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

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First adiabatic invariant of a charged particle modified in a time-dependent magnetic field

S. Olszewski and T. Roliński

Phys. Plasmas 6, 425 (1999); http://dx.doi.org/10.1063/1.873208 (10 pages)

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The mechanics of the change of the first adiabatic invariant of a nonrelativistic charged particle due to the linear change with time of the spatially-uniform magnetic induction is studied with the aid of an approximate analytic formalism. The same formalism enables one also to undertake an analytic study of the motion of the guiding center of the gyrating particle. The accuracy of the formalism is checked by comparing it with numerical calculations. The results obtained within the formalism are thoroughly compared with a former study of the mechanics of the change of the first adiabatic invariant done by Borovsky and Hansen [Phys. Rev. A 43, 560 (1991)] mainly on the basis of computer simulations. The examined changes of the magnetic field are small compared to the original field and occupy a time period much longer than one gyroperiod. © 1999 American Institute of Physics.

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52.20.-j	Elementary processes in plasmas
52.25.-b	Plasma properties

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The dynamic form factor for ion-collisional plasmas

Jian Zheng, C. X. Yu, and Z. J. Zheng

Phys. Plasmas 6, 435 (1999); http://dx.doi.org/10.1063/1.873209 (9 pages) | Cited 8 times

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Based on the fluctuation-dissipation theorem, this work is concerned with the dynamic form factor of Thomson scattering for ion-collisional plasmas. The main effort is to calculate the ion susceptibility by analytically solving the linearized ion Fokker–Planck equation through the Chang–Callen 13-moment approach. Comparison to other theories shows that this theory can provide an accurate prediction of the position and width for ion-acoustic peaks and a proper description of the entropy wave with some underestimation of its damping. The theory may be useful for explaining experimental data and making measurement more precise. © 1999 American Institute of Physics.

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52.25.Gj	Fluctuation and chaos phenomena
52.25.Fi	Transport properties
52.65.Ff	Fokker-Planck and Vlasov equation
52.70.Nc	Particle measurements
52.20.-j	Elementary processes in plasmas
52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)

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The effect of dust charge fluctuations on ion cyclotron wave instability in the presence of an ion beam in a plasma cylinder

Suresh C. Sharma and M. Sugawa

Phys. Plasmas 6, 444 (1999); http://dx.doi.org/10.1063/1.873210 (5 pages) | Cited 10 times

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An ion beam propagating through a magnetized dusty plasma cylinder drives electrostatic dust ion cyclotron waves to instability via Cerenkov interaction. The growth rate of the instability increases with the relative density δ ( = n_0i/n_0e) of negatively charged dust. The growth rate scales as the one-third power of the beam density. The frequency of the unstable wave also increases with the relative density δ of negatively charged dust. The results of the theory are applied to explain some of the experimental observations of Barkan et al. [Planet. Space Sci. 43, 905 (1995)]. © 1999 American Institute of Physics.

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52.27.Lw	Dusty or complex plasmas; plasma crystals
52.25.Vy	Impurities in plasmas
52.40.Mj	Particle beam interactions in plasmas
52.25.Gj	Fluctuation and chaos phenomena
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.)

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Mode conversion in a weakly magnetized plasma with a longitudinal density profile

L. Yin and M. Ashour-Abdalla

Phys. Plasmas 6, 449 (1999); http://dx.doi.org/10.1063/1.873211 (14 pages) | Cited 17 times

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Motivated by conditions in the terrestrial foreshock, the mode conversion process in the inner region for a weakly magnetized plasma with a longitudinal linear density profile is examined. Coupled differential equations are employed to describe the wave energy coupling and the mode structure of electrostatic Langmuir and upper-hybrid branches, and electromagnetic O, X, and Z modes. For an incident electrostatic wave (the “inverse” problem), the coupled equations are solved using Green’s function method, and the mode conversion coefficient is determined from the asymptotic solutions. In the limit of a vanishing magnetic field, solutions converge to previous unmagnetized solutions. It is found that the magnetic field narrows the window of conversion and reduces the angles of propagation of electromagnetic waves with respect to the magnetic field, in agreement with results from previous solutions (of the “direct” problem) for a magnetized cold plasma. The narrowing of the window occurs at angles of propagation larger than the angle corresponding to the maximum conversion. © 1999 American Institute of Physics.

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52.40.Db	Electromagnetic (nonlaser) radiation interactions with plasma
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)
94.30.Va	Magnetosphere interactions
96.60.Vg	Particle emission, solar wind
94.30.Tz	Electromagnetic wave propagation
94.30.cq	MHD waves, plasma waves, and instabilities
52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Qz	Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

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Accurate formulas for the Landau damping rates of electrostatic waves

C. J. McKinstrie, R. E. Giacone, and E. A. Startsev

Phys. Plasmas 6, 463 (1999); http://dx.doi.org/10.1063/1.873212 (4 pages) | Cited 12 times

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Systematic perturbation methods are used to derive formulas for the Landau damping rates of electron-plasma and ion-acoustic waves. These formulas are more accurate than the standard formulas found in textbooks. © 1999 American Institute of Physics.

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52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Dm	Sound waves

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Parametric study of kinetic Alfvén solitons in a two electron temperature plasma

Matthieu Berthomier, Raymond Pottelette, and Rudolf A. Treumann

Phys. Plasmas 6, 467 (1999); http://dx.doi.org/10.1063/1.873213 (9 pages) | Cited 19 times

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The nonlinear regime of the kinetic Alfvén wave is studied in a collisionless low-β plasma that is composed of a cold ion population and of two electron populations. In the one electron population plasma, it is known that solitary kinetic Alfvén waves (SKAW) propagate either at the Alfvén velocity υ_A or at the ion-acoustic velocity c_s. In this latter case, only plasma compressions exist. In the two electron population plasma, rarefactions, as well as compressions, may exist at this velocity. Furthermore, when the electron-acoustic mode exists and when υ_A>υ_ea (v_ea is the electron-acoustic velocity), the inertia of the cold electron component allows for the existence of compressive SKAW which propagate with a velocity lying in a limited interval above υ_ea. When υ_A<v_ea, these solitons are rarefactive and continuously evolve from classical SKAW moving at υ_A to electron-acoustic-like SKAW moving at υ_ea. The possibility of applying these results to some astrophysical plasma observations is investigated. © 1999 American Institute of Physics.

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52.70.-m	Plasma diagnostic techniques and instrumentation
52.35.Sb	Solitons; BGK modes
52.25.Kn	Thermodynamics of plasmas
52.35.Bj	Magnetohydrodynamic waves (e.g., Alfven waves)

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A test-bed for Langmuir wave turbulence modeling of stimulated Raman backscatter

Harvey A. Rose

Phys. Plasmas 6, 476 (1999); http://dx.doi.org/10.1063/1.873214 (9 pages) | Cited 1 time

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Stimulated Raman backscatter (SRS) may incorporate several, qualitatively different regimes of Langmuir wave dynamics, as it grows convectively in space. These typically include a strictly linear regime at the far end of the plasma from the laser, where SRS comes up from thermal Langmuir wave fluctuations; which may progress to a regime where the primary SRS daughter Langmuir wave is unstable to the Langmuir wave decay instability (LDI); and perhaps to a regime of strong Langmuir wave turbulence (SLT). The accurate description of the spatial transition between these regimes, which may involve large Langmuir wave correlation lengths, is a great challenge for turbulence modeling. In this paper a highly idealized model of SRS in periodic geometry is introduced which allows for the presence of a unique Langmuir wave regime for a given set of physical parameters, and therefore presents the minimal challenge for a turbulence model. One- and two-dimensional simulations of this SRS model, which allows for LDI and SLT as described by Zakharov’s model of nonlinear Langmuir wave dynamics, are compared with the predictions of a recently introduced turbulence model, and quantitative agreement is obtained, without the use of any ad hoc parameters, for the SRS reflectivity and correlation length, and Langmuir and acoustic wave energy densities, over an order of magnitude variation of SRS growth rate and ion acoustic damping rate. © 1999 American Institute of Physics.

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52.38.-r	Laser-plasma interactions
52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Ra	Plasma turbulence
52.25.Gj	Fluctuation and chaos phenomena
52.65.-y	Plasma simulation

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Long-range time dependence in the cross-correlation function

B. A. Carreras, D. E. Newman, B. Ph. van Milligen, and C. Hidalgo

Phys. Plasmas 6, 485 (1999); http://dx.doi.org/10.1063/1.873192 (10 pages) | Cited 9 times

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Detection of a long-range time dependence in the radial cross-correlation function is normally difficult because of the oscillatory behavior of the cross-correlation tail, its low level of coherence, and noise contamination. This problem persists, even with large statistical samples. In this paper, a method for investigating long-range dependence in a single time series is extended to the calculation of the cross-correlation function. With this method and for time series with long-range time correlations, the accuracy of the determination of the cross-correlation function for long time lags is improved. The method is tested by applying it to fractional Gaussian noise and to the fluxes in a running sandpile model. This analysis technique can be applied to the detection of avalanche-type transport in magnetic confinement devices. © 1999 American Institute of Physics.

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52.25.Fi	Transport properties
05.40.Ca	Noise
52.25.Gj	Fluctuation and chaos phenomena
05.65.+b	Self-organized systems
05.45.Tp	Time series analysis

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Reconnection of coalescing magnetic islands

C. Marliani and H. R. Strauss

Phys. Plasmas 6, 495 (1999); http://dx.doi.org/10.1063/1.873193 (8 pages) | Cited 4 times

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The dynamics of magnetic reconnection in the framework of two-dimensional incompressible magnetohydrodynamics is studied numerically. The case of a doubly periodic array of magnetic islands where coalescence of neighboring islands occurs due to self-consistent magnetic forces is investigated. To adequately resolve the current sheets which evolve in between two islands adaptive structured mesh methods are applied. At the onset of the reconnection process the kinetic energy rises and drops rapidly and afterward settles into an oscillatory phase. The time scale of the magnetic reconnection process is not affected by these fast events but consistent with the Sweet–Parker model of stationary reconnection. When the spatial extension of the system is enlarged it undergoes a sequence of merging processes and unstable equilibria towards a large-scale pattern of magnetic islands. During this process the frequency of the oscillations in the kinetic energy is found to scale with the island size. © 1999 American Institute of Physics.

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52.30.-q	Plasma dynamics and flow
52.25.Dg	Plasma kinetic equations
52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.38.Bv	Rayleigh scattering; stimulated Brillouin and Raman scattering

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Simulation of photon acceleration in a plasma wake

A. A. Solodov, P. Mora, and P. Chessa

Phys. Plasmas 6, 503 (1999); http://dx.doi.org/10.1063/1.873194 (10 pages) | Cited 6 times

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The frequency shifting of an ultrashort (femtosecond) low intensity laser pulse in the presence of a plasma wave is investigated using particle simulations. One-dimensional simulations confirm the existence of photon trajectories similar to the trajectories of trapped or untrapped charged particles in a plasma wave. In the case when a plasma wake is produced by a relativistically intense laser pulse with a duration of the order of one plasma period, some full oscillations of the photon frequency take place only for the untrapped photons moving backward in the plasma wave frame before the intense laser pulse depletion due to the energy transfer to the plasma wake occurs. An analytical estimate of the probe pulse phase and frequency shift in two-dimensional (2-D) axially symmetrical plasma wake is performed. Axially symmetrical particle simulations in 2-D, with experimentally attainable parameters, display a frequency shift of the probe pulse of a few percent. In these analytical estimates and 2-D simulations special attention has been given to the modeling of the probe pulse optical collecting line that is typically used in plasma diagnostics. © 1999 American Institute of Physics.

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52.65.-y	Plasma simulation
52.35.-g	Waves, oscillations, and instabilities in plasmas and intense beams
52.38.-r	Laser-plasma interactions

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On the orbit-averaged Monte Carlo operator describing ion cyclotron resonance frequency wave–particle interaction in a tokamak

L.-G. Eriksson, M. J. Mantsinen, T. Hellsten, and J. Carlsson

Phys. Plasmas 6, 513 (1999); http://dx.doi.org/10.1063/1.873195 (6 pages) | Cited 14 times

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In a toroidal plasma the distribution function of ions interacting resonantly with waves in the ion cyclotron range of frequencies (ICRF) can be described with a three-dimensional orbit-averaged Fokker–Planck equation. This equation can be solved with a Monte Carlo method. Explicit expressions for the Monte Carlo operator describing wave–particle interaction, within the framework of quasilinear theory, are given. Furthermore, properties of the operator are discussed. © 1999 American Institute of Physics.

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52.55.Fa	Tokamaks, spherical tokamaks
52.65.Pp	Monte Carlo methods
52.65.Ff	Fokker-Planck and Vlasov equation
52.35.-g	Waves, oscillations, and instabilities in plasmas and intense beams
52.20.Hv	Atomic, molecular, ion, and heavy-particle collisions

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Effect of neutrals on scrape-off-layer and divertor stability in tokamaks

D. A. D’Ippolito and J. R. Myra

Phys. Plasmas 6, 519 (1999); http://dx.doi.org/10.1063/1.873196 (11 pages) | Cited 4 times

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The influence of ion–neutral interactions (charge exchange, elastic scattering) on scrape-off-layer (SOL) stability is studied in the eikonal limit for a single-null X-point geometry typical of tokamak divertors. Instability drives due to curvature and to the ion–neutral drag effect are included in the model. The ion–neutral interaction terms are highly localized near the divertor plates; these terms are stabilizing for typical parameters and large enough to affect the SOL ballooning-interchange stability in the absence of resistivity. It is shown that the growth rate of ideal curvature-driven modes is significantly reduced by the ion–neutral interaction terms; the growth rate of resistive ballooning modes is not affected much by the neutrals, because resistivity allows the mode to disconnect from the divertor region. In both cases, the X-point geometry significantly affects the stability. An ion–neutral drag instability localized near the plates is only found in a small region of parameter space. Conditions for the existence of this instability in X-point geometry are discussed. © 1999 American Institute of Physics.

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52.55.Fa	Tokamaks, spherical tokamaks
52.40.Hf	Plasma-material interactions; boundary layer effects
52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Qz	Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

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Resistive ballooning modes near the edge of toroidal configurations

Darío Correa-Restrepo

Phys. Plasmas 6, 530 (1999); http://dx.doi.org/10.1063/1.873197 (11 pages) | Cited 3 times

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The resistive ballooning mode equations are cast in a new form appropriate for evaluation near the plasma edge of toroidal (axisymmetric as well as three-dimensional) configurations, where the resistive ballooning effects outweigh the diamagnetic effects. Explicit evaluation is carried out for cylindrically symmetric plasmas and for a tokamak model with circular cross sections. Owing to the large electric resistivity of the regions considered, resistive ballooning modes with growth rates comparable to the characteristic growth rate of ideal ballooning modes are possible. A general feature is that modes with large growth rates are localized around the regions of bad curvature and become less unstable with increasing shear, while those with smaller growth rates are extended along the magnetic field lines and are insensitive to shear. © 1999 American Institute of Physics.

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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
52.55.Jd	Magnetic mirrors, gas dynamic traps
52.25.Fi	Transport properties

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Spectroscopic analysis of normal and reversed ion flows in the DIII-D divertor

R. C. Isler, N. H. Brooks, W. P. West, A. W. Leonard, G. R. McKee, and G. D. Porter

Phys. Plasmas 6, 541 (1999); http://dx.doi.org/10.1063/1.873198 (9 pages) | Cited 20 times

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Flow velocities of C⁺, C²⁺, B⁺, and D⁺ parallel to the magnetic field in the DIII-D [J. Luxon, P. Anderson, F. Batty et al., Plasma Physics Controlled Nuclear Fusion Research, Proceedings of the 11th International Conference, Tokyo, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] divertor have been measured from Doppler shifts of spectral lines. In general, both normal flows (toward the target plate) and reversed flows (away from the target plate) are observed in the outer scrape-off layer with the reversed flows occurring near the separatrix. Following the transition from attached to partially detached conditions, normal flow velocities generally speed up while in some regions reversed flows are observed to slow down. In high density plasmas, deuteron velocities are reflected in Balmer line emission which originates mainly from atoms which have thermalized by charge exchange or which have been formed by recombination. Low-temperature areas of nearly stagnated deuteron flow have been observed. In these regions recombination should be efficient for neutralizing the divertor plasma. © 1999 American Institute of Physics.

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52.55.Fa	Tokamaks, spherical tokamaks
52.70.Kz	Optical (ultraviolet, visible, infrared) measurements
52.30.-q	Plasma dynamics and flow
52.25.Vy	Impurities in plasmas
52.55.Pi	Fusion products effects (e.g., alpha-particles, etc.), fast particle effects
52.40.Hf	Plasma-material interactions; boundary layer effects
52.20.Fs	Electron collisions
52.20.Hv	Atomic, molecular, ion, and heavy-particle collisions
52.25.Os	Emission, absorption, and scattering of electromagnetic radiation

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Collisionless transport parallel to the magnetic field in a toroidal plasma

R. D. Hazeltine

Phys. Plasmas 6, 550 (1999); http://dx.doi.org/10.1063/1.873199 (6 pages) | Cited 5 times

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Transport parallel to the magnetic field of a toroidal plasma confinement system is investigated through kinetic theory, with emphasis on the long mean-free path limit. The crucial differences between transport on rational and irrational (ergodic) magnetic surfaces is discussed in detail. A collisionless transport law, involving a nonlocal operator that accounts for toroidal topology, is derived for parallel heat conduction on irrational magnetic surfaces. In the rational surface case, perpendicular diffusion is included in the kinetic equation to avoid singularity; this allows a calculation of the width and amplitude of resonant temperature perturbations that will be excited by heat sources with sufficiently broad Fourier spectra. © 1999 American Institute of Physics.

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52.25.Fi	Transport properties
52.25.Dg	Plasma kinetic equations
52.55.Fa	Tokamaks, spherical tokamaks
52.55.Jd	Magnetic mirrors, gas dynamic traps
02.40.Pc	General topology

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Effects of magnetic shear on electron cyclotron resonance heating in heliotron/torsatron configurations

K. Nagasaki, A. Ejiri, T. Mizuuchi, T. Obiki, H. Okada, F. Sano, H. Zushi, S. Besshou, and K. Kondo

Phys. Plasmas 6, 556 (1999); http://dx.doi.org/10.1063/1.873200 (9 pages) | Cited 10 times

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Effects of magnetic shear on electron cyclotron resonance heating (ECRH) are studied in heliotron/torsatron configurations. In such configurations, the poloidal magnetic field is comparable to the toroidal magnetic field, and varies spatially along the minor radius, making a strong magnetic shear. When high power millimeter waves are launched into a plasma, it is coupled to propagating modes at the plasma peripheral region. The existence of a transition layer between the core plasma region and the vacuum region, where the magnetic field direction is largely changed, requires accurate polarization control for good single pass absorption. The mode conversion between the propagation modes due to the magnetic shear also affects the launching conditions. The polarization control experiment by using second harmonic ECRH in Heliotron E [T. Obiki, Fusion Technol. 17, 101 (1990)] are compared with the numerical calculation in which one dimensional second order coupled equations are solved. The polarization dependence experimentally measured is in good agreement with the numerical results including the magnetic shear terms. © 1999 American Institute of Physics.

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52.55.Jd	Magnetic mirrors, gas dynamic traps
52.50.Gj	Plasma heating by particle beams
52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

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Observation of Rayleigh–Taylor growth to short wavelengths on Nike

C. J. Pawley, S. E. Bodner, J. P. Dahlburg, S. P. Obenschain, A. J. Schmitt, J. D. Sethian, C. A. Sullivan, J. H. Gardner, Y. Aglitskiy, Y. Chan, and T. Lehecka

Phys. Plasmas 6, 565 (1999); http://dx.doi.org/10.1063/1.873201 (6 pages) | Cited 8 times

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The uniform and smooth focal profile of the Nike KrF laser [S. Obenschain et al., Phys. Plasmas 3, 2098 (1996)] was used to ablatively accelerate 40 μm thick polystyrene planar targets with pulse shaping to minimize shock heating of the compressed material. The foils had imposed small-amplitude sinusoidal wave perturbations of 60, 30, 20, and 12.5 μm wavelength. The shortest wavelength is near the ablative stabilization cutoff for Rayleigh–Taylor growth. Modification of the saturated wave structure due to random laser imprint was observed. Excellent agreement was found between the two-dimensional simulations and experimental data for most cases where the laser imprint was not dominant. © 1999 American Institute of Physics.

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52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.50.Jm	Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.57.-z	Laser inertial confinement
28.52.Cx	Fueling, heating and ignition
52.70.La	X-ray and γ-ray measurements
52.65.-y	Plasma simulation

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Stimulated Brillouin backscatter in the presence of transverse plasma flow

D. E. Hinkel, R. L. Berger, E. A. Williams, A. B. Langdon, C. H. Still, and B. F. Lasinski

Phys. Plasmas 6, 571 (1999); http://dx.doi.org/10.1063/1.873202 (11 pages) | Cited 6 times

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Three-dimensional simulations show that stimulated Brillouin backscattered (SBS) light can be deflected in a direction opposite to transverse plasma flow. When the backscatter gain occurs predominantly in the region beyond where the incident light is deflected by transverse flow, and when the backscatter gain from the deflected incident light region is detuned from the undeflected incident light region by axial flow gradients, the SBS deflection correlates well with the steering of the incident beam. The level of Brillouin backscatter gain in the presence of transverse flow is less than that in the absence of transverse flow because of convective damping, where ion acoustic waves are swept out of the high intensity regions(s) of a beam. © 1999 American Institute of Physics.

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52.38.Bv	Rayleigh scattering; stimulated Brillouin and Raman scattering
52.38.-r	Laser-plasma interactions
52.65.-y	Plasma simulation
52.35.Dm	Sound waves
52.30.-q	Plasma dynamics and flow
42.65.Es	Stimulated Brillouin and Rayleigh scattering

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Electron production in low pressure gas ionized by an intense proton beam

B. V. Oliver, P. F. Ottinger, D. V. Rose, D. D. Hinshelwood, J. M. Neri, and F. C. Young

Phys. Plasmas 6, 582 (1999); http://dx.doi.org/10.1063/1.873203 (9 pages) | Cited 5 times

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Electron density measurements from previous ion-beam-induced gas ionization experiments [F. C. Young et al., Phys. Plasmas 1, 1700 (1994)] are re-analyzed and compared with a recent theoretical model [B. V. Oliver et al., Phys. Plasmas 3, 3267 (1996)]. Ionization is produced by a 1 MeV, 3.5 kA, 55 ns pulse-duration, proton beam, injected into He, Ne, or Ar gas in the 1 Torr pressure regime. Theoretical and numerical analysis indicates that, after an initial electron population is produced by ion beam impact, ionization is dominated by the background plasma electrons and is proportional to the beam stopping power. The predicted electron density agrees with the measured electron densities within the factor of 2 uncertainty in the measurement. However, in the case of Ar, the theoretically predicted electron densities are systematically greater than the measured values. The assumptions of a Maxwellian distribution for the background electrons and neglect of beam energy loss to discrete excitation and inner shell ionization in the model equations are considered as explanations for the discrepancy. © 1999 American Institute of Physics.

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34.50.Fa	Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)
51.50.+v	Electrical properties (ionization, breakdown, electron and ion mobility, etc.)

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Theory of laser wakes in plasma channels

G. Shvets and X. Li

Phys. Plasmas 6, 591 (1999); http://dx.doi.org/10.1063/1.873204 (12 pages) | Cited 11 times

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Excitation of accelerating modes in transversely inhomogeneous plasma channels is considered as an initial value problem. Discrete eigenmodes are supported by plasma channels with sharp density gradients. These eigenmodes are collisionlessly damped as the gradients are smoothed. Using collisionless Landau damping as the analogy, the existence and damping of these “quasi-modes” is studied by constructing and analytically continuing the causal Green’s function of wake excitation into the lower half of the complex frequency plane. Electromagnetic nature of the plasma wakes in the channel makes their excitation nonlocal. This results in the algebraic decay of the fields with time due to phase-mixing of plasma oscillations with spatially-varying frequencies. Characteristic decay rate is given by the mixing time τ_m, which corresponds to the dephasing of two plasma fluid elements separated by the collisionless skin depth. For wide channels analytic expressions for the field evolution are derived. Implications for electron acceleration in plasma channels are discussed. © 1999 American Institute of Physics.

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52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.38.-r	Laser-plasma interactions
52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Qz	Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

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Three-dimensional particle-in-cell simulation study of a relativistic magnetron

R. W. Lemke, T. C. Genoni, and T. A. Spencer

Phys. Plasmas 6, 603 (1999); http://dx.doi.org/10.1063/1.873205 (11 pages) | Cited 26 times

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The A6 (six cavity) magnetron operated at relativistic voltages is investigated using three-dimensional particle-in-cell simulation. Previous experiments [A. Palevsky and G. Bekefi, Phys. Fluids 22, 986 (1979)] are repeated numerically for the purpose of ascertaining fidelity of code results in addition to obtaining insight into magnetron operation at high voltage. Simulations produce all qualitative behavior observed in experiments, with good quantitative agreement in most cases. This numerical study also reveals details concerning mode control, the cause and prevention of leakage current, and voltage scaling in the A6. It is shown that: (1) leakage current substantially reduces efficiency, (2) elimination of leakage current using cathode endcaps substantially increases efficiency, and (3) the functional dependence of operating voltage on applied magnetic field may depart from conventional scaling at very high voltage. © 1999 American Institute of Physics.

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84.40.Fe

Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)

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On the heating mode transition in high-frequency inductively coupled argon discharge

Sang-Hun Seo, Jung-In Hong, Keun-Hee Bai, and Hong-Young Chang

Phys. Plasmas 6, 614 (1999); http://dx.doi.org/10.1063/1.873206 (5 pages) | Cited 30 times

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In high-frequency inductively coupled argon discharges with a planar-type coil the phenomena of discharge mode transition (E–H mode transition) are investigated. Experimental observation is done at the low pressure of 10 mTorr and the high frequency of 19 MHz over a range of rf power, 40–525 W. First of all, the discharge mode transition is observed through a change of luminous intensity. This transition is found to occur at the relatively high power of about 280 W compared with the mode transition in a 6.5 MHz discharge. Also, some distinctive features are compared to low-frequency discharges during this transition. In particular, during the E–H mode transition the apparent changes of plasma potential are observed and the sudden variation of plasma potential is proposed as an important factor that indicates the change of power coupling. The features of the discharge mode transition in high-frequency discharge are discussed by considering the power coupling at each mode by measurements of the electron energy distribution functions. © 1999 American Institute of Physics.

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52.80.Pi	High-frequency and RF discharges
52.25.-b	Plasma properties
52.50.Gj	Plasma heating by particle beams

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Wave and Joule heating in a rotating plasma

W. E. Amatucci, G. Ganguli, D. N. Walker, and D. Duncan

Phys. Plasmas 6, 619 (1999); http://dx.doi.org/10.1063/1.873207 (4 pages) | Cited 2 times

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Laboratory experiments were conducted to investigate ion energization by the wave and Joule heating mechanisms in plasma with a radial electric field and an axial magnetic field subjected to increasing ion–neutral collision frequency. Wave and Joule heating regimes were isolated and a transition between the two regimes was observed as the ion–neutral collision frequency was varied. The data show that the dissipation of energy occurs via the mechanism operating on the shortest time scale. © 1999 American Institute of Physics.

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52.50.Gj	Plasma heating by particle beams
52.30.-q	Plasma dynamics and flow

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Influence of chamber temperature on properties of the corona discharge system

Han S. Uhm

Phys. Plasmas 6, 623 (1999); http://dx.doi.org/10.1063/1.873218 (4 pages) | Cited 7 times

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This paper investigates the influence of the chamber temperature on properties of the corona discharge system. It is found that the critical voltage V_c required for the corona discharge breakdown is inversely proportional to the chamber temperature T. The electrical energy w_c required for corona discharge breakdown is inversely proportional to the square of the chamber temperature T. Thus, the electrical energy consumption for the corona discharge system decreases significantly as the temperature increases. The plasma generation by corona discharge in a hot chamber is much more efficient than that in a cold chamber. © 1999 American Institute of Physics.

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52.80.Hc	Glow; corona
52.50.Dg	Plasma sources
52.25.Kn	Thermodynamics of plasmas

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Equivalent electric charge of photons in magnetized plasmas

P. K. Shukla, N. L. Tsintsadze, J. T. Mendonça, and L. Stenflo

Phys. Plasmas 6, 627 (1999); http://dx.doi.org/10.1063/1.873215 (2 pages) | Cited 3 times

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Explicit expressions for the induced electric charge of photons in magnetized plasmas are derived. The electric charges arise due to the electric fields that are created by the photon pressure. © 1999 American Institute of Physics.

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