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Nov 2006

Volume 13, Issue 11, Articles (11xxxx)

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Programmable fabrication of spatial structures in a gas jet by laser machining with a spatial light modulator

M.-W. Lin, Y.-M. Chen, C.-H. Pai, C.-C. Kuo, K.-H. Lee, J. Wang, S.-Y. Chen, and J.-Y. Lin

Phys. Plasmas 13, 110701 (2006); http://dx.doi.org/10.1063/1.2372795 (4 pages) | Cited 12 times

Online Publication Date: 13 November 2006

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Programmable fabrication of longitudinal spatial structures in a gas jet was achieved by using laser machining with a liquid-crystal spatial light modulator as the pattern mask. By this technique single-shot fabrication of arbitrary gas and/or plasma structures is demonstrated, which establishes the crucial step toward raising the designs and applications of high-field plasma devices to the level of adaptive feedback optimization.
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52.75.-d Plasma devices
52.59.Ye Plasma devices for generation of coherent radiation
42.62.Cf Industrial applications
42.79.Hp Optical processors, correlators, and modulators
42.79.Kr Display devices, liquid-crystal devices

Dense quasi-monoenergetic attosecond electron bunches from laser interaction with wire and slice targets

Yan-Yun Ma, Zheng-Ming Sheng, Yu-Tong Li, Wen-Wei Chang, Xiao-Hui Yuan, Min Chen, Hui-Chun Wu, Jun Zheng, and Jie Zhang

Phys. Plasmas 13, 110702 (2006); http://dx.doi.org/10.1063/1.2388958 (4 pages) | Cited 23 times

Online Publication Date: 13 November 2006

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A scheme is proposed to produce high-quality quasi-monoenergetic attosecond electron bunches based on laser ponderomotive-force acceleration along the surface of wire or slice targets. Two- and three-dimensional particle-in-cell simulations demonstrate that the electron energy depends weakly on the target density. A simple analytical model shows that the electron energy scales linearly with the laser field amplitude, in good agreement with the simulation results. Electron bunches produced by this scheme are suitable for applications such as coherent x-ray radiation, radiography, and injectors in accelerators, etc.
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52.38.Kd Laser-plasma acceleration of electrons and ions
52.65.Rr Particle-in-cell method
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
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back to top Basic Plasma Phenomena, Waves, Instabilities

Secondary shock formation in xenon-nitrogen mixtures

J. F. Hansen, M. J. Edwards, D. H. Froula, A. D. Edens, G. Gregori, and T. Ditmire

Phys. Plasmas 13, 112101 (2006); http://dx.doi.org/10.1063/1.2359283 (6 pages) | Cited 3 times

Online Publication Date: 3 November 2006

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The expansion of shock waves has been studied in mediums with different opacities and heat capacities, varied in systematic ways by mixing xenon with nitrogen keeping the mass density constant. An initial shock is generated through the brief (5 ns) deposition of laser energy (5 J) on the tip of a pin surrounded by the xenon-nitrogen mixture. The initial shock is spherical, radiative, with a high Mach number, and it sends a supersonic radiatively driven heat wave far ahead of itself. The heat wave rapidly slows to a transonic regime and when its Mach number drops to ∼ 2 with respect to the downstream plasma, the heat wave becomes of the ablative type, driving a second shock ahead of itself to satisfy mass and momentum conservation in the heat wave reference frame. The details of this sequence of events depend, among other things, on the opacity and heat capacity of the surrounding medium. Second shock formation is observed over the entire range from 100% Xe mass fraction to 100% N2. The formation radius of the second shock as a function of Xe mass fraction is consistent with an analytical estimate.
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52.35.Tc Shock waves and discontinuities
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.25.Kn Thermodynamics of plasmas
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)

Active control of the ion resonance instability by ion removing fields

G. Bettega, F. Cavaliere, M. Cavenago, F. De Luca, A. Illiberi, R. Pozzoli, and M. Romé

Phys. Plasmas 13, 112102 (2006); http://dx.doi.org/10.1063/1.2363175 (6 pages) | Cited 1 time

Online Publication Date: 7 November 2006

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The off-axis bulk rotation (l = 1 diocotron mode) of an electron plasma column confined in a Malmberg-Penning trap is strongly destabilized by a small population of positive ions formed by energetic electron-neutral collisions. The instability, known as ion resonance instability, drives the plasma against the wall, destroying the confinement. A new experimental technique based on the static or time dependent application of low voltages to the inner conductors of the trap is shown to be effective in controlling the instability. The efficiency of the control technique is experimentally investigated by a systematic variation of the amplitudes, time duration, and periodicity of the additional potentials.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.40.Mj Particle beam interactions in plasmas
52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps
52.70.Ds Electric and magnetic measurements
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

New regimes of stochastic wave growth: Theory, simulation, and comparison with data

P. A. Robinson, B. Li, and I. H. Cairns

Phys. Plasmas 13, 112103 (2006); http://dx.doi.org/10.1063/1.2363174 (14 pages) | Cited 7 times

Online Publication Date: 8 November 2006

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Stochastic growth theory (SGT) of bursty waves is generalized and it is shown that the theory of “elementary bursts,” previously used to describe bursty emission in certain solar plasmas, is a limiting case of the generalized theory. New regimes of strong and weak stochastic growth are found, the boundaries separating the regimes are elucidated, and a reduced-parameter quasilinear model is used to constrain growth dynamics. The analytic results are then compared with simulations using the reduced-parameter model. Upon re-analysis of data from situations previously studied using SGT or other theories, including spacecraft data and results of particle-in-cell and quasilinear simulations, good agreement is found with the predictions of the generalized theory. In particular, data collapse of stochastic wave statistics is accomplished onto a universal curve with no free parameters.
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42.25.Dd Wave propagation in random media
52.35.−g
52.65.−y

Effect of non-Maxwellian particle trapping and dust grain charging on dust acoustic solitary waves

N. Rubab, G. Murtaza, and A. Mushtaq

Phys. Plasmas 13, 112104 (2006); http://dx.doi.org/10.1063/1.2364155 (7 pages) | Cited 7 times

Online Publication Date: 10 November 2006

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The role of adiabatic trapped ions on a small but finite amplitude dust acoustic wave, including the effect of adiabatic dust charge variation, is investigated in an unmagnetized three-component dusty plasma consisting of electrons, ions and massive micron sized negatively charged dust particulates. We have assumed that electrons and ions obey (r,q) velocity distribution while the dust species is treated fluid dynamically. It is found that the dynamics of dust acoustic waves is governed by a modified r dependent Korteweg-de Vries equation. Further, the spectral indices (r,q) affect the charge fluctuation as well as the trapping of electrons and ions and consequently modify the dust acoustic solitary wave.
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52.27.Lw Dusty or complex plasmas; plasma crystals
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
52.25.Fi Transport properties
52.25.Gj Fluctuation and chaos phenomena

A generalized Petschek magnetic reconnection rate

T. D. Arber and M. Haynes

Phys. Plasmas 13, 112105 (2006); http://dx.doi.org/10.1063/1.2375039 (5 pages) | Cited 1 time

Online Publication Date: 10 November 2006

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Simple physical arguments show that a generalization of the basic Petschek reconnection rate allows it to be extended to the Hall magnetohydrodynamic (MHD) rate. This result is confirmed by direct numerical simulations of the compressible fluid equations. To ensure that Petschek reconnection is obtained we specify a localized resistivity. The new generalized reconnection rate therefore gives an accurate estimate of the unforced Petschek reconnection rate for both MHD and Hall MHD. Since the Hall Petschek rate does not vanish in the limit of zero resistivity this generalized rate may also give the collisionless Hall Petschek reconnection rate.
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52.35.Vd Magnetic reconnection
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.Fi Transport properties

Evolution of an expanding dusty plasma with negative ions

B. Kechouri and M. Djebli

Phys. Plasmas 13, 112106 (2006); http://dx.doi.org/10.1063/1.2378629 (4 pages) | Cited 2 times

Online Publication Date: 10 November 2006

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The dusty plasma radial expansion is studied in the case of a spherical as well as cylindrical configuration. The effect of negative ions is introduced through the dust charge fluctuation equation. Electrons, positive, and negative ions are modelled by the Boltzmann distribution function and the dust grains by fluid equations. Using the self-similar theory, the nonlinear set of differential equations is solved numerically. It is found that the dust charge presents a critical value which depends on the negative ion species type. It is also found that the dust expansion ends earlier and the lighter particle densities profiles depend on the dust initial charge.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.25.Gj Fluctuation and chaos phenomena
52.25.Dg Plasma kinetic equations
52.25.Fi Transport properties
02.60.Lj Ordinary and partial differential equations; boundary value problems

Propagation of Alfvén waves in shear flows: Nature of driven longitudinal velocity and density fluctuations

Edisher Kh. Kaghashvili, Joachim Raeder, Gary M. Webb, and Gary P. Zank

Phys. Plasmas 13, 112107 (2006); http://dx.doi.org/10.1063/1.2387148 (7 pages) | Cited 5 times

Online Publication Date: 16 November 2006

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The nature of driven longitudinal velocity fluctuations and density fluctuations is studied when there is an Alfvén wave propagating in the medium characterized by an inhomogeneous velocity field. A system of governing equations that describes driven fluctuations is obtained and the properties of this system are analyzed. For some circumstances considering general properties of the Alfvén wave, the system allows us to obtain analytical solutions for driven waves that can be compared with ones obtained by numerical integration of the wave interaction equations. It is shown that for the low β plasma, the analytical solutions are in a good agreement with the numerical ones. The natural frequencies of individual wave components (“uncoupled natural frequencies”) are analyzed and how these frequencies are related to the natural frequencies of the coupled system are shown. In the summary, it is discussed where this process can be important. The possible observations in different areas where its signature can be found are outlined.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Fi Transport properties
52.25.Gj Fluctuation and chaos phenomena

Observation of coherent nonlinear interactions in the ion velocity distribution function

Ilker Ü. Uzun-Kaymak and Frederick Skiff

Phys. Plasmas 13, 112108 (2006); http://dx.doi.org/10.1063/1.2387143 (8 pages) | Cited 3 times

Online Publication Date: 17 November 2006

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Using laser induced fluorescence (LIF) and higher order spectral analysis, we present the first measurements of phase space resolved coherent nonlinear interactions among the components of low frequency density fluctuations, (ω ⩽ ωci), in a linearly magnetized device. The bicoherence calculations employing the two point correlation technique suggest that there are two different coherent nonlinear wave-wave interactions in the measured spectrum. The first one, having a short correlation length and existing for slow moving ions, for which ∣υi‖∣ ⩽ ∣υith∣, is an interaction between fluctuations below the electron drift frequency, ω*. The second one is the strongest for fast moving ions, for which ∣υi‖∣ ≥ ∣υith∣, and is a mode coupling between the azimuthal drift wave modes, m = 1 and m = 2. Combining these bispectral results with earlier linear analysis based on the power spectra of the fluctuations, we suggest that the nonlinear coupling observed between the spectral components below ω* for the case of slow moving ions is associated with the anomalous kinetic component. For slow moving ions, as we increase the neutral collision frequencies, the nonlinear interaction observed for spectral components below ω* decreases and the harmonic mode coupling for ω* takes over.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.Fi Transport properties
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Xz Magnetized plasmas
52.25.Gj Fluctuation and chaos phenomena
52.35.Kt Drift waves

Determination of equilibrium density distribution and temperature of a pure electron plasma confined in a Penning trap

J. Aoki, Y. Kiwamoto, and Y. Kawai

Phys. Plasmas 13, 112109 (2006); http://dx.doi.org/10.1063/1.2387544 (8 pages) | Cited 7 times

Online Publication Date: 17 November 2006

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A fast scheme is proposed for determining the three-dimensional density distribution of a pure electron plasma under the thermal relaxation in a Penning trap on the basis of the observation of the axially integrated density distribution. The analysis that includes the contribution of the conducting wall reveals the appearance of a halo distribution surrounding the core distribution around the midplane. The core is confirmed to approach the Penning-type equilibrium distribution. Also proposed is a new scheme of the temperature determination of the electrons by analyzing a radial profile of the particles extracted with energy selection. This method is available on the basis of the self-consistent potential distribution associated with the equilibrium density distribution. The application of the two schemes of data analysis shows that the electron temperature decreases well below 0.1 eV with a 1/e folding time of ≈ 4× cyclotron-cooling time in the trap kept at room temperature.
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52.27.Jt Nonneutral plasmas
52.27.Aj Single-component, electron-positive-ion plasmas
52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Fi Transport properties

Evolution of the fastest-growing relativistic mixed mode instability driven by a tenuous plasma beam in one and two dimensions

M. E. Dieckmann, J. T. Frederiksen, A. Bret, and P. K. Shukla

Phys. Plasmas 13, 112110 (2006); http://dx.doi.org/10.1063/1.2390687 (8 pages) | Cited 18 times

Online Publication Date: 30 November 2006

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Particle-in-cell simulations confirm here that a mixed plasma mode is the fastest growing when a highly relativistic tenuous electron-proton beam interacts with an unmagnetized plasma. The mixed modes grow faster than the filamentation and two-stream modes in simulations with beam Lorentz factors Γ of 4, 16, and 256, and are responsible for thermalizing the electrons. The mixed modes are followed to their saturation for the case of Γ = 4 and electron phase space holes are shown to form in the bulk plasma, while the electron beam becomes filamentary. The initial saturation is electrostatic in nature in the considered one- and two-dimensional geometries. Simulations performed with two different particle-in-cell simulation codes evidence that a finite grid instability couples energy into high-frequency electromagnetic waves, imposing simulation constraints.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Ra Plasma turbulence

Nonlinear wave interactions in quantum magnetoplasmas

P. K. Shukla, S. Ali, L. Stenflo, and M. Marklund

Phys. Plasmas 13, 112111 (2006); http://dx.doi.org/10.1063/1.2390688 (6 pages) | Cited 38 times

Online Publication Date: 30 November 2006

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Nonlinear interactions involving electrostatic upper-hybrid (UH), ion-cyclotron (IC), lower-hybrid (LH), and Alfvén waves in quantum magnetoplasmas are considered. For this purpose, the quantum hydrodynamical equations are used to derive the governing equations for nonlinearly coupled UH, IC, LH, and Alfvén waves. The equations are then Fourier analyzed to obtain nonlinear dispersion relations, which admit both decay and modulational instabilities of the UH waves at quantum scales. The growth rates of the instabilities are presented. They can be useful in applications of our work to diagnostics in laboratory and astrophysical settings.
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05.30.−d
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
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.)
back to top Nonlinear Phenomena, Turbulence, Transport

Effects of a fluctuating sheared flow on cross phase in passive-scalar turbulent diffusion

M. Leconte, P. Beyer, S. Benkadda, and X. Garbet

Phys. Plasmas 13, 112301 (2006); http://dx.doi.org/10.1063/1.2363349 (8 pages) | Cited 11 times

Online Publication Date: 3 November 2006

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Transport barriers are key elements concerning energy and particle confinement in fusion devices. They play a fundamental role in the L→H transition observed in most tokamaks' edges. It has been shown that a shear in the E×B velocity could trigger and sustain such a barrier. The E×B velocity shear model has proven to be of great interest in the study of the formation and characteristics of transport barriers. Here we address a particular case of flow shear stabilization, namely the effect of a shear flow on the diffusion of a passive scalar. A shear flow reduces the radial flux (radial transport) Γ of a passive scalar field (we consider the pressure field) via the reduction of the turbulence energy math and/or via the reduction of the cross phase cos δ between the fluctuations of the pressure and velocity fields. We compare our results with those of different analytical models for passive-scalar advection or diffusion [ Terry et al., Phys. Rev. Lett. 87, 185001 (2001) ; Kim and Diamond, Phys. Rev. Lett. 91, 075001 (2003) ]. However, these studies yielded contradictory results. The purpose of this study is to shed light on this particular issue using numerical simulations to clarify the role of the reduction of the amplitude of turbulence and cross phase in regulating the radial transport.
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52.25.Fi Transport properties
52.30.-q Plasma dynamics and flow
52.25.Gj Fluctuation and chaos phenomena
52.35.Ra Plasma turbulence
52.55.Fa Tokamaks, spherical tokamaks
52.40.Hf Plasma-material interactions; boundary layer effects

Obliquely propagating ion acoustic solitary waves in a dusty plasma in the presence of an external magnetic field

Sarit Maitra and Rajkumar Roychoudhury

Phys. Plasmas 13, 112302 (2006); http://dx.doi.org/10.1063/1.2364140 (7 pages) | Cited 9 times

Online Publication Date: 8 November 2006

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The obliquely propagating nonlinear ion acoustic wave in a dusty plasma subjected to an external magnetic field is studied in the Sagdeev’s pseudopotential framework. The Sagdeev’s potential is derived in two cases, one of which assumes the quasineutrality condition and the other uses the Poisson equation instead. The respective ranges of parameters for which solitary waves exist in both the cases are studied in some detail numerically.
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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
52.27.Lw Dusty or complex plasmas; plasma crystals
52.25.Fi Transport properties
52.25.Dg Plasma kinetic equations

Turbulent transport of alpha particles in reactor plasmas

C. Estrada-Mila, J. Candy, and R. E. Waltz

Phys. Plasmas 13, 112303 (2006); http://dx.doi.org/10.1063/1.2364149 (15 pages) | Cited 26 times

Online Publication Date: 8 November 2006

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A systematic study of the behavior of energetic ions in reactor plasmas is presented. Using self-consistent gyrokinetic simulations, in concert with an analytic asymptotic theory, it is found that alpha particles can interact significantly with core ion-temperature-gradient turbulence. Specifically, the per-particle flux of energetic alphas is comparable to the per-particle flux of thermal species (deuterium or helium ash). This finding opposes the conventional wisdom that energetic ions, because of their large gyroradii, do not interact with the turbulence. For the parameters studied, a turbulent modification of the alpha-particle density profile appears to be stronger than turbulent modification of the alpha-particle pressure profile. Crude estimates indicate that the alpha density modification, which is directly proportional to the core turbulence intensity, could be in the range of 15% at midradius in a reactor. The corresponding modification of the alpha-particle pressure profile is predicted to be smaller (in the 1% range).
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52.25.Fi Transport properties
52.25.Vy Impurities in plasmas
52.30.−q
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.55.Pi Fusion products effects (e.g., alpha-particles, etc.), fast particle effects

Relativistically intense plane electromagnetic waves in electron–positron plasmas: Nonlinear self-modulation and harmonics generation regimes

O. B. Shiryaev

Phys. Plasmas 13, 112304 (2006); http://dx.doi.org/10.1063/1.2370695 (7 pages) | Cited 10 times

Online Publication Date: 10 November 2006

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A fully nonlinear one-dimensional problem describing the interactions of relativistically intense plane electromagnetic waves and cold locally non-neutral electron–positron plasmas is derived from Maxwell and fluid dynamics equations. Numerical and asymptotic solutions to this problem for phase velocities close to the speed of light are presented. Depending on the magnitude of the plasma longitudinal electric-field potential, the system considered is found to support two distinct regimes of plane electromagnetic wave propagation: a nonlinear self-modulation one with the coupling of a fast transversely polarized electromagnetic field to a slow longitudinal plasma field, and a harmonics generation one with both of these fields oscillating with comparable frequencies. In the former case, a splitting of the electromagnetic field spectrum into a series of closely located bands occurs, whereas in the latter one the propagating field spectrum is a set of radiation harmonics.
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52.35.−g
04.30.Nk Wave propagation and interactions
42.65.−k
11.80.−m
96.50.Tf MHD waves; plasma waves, turbulence

Charging-delay induced dust acoustic collisionless shock wave: Roles of negative ions

Samiran Ghosh, R. Bharuthram, Manoranjan Khan, and M. R. Gupta

Phys. Plasmas 13, 112305 (2006); http://dx.doi.org/10.1063/1.2374861 (6 pages) | Cited 6 times

Online Publication Date: 16 November 2006

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The effects of charging-delay and negative ions on nonlinear dust acoustic waves are investigated. It has been found that the charging-delay induced anomalous dissipation causes generation of dust acoustic collisionless shock waves in an electronegative dusty plasma. The small but finite amplitude wave is governed by a Korteweg-de Vries Burger equation in which the Burger term arises due to the charging-delay. Numerical investigations reveal that the charging-delay induced dissipation and shock strength decreases (increases) with the increase of negative ion concentration (temperature).
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52.35.Tc Shock waves and discontinuities
52.27.Lw Dusty or complex plasmas; plasma crystals
52.35.Dm Sound waves
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.Fi Transport properties
52.27.Cm Multicomponent and negative-ion plasmas

The Hall dynamo effect and nonlinear mode coupling during sawtooth magnetic reconnection

W. X. Ding, D. L. Brower, B. H. Deng, A. F. Almagri, D. Craig, G. Fiksel, V. Mirnov, S. C. Prager, J. S. Sarff, and V. Svidzinski

Phys. Plasmas 13, 112306 (2006); http://dx.doi.org/10.1063/1.2363353 (11 pages) | Cited 4 times

Online Publication Date: 29 November 2006

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During magnetic reconnection associated with sawtooth activity in a reversed field pinch, we observe a large fluctuation-induced Hall electromotive force, 〈δJ×δB〉/nee, which is capable of modifying the equilibrium current. This Hall dynamo effect is determined in the hot plasma core by laser Faraday rotation which measures equilibrium and fluctuating magnetic field and current density. We find that the Hall dynamo is strongest when nonlinear mode coupling between three spatial Fourier modes of the resistive tearing instability is present. Mode coupling alters the phase relation between magnetic and current density fluctuations for individual Fourier modes leading to a finite Hall effect. Detailed measurements of the spatial and temporal dynamics for the dominant core resonant mode under various plasma configurations are described providing evidence regarding the origin of the Hall dynamo.
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52.25.Gj Fluctuation and chaos phenomena
52.35.Vd Magnetic reconnection
52.55.Jd Magnetic mirrors, gas dynamic traps
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.)

Nonlinear ponderomotive force by low frequency waves and nonresonant current drive

Zhe Gao, Nathaniel J. Fisch, and Hong Qin

Phys. Plasmas 13, 112307 (2006); http://dx.doi.org/10.1063/1.2397584 (6 pages) | Cited 3 times

Online Publication Date: 30 November 2006

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The collisionless nonresonant force by low frequency waves has been thought to be capable of driving the nonresonant current. However, for a single particle, the ponderomotive force is in the direction of the gradient of the wave field energy. For cold plasmas, the Reynolds stress acting on the Lagrangian fluid element fully counteracts the nonresonant force offered by the quasilinear electromagnetic force. For hot plasmas, the collisionless nonresonant force is also cancelled by the nonlinear kinetic stress force. Therefore, in collisionless plasmas, none of the ponderomotive forces by low frequency waves can drive the nonresonant current.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.25.Fi Transport properties
52.25.Dg Plasma kinetic equations
back to top Magnetically Confined Plasmas, Heating, Confinement

Stochastic couplings of neoclassical tearing modes in ITER plasmas

Hinrich Lütjens and Jean-François Luciani

Phys. Plasmas 13, 112501 (2006); http://dx.doi.org/10.1063/1.2360508 (10 pages) | Cited 6 times

Online Publication Date: 3 November 2006

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Three-dimensional magnetohydrodynamic (MHD) computations of multiple neoclassical tearing modes growths in International Thermonuclear Experimental Reactor plasmas are presented. It is shown that within the MHD framework, these modes do not couple until significant stochastization between two tearing island chains occurs. After stochastization a quick amplitude drop of one or several modes is observed. This behavior is very similar to that observed for example in ASDEX-Upgrade [ A. Gude et al., Nucl. Fusion 42, 833 (2002) ].
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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.)
52.55.Fa Tokamaks, spherical tokamaks
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.Kj Magnetohydrodynamic and fluid equation
02.50.Ey Stochastic processes

Collisionality and magnetic geometry effects on tokamak edge turbulent transport. I. A two-region model with application to blobs

J. R. Myra, D. A. Russell, and D. A. D’Ippolito

Phys. Plasmas 13, 112502 (2006); http://dx.doi.org/10.1063/1.2364858 (9 pages) | Cited 17 times

Online Publication Date: 9 November 2006

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A two-region model is proposed to study the effect of collisionality and magnetic geometry on electrostatic turbulence and on the propagation of filamentary coherent structures (blobs) in the edge and scrape-off layer. The model invokes coupled vorticity and continuity equations in two different spatial regions along the magnetic field, taking into account the effect of magnetic field fanning and shear, e.g., near magnetic X-points. A linear dispersion relation for unstable modes illustrates the physics of mode disconnection (ballooning) along the magnetic field and its dependence on collisionality and wave number (scale size). Employing an invariant scaling analysis, dimensionless parameters for the nonlinear model are developed and used to describe the regimes of the system. A blob correspondence rule is postulated to relate the linear mode growth rates and regimes to the convective velocity of blobs. Nonlinear numerical simulations of blob convection show good agreement with a blob dispersion relation derived from the correspondence rule. It is found that collisionality increases the convective velocity. The convective velocity also depends on blob scale size, with either positive or negative exponent, depending on the collisionality regime. Finally, the dimensionless scaling analysis is employed to obtain bounds on the convective velocity suitable for experimental tests.
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52.55.Fa Tokamaks, spherical tokamaks
52.40.Hf Plasma-material interactions; boundary layer effects
52.35.Ra Plasma turbulence
52.25.Fi Transport properties
52.35.We Plasma vorticity
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Relativistic description of electron Bernstein waves

Joan Decker and Abhay K. Ram

Phys. Plasmas 13, 112503 (2006); http://dx.doi.org/10.1063/1.2366585 (14 pages) | Cited 10 times

Online Publication Date: 10 November 2006

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The application of the extraordinary and ordinary electron cyclotron waves for heating and current drive in overdense, magnetized plasmas is restricted. For frequencies near low harmonics of the electron cyclotron frequency these waves are cutoff near the edge of the plasma. For higher frequencies the interaction of the waves with electrons is weak leading to very low absorption of wave power. However, electron Bernstein waves provide means for heating and current drive in overdense plasmas since they have no density cutoffs and are strongly damped near harmonics of the electron cyclotron resonance. This paper discusses properties of electron Bernstein waves that make them an attractive means for delivering energy and momentum to electrons. An approximate analytical model for electrostatic waves in the weakly relativistic and weak damping limits is developed. From this model the propagation and damping characteristics of electron Bernstein waves and their dependence on plasma parameters are derived. It is found that relativistic effects are necessary to properly describe the resonant interaction of electron Bernstein waves with electrons. The characteristics of electron Bernstein wave propagation and damping are very different depending on whether the electron cyclotron harmonic resonance is approached from the low- or high-field side. The results from the analytical model and the associated analysis agree well with the results from the exact numerical calculations. This validates the physics of the simplifying assumptions on which the model is based. The electron Bernstein waves are completely damped well before the electron cyclotron resonance due to the Doppler shift. Within the damping region the waves interact with suprathermal electrons thereby having the potential for efficient current drive.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.27.Ny Relativistic plasmas
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.25.Fi Transport properties
52.40.Hf Plasma-material interactions; boundary layer effects

Impurity transport in ITER-like plasmas

T. Fülöp and J. Weiland

Phys. Plasmas 13, 112504 (2006); http://dx.doi.org/10.1063/1.2375042 (7 pages) | Cited 11 times

Online Publication Date: 15 November 2006

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Neoclassical impurity transport is compared with transport calculated from the reactive drift wave model of turbulent transport for an ITER-like [ R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002) ] scenario. The turbulent transport is inward for both main ions and impurities, but the impurity ion inward transport is much weaker than the main ion inward transport. The neoclassical impurity transport is outward because of temperature screening. The total impurity transport, determined by a balance between turbulent and neoclassical transport, depends sensitively on the charge number of the impurity and the ratio of the ion density and temperature scale lengths, ηi.
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52.25.Fi Transport properties
52.25.Vy Impurities in plasmas
52.55.Fa Tokamaks, spherical tokamaks
52.35.Kt Drift waves
52.35.Ra Plasma turbulence
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Kinetic stability of the internal kink mode in ITER

Bo Hu, R. Betti, and J. Manickam

Phys. Plasmas 13, 112505 (2006); http://dx.doi.org/10.1063/1.2364147 (9 pages) | Cited 17 times

Online Publication Date: 17 November 2006

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The kinetic stability of the n = 1, m = 1 internal kink mode is analyzed for realistic equilibria typical of the standard operation scenario of ITER (the International Thermonuclear Experimental Reactor) [ ITER Physics Basis Editors, Nucl. Fusion 39, 2137 (1999) ]. The kinetic effects modify the inertia and the perturbed potential energy δW of the mode, the two key elements determining the mode stability. Numerical results are obtained for ITER-like equilibria with different q profiles. For moderate magnetic shear within the q = 1 surface, the low frequency magnetohydrodynamic (MHD) branch is fully suppressed by the kinetic effects for the expected profiles and parameters up to twice the expected plasma β while the high frequency fishbone branch is found to be destabilized as the plasma β and the radius of the q = 1 surface increase. The MHD branch can be destabilized at higher plasma β or larger radii of the q = 1 surface only for q profiles with a low magnetic shear within the q = 1 surface.
Show PACS
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.30.−q
52.55.Fa Tokamaks, spherical tokamaks
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