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Sep 2009

Volume 16, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Phys. Plasmas 16, 093102 (2009); http://dx.doi.org/10.1063/1.3216549 (8 pages)

J. G. Gallacher, M. P. Anania, E. Brunetti, F. Budde, A. Debus, B. Ersfeld, K. Haupt, M. R. Islam, O. Jäckel, S. Pfotenhauer, A. J. W. Reitsma, E. Rohwer, H.-P. Schlenvoigt, H. Schwoerer, R. P. Shanks, et al.
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Full wave simulation of lower hybrid waves in Maxwellian plasma based on the finite element method

O. Meneghini, S. Shiraiwa, and R. Parker

Phys. Plasmas 16, 090701 (2009); http://dx.doi.org/10.1063/1.3216548 (4 pages) | Cited 12 times

Online Publication Date: 3 September 2009

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A full wave simulation of the lower-hybrid (LH) wave based on the finite element method is presented. For the LH wave, the most important terms of the dielectric tensor are the cold plasma contribution and the electron Landau damping (ELD) term, which depends only on the component of the wave vector parallel to the background magnetic field. The nonlocal hot plasma ELD effect was expressed as a convolution integral along the magnetic field lines and the resultant integro-differential Helmholtz equation was solved iteratively. The LH wave propagation in a Maxwellian tokamak plasma based on the Alcator C experiment was simulated for electron temperatures in the range of 2.5–10 keV. Comparison with ray tracing simulations showed good agreement when the single pass damping is strong. The advantages of the new approach include a significant reduction of computational requirements compared to full wave spectral methods and seamless treatment of the core, the scrape off layer and the launcher regions.
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52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.55.Fa Tokamaks, spherical tokamaks
52.55.Wq Current drive; helicity injection

Excitation frequency dependent mode manipulation in radio-frequency atmospheric argon glow discharges

Jie Zhang, Ke Ding, Kaya Wei, Jing Zhang, and Jianjun Shi

Phys. Plasmas 16, 090702 (2009); http://dx.doi.org/10.1063/1.3240350 (4 pages) | Cited 2 times

Online Publication Date: 24 September 2009

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An experimental investigation is presented to characterize the dependence of discharge operation modes (α and γ modes) and their transition on excitation frequency in radio-frequency atmospheric argon glow discharges. The current-voltage characteristics are used to distinguish the α and γ modes at an excitation frequency range of 5–24 MHz. The operation regime of α mode with stable and uniform discharge in large volume is found to expand at higher excitation frequency. It is shown that, when excitation frequency is below 10 MHz, the discharge evolves directly into γ mode after gas breakdown and, when excitation frequency is above 10 MHz, the discharge operates in the coexistence mode of α and γ after mode transition.
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52.80.Pi High-frequency and RF discharges
52.25.Fi Transport properties
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.80.Hc Glow; corona

The third-order law for increments in magnetohydrodynamic turbulence with constant shear

M. Wan, S. Servidio, S. Oughton, and W. H. Matthaeus

Phys. Plasmas 16, 090703 (2009); http://dx.doi.org/10.1063/1.3240333 (4 pages) | Cited 6 times

Online Publication Date: 29 September 2009

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We extend the theory for third-order structure functions in homogeneous incompressible magnetohydrodynamic turbulence to the case in which a constant velocity shear is present. A generalization is found of the usual relation [ Politano and Pouquet, Phys. Rev. E 57, 21 (1998) ] between third-order structure functions and the dissipation rate in steady inertial range turbulence, in which the shear plays a crucial role. In particular, the presence of shear leads to a third-order law which is not simply proportional to the relative separation. Possible implications for laboratory and space plasmas are discussed.
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52.35.Ra Plasma turbulence
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
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back to top Basic Plasma Phenomena, Waves, Instabilities

Two-stream stability properties of the return-current layer for intense ion beam propagation through background plasma

Edward A. Startsev, Ronald C. Davidson, and Mikhail Dorf

Phys. Plasmas 16, 092101 (2009); http://dx.doi.org/10.1063/1.3213566 (8 pages) | Cited 3 times

Online Publication Date: 3 September 2009

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When an ion beam with sharp edge propagates through a background plasma, its current is neutralized by the plasma return current everywhere except at the beam edge over a characteristic transverse distance Δx⊥ ∼ δpe, where δpe = c/ωpe is the collisionless skin depth and ωpe is the electron plasma frequency. Because the background plasma electrons neutralizing the ion beam current inside the beam are streaming relative to the background plasma electrons outside the beam, the background plasma can support a two-stream surface-mode excitation. Such surface modes have been studied previously assuming complete charge and current neutralization, and have been shown to be strongly unstable. In this paper we study the detailed stability properties of this two-stream surface mode for an electron flow velocity profile self-consistently driven by the ion beam. In particular, it is shown that the self-magnetic field generated inside the unneutralized current layer, which has not been taken into account previously, completely eliminates the instability.
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52.40.Mj Particle beam interactions in plasmas
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.25.Fi Transport properties
52.30.Ex Two-fluid and multi-fluid plasmas
52.65.-y Plasma simulation

On generation of Alfvénic-like fluctuations by drift wave–zonal flow system in large plasma device experiments

W. Horton, C. Correa, G. D. Chagelishvili, V. S. Avsarkisov, J. G. Lominadze, J. C. Perez, J.-H. Kim, and T. A. Carter

Phys. Plasmas 16, 092102 (2009); http://dx.doi.org/10.1063/1.3211197 (11 pages) | Cited 2 times

Online Publication Date: 3 September 2009

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According to recent experiments, magnetically confined fusion plasmas with “drift wave–zonal flow turbulence” (DW-ZF) give rise to broadband electromagnetic waves. Sharapov et al. [Europhysics Conference Abstracts, 35th EPS Conference on Plasma Physics, Hersonissos, 2008, edited by P. Lalousis and S. Moustaizis (European Physical Society, Switzerland, 2008), Vol. 32D, p. 4.071 ] reported an abrupt change in the magnetic turbulence during L-H transitions in Joint European Torus [ P. H. Rebut and B. E. Keen, Fusion Technol. 11, 13 (1987) ] plasmas. A broad spectrum of Alfvénic-like (electromagnetic) fluctuations appears from E×B flow driven turbulence in experiments on the large plasma device (LAPD) [ W. Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991) ] facility at UCLA. Evidence of the existence of magnetic fluctuations in the shear flow region in the experiments is shown. We present one possible theoretical explanation of the generation of electromagnetic fluctuations in DW-ZF systems for an example of LAPD experiments. The method used is based on generalizing results on shear flow phenomena from the hydrodynamics community. In the 1990s, it was realized that fluctuation modes of spectrally stable nonuniform (sheared) flows are non-normal. That is, the linear operators of the flows modal analysis are non-normal and the corresponding eigenmodes are not orthogonal. The non-normality results in linear transient growth with bursts of the perturbations and the mode coupling, which causes the generation of electromagnetic waves from the drift wave–shear flow system. We consider shear flow that mimics tokamak zonal flow. We show that the transient growth substantially exceeds the growth of the classical dissipative trapped-particle instability of the system.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Kt Drift waves
52.55.Fa Tokamaks, spherical tokamaks

Analytic models of warm plasma dispersion relations

J. J. Seough and P. H. Yoon

Phys. Plasmas 16, 092103 (2009); http://dx.doi.org/10.1063/1.3216459 (5 pages) | Cited 4 times

Online Publication Date: 9 September 2009

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The present paper is concerned with analytic models of warm plasma dispersion relations for electromagnetic waves propagating parallel to the ambient magnetic field. Specifically, effects of finite betas on two slow modes, namely, the left-hand circularly polarized ion-cyclotron mode and the right-hand circularly polarized whistler mode, are investigated. Analytic models of the warm plasma dispersion relations are constructed on the basis of conjecture and upon comparisons with numerically found roots. It is shown that the model solutions are good substitutes for actual roots. The significance of the present work in the context of nonlinear plasma research is discussed.
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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.)

Landau and non-Landau linear damping: Physics of the dissipation

T. Chust, G. Belmont, F. Mottez, and S. Hess

Phys. Plasmas 16, 092104 (2009); http://dx.doi.org/10.1063/1.3205896 (13 pages) | Cited 2 times

Online Publication Date: 11 September 2009

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For linear Langmuir waves, it is well known that the energy exchanges generally lead to a continuous dissipation, on average, from the electric form to the kinetic one. Many papers have estimated these exchanges and indeed shown that the classical Landau value γL, characterizing the electric field damping, can be derived from this estimation. The paper comes back to this demonstration and its implicit assumption of “forgetting the initial conditions.” The limits of the usual energy calculations have become much apparent recently when non-Landau solutions, decreasing with damping rates smaller than γL, have been evidenced [ Belmont et al., Phys. Plasmas 15, 052310 (2008) ]. Taking advantage of the explicit form provided in this paper for the perturbed distribution function, the dissipation process is revisited here in a more general way. It is shown that the energy calculations, when complete (i.e., when the role of the initial conditions is not excluded by the very hypotheses of the calculations), are indeed in full agreement with the existence of non-Landau solutions; Landau damping, by the way, appears as a particular mode of dissipation, in which the ballistic transport of the initial plasma perturbation leads to negligible effects. Two approaches are presented for this demonstration, Eulerian and Lagrangian, the first one starting from the Vlasov equation and the second from the dynamics of the individual particles. The specific role of the so-called resonant particles is investigated in both formalisms, which provides complementary pictures of the microphysics involved in the energy transfers between field and particles for Landau as well as for non-Landau solutions.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Excitation of stable Alfvén eigenmodes by application of alternating magnetic field perturbations in the Compact Helical System

T. Ito, K. Toi, G. Matsunaga, M. Isobe, K. Nagaoka, M. Takeuchi, T. Akiyama, K. Matsuoka, T. Minami, S. Nishimura, S. Okamura, A. Shimizu, C. Suzuki, Y. Yoshimura, C. Takahashi, et al.

Phys. Plasmas 16, 092105 (2009); http://dx.doi.org/10.1063/1.3223845 (13 pages) | Cited 1 time

Online Publication Date: 14 September 2009

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Stable toroidicity-induced Alfvén eigenmodes (TAEs) with low toroidal mode number (n = 1 and n = 2) were excited by application of alternating magnetic field perturbations generated with a set of electrodes inserted into the edge region of neutral beam injection heated plasmas on the Compact Helical System [ K. Nishimura, K. Matsuoka, M. Fujiwara et al., Fusion Technol. 17, 86 (1990) ]. The gap locations of TAEs excited by the electrodes are in the plasma peripheral region of ρ>0.7 (ρ is the normalized minor radius) where energetic ion drive is negligibly small, while some AEs are excited by energetic ions in the plasma core region of ρ<0.4. The damping rate of these stable TAEs derived from plasma responses to applied perturbations is fairly large, that is, ∼ 9% to ∼ 12% of the angular eigenfrequency. This large damping rate is thought to be dominantly caused by continuum damping and radiative damping.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.55.Jd Magnetic mirrors, gas dynamic traps
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.50.Gj Plasma heating by particle beams

Generation of polarized shear Alfvén waves by a rotating magnetic field source

A. Gigliotti, W. Gekelman, P. Pribyl, S. Vincena, A. Karavaev, X. Shao, A. Surjalal Sharma, and D. Papadopoulos

Phys. Plasmas 16, 092106 (2009); http://dx.doi.org/10.1063/1.3224030 (8 pages) | Cited 6 times

Online Publication Date: 16 September 2009

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Experiments are performed in the Large Plasma Device at the University of California, Los Angeles to study the propagation of field-aligned, polarized kinetic shear Alfvén waves radiated from a rotating magnetic field source created via a novel phased orthogonal loop antenna. Both right and left hand circular polarizations are generated at a wide range of frequencies from 0.21 ≤ ω/Ωci<0.93. Propagation parallel to the background magnetic field near the Alfvén velocity is observed along with a small parallel wave magnetic field component implying a shear mode. The peak-to-peak magnitude of the wave magnetic field, 33 cm away from the antenna, is on the order of 0.8% of the background field and drops off in the far field. The full width at half maximum of the wave energy changes little over a distance of 2.5 parallel wavelengths while the exponential decrease in wave energy as a function of distance can be attributed to collisional damping. Evidence of electron heating and ionization is observed during the pulse.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.50.-b Plasma production and heating
52.55.-s Magnetic confinement and equilibrium
52.75.-d Plasma devices

Translating oscillatory nonlinear structure in a plasma boundary

F. Haas and P. K. Shukla

Phys. Plasmas 16, 092107 (2009); http://dx.doi.org/10.1063/1.3240889 (6 pages) | Cited 2 times

Online Publication Date: 29 September 2009

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By means of a Madelung decomposition, exact periodic traveling solutions are constructed for a modified nonlinear Schrödinger equation derived by Stenflo and Gradov, describing electrostatic surface waves in semi-infinite plasma. The condition for the existence of bistable equilibria is discussed. A conservation law as well as the modulational instability admitted by the model are analyzed.
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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)
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
back to top Nonlinear Phenomena, Turbulence, Transport

Similarity theory of nonlinear cold pair-plasma dynamics

D. A. Diver and E. W. Laing

Phys. Plasmas 16, 092301 (2009); http://dx.doi.org/10.1063/1.3216545 (11 pages) | Cited 2 times

Online Publication Date: 1 September 2009

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In this article the waves and dynamics of an inhomogeneous cold magnetized electron-positron plasma are investigated using similarity methods to study particular classes of plasma wave behavior. A cold two-fluid plasma model in a cylindrical geometry (ρ,θ,z) and time t is assumed, but attention is restricted to (ρ,t) variations only. The application of similarity procedures reduces the set of partial differential equations which describe the spatial and temporal evolution of the plasma to a set of ordinary differential equations. This model has particular relevance to the description of the evolution of the electron-positron component of pulsar magnetospheres. Some typical solutions of these similarity equations are presented which characteristically have the property of blow-up phenomena.
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52.25.Xz Magnetized plasmas
52.27.Ep Electron-positron plasmas
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Tc Shock waves and discontinuities
52.65.Kj Magnetohydrodynamic and fluid equation
97.60.Gb Pulsars
02.60.Lj Ordinary and partial differential equations; boundary value problems

Two dimensional planar and nonplanar ion acoustic shock waves in electron-positron-ion plasmas

W. Masood and H. Rizvi

Phys. Plasmas 16, 092302 (2009); http://dx.doi.org/10.1063/1.3208695 (6 pages) | Cited 3 times

Online Publication Date: 3 September 2009

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Two dimensional ion acoustic shock waves (IASWs) are studied in an unmagnetized plasma consisting of electrons, positrons, and adiabatically hot positive ions. This is done by deriving the nonplanar Kadomstev–Petviashvili–Burgers (KPB) equation under the small amplitude perturbation expansion method. The dissipation is introduced by taking into account the kinematic viscosity among the plasma constituents. The limiting cases of the nonplanar KPB equation are also discussed. The analytical solution of the planar KPB equation is obtained using the tangent hyperbolic method that is used as the initial profile to numerically solve the nonplanar KPB equation. It is found that the strength of IASW is maximum for spherical, intermediate for cylindrical, and minimum for planar geometry. It is observed that the positron concentration and the plasma kinematic viscosity significantly modify the shock structure. Finally, the temporal evolution of the nonplanar IASW is investigated and the results are discussed from the numerical stand point. The results of the present study may be applicable in the study of small amplitude localized electrostatic shock structures in electron-positron-ion plasmas.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.25.Dg Plasma kinetic equations
52.35.Tc Shock waves and discontinuities

Anomalous parallel momentum transport due to E×B flow shear in a tokamak plasma

F. J. Casson, A. G. Peeters, Y. Camenen, W. A. Hornsby, A. P. Snodin, D. Strintzi, and G. Szepesi

Phys. Plasmas 16, 092303 (2009); http://dx.doi.org/10.1063/1.3227650 (10 pages) | Cited 20 times

Online Publication Date: 15 September 2009

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Nondiffusive anomalous momentum transport in toroidal plasmas occurs through symmetry breaking mechanisms. In this paper the contribution of sheared E×B flows to parallel momentum transport [ R. R. Dominguez and G. M. Staebler, Phys Fluids B 5, 3876 (1993) ] is investigated with nonlinear gyrokinetic simulations in toroidal geometry. The background perpendicular shear is treated independently from the parallel velocity shear to isolate a nondiffusive, nonpinch contribution to the parallel momentum flux. It is found that the size of the term depends strongly on the magnetic shear, with the sign reversing for negative magnetic shear. Perpendicular shear flows are responsible for both symmetry breaking and suppression of turbulence, resulting in a shearing rate at which there is a maximum contribution to the momentum transport. The E×B momentum transport is shown to be quenched by increasing flow shear more strongly than the standard linear quench rule for turbulent heat diffusivity.
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52.25.Fi Transport properties
52.25.Xz Magnetized plasmas
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.)
52.55.Fa Tokamaks, spherical tokamaks
52.65.Tt Gyrofluid and gyrokinetic simulations

Kinetic dispersion of Langmuir waves. I. The Langmuir decay instability

J. P. Palastro, E. A. Williams, D. E. Hinkel, L. Divol, and D. J. Strozzi

Phys. Plasmas 16, 092304 (2009); http://dx.doi.org/10.1063/1.3234245 (12 pages) | Cited 4 times

Online Publication Date: 22 September 2009

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We derive a fully kinetic, three-dimensional dispersion relation for Langmuir waves with a focus on the Langmuir decay instability (LDI). The kinetic dispersion is compared to the standard fluid dispersion found with an equation of state (EOS) closure. The EOS closure fails to capture the intricacies of the nonlinear pressure when high frequency electron plasma waves (EPWs) couple to low frequency ion acoustic waves (IAWs). In particular, we find discrepancies in the kλd scaling of the LDI growth rate, where k is the wavenumber of the incident EPW and λd is the Debye length. As a result, the kinetic dispersion relation for LDI results in instability thresholds that can be in excess of twice those predicted by the fluid theory. Both the fluid and kinetic dispersion relations predict a nonlinear frequency shift due to the beating of the pump and scattered EPWs, but again the kλd scaling of these frequency shifts differ. In addition, the kinetic dispersion predicts a nonlinear reduction in the IAW damping from the three-wave interaction.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.25.Dg Plasma kinetic equations

Fully nonlinear features of the energetic beam-driven instability

M. Lesur, Y. Idomura, and X. Garbet

Phys. Plasmas 16, 092305 (2009); http://dx.doi.org/10.1063/1.3234249 (12 pages) | Cited 6 times

Online Publication Date: 25 September 2009

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The so-called Berk–Breizman model is applied to a cold bulk, weak warm beam, one-dimensional plasma, to investigate the kinetic instability arising from the resonance of a single electrostatic wave with an energetic particle beam. A Vlasov code is developed to solve the initial value problem for the full-f distribution, and the nonlinear evolution is categorized in the whole parameter space as damped, steady-state, periodic, chaotic, or chirping. The saturation level of steady-state solutions and the bifurcation between steady-state and periodic solutions near marginal stability match analytic predictions. The limit of a perturbative numerical approach when the resonant region extends into the bulk is shown. Frequency sweeping is observed, with time-evolution approaching theoretical results. A new method to extract the dissipation rate from frequency diagnostics is proposed. For small collision rates, instabilities are observed in the linearly barely stable region.
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52.40.Mj Particle beam interactions in plasmas
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.)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Spatiotemporal dynamics and transport reduction in helical magnetic configuration

Milan Rajković, Tomo-Hiko Watanabe, and Miloš Škorić

Phys. Plasmas 16, 092306 (2009); http://dx.doi.org/10.1063/1.3237133 (7 pages) | Cited 2 times

Online Publication Date: 28 September 2009

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Effects of multihelicity confinement magnetic fields on turbulent transport and zonal flows are investigated by means of spatiotemporal analysis of gyrokinetic Vlasov simulation results for the ion temperature gradient turbulence, where the standard and the inward-shifted configurations of the Large Helical Device are considered. The analysis of simulation results demonstrates that fluctuations of electrostatic potential for zonal flows exhibit spatiotemporal chaos in both configurations. However, the intensity of chaos found is considerably decreased in the inward-shifted configuration consistent with improved confinement. Enhanced zonal flow generation in the inward shifted case is accompanied by transport reduction which may be a direct consequence of chaos suppression.
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52.55.Jd Magnetic mirrors, gas dynamic traps
52.25.Fi Transport properties
52.25.Gj Fluctuation and chaos phenomena
52.35.Ra Plasma turbulence
52.65.Tt Gyrofluid and gyrokinetic simulations

Three-dimensional fluid simulations of a simple magnetized toroidal plasma

Paolo Ricci and B. N. Rogers

Phys. Plasmas 16, 092307 (2009); http://dx.doi.org/10.1063/1.3230119 (10 pages) | Cited 6 times

Online Publication Date: 28 September 2009

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Three-dimensional fluid simulations are performed in a simple magnetized toroidal plasma, in which vertical and toroidal magnetic fields create helicoidal magnetic field lines that terminate on the torus vessel. The simulations are carried out in the three-dimensional flux tube that wraps around the torus and are able to describe both interchange and drift-wave dynamics. The presence of different turbulence regimes is pointed out; in particular, it is shown that turbulence can be quenched by either a sufficiently large plasma source, or a sufficiently small vertical field, or a sufficiently high parallel resistivity. The simulations considered herein reveal that interchange turbulence dominates over the drift-wave dynamics. Considering the experimental observations, we finally discuss the limitations of the present model.
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52.55.Jd Magnetic mirrors, gas dynamic traps
52.35.Ra Plasma turbulence
52.35.Kt Drift waves
52.65.Kj Magnetohydrodynamic and fluid equation

Electron temperature difference between the o-point and x-point of a magnetic island

Jinhong Yang, Qingquan Yu, Sizheng Zhu, and G. Zhuang

Phys. Plasmas 16, 092308 (2009); http://dx.doi.org/10.1063/1.3240329 (6 pages) | Cited 2 times

Online Publication Date: 29 September 2009

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The electron temperature difference between the o-point and the x-point of a magnetic island is studied numerically by solving the two-dimensional energy transport equation. It is found that, even without a localized radio-frequency heating at the island's o-point, there is usually a temperature difference between these two points. This difference depends on the radial profile of the heating power deposition, the ratio between the parallel and the perpendicular heat conductivity and the island width, and it takes a minimum when the island width is about twice the local heat diffusion layer width. The effect of the temperature difference on the island growth is further studied, and the peaked heating power density profile at magnetic axis is found be destabilizing.
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52.25.Fi Transport properties
52.50.-b Plasma production and heating
52.55.Fa Tokamaks, spherical tokamaks
back to top Magnetically Confined Plasmas, Heating, Confinement

Observation of a critical pressure gradient for the stabilization of interchange modes in simple magnetized toroidal plasmas

L. Federspiel, B. Labit, P. Ricci, A. Fasoli, I. Furno, and C. Theiler

Phys. Plasmas 16, 092501 (2009); http://dx.doi.org/10.1063/1.3204704 (6 pages) | Cited 4 times

Online Publication Date: 3 September 2009

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The existence of a critical pressure gradient needed to drive the interchange instability is experimentally demonstrated in the simple magnetized torus TORoidal Plasma EXperiment [ A. Fasoli et al., Phys. Plasmas 13, 055902 (2006) ]. This gradient is reached during a scan in the neutral gas pressure pn. Around a critical value for pn, depending on the magnetic configuration and on the injected rf power, a small increase in the neutral gas pressure triggers a transition in the plasma behavior. The pressure profile is locally flattened, stabilizing the interchange mode observed at lower neutral gas densities. The measured value for the critical gradient is close to the linear theory estimate.
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52.55.-s Magnetic confinement and equilibrium
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Low-frequency global Alfvén eigenmodes in low-shear tokamaks with trapped energetic ions

V. S. Marchenko, Ya. I. Kolesnichenko, and S. N. Reznik

Phys. Plasmas 16, 092502 (2009); http://dx.doi.org/10.1063/1.3195072 (4 pages) | Cited 1 time

Online Publication Date: 4 September 2009

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It is shown that, in the tokamak plasmas with broad low-shear central core and safety factor q0≳1, there exists a low-frequency global Alfvén eigenmode capable of resonating with precession of the trapped energetic ions. This mode has the dominant numbers m = n = 1, but the coupling with the upper toroidal sideband is crucial both for the eigenmode formation and its excitation by energetic ions. The properties of this mode are consistent with observations of the low-frequency n = 1 mode driven by energetic ions in the “hybrid” discharges with perpendicular injection on the JT-60U tokamak [ N. Oyama, A. Isayama, G. Matsunaga et al., Nucl. Fusion 49, 065026 (2009) ].
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.55.Fa Tokamaks, spherical tokamaks
52.80.-s Electric discharges
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Some properties of the M3D-C1 form of the three-dimensional magnetohydrodynamics equations

J. Breslau, N. Ferraro, and S. Jardin

Phys. Plasmas 16, 092503 (2009); http://dx.doi.org/10.1063/1.3224035 (10 pages) | Cited 4 times

Online Publication Date: 8 September 2009

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A set of scalar variables and projection operators for the vector momentum and magnetic field evolution equations is presented that has several unique and desirable properties, making it a preferred system for solving the magnetohydrodynamic equations in a torus with a strong toroidal magnetic field. A “weak form” of these equations is derived that explicitly conserves energy and is suitable for a Galerkin finite element formulation provided the basis elements have C1 continuity. Systems of reduced equations are discussed, along with their energy conservation properties. An implicit time advance is presented that adds diagonally dominant self-adjoint energy terms to the mass matrix to obtain numerical stability.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Vd Magnetic reconnection
52.55.Fa Tokamaks, spherical tokamaks

Symmetry breaking and self-consistent rotation of magnetic islands in neoclassical viscous regimes

E. Lazzaro

Phys. Plasmas 16, 092504 (2009); http://dx.doi.org/10.1063/1.3216546 (6 pages) | Cited 5 times

Online Publication Date: 9 September 2009

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Classical or neoclassical tearing modes (NTMs) perturb the ideal axisymmetry of tokamaks. As a consequence of symmetry breaking a neoclassical toroidal viscosity (NTV) appears, that depends on the island amplitude. This work shows that in the low collisionality regimes NTV has a key role in determining self-consistently the magnetic island velocity and at the same time modifies significantly the ion polarization current effects on NTM instability. This finding can provide a better understanding of the mechanism of onset of NTMs, observed experimentally, and improve the concepts for their control or avoidance.
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52.55.Fa Tokamaks, spherical tokamaks
52.55.Tn Ideal and resistive MHD modes; kinetic modes
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Vd Magnetic reconnection

Tearing relaxation and the globalization of transport in field-reversed configurations

Loren Steinhauer and D. C. Barnes

Phys. Plasmas 16, 092505 (2009); http://dx.doi.org/10.1063/1.3223847 (6 pages) | Cited 2 times

Online Publication Date: 9 September 2009

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Tearing instability of field-reversed configurations (FRC) is investigated using the method of neighboring equilibria. It is shown that the conducting wall position in experiment lies very close to the location needed for tearing stability. This strongly suggests that vigorous but benign tearing modes, acting globally, are the engine of continual self-organization in FRCs, i.e., tearing relaxation. It also explains the “profile consistency” and anomalous loss rate of magnetic flux. In effect, tearing globalizes the effect of edge-driven transport.
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52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Plasma physics in noninertial frames

A. Thyagaraja and K. G. McClements

Phys. Plasmas 16, 092506 (2009); http://dx.doi.org/10.1063/1.3238485 (10 pages) | Cited 4 times

Online Publication Date: 24 September 2009

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Equations describing the nonrelativistic motion of a charged particle in an arbitrary noninertial reference frame are derived from the relativistically invariant form of the particle action. It is shown that the equations of motion can be written in the same form in inertial and noninertial frames, with the effective electric and magnetic fields in the latter modified by inertial effects associated with centrifugal and Coriolis accelerations. These modifications depend on the particle charge-to-mass ratio, and also the vorticity, specific kinetic energy, and compressibility of the frame flow. The Newton–Lorentz, Vlasov, and Fokker–Planck equations in such a frame are derived. Reduced models such as gyrokinetic, drift-kinetic, and fluid equations are then derivable from these equations in the appropriate limits, using standard averaging procedures. The results are applied to tokamak plasmas rotating about the machine symmetry axis with a nonrelativistic but otherwise arbitrary toroidal flow velocity. Astrophysical applications of the analysis are also possible since the power of the action principle is such that it can be used to describe relativistic flows in curved spacetime.
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52.27.Ny Relativistic plasmas
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.25.Fi Transport properties
52.25.Dg Plasma kinetic equations
52.55.Fa Tokamaks, spherical tokamaks

The bootstrap current in small rotating magnetic islands

A. Bergmann, E. Poli, and A. G. Peeters

Phys. Plasmas 16, 092507 (2009); http://dx.doi.org/10.1063/1.3234252 (9 pages) | Cited 3 times

Online Publication Date: 24 September 2009

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The bootstrap current in small magnetic islands of neoclassical tearing modes is studied with guiding center particle simulations including pitch angle scattering. A model for a rotating island and its electric field is used and a new approximation to the electric potential in small islands is derived. Islands with sizes of the order of the ion banana orbit width are studied by means of a two-step model, which allows to treat both ions and electrons kinetically. The bootstrap current in such small islands is found to depend strongly on the direction of rotation of the island. The bootstrap current in small islands rotating in the ion diamagnetic direction is strongly diminished, similarly to what happens in big islands. In small islands rotating in the electron diamagnetic direction, on the contrary, the bootstrap current is almost completely preserved, implying a reduced neoclassical drive of the island growth.
Show PACS
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Fa Tokamaks, spherical tokamaks
52.65.Cc Particle orbit and trajectory
52.65.Pp Monte Carlo methods
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