturbation technique in a three-dimensional system. A nonlinear double layer solution is presented. Furthermore using Sagdeev’s pseudopotential technique, nonlinear double layer solution, which is associated with a set of nonlinear eigenvalue conditions, is also presented. These solutions are the analytic extensions of the monotonic double layers and solitary holes. The effects of physical parameters of nonlinear double layers are discussed. In particle simulations of a current driven system, physical relations among the obliqueness, the propagating velocity, the inverse scale length, and the maximum potential are investigated. The maximum potential and the width of the NDL decreases as the degree of the angle increases. In a chosen field, a decrease of potential width (or maximum potential) is clearly shown in the case of less than 10°. Variation of propagating velocity is clearly shown in the range of 10°–16°. Particle simulations are performed with an axially bounded electrostatic particle-in-cell code XPDP1, which is a workstation version of a one-dimensional bounded plasma code PDW1 [J. Comput. Phys. 80, 253 (1989)] . These particle simulation results are in good agreement with the qualitative theoretical results.
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52.40.Kh Plasma sheaths
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.65.Rr Particle-in-cell method
52.25.Fi Transport properties
52.25.Xz Magnetized plasmas

Nonlinear growth of marginally unstable tearing modes

R. Coelho

Phys. Plasmas 14, 052302 (2007); http://dx.doi.org/10.1063/1.2722306 (4 pages) | Cited 1 time

Online Publication Date: 1 May 2007

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In this work, the nonlinear growth of the classical tearing mode is revisited, using reduced magnetohydrodynamic numerical simulations in cylindrical geometry, emphasizing the limiting scenario of a marginally unstable mode, i.e., 0 ∼ Δ′a<4, where a is the minor radius and Δ′ is the stability parameter [ H. Furth, J. Killeen, and M. N. Rosenbluth, Phys. Fluids 6, 459 (1963) ]. Conventionally, the mode becomes unstable when Δ′>0 and, eventually, a steady state island width (saturated island width) is achieved. It is found that, contrary to theoretical predictions, no steady state solution is obtained for typically low temperature plasmas with perpendicular viscosity and magnetic Reynolds number below a certain threshold. Plasma inertial forces are identified as the physical mechanism behind such nonlinear evolution.
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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)
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.Fi Transport properties

Influence of magnetic shear on impurity transport

H. Nordman, T. Fülöp, J. Candy, P. Strand, and J. Weiland

Phys. Plasmas 14, 052303 (2007); http://dx.doi.org/10.1063/1.2730491 (8 pages) | Cited 8 times

Online Publication Date: 4 May 2007

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The magnetic shear dependence of impurity transport in tokamaks is studied using a quasilinear fluid model for ion temperature gradient (ITG) and trapped electron (TE) mode driven turbulence in the collisionless limit and the results are compared with nonlinear gyrokinetic results using GYRO [ J. Candy and R. E. Waltz, J. Comput. Phys 186, 545 (2003) ]. It is shown that the impurity transport is sensitive to the magnetic shear, in particular for weak, negative, and large positive shear where a strong reduction of the effective impurity diffusivity is obtained. The fluid and gyrokinetic results are in qualitative agreement, with the gyrokinetic diffusivities typically a factor 2 larger than the fluid diffusivities. The steady state impurity profiles in source-free plasmas are found to be considerably less peaked than the electron density profiles for moderate shear. Comparisons between anomalous and neoclassical transport predictions are performed for ITER-like profiles [ R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002) ].
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52.25.Fi Transport properties
52.25.Vy Impurities in plasmas
52.55.Fa Tokamaks, spherical tokamaks
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Ra Plasma turbulence
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)

Solitary Alfvén waves in a dusty plasma

Cheong Rim Choi and D.-Y. Lee

Phys. Plasmas 14, 052304 (2007); http://dx.doi.org/10.1063/1.2727461 (5 pages) | Cited 5 times

Online Publication Date: 8 May 2007

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The nonlinear solitary Alfvén wave in a magnetized dusty plasma with a low β assumption, obliquely propagating to an external magnetic field, is investigated based on the Sagdeev potential. It is found that there exists a double layer solution as well as the compressive solitary Alfvén waves. It is shown that the amplitude of the compressive and rarefactive solitary Alfvén waves decreases with a dust charge density, whereas that of the double layer behaves in the opposite way. In addition, it is found that the speed of the solitary Alfvén wave is independent of the dust charge density.
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52.27.Lw Dusty or complex plasmas; plasma crystals
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

Generation mechanism for electron acoustic solitary waves

A. P. Kakad, S. V. Singh, R. V. Reddy, G. S. Lakhina, S. G. Tagare, and F. Verheest

Phys. Plasmas 14, 052305 (2007); http://dx.doi.org/10.1063/1.2732176 (5 pages) | Cited 12 times

Online Publication Date: 14 May 2007

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Nonlinear electron acoustic solitary waves (EASWs) are studied in a collisionless and unmagnetized plasma consisting of cold background electrons, cold beam electrons, and two different temperature ion species. Using pseudopotential analysis, the properties of arbitrary amplitude EASWs are investigated. The present model supports compressive as well as rarefactive electron acoustic solitary structures. Furthermore, there is an interesting possibility of the coexistence of compressive and rarefactive solitary structures in a specific plasma parameter range. The application of our results in interpreting the salient features of the broadband electrostatic noise in the plasma sheet boundary layer is discussed.
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94.30.cq MHD waves, plasma waves, and instabilities
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Sb Solitons; BGK modes

Electrostatic coherent structures: The role of the ions dynamics

F. Califano, L. Galeotti, and C. Briand

Phys. Plasmas 14, 052306 (2007); http://dx.doi.org/10.1063/1.2724807 (7 pages) | Cited 1 time

Online Publication Date: 16 May 2007

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The Vlasov–Poisson model is the basic framework for the investigation of electrostatic coherent structures (e.g., phase space holes). Directly observed by high resolution space instruments, they are considered as one of the key ingredients of collisionless space and laboratory plasmas. These structures are in general studied numerically in the 1D limit of nonmoving ions eventually leading to a one single final structure (vortex merging). Here we show that, despite the electronic nature of such vortex, the merging process is inhibited by the ions so that many structures are still observed after several ion periods. Furthermore, the ion mass cannot be considered just as a rescaling parameter in the system evolution. Finally, numerical discretization effects significantly influence the nonlinear plasma dynamics even if statistically the number and typical dimension of the structures is unchanged, thus making the results relevant to space observations.
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52.35.Sb Solitons; BGK modes
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
94.20.wf Plasma waves and instabilities
52.65.Ff Fokker-Planck and Vlasov equation
52.65.-y Plasma simulation

Ion acoustic solitary wave with weakly transverse perturbations in quantum electron-positron-ion plasma

A. Mushtaq and S. A. Khan

Phys. Plasmas 14, 052307 (2007); http://dx.doi.org/10.1063/1.2727474 (6 pages) | Cited 39 times

Online Publication Date: 16 May 2007

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The characteristics and stability of ion acoustic solitary wave with transverse perturbations are examined in ultracold quantum magnetospheric plasma consisting of electrons, positrons, and ions. Using the quantum hydrodynamic model, a dispersion relation in the linear regime, and the Kadomtsev-Petviashvili equation in the nonlinear regime are derived. The quantum corrections are studied through quantum statistics and diffraction effects. It is found that compressive solitary wave can propagate in this system. The quantum effects are also studied graphically for both linear and nonlinear profiles of ion acoustic wave. Using energy consideration method, conditions for existence of stable solitary waves are obtained. It is found that stable solitary waves depend on quantum corrections, positron concentration, and direction cosine of the wave vector k along the x axis.
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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.)
52.35.Dm Sound waves
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.27.Cm Multicomponent and negative-ion plasmas

Nonlinear excitation of geodesic acoustic modes by drift waves

N. Chakrabarti, R. Singh, P. K. Kaw, and P. N. Guzdar

Phys. Plasmas 14, 052308 (2007); http://dx.doi.org/10.1063/1.2732167 (6 pages) | Cited 23 times

Online Publication Date: 17 May 2007

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In this paper, two mode-coupling analyses for the nonlinear excitation of the geodesic acoustic modes (GAMs) in tokamak plasmas by drift waves are presented. The first approach is a coherent parametric process, which leads to a three-wave resonant interaction. This investigation allows for the drift waves and the GAMs to have comparable scales. The second approach uses the wave-kinetic equations for the drift waves, which then couples to the GAMs. This requires that the GAM scale length be large compared to the wave packet associated with the drift waves. The resonance conditions for these two cases lead to specific predictions of the radial wave number of the excited GAMs.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Kt Drift waves
52.55.Fa Tokamaks, spherical tokamaks

Diffusion and drift of a blob of partially ionized plasma in a magnetic field

V. Rozhansky, I. Senichenkov, and I. Veselova

Phys. Plasmas 14, 052309 (2007); http://dx.doi.org/10.1063/1.2735938 (8 pages) | Cited 3 times

Online Publication Date: 21 May 2007

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Considered is the three-dimensional expansion and drift of a partially ionized plasma blob in a magnetic field. The pressure and density of neutrals are assumed to be strongly inhomogeneous functions of coordinates. It is shown that when the magnetic field pressure is much stronger than the net blob pressure and the mean free path of neutrals is smaller than the blob perpendicular size, the blob expands diffusively across the magnetic field. The strong radial electric field arises to provide quasineutrality, which causes the blob rotation in the azimuth direction. It is demonstrated that the blob injected with an initial velocity V0 across a magnetic field continues its motion with the same velocity due to additional polarization electric field of a dipole type. The total electric field structure of the blob is rather complicated. It is demonstrated that the partially ionized blob continues to move with the initial velocity even if the pressure of the ambient plasma is higher than the blob pressure.
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52.25.Fi Transport properties
52.25.Jm Ionization of plasmas
52.25.Ya Neutrals in plasmas
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Parametric up-conversion of an electron Bernstein mode by a relativistic electron beam in a plasma

Asheel Kumar and V. K. Tripathi

Phys. Plasmas 14, 052310 (2007); http://dx.doi.org/10.1063/1.2736368 (4 pages)

Online Publication Date: 21 May 2007

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A relativistic electron beam, propagating with velocity v0b‖math in a magnetized plasma, parametrically up-converts a pre-existing electron Bernstein wave (ω0,k0) into electromagnetic radiation when k0∙v0b<0. The Bernstein wave couples with a negative energy space-charge mode (ω,k) to produce a frequency up-converted sideband electromagnetic wave. The sideband and the Bernstein wave exert a ponderomotive force, driving space-charge mode. In the Compton regime, the growth rate of the parametric instability scales as two-third power of the pump amplitude, whereas in the Raman regime, it goes linearly.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.40.Mj Particle beam interactions in plasmas
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Development of electrostatic turbulence from drift-interchange instabilities in a toroidal plasma

F. M. Poli, M. Podestà, and A. Fasoli

Phys. Plasmas 14, 052311 (2007); http://dx.doi.org/10.1063/1.2731323 (9 pages) | Cited 7 times

Online Publication Date: 23 May 2007

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Electrostatic instabilities develop on TORPEX (TORoidal Plasma EXperiment) [ A. Fasoli et al., Phys. of Plasmas, 13, 55902 (2006) ] in the bad curvature region and propagate consistently with the drift wave dispersion relation. The wave number and frequency spectra are coherent at the location where the instabilities are generated, then broaden along the E×B convection. The phase coupling between spectral components at different frequencies, measured at different locations over the plasma cross section, indicates that the transition from a coherent to a turbulent spectrum is mainly due to three-wave interaction processes. Nonlinear interactions are measured between the linearly unstable mode and fluctuations with larger frequency, with transfer of energy away from the linearly unstable mode. The results are consistent with a nonlinearity induced by the convection of density fluctuations by the E×B fluctuating velocity.
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52.35.Ra Plasma turbulence
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.55.Fa Tokamaks, spherical tokamaks
52.35.Kt Drift waves
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.Gj Fluctuation and chaos phenomena
back to top Magnetically Confined Plasmas, Heating, Confinement

Numerical modeling of diffusive heat transport across magnetic islands and highly stochastic layers

M. Hölzl, S. Günter, Q. Yu, and K. Lackner

Phys. Plasmas 14, 052501 (2007); http://dx.doi.org/10.1063/1.2722980 (6 pages) | Cited 11 times

Online Publication Date: 2 May 2007

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Diffusive heat transport across magnetic islands and highly stochastic layers is studied numerically for realistic values of χ‖/χ⊥ in cylindrical geometry, where χ‖ denotes the heat diffusion coefficient parallel and χ⊥ the one perpendicular to the magnetic field lines. The computations are performed with a second-order finite difference scheme, for which the numerical errors are independent from the value of χ‖/χ⊥ [ S. Günter et al., J. Comput. Phys. 209, 354 (2005) ]. Sufficient spatial resolution is ensured by using an unsheared helical coordinate system. The heat flux around magnetic islands as well as the effective radial heat diffusivity χr are examined and compared to analytical theory. The temperature perturbations caused by magnetic islands and the resulting bootstrap current perturbations essential for the stability of neoclassical tearing modes are analyzed and compared to analytical predictions [ R. Fitzpatrick, Phys. Plasmas 2, 825 (1995) ]. Agreement is found in the “small” and “large” island limits, but an enhanced NTM drive is observed in between. A correction factor that can reproduce the numerical results very well is presented. For a highly stochastic layer, produced by five strongly overlapping islands, the radial heat diffusivity χr is determined and compared to several analytical theories.
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52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Xz Magnetized plasmas
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
02.70.Bf Finite-difference methods

Collisional diffusion in toroidal plasmas with elongation and triangularity

P. Martín, E. Castro, and M. G. Haines

Phys. Plasmas 14, 052502 (2007); http://dx.doi.org/10.1063/1.2727455 (10 pages) | Cited 2 times

Online Publication Date: 4 May 2007

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Collisional diffusion is analyzed for plasma tokamaks with different ellipticities and triangularities. Improved nonlinear equations for the families of magnetic surfaces are used here. Dimensionless average velocities are calculated as a function of the inductive electric field, elongation, triangularity, and Shafranov shift. Confinement has been found to depend significantly on triangularity.
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52.55.Dy General theory and basic studies of plasma lifetime, particle and heat loss, energy balance, field structure, etc.
52.55.Fa Tokamaks, spherical tokamaks
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