Phys. Plasmas (1994-Present) - Physics of Plasmas

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Bifurcated equilibria in centrifugally confined plasma

I. Shamim, C. Teodorescu, P. N. Guzdar, A. B. Hassam, R. Clary, R. Ellis, and R. Lunsford

Phys. Plasmas 15, 120701 (2008); http://dx.doi.org/10.1063/1.2936924 (4 pages)

Online Publication Date: 1 December 2008

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A bifurcation theory and associated computational model are developed to account for abrupt transitions observed recently on the Maryland Centrifugal eXperiment (MCX) [ R. F. Ellis et al. Phys. Plasmas 8, 2057 (2001) ], a supersonically rotating magnetized plasma that relies on centrifugal forces to prevent thermal expansion of plasma along the magnetic field. The observed transitions are from a well-confined, high-rotation state (HR-mode) to a lower-rotation, lesser-confined state (O-mode). A two-dimensional time-dependent magnetohydrodynamics code is used to simulate the dynamical equilibrium states of the MCX configuration. In addition to the expected viscous drag on the core plasma rotation, a momentum loss term is added that models the friction of plasma on the enhanced level of neutrals expected in the vicinity of the insulators at the throats of the magnetic mirror geometry. At small values of the external rotation drive, the plasma is not well-centrifugally confined and hence experiences the drag from near the insulators. Beyond a critical value of the external drive, the system makes an abrupt transition to a well-centrifugally confined state in which the plasma has pulled away from the end insulator plates; more effective centrifugal confinement lowers the plasma mass near the insulators allowing runaway increases in the rotation speed. The well-confined steady state is reached when the external drive is balanced by only the viscosity of the core plasma. A clear hysteresis phenomenon is shown.

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52.58.Qv	Electrostatic and high-frequency confinement
52.35.Ra	Plasma turbulence
52.65.Kj	Magnetohydrodynamic and fluid equation

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Three-dimensional filamentary structures of a relativistic electron beam in fast ignition plasmas

Anupam Karmakar, Naveen Kumar, Alexander Pukhov, O. Polomarov, and G. Shvets

Phys. Plasmas 15, 120702 (2008); http://dx.doi.org/10.1063/1.3042208 (4 pages) | Cited 4 times

Online Publication Date: 12 December 2008

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The filamentary structures and associated electromagnetic fields of a relativistic electron beam have been studied by three-dimensional particle-in-cell simulations in the context of fast ignition fusion. The simulations explicitly include collisions in return plasma current and distinctly examine the effects of beam temperature and collisions on the growth of filamentary structures generated.

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52.57.-z	Laser inertial confinement
52.35.-g	Waves, oscillations, and instabilities in plasmas and intense beams
52.65.Rr	Particle-in-cell method

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Experimental evidence of coupling between local turbulent transport and large scale fluctuations in the ISTTOK edge plasma

C. Silva, C. Hidalgo, H. Figueiredo, P. Duarte, H. Fernandes, I. Nedzelskiy, and M. A. Pedrosa

Phys. Plasmas 15, 120703 (2008); http://dx.doi.org/10.1063/1.3042221 (4 pages) | Cited 8 times

Online Publication Date: 12 December 2008

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The interplay between large scale fluctuations and the local turbulent transport has been investigated in the tokamak ISTTOK [ C. A. F. Varandas et al., Fusion Technol. 29, 105 (1996) ] plasma boundary region. It has been found that the floating potential fluctuations, dominated by low frequency oscillations, exhibit a significant toroidal correlation at large distances that can be attributed to the geodesic acoustic mode. The level of long-distance correlations is strongly bursty, showing a significant degree of coupling with the local electrostatic turbulent transport. Experimental findings show the key role of multiscale physics in the regulation of transport in the edge region of fusion plasmas.

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52.35.Ra	Plasma turbulence
52.25.Gj	Fluctuation and chaos phenomena
52.40.Hf	Plasma-material interactions; boundary layer effects
52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)

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Action-angle variables for the continuous spectrum of ideal magnetohydrodynamics

M. Hirota and Y. Fukumoto

Phys. Plasmas 15, 122101 (2008); http://dx.doi.org/10.1063/1.3035912 (11 pages) | Cited 6 times

Online Publication Date: 3 December 2008

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Action-angle variables corresponding to singular (or improper) eigenmodes are rigorously formulated for the Alfvén and slow (or cusp) continuous spectra of ideal magnetohydrodynamics. The perturbation energy is then transformed into the normal form, namely, the eigenfrequency multiplied by the action variable. It is shown that the Laplace transform approach expedites this action-angle formulation more efficiently than the existing ones devoted to other kinds of continuous spectra. The presence of flow that is either nonparallel to the magnetic field or supersonic at some places brings about singular eigenmodes with negative energy. The Alfvén and slow singular eigenmodes are neutrally stable even in the presence of any external potential fields, but may cause instability when coupled with another singular or nonsingular eigenmode with the opposite sign of energy.

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52.55.Tn	Ideal and resistive MHD modes; kinetic modes
52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.Vv	Perturbative methods

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Electrostatic mode associated with the pinch velocity in reversed field pinch simulations

Gian Luca Delzanno, Luis Chacón, and John M. Finn

Phys. Plasmas 15, 122102 (2008); http://dx.doi.org/10.1063/1.3026714 (13 pages) | Cited 1 time

Online Publication Date: 4 December 2008

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The existence of a new phenomenon in reversed field pinch (RFP) simulations related to the equilibrium pinch flow is discussed. This behavior is due to the inward equilibrium flow, but is strongly affected by boundary conditions on the perturbed azimuthal flow. It is important to understand and control this mechanism in single helicity simulations of RFPs. This mechanism can be explained in terms of an electrostatic instability related to a mode which can occur in fluid dynamics. In a simple linear model, it is shown that the mode, which is related to the inward advection of angular momentum from the edge, can be stabilized by using homogeneous Dirichlet (no-slip) boundary conditions at the wall. Behavior due to this mode is present in nonlinear simulations with zero-viscous-stress boundary conditions on the tangential velocity at the wall and, even in the presence of the usual magnetohydrodynamic modes, this mode can dominate the nonlinear dynamics of the velocity. In nonlinear simulations with Dirichlet boundary conditions on the tangential velocity, behavior associated with this electrostatic mode is not observed.

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52.55.Ez	Theta pinch
52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic 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)
52.35.Mw	Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.65.Kj	Magnetohydrodynamic and fluid equation

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Gyrokinetic-water-bag modeling of low-frequency instabilities in a laboratory magnetized plasma column

E. Gravier, R. Klein, P. Morel, N. Besse, and P. Bertrand

Phys. Plasmas 15, 122103 (2008); http://dx.doi.org/10.1063/1.3036930 (11 pages) | Cited 4 times

Online Publication Date: 4 December 2008

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A new model is presented, named collisional-gyro-water-bag (CGWB), which describes the collisional drift waves and ion-temperature-gradient (ITG) instabilities in a plasma column. This model is based on the kinetic gyro-water-bag approach recently developed [ P. Morel et al., Phys. Plasmas 14, 112109 (2007) ] to investigate ion-temperature-gradient modes. In CGWB electron-neutral collisions have been introduced and are now taken into account. The model has been validated by comparing CGWB linear analysis with other models previously proposed and experimental results as well. Kinetic effects on collisional drift waves are investigated, resulting in a less effective growth rate, and the transition from collisional drift waves to ITG instability depending on the ion temperature gradient is studied.

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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)
94.20.Fg	Plasma temperature and density

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Oscillating Ponomarenko dynamo in the highly conducting limit

Marine Peyrot, Andrew Gilbert, and Franck Plunian

Phys. Plasmas 15, 122104 (2008); http://dx.doi.org/10.1063/1.3035911 (8 pages) | Cited 3 times

Online Publication Date: 8 December 2008

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This paper considers dynamo action in smooth helical flows in cylindrical geometry, otherwise known as Ponomarenko dynamos, with periodic time dependence. An asymptotic framework is developed that gives growth rates and frequencies in the highly conducting limit of large magnetic Reynolds number, when modes tend to be localized on resonant stream surfaces. This theory is validated by means of numerical simulations.

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52.30.-q	Plasma dynamics and flow
52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.65.-y	Plasma simulation

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An analytic study of the perpendicularly propagating electromagnetic drift instabilities in the Magnetic Reconnection Experiment

Yansong Wang, Russell Kulsrud, and Hantao Ji

Phys. Plasmas 15, 122105 (2008); http://dx.doi.org/10.1063/1.3035907 (11 pages) | Cited 3 times

Online Publication Date: 10 December 2008

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A local linear theory is proposed for a perpendicularly propagating drift instability driven by relative drifts between electrons and ions. The theory takes into account local cross-field current, pressure gradients, and modest collisions as in the Magnetic Reconnection Experiment [ M. Yamada et al., Phys. Plasmas 4, 1936 (1997) ]. The unstable waves have very small group velocities in the direction of the pressure gradient, but have a large phase velocity near the relative drift velocity between electrons and ions in the direction of the cross-field current. By taking into account the electron-ion collisions and applying the theory in the Harris sheet, we establish that this instability could be excited near the center of the Harris sheet and have enough e-foldings to grow to large amplitude before it propagates out of the unstable region. Comparing with the other magnetic reconnection related instabilities (lower-hybrid-drift instability, modified two-stream instability, etc.) studied previously, we believe the instability we found is a favorable candidate to produce anomalous resistivity because of its unique wave characteristics, such as electromagnetic component, large phase velocity, and small group velocity in the cross-current-layer direction.

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52.35.Qz	Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.40.Db	Electromagnetic (nonlaser) radiation interactions with plasma
52.35.Vd	Magnetic reconnection
52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)
52.20.Fs	Electron collisions
52.20.Hv	Atomic, molecular, ion, and heavy-particle collisions

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The role of curvature and stretching on the existence of fast dynamo plasma in Riemannian space

L. C. Garcia de Andrade

Phys. Plasmas 15, 122106 (2008); http://dx.doi.org/10.1063/1.3041158 (8 pages) | Cited 1 time

Online Publication Date: 18 December 2008

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Vishik’s anti-dynamo theorem is applied to a nonstretched twisted magnetic flux tube in Riemannian space. Marginal or slow dynamos along curved (folded), torsioned (twisted), and nonstretching flux tubes plasma flows are obtained. Riemannian curvature of the twisted magnetic flux tube is computed in terms of the Frenet curvature in the thin tube limit. It is shown that, for nonstretched filaments, fast dynamo action in the diffusive case cannot be obtained, in agreement with Vishik’s argument that fast dynamos cannot be obtained in nonstretched flows. Instead of a fast dynamo, a nonuniform stretching slow dynamo is obtained. An example is given, which generalizes plasma dynamo laminar flows, recently presented by Wang et al. [Phys Plasmas 9, 1491 (2002) ], in the case of low magnetic Reynolds number Re_m ≥ 210. Curved and twisting Riemannian heliotrons, where nondynamo modes are found even when stretching is present, shows that the simple presence of stretching is not enough for the existence of dynamo action. In this paper, folding plays the role of Riemannian curvature and can be used to cancel magnetic fields, not enhancing the dynamo action. Nondynamo modes are found for certain values of torsion, or Frenet curvature (folding) in the spirit of the anti-dynamo theorem. It is also shown that curvature and stretching are fundamental for the existence of fast dynamos in plasmas.

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02.40.Hw	Classical differential geometry
91.25.Cw	Origins and models of the magnetic field; dynamo theories

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Relativistic modulational instability of electron-acoustic waves in an electron-pair ion plasma

A. P. Misra and P. K. Shukla

Phys. Plasmas 15, 122107 (2008); http://dx.doi.org/10.1063/1.3050062 (5 pages) | Cited 9 times

Online Publication Date: 23 December 2008

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The modulational instability of finite amplitude electron-acoustic waves (EAWs) along the external magnetic field is studied in an electron-pair ion plasma. Accounting for the relativistic electron mass variation nonlinearity and the Boltzmann distribution of both positive and negative ions, new regimes for the relativistic modulational instability (MI) for the low frequency (below the electron gyrofrequency) short-wavelength (in comparison with the ion gyroradius) modes are obtained numerically. It is found that the presence of a significant fraction of negative ions suppresses the MI growth/decay rate for the modulated EAW packets. The results could be of important for understanding the origin of amplitude modulated EAW packets in space (e.g., Earth’s magnetotail) as well as in laboratory plasmas.

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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.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Mw	Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.-y	Plasma simulation

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Verification and application of numerically generated magnetic coordinate systems in gyrokinetics

P. Xanthopoulos, D. Mikkelsen, F. Jenko, W. Dorland, and O. Kalentev

Phys. Plasmas 15, 122108 (2008); http://dx.doi.org/10.1063/1.3010708 (8 pages) | Cited 3 times

Online Publication Date: 31 December 2008

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In the context of linear gyrokinetic simulations, an analysis of the application of field-aligned coordinate systems generated numerically from magnetohydrodynamic equilibria is presented. This family of systems allows some flexibility in the choice of the coordinates, and gyrokinetic solvers often differ in this respect. Certain transformations are therefore required in order to compare physics results. Accordingly, benchmarks of a linear microinstability are carried out between two similar gyrokinetic codes. Effort is also put on the verification of the special properties of the generated systems through certain diagnostics.

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52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Qz	Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.65.Kj	Magnetohydrodynamic and fluid equation

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Analytic theory of L→H transition, barrier structure, and hysteresis for a simple model of coupled particle and heat fluxes

M. A. Malkov and P. H. Diamond

Phys. Plasmas 15, 122301 (2008); http://dx.doi.org/10.1063/1.3028305 (16 pages) | Cited 10 times

Online Publication Date: 3 December 2008

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The two-field (pressure/density) model for the L→H transition is extended and analyzed qualitatively. In its original form the model is ambiguous as to the location of the transition within the range of bistability of particle and thermal fluxes. Here, the model is regularized by including (i) hyperdiffusion, (ii) time dependence, and (iii) curvature of the pressure profile. The regularizations (i)–(ii) agree and indicate that the Maxwell rule for the forward and back transition applies, as opposed to the maximum flux forward and minimum flux backward transition rules (which yields hysteresis) as suggested previously. Regarding (i)–(ii), simple models suggest that for a pressure gradient driven electric field shear bifurcation, the basic scale of the pedestal is inexorably tied to the particle fueling depth, which normally is the neutral penetration depth. There is no hysteresis predicted by the local model of transport suppression. However, the effect of pressure profile curvature (iii) changes these results substantially. When it dominates, the curvature effect reduces the transition threshold to the lower end of the range of heating power, which falls within the phase coexistence region for both forward and back transitions. This softens the transition threshold requirements. In this limit, the model with pressure curvature also predicts transitions which occur in regimes of flat density and driven exclusively by the temperature gradient. This allows the pedestal to extend beyond the fueling depth, and also allows some decoupling of density and pressure profiles. In a parameter range where the pressure curvature is less important the transition occurs somewhere between the above two limits.

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52.55.Dy	General theory and basic studies of plasma lifetime, particle and heat loss, energy balance, field structure, etc.
52.25.Fi	Transport properties
52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

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Electron acoustic solitary waves in unmagnetized two electron population dense plasmas

S. Mahmood and W. Masood

Phys. Plasmas 15, 122302 (2008); http://dx.doi.org/10.1063/1.3010705 (6 pages) | Cited 6 times

Online Publication Date: 4 December 2008

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The electron acoustic solitary waves are studied in unmagnetized two population electron quantum plasmas. The quantum hydrodynamic model is employed with the Sagdeev potential approach to describe the arbitrary amplitude electron acoustic waves in a two electron population dense Fermi plasma. It is found that hot electron density hump structures are formed in the subsonic region in such type of quantum plasmas. The wave amplitude as well as the width of the soliton are increased with the increase of percentage presence of cold (thinly populated) electrons in a multicomponent quantum plasma. It is found that an increase in quantum diffraction parameter broadens the nonlinear structure. Furthermore, the amplitude of the nonlinear electron acoustic wave is found to increase with the decrease in Mach number. The numerical results are also presented to understand the formation of solitons in two electron population Fermi plasmas.

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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.Dm	Sound waves
52.35.Sb	Solitons; BGK modes

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Nonperturbative models of intermittency in edge turbulence

Johan Anderson and Eun-jin Kim

Phys. Plasmas 15, 122303 (2008); http://dx.doi.org/10.1063/1.3036932 (6 pages) | Cited 3 times

Online Publication Date: 4 December 2008

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A theory of the probability distribution function (PDF) tails of the blob density in plasma edge turbulence is provided. A simplified model of the fast convective radial transport is used. The theoretically predicted PDF tails corroborate earlier measurements of edge transport, further confirming the strongly non-Gaussian feature of edge transport. It is found that increasing the cross-sectional spatial scale length (L_x and L_y) of the blob results in larger transport, whereas increasing the toroidal scale length (L_z) decreases the PDF. The results imply that the PDF decreases for larger blob speed v_b.

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52.35.Ra	Plasma turbulence
52.40.Hf	Plasma-material interactions; boundary layer effects

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Exponential frequency spectrum and Lorentzian pulses in magnetized plasmas

D. C. Pace, M. Shi, J. E. Maggs, G. J. Morales, and T. A. Carter

Phys. Plasmas 15, 122304 (2008); http://dx.doi.org/10.1063/1.3023155 (13 pages) | Cited 8 times

Online Publication Date: 8 December 2008

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Two different experiments involving pressure gradients across the confinement magnetic field in a large plasma column are found to exhibit a broadband turbulence that displays an exponential frequency spectrum for frequencies below the ion cyclotron frequency. The exponential feature has been traced to the presence of solitary pulses having a Lorentzian temporal signature. These pulses arise from nonlinear interactions of drift-Alfvén waves driven by the pressure gradients. In both experiments the width of the pulses is narrowly distributed resulting in exponential spectra with a single characteristic time scale. The temporal width of the pulses is measured to be a fraction of a period of the drift-Alfvén waves. The experiments are performed in the Large Plasma Device (LAPD-U) [ W. Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991) ] operated by the Basic Plasma Science Facility at the University of California, Los Angeles. One experiment involves a controlled, pure electron temperature gradient associated with a microscopic (6 mm gradient length) hot electron temperature filament created by the injection a small electron beam embedded in the center of a large, cold magnetized plasma. The other experiment is a macroscopic (3.5 cm gradient length) limiter-edge experiment in which a density gradient is established by inserting a metallic plate at the edge of the nominal plasma column of the LAPD-U. The temperature filament experiment permits a detailed study of the transition from coherent to turbulent behavior and the concomitant change from classical to anomalous transport. In the limiter experiment the turbulence sampled is always fully developed. The similarity of the results in the two experiments strongly suggests a universal feature of pressure-gradient driven turbulence in magnetized plasmas that results in nondiffusive cross-field transport. This may explain previous observations in helical confinement devices, research tokamaks, and arc plasmas.

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52.35.Ra	Plasma turbulence
52.35.Bj	Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Kt	Drift waves
52.25.Fi	Transport properties
52.40.Mj	Particle beam interactions in plasmas
52.55.-s	Magnetic confinement and equilibrium

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Ion-acoustic vortices in a nonuniform, dissipative quantum magnetoplasma with sheared ion flows

W. Masood, Arshad M. Mirza, and Shahida Nargis

Phys. Plasmas 15, 122305 (2008); http://dx.doi.org/10.1063/1.3036931 (5 pages) | Cited 9 times

Online Publication Date: 8 December 2008

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By employing the quantum hydrodynamic model, linear and nonlinear properties of quantum ion-acoustic waves are studied in a nonuniform, dissipative quantum plasma with sheared ion flow parallel to the ambient magnetic field. It is shown that the shear flow parallel to the magnetic field can drive the quantum ion-acoustic wave unstable. Stationary solutions of the nonlinear equations that govern the quantum ion-acoustic waves are also obtained. It is found that electrostatic monopolar, dipolar, and vortex street type solutions can appear in such a plasma. It is observed that the inclusion of the quantum statistical and Bohm potential terms significantly modify the scalelengths of these structures. The present work may have relevance in the dense astrophysical environments where quantum effects are expected to play a significant role.

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52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.We	Plasma vorticity

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Nonlinear behavior in the time domain in argon atmospheric dielectric-barrier discharges

Hong Shi, Yanhui Wang, and Dezhen Wang

Phys. Plasmas 15, 122306 (2008); http://dx.doi.org/10.1063/1.3033754 (6 pages) | Cited 10 times

Online Publication Date: 9 December 2008

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A vast majority of nonlinear behavior in atmospheric pressure discharges has so far been studied in the space domain, and their time-domain characters are often believed to exact the periodicity of the externally applied voltage. In this paper, based on one-dimensional fluid mode, we study complex nonlinear behavior in the time domain in argon atmospheric dielectric-barrier discharges at very broad frequency range from kilohertz to megahertz. Under certain conditions, the discharge not only can be driven to chaos from time-periodic state through period-doubling bifurcation, but also can return stable periodic motion from chaotic state through an inverse period-doubling bifurcation sequence. Upon changing the parameter the discharge undergoes alternatively chaotic and periodic behavior. Some periodic windows embedded in chaos, as well as the secondary bifurcation occurring in the periodic windows can also be observed. The corresponding discharge characteristics are investigated.

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52.80.Hc	Glow; corona
52.35.Mw	Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.65.-y	Plasma simulation

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Quantum electron-acoustic double layers in a magnetoplasma

A. P. Misra and S. Samanta

Phys. Plasmas 15, 122307 (2008); http://dx.doi.org/10.1063/1.3040014 (8 pages) | Cited 10 times

Online Publication Date: 18 December 2008

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Using a quantum magnetohydrodynamic (QMHD) model, the existence of small but finite amplitude quantum electron-acoustic double layers (QEADLs) is reported in a magnetized collisionless dense quantum plasma whose constituents are two distinct groups of cold and hot electrons, and the stationary ions forming only the neutralizing background. It is shown that the existence of steady state solutions of these double layers obtained from an extended Korteweg-de Vries (KdV) equation depends parametrically on the ratio of the cold to hot electron unperturbed number density (δ), the quantum diffraction parameter (H), the obliqueness parameter (l_z), and the external magnetic field via the normalized electron-cyclotron frequency (Ω). It is found that the system supports both compressive and rarefactive double layers depending on the parameters δ and l_z. The effects of all these parameters on the profiles of the double layers are also examined numerically.

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52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.-b	Plasma properties

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Nonlinear structures: Explosive, soliton, and shock in a quantum electron-positron-ion magnetoplasma

R. Sabry, W. M. Moslem, F. Haas, S. Ali, and P. K. Shukla

Phys. Plasmas 15, 122308 (2008); http://dx.doi.org/10.1063/1.3037265 (7 pages) | Cited 25 times

Online Publication Date: 22 December 2008

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Theoretical and numerical studies are performed for the nonlinear structures (explosive, solitons, and shock) in quantum electron-positron-ion magnetoplasmas. For this purpose, the reductive perturbation method is employed to the quantum hydrodynamical equations and the Poisson equation, obtaining extended quantum Zakharov–Kuznetsov equation. The latter has been solved using the generalized expansion method to obtain a set of analytical solutions, which reflects the possibility of the propagation of various nonlinear structures. The relevance of the present investigation to the white dwarfs is highlighted.

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52.35.Sb	Solitons; BGK modes
52.35.Tc	Shock waves and discontinuities
52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)
95.30.Qd	Magnetohydrodynamics and plasmas
97.20.Rp	Faint blue stars (including blue stragglers), white dwarfs, degenerate stars, nuclei of planetary nebulae

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Higher order solutions to ion-acoustic solitons in a weakly relativistic two-fluid plasma

Tarsem Singh Gill, Parveen Bala, and Harvinder Kaur

Phys. Plasmas 15, 122309 (2008); http://dx.doi.org/10.1063/1.3050061 (10 pages) | Cited 11 times

Online Publication Date: 22 December 2008

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The nonlinear wave structure of small amplitude ion-acoustic solitary waves (IASs) is investigated in a two-fluid plasma consisting of weakly relativistic streaming ions and electrons. Using the reductive perturbation theory, the basic set of governing equations is reduced to the Korteweg–de Vries (KdV) equation for the lowest order perturbation. This analysis is further extended using the renormalization technique for the inclusion of higher order nonlinear and dispersive effects for better accuracy. The effect of higher order correction and various parameters on the soliton characteristics is investigated and also discussed.

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52.35.Sb	Solitons; BGK modes
52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.27.Ny	Relativistic plasmas
52.65.Vv	Perturbative methods

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Nonlinear wave modulation of cylindrical and spherical quantum ion-acoustic solitary waves

R. Sabry, S. K. El-Labany, and P. K. Shukla

Phys. Plasmas 15, 122310 (2008); http://dx.doi.org/10.1063/1.3050066 (8 pages) | Cited 2 times

Online Publication Date: 23 December 2008

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Cylindrical and spherical amplitude modulation of quantum ion-acoustic (QIA) envelope solitary waves in a dense quantum plasma comprised of electrons and ions is investigated. For this purpose, a one-dimensional quantum hydrodynamic model and the Poisson equation are considered. By using the standard reductive perturbation technique, a modified nonlinear Schrödinger equation with the geometrical and the quantum effects is derived. The effect of quantum corrections and the effect due to the cylindrical and spherical geometries on the propagation of the QIA envelope solitary waves are examined. It is shown that there exists a modulation instability period depending on the quantum parameter, which does not exist for the one-dimensional classical case.

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52.35.Sb	Solitons; BGK modes
52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.65.Kj	Magnetohydrodynamic and fluid equation
52.65.Vv	Perturbative methods

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Evolution of electron holes in two electron population plasmas

K. Saharia and K. S. Goswami

Phys. Plasmas 15, 122311 (2008); http://dx.doi.org/10.1063/1.3050065 (6 pages)

Online Publication Date: 30 December 2008

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Formations and existence conditions of electron holes from one-dimensional Vlasov simulations in a collisionless unmagnetized two component plasma are presented. Kinetic simulation results quantitatively confirm the Fast Auroral SnapshoT (FAST) observations of large amplitude (up to 500 mV/m) solitary waves at the edge of the auroral kilometric radiation (AKR) source region.

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52.35.Sb	Solitons; BGK modes
52.65.-y	Plasma simulation

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Kinetic theory for low-frequency turbulence in magnetized plasmas including discrete-particle effects

Peter H. Yoon and Ta-Ming Fang

Phys. Plasmas 15, 122312 (2008); http://dx.doi.org/10.1063/1.3050069 (13 pages) | Cited 3 times

Online Publication Date: 30 December 2008

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In a recently developed kinetic theory for low-frequency turbulence propagating parallel to the ambient magnetic field [ P. H. Yoon, Phys. Plasmas 14, 10230 (2007); P. H. Yoon and T.-M. Fang, Phys. Plasmas 14, 102303 (2007); P. H. Yoon and T.-M. Fang, Plasmas Phys. Control. Fusion 50, 085007 (2008) ], the effects arising from the discrete particle nature, or the spontaneous thermal effects were ignored. Such an assumption thus limited the theory to purely collisionless “Vlasov” regime. In the present paper the previous formalism is generalized to include discrete-particle effects by reformulating the problem on the basis of the Klimontovich equation. The new terms that appear in the particle and wave kinetic equations as a result of the new formalism are the spontaneous drag term associated with the particles and the spontaneous emission and scattering terms associated with the waves.

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52.35.Ra	Plasma turbulence
52.25.Dg	Plasma kinetic equations
52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)

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Quasilinear theory of electron transport by radio frequency waves and nonaxisymmetric perturbations in toroidal plasmas

Y. Kominis, A. K. Ram, and K. Hizanidis

Phys. Plasmas 15, 122501 (2008); http://dx.doi.org/10.1063/1.3029736 (10 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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The use of radio frequency waves to generate plasma current and to modify the current profile in magnetically confined fusion devices is well documented. The current is generated by the interaction of electrons with an appropriately tailored spectrum of externally launched rf waves. In theoretical and computational studies, the interaction of rf waves with electrons is represented by a quasilinear diffusion operator. The balance, in steady state, between the quasilinear operator and the collision operator gives the modified electron distribution from which the generated current can be calculated. In this paper the relativistic operator for momentum and spatial diffusion of electrons due to rf waves and nonaxisymmetric magnetic field perturbations is derived. Relativistic treatment is necessary for the interaction of electrons with waves in the electron cyclotron range of frequencies. The spatial profile of the rf waves is treated in general so that diffusion due to localized beams is included. The nonaxisymmetric magnetic field perturbations can be due to magnetic islands as in neoclassical tearing modes. The plasma equilibrium is expressed in terms of the magnetic flux coordinates of an axisymmetric toroidal plasma. The electron motion is described by guiding center coordinates using the action-angle variables of motion in an axisymmetric toroidal equilibrium. The Lie perturbation technique is used to derive a diffusion operator which is nonsingular and time dependent. The resulting action diffusion equation describes resonant and nonresonant momentum and spatial diffusion. Momentum space diffusion leads to current generation in the plasma and spatial diffusion describes the effect of rf waves and magnetic perturbations on spatial evolution of the current profile. Depending on the symmetry of the equilibrium and the corresponding relation of the action variables to the configuration space variables, in addition to diffusion along the radial direction, poloidal, and toroidal electron diffusion, is also described. In deriving the diffusion operator, no statistical assumption, such as, the Markovian assumption, for the underlying electron dynamics, is imposed. Consequently, the operator is time dependent and valid for a dynamical phase space that is a mix of correlated regular orbits and decorrelated chaotic orbits. The diffusion operator is expressed in a form suitable for implementation in a numerical code.

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52.25.Fi	Transport properties
52.50.Qt	Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)
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.)

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Symplectic approach to calculation of magnetic field line trajectories in physical space with realistic magnetic geometry in divertor tokamaks

Alkesh Punjabi and Halima Ali

Phys. Plasmas 15, 122502 (2008); http://dx.doi.org/10.1063/1.3028310 (10 pages) | Cited 7 times

Online Publication Date: 2 December 2008

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A new approach to integration of magnetic field lines in divertor tokamaks is proposed. In this approach, an analytic equilibrium generating function (EGF) is constructed in natural canonical coordinates (ψ,θ) from experimental data from a Grad–Shafranov equilibrium solver for a tokamak. ψ is the toroidal magnetic flux and θ is the poloidal angle. Natural canonical coordinates (ψ,θ,φ) can be transformed to physical position (R,Z,φ) using a canonical transformation. (R,Z,φ) are cylindrical coordinates. Another canonical transformation is used to construct a symplectic map for integration of magnetic field lines. Trajectories of field lines calculated from this symplectic map in natural canonical coordinates can be transformed to trajectories in real physical space. Unlike in magnetic coordinates [ O. Kerwin, A. Punjabi, and H. Ali, Phys. Plasmas 15, 072504 (2008) ], the symplectic map in natural canonical coordinates can integrate trajectories across the separatrix surface, and at the same time, give trajectories in physical space. Unlike symplectic maps in physical coordinates (x,y) or (R,Z), the continuous analog of a symplectic map in natural canonical coordinates does not distort trajectories in toroidal planes intervening the discrete map. This approach is applied to the DIII-D tokamak [ J. L. Luxon and L. E. Davis, Fusion Technol. 8, 441 (1985) ]. The EGF for the DIII-D gives quite an accurate representation of equilibrium magnetic surfaces close to the separatrix surface. This new approach is applied to demonstrate the sensitivity of stochastic broadening using a set of perturbations that generically approximate the size of the field errors and statistical topological noise expected in a poloidally diverted tokamak. Plans for future application of this approach are discussed.

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52.55.Fa

Tokamaks, spherical tokamaks