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Oct 2002

Volume 9, Issue 10, pp. 4103-4418

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Radial and zonal modes in hyperfine-scale stellarator turbulence

F. Jenko and A. Kendl

Phys. Plasmas 9, 4103 (2002); http://dx.doi.org/10.1063/1.1507591 (4 pages) | Cited 19 times

Online Publication Date: 19 September 2002

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Electromagnetic plasma turbulence at hyperfine (i.e., electron gyroradius) scales is studied in the geometry of an advanced stellarator fusion experiment, Wendelstein 7-AS [H. Renner, Plasma Phys. Controlled Fusion 31, 1579 (1989)], by means of nonlinear gyrokinetic simulations. It is demonstrated that high-amplitude radial streamers may also exist in non-tokamak devices, raising the electron heat flux to experimentally relevant values. Moreover, some statistical characteristics of the fully developed turbulence are computed, highlighting the (co-)existence, nature, and role of self-generated zonal flows and fields. © 2002 American Institute of Physics.
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52.55.Jd Magnetic mirrors, gas dynamic traps
52.35.Ra Plasma turbulence
52.65.-y Plasma simulation

Dust grain acceleration during plasma expansion

M. Djebli, S. Bahamida, and R. Annou

Phys. Plasmas 9, 4107 (2002); http://dx.doi.org/10.1063/1.1504716 (3 pages) | Cited 7 times

Online Publication Date: 19 September 2002

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A dusty plasma adiabatic expansion model, where an exact ion charging current as well as ion-dust charge exchange reaction produced neutrals are taken into account, is proposed and numerically solved. Particle cooling, dust fronts associated with excitation of dust sound waves along with acceleration of bursts of grains, are demonstrated. © 2002 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.35.Dm Sound waves

Effects of E×B velocity shear on electrostatic structures

M. Spolaore, V. Antoni, R. Cavazzana, G. Regnoli, G. Serianni, E. Spada, N. Vianello, H. Bergsåker, and J. R. Drake

Phys. Plasmas 9, 4110 (2002); http://dx.doi.org/10.1063/1.1506310 (4 pages) | Cited 13 times

Online Publication Date: 19 September 2002

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Bursts of electrostatic turbulence measured in the edge region of two reversed field pinch experiments (RFX and T2R) are observed to be associated with electrostatic structures. The corresponding E×B velocity drifts have been reconstructed showing features reminiscent of monopolar vortices. These vortices have been grouped in two classes depending on their rotation direction. It is observed that the prevalent rotation direction depends on the shear of the surrounding mean E×B drift velocity, showing a clear analogy with ordinary fluids. © 2002 American Institute of Physics.
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52.35.Ra Plasma turbulence
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.55.Ez Theta pinch
52.40.Hf Plasma-material interactions; boundary layer effects

Realization of high efficiency in a plasma-assisted microwave source with two-dimensional electron motion

A. G. Shkvarunets, Y. Carmel, G. S. Nusinovich, T. M. Abu-elfadl, J. Rodgers, T. M. Antonsen, V. Granatstein, and D. M. Goebel

Phys. Plasmas 9, 4114 (2002); http://dx.doi.org/10.1063/1.1509065 (4 pages) | Cited 11 times

Online Publication Date: 19 September 2002

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Conventional microwave sources utilize a strong axial magnetic field to guide an electron beam through an interaction region. A plasma-assisted slow wave microwave oscillator (Pasotron) can operate without an external magnetic field because the presence of ions neutralizes the space charge in the beam, permits the self-pinch forces to provide beam propagation, and allows for the radial motion of electrons under the action of transverse fields of the wave. While the inherent efficiency of conventional microwave sources with 1D electron flow is limited to 15%–20%, it is shown in this work that both the calculated and measured inherent efficiency of devices with 2D electron flow can be higher than 50%. Both in situ diagnostics and analysis confirmed that the enhanced efficiency is due to the fact that rf forces dominate the beam dynamics. © 2002 American Institute of Physics.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
84.47.+w Vacuum tubes
52.75.-d Plasma devices
52.58.Lq Z-pinches, plasma focus, and other pinch devices
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
52.25.Fi Transport properties
52.30.-q Plasma dynamics and flow
52.70.-m Plasma diagnostic techniques and instrumentation
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back to top Basic Plasma Phenomena, Waves, Instabilities

Acoustic modes in dense dusty plasmas

K. Avinash, A. Bhattacharjee, and S. Hu

Phys. Plasmas 9, 4118 (2002); http://dx.doi.org/10.1063/1.1503357 (9 pages) | Cited 3 times

Online Publication Date: 19 September 2002

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Properties of acoustic modes in high dust density dusty plasmas are studied. The solutions of fluid equations for electrons, ions, and dust grains with collisional and ionization effects are solved along with an equation for grain charging. The high dust density effects on the acoustic modes are interpreted in terms of a change in the screening properties of the grain charge. At low dust density, the grain charge is screened due to electrons and ions. However, at high dust density, the screening of the grain charge due to other grains also becomes important. This leads to a reduction of the phase-velocity, which in turn is shown to make the plasma more unstable at high dust density. In this regime the role of the ion acoustic mode is replaced by the charging mode. The relevance of these results to earlier theoretical studies and experimental results are discussed. © 2002 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Collisionless reconnection of magnetic field lines in dusty plasmas

D. Jovanović and P. K. Shukla

Phys. Plasmas 9, 4127 (2002); http://dx.doi.org/10.1063/1.1503799 (8 pages) | Cited 4 times

Online Publication Date: 19 September 2002

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Stability of a thin current sheet in an inhomogeneous dusty plasma is investigated. A new mechanism for the collisionless reconnection of the magnetic field is found. It is associated with the linear instability of a surface shear-Alfvén mode which exists at the boundary between two plasma regions with different orientations of the sheared magnetic field. This new mode is possible only in dusty plasmas in which the electron and ion densities are inhomogeneous and different from each other. The dispersion properties of the surface mode are found to be strongly dependent on the spatial profile of the current sheet. The unstable linear mode is found in the case of a current sheet with steep edges. It is identified as the bending- (or kink-) mode, whose electrostatic and vector potentials, ϕ and Az, are symmetric and antisymmetric functions, respectively. In such a plasma configuration, the surface tearing mode (ϕ-antisymmetric, Az-symmetric) cannot propagate as an eigenmode. It arises only as a forced mode through the resonant coupling with the bending mode and the local convective cell. The increment of the bending/tearing instability is estimated from the second-order contribution of the resonance. © 2002 American Institute of Physics.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.27.Lw Dusty or complex plasmas; plasma crystals
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Vd Magnetic reconnection

Probe measurements of low-frequency plasma potential and electric field fluctuations in a magnetized plasma

S. V. Ratynskaia, V. I. Demidov, and K. Rypdal

Phys. Plasmas 9, 4135 (2002); http://dx.doi.org/10.1063/1.1505846 (9 pages) | Cited 15 times

Online Publication Date: 19 September 2002

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A system of two cylindrical probes aligned along the magnetic field, and equipped with insulating end plugs, is proposed for measurement of low-frequency fluctuations of the electrostatic field in a magnetized plasma. It is demonstrated by modeling and experiments that the plug probe floats close to the plasma potential. The electric field component in a given direction is obtained by subtracting the plasma potentials obtained on two spatially separated plug probes. The probe system is applied to low-frequency electrostatic fluctuations in a simple magnetized torus, and reveals the presence of global oscillations, large scale propagating structures (m = 1 modes), and developed turbulence with power-law spectra. Two different mode branches for the fluctuations are identified by comparing results from plug probes with results from conventional probes. Sources of errors arising from applying floating potential of conventional probes for electric field measurements are pointed out and discussed. © 2002 American Institute of Physics.
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52.70.Ds Electric and magnetic measurements
52.25.Gj Fluctuation and chaos phenomena
52.25.Kn Thermodynamics of plasmas
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Ra Plasma turbulence
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.)
back to top Nonlinear Phenomena, Turbulence, Transport

Drift wave vortices in multicomponent plasmas

G. Gogoi and K. S. Goswami

Phys. Plasmas 9, 4144 (2002); http://dx.doi.org/10.1063/1.1502673 (5 pages) | Cited 3 times

Online Publication Date: 19 September 2002

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The effect of negative ions in the dynamics of the drift vortex in inhomogeneous plasma is analytically studied. It is found that when the drift velocity is not constant, vortex solutions exist only in the short wavelength region. It is observed that the gradient of drift velocity is responsible for the formation of monopole vortices. © 2002 American Institute of Physics.
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52.27.Cm Multicomponent and negative-ion plasmas
52.35.We Plasma vorticity
52.35.Kt Drift waves
52.30.-q Plasma dynamics and flow
52.25.-b Plasma properties

Unified theory of monochromatic and broadband modulational and decay instabilities of Langmuir waves

P. A. Robinson, Iver H. Cairns, and N. I. Smith

Phys. Plasmas 9, 4149 (2002); http://dx.doi.org/10.1063/1.1503358 (11 pages) | Cited 10 times

Online Publication Date: 19 September 2002

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Modulational and decay instabilities driven by pump Langmuir waves are investigated using a nonlinear dispersion equation that incorporates both classes of instability simultaneously, along with the effects of finite bandwidth of the pump. A rational-function approximation of the plasma density response is then introduced to convert this equation into polynomial form. The resulting equation is used to explore the five instability types: decay, modulational, subsonic modulational, supersonic modulational, and modified decay. Growth rates, corresponding wave numbers, stability boundaries, and instability thresholds for the various instabilities are obtained analytically and verified numerically. In the case of a monochromatic pump the results generalize and clarify the limits of validity of many results in the literature. For broadband pumps, existing results for the growth rate of decay instabilities are reproduced, and it is confirmed that broadband modulational and subsonic-modulational interactions are necessarily stable. New results for the behavior of supersonic modulational instabilities are found, and it is also shown that both supersonic modulational and modified decay instabilities have random phase counterparts, the former conclusion contrasting with implications in the literature. The parameter-space transition between modulational and decay instability classes is found to be much sharper than between instability types within either of these classes. © 2002 American Institute of Physics.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Pseudopotential approach to nonlinear dust acoustic waves in dusty plasma

Rajkumar Roychoudhury and Sarit Maitra

Phys. Plasmas 9, 4160 (2002); http://dx.doi.org/10.1063/1.1505640 (6 pages) | Cited 9 times

Online Publication Date: 19 September 2002

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A method is outlined to derive Sagdeev’s pseudopotential which can take into account the dusty charge fluctuation. Numerical solutions of Sagdeev’s master equations are obtained to show the existence of solitary waves. Also, for small amplitude, explicit analytical expressions for solitary waves and double layers are obtained. © 2002 American Institute of Physics.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.27.Lw Dusty or complex plasmas; plasma crystals
52.25.Gj Fluctuation and chaos phenomena
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.40.Kh Plasma sheaths

Nonlinear frequency shifts of plasma eigenmodes

Peter H. Yoon and Rudi Gaelzer

Phys. Plasmas 9, 4166 (2002); http://dx.doi.org/10.1063/1.1506926 (8 pages) | Cited 7 times

Online Publication Date: 19 September 2002

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In the present article, the classic problem of nonlinear frequency shifts of electrostatic plasma eigenmodes in an unmagnetized plasma (i.e., the Langmuir and ion-acoustic waves) is revisited. In the standard literature, only the frequency shift of Langmuir waves by the finite-amplitude Langmuir waves themselves is usually treated. In the present approach, the discussion is generalized to include the ion-sound waves. The significance of the present article is that the analytical approach employed in the present discussion can be utilized to resolve certain apparently singular terms in the induced scattering coefficients of the wave kinetic equations. The detailed discussion of such a problem will be reported in a forthcoming article. © 2002 American Institute of Physics.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.25.Dg Plasma kinetic equations
back to top Magnetically Confined Plasmas, Heating, Confinement

Thermal instability analysis of different types of density limits in DIII-D gas fueled, high-mode discharges

W. M. Stacey, T. W. Petrie, and T. H. Osborne

Phys. Plasmas 9, 4174 (2002); http://dx.doi.org/10.1063/1.1503356 (5 pages)

Online Publication Date: 19 September 2002

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High density, gas fueled, high confinement mode, DIII-D [Luxon, Anderson, Batty et al., Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] shots that were limited in density buildup by: (1) an H–L (high-to-low confinement mode) transition apparently triggered by a core X-point MARFE (multifaceted asymmetric radiation from edge), following the thermal instability sequence of detachment-divertor MARFE-core X-point MARFE; (2) a density limit apparently triggered by large scale core magnetohydrodynamic activity; and (3) an H–L transition apparently triggered by excessive radiated power from the plasma core are analyzed. The presence or absence of a MARFE was correctly predicted by thermal instability theory. A sharp edge temperature gradient was identified as an important factor inhibiting the usual detachment-MARFE sequence in DIII-D and thus leading to the achievement of higher density. © 2002 American Institute of Physics.
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52.55.-s Magnetic confinement and equilibrium

Observation of low impurity diffusivity inside the neoclassical transport barrier in the Compact Helical System

Y. Liang, K. Ida, J. E. Rice, T. Minami, H. Funaba, S. Kado, A. Fujisawa, Y. Yoshimura, S. Nishimura, M. Isobe, S. Okamura, and K. Matsuoka

Phys. Plasmas 9, 4179 (2002); http://dx.doi.org/10.1063/1.1506160 (9 pages) | Cited 4 times

Online Publication Date: 19 September 2002

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The radial profiles of titanium Kα spectra are measured with photon counting x-ray charge coupled device cameras for plasmas with a neoclassical internal transport barrier (N-ITB) in the Compact Helical System Heliotron/Torsatron [K. Matsuoka et al., Plasma Phys. Controlled Fusion 42, 1145 (2000)]. The Kα lines are dominated by the resonance line of He-like titanium in the plasma core where a thermal transport barrier results in a high electron temperature of ∼ 3 keV. The impurity diffusion coefficients are evaluated from the ionization levels of titanium. The diffusion coefficient inside the neoclassical ITB is <0.03 m2/s, which is one order of magnitude lower than that of the plasma without neoclassical ITB. © 2002 American Institute of Physics.
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52.55.Jd Magnetic mirrors, gas dynamic traps
52.25.Vy Impurities in plasmas
52.25.Fi Transport properties

Measurements of large poloidal variations of impurity density in the Alcator C-Mod H-mode barrier region

T. Sunn Pedersen, R. S. Granetz, E. S. Marmar, D. Mossessian, J. W. Hughes, I. H. Hutchinson, J. Terry, and J. E. Rice

Phys. Plasmas 9, 4188 (2002); http://dx.doi.org/10.1063/1.1506162 (5 pages) | Cited 4 times

Online Publication Date: 19 September 2002

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Simultaneous high resolution measurements of the soft x-ray emission at the top and outboard edge of the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] are presented. Impurity density profiles are derived from these measurements. The impurity density varies considerably on a flux surface in the high confinement mode (H-mode) pedestal region. The soft x-ray and impurity density pedestals are not on the same flux surface at the top and outboard edge. The pedestal widths are consistently larger at the outboard edge in the Enhanced D-alpha (EDA) H-mode, suggesting a ballooning-like character of the EDA quasi-coherent mode. The usual separation of time scales between radial and parallel impurity transport does not hold in the H-mode pedestal region of Alcator C-Mod. Thus, one should not necessarily expect that the impurity density be constant on a flux surface in this region. © 2002 American Institute of Physics.
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52.25.Kn Thermodynamics of plasmas
52.55.Fa Tokamaks, spherical tokamaks
52.25.Vy Impurities in plasmas
52.70.-m Plasma diagnostic techniques and instrumentation

Hamiltonian guiding center equations in a toroidal system

S. S. Abdullaev and K. H. Finken

Phys. Plasmas 9, 4193 (2002); http://dx.doi.org/10.1063/1.1502672 (12 pages) | Cited 9 times

Online Publication Date: 19 September 2002

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A Hamiltonian method to study the guiding center motion of charged particles in a toroidal magnetic system has been developed. It uses a cylindrical coordinate system instead of a magnetic coordinate system on which many conventional standard methods are based. The six-dimensional (6D) Hamiltonian equations for the guiding center motion are derived by a canonical transformation of fast-oscillating variables to slowly varying ones which are guiding center coordinates. It is shown that one of these slowly varying variables, i.e., the action variable conjugated to the fast-oscillating gyrophase is an adiabatic invariant for the tokamak equilibrium magnetic field perturbed by the external time-dependent magnetic field. This allows to reduce the 6D Hamiltonian system to the 4D one. The method is valid for the study of the guiding center motion of particles in time-dependent magnetic and electric fields, especially, ergodic magnetic fields, where spatial and temporal scales of variation are much larger than the gyroradius and the gyroperiod. © 2002 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Simulation of neoclassical tearing modes (NTMs) in the DIII-D tokamak. I. NTM excitation

A. M. Popov, R. J. La Haye, Y. Q. Liu, M. Murakami, N. N. Popova, and A. D. Turnbull

Phys. Plasmas 9, 4205 (2002); http://dx.doi.org/10.1063/1.1505842 (24 pages) | Cited 7 times

Online Publication Date: 19 September 2002

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Nonlinear self-consistent magnetohydrodynamic (MHD) stability simulations of neoclassical tearing modes (NTM) are performed with the three-dimensional (3-D) MHD code Nonlinear Full Toroidal Code (NFTC) [Phys. Plasmas 8, 3605 (2001)] in real geometry. The numerical model is based on the nonlinear 3-D MHD equations including neoclassical effects: bootstrap current perturbations, and the transport and the polarization current thresholds. Neoclassical terms are included in the basic equations for magnetic field and pressure. An effective fully implicit numerical scheme allows the transport profile to evolve self-consistently with the nonlinear MHD instabilities and externally applied sources. A direct comparison of NTM evolution with experimental observations in different DIII-D discharges is performed. As a result, the nonlinear NTM stability diagram—dependences of the critical and the saturated island width on plasma current profile parameters are obtained. The stability criterion for the time evolution of the plasma profiles against neoclassical tearing modes is also investigated. © 2002 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
52.65.Kj Magnetohydrodynamic and fluid equation

Simulation of neoclassical tearing modes in the DIII-D tokamak. II. Suppression by radially localized electron cyclotron current drive

A. M. Popov, R. J. La Haye, Y. Q. Liu, M. Murakami, N. N. Popova, and A. D. Turnbull

Phys. Plasmas 9, 4229 (2002); http://dx.doi.org/10.1063/1.1505843 (12 pages) | Cited 3 times

Online Publication Date: 19 September 2002

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The problem of neoclassical tearing mode (NTM) suppression by a radially localized toroidal current from electron cyclotron current drive (ECCD) is considered. Simulation of NTM stabilization by ECCD is performed with the Nonlinear Fully Toroidal Code (NFTC) [Phys. Plasmas 8, 3605 (2001)] for DIII-D discharges. The optimal parameters are determined for the radially localized ECCD current required to reduce the NTM instability. The time response and nonlinear evolution of the magnetic island width for ECCD and the required modulation phasing, the current drive location with respect to the rational surface, and the width of the spatial distribution are determined for both monotonic q-profile and negative central shear discharges. © 2002 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
52.65.Kj Magnetohydrodynamic and fluid equation

Predictive simulations of radio frequency heated plasmas of Tore Supra using the Multi-Mode model

Irina Voitsekhovitch, Glenn Bateman, Arnold H. Kritz, and Alexei Pankin

Phys. Plasmas 9, 4241 (2002); http://dx.doi.org/10.1063/1.1508106 (11 pages) | Cited 2 times

Online Publication Date: 19 September 2002

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Multichannel integrated predictive simulations using the Multi-Mode transport model are carried out for radio frequency heated Tore Supra tokamak discharges in which helium is the primary ion component. Lower hybrid heated discharges in which the total current is driven noninductively [X. Litaudon et al., Plasma Phys. Controlled Fusion 43, 677 (2001)] and a discharge with ion cyclotron radio frequency heating of the hydrogen minority ions [G. T. Hoang et al., Nucl. Fusion 38, 117 (1998)] are simulated. The simulations of these discharges represent the first test of the Multi-Mode model in helium plasmas with dominant electron heating. Also for the first time, the particle transport in Tore Supra discharges is computed and the density profiles are predicted self-consistently with other transport channels. It is found in these simulations that the anomalous transport driven by trapped electron mode turbulence is dominant compared to the transport driven by the ion temperature gradient turbulence. The feature of the Multi-Mode model to calculate the impurity transport self-consistently with other transport channels is used in this study to predict the influence of carbon impurity influx on the discharge evolution. © 2002 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.65.-y Plasma simulation
52.25.Fi Transport properties
52.35.Ra Plasma turbulence
52.25.Vy Impurities in plasmas
back to top Inertially Confined Plasmas, Dense Plasmas, Equations of State

Laser Mégajoule irradiation uniformity for direct drive

B. Canaud, X. Fortin, N. Dague, and J. L. Bocher

Phys. Plasmas 9, 4252 (2002); http://dx.doi.org/10.1063/1.1504102 (9 pages) | Cited 15 times

Online Publication Date: 19 September 2002

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In the context of the direct-drive Laser-Mégajoule (LMJ) fusion-research program, the characteristic long-wavelength nonuniformities produced by irradiating a pellet with multiple overlapping laser beams are studied with or without imperfections coming from power imbalance and pointing errors. The intensity profiles are modeled by super-Gaussian shapes. The beam pattern which minimizes the intrinsic LMJ nonuniformity is determined. It is shown the LMJ beam placement creates untractable nonuniformities from even modes. The laser imperfections create odd and low modes of nonuniformity which can dominate the even modes. © 2002 American Institute of Physics.
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52.57.-z Laser inertial confinement
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
28.52.Cx Fueling, heating and ignition

Strong absorption, intense forward-Raman scattering and relativistic electrons driven by a short, high intensity laser pulse through moderately underdense plasmas

C. Rousseaux, M. Rabec le Gloahec, S. D. Baton, F. Amiranoff, J. Fuchs, L. Gremillet, J. C. Adam, A. Héron, and P. Mora

Phys. Plasmas 9, 4261 (2002); http://dx.doi.org/10.1063/1.1504715 (9 pages) | Cited 19 times

Online Publication Date: 19 September 2002

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The propagation of a short and intense laser pulse (1.057 μm, 350 fs, 1017 W/cm2–2×1019 W/cm2) through preformed undercritical plasmas (≈5%–40% of nc) has been experimentally investigated on the 100-TW laser facility at the Laboratoire pour l’Utilisation des Lasers Intenses. The transmission and reflection of the 1 μm laser pulse, the forward- and backward-Raman (respectively, F-SRS and B-SRS) scattered light and the emission of fast electrons are reported. Significant absorption occurs in these plasmas, which is found to increase with the laser intensity. B-SRS is strongly driven at 1017 W/cm2 and gradually decreases at higher intensities. It is shown that the transmission is low and only weakly dependent on the laser intensity. In contrast, the forward Raman scattering continuously increases with the laser intensity, up to 7% of the incident energy at 2×1019 W/cm2 in the lowest density case. The relativistic electrons accelerated in the forward direction appear to be correlated with the F-SRS. The experimental data are discussed in the light of recent theoretical and numerical investigations, indicating that intense electron heating is likely to play a major role in the temporal growth or inhibition of the instabilities. The theoretical predictions are in agreement with the experiments. © 2002 American Institute of Physics.
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52.38.-r Laser-plasma interactions
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.Nc Particle measurements

Generation of magnetic field, vortices and relativistic particles by the nonpotential ponderomotive force

Nodar L. Tsintsadze, Kunioki Mima, Levan N. Tsintsadze, and Kyoji Nishikawa

Phys. Plasmas 9, 4270 (2002); http://dx.doi.org/10.1063/1.1506311 (10 pages) | Cited 10 times

Online Publication Date: 19 September 2002

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Effects of nonpotential ponderomotive force on kinetic phenomena in a plasma are presented. The particle distribution function is derived, which allows one to calculate the particle and heat fluxes. A novel relativistic hydrodynamic equation of motion, incorporating self-generated magnetic fields, is obtained, which admits no frozen-in condition. The generation of electron fluid vortices by a laser pulse in initially unmagnetized plasma is demonstrated. The merging, decay, and annihilation of vortices (filaments) are discussed. The launching of plasma jets by the vortex structures is disclosed. Self-consistent problem of magnetic, modulational, and filamentational instabilities is studied. The decay of photons into photons and the helicon waves are also discussed. The relevance of this work to recent PetaWatt experiments in connection with high-energy particle generation is pointed out. In addition, highly collimated, mass outflows (jets) are ubiquitous phenomena relevant to astrophysics. © 2002 American Institute of Physics.
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41.75.Ht Relativistic electron and positron beams
52.25.Dg Plasma kinetic equations
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
back to top Ionospheric, Solar-system, and Astrophysical Plasmas

Extended Leibovich–Roberts equation in rarefied plasmas

Istvan Ballai and Yuzef D. Zhugzhda

Phys. Plasmas 9, 4280 (2002); http://dx.doi.org/10.1063/1.1504103 (5 pages) | Cited 5 times

Online Publication Date: 19 September 2002

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Weakly nonlinear magnetoacoustic waves in thin magnetic flux tubes are investigated in rarefied plasmas when an anisotropic kinetic pressure is taken into account. The parallel and perpendicular pressures are defined by two polytropic pressure laws. This model can be considered as a natural extension of the magnetohydrodynamics approximation when the plasma is rarefied. The dispersion relation for slow surface sausage waves propagating in magnetically embedded flux tubes in the presence of pressure anisotropy is used to derive the extended Leibovich–Roberts equation in rarefied and anisotropic plasmas. The properties and limitations of this equation are discussed. © 2002 American Institute of Physics.
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52.35.Sb Solitons; BGK modes
42.65.Tg Optical solitons; nonlinear guided waves
43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound
96.50.Ry Discontinuities

Self-magnetization of protoplanetary accretion disk matter

Heinz Wiechen, Guido T. Birk, Andreas Kopp, and Harald Lesch

Phys. Plasmas 9, 4285 (2002); http://dx.doi.org/10.1063/1.1507119 (8 pages) | Cited 1 time

Online Publication Date: 19 September 2002

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Shear-flow induced friction between neutral gas and charged particle components of different mass can yield a significant self-magnetization of matter. In this paper this process is discussed with respect to protoplanetary disk matter consisting of charged massive dust grains, neutral gas, ions and electrons. Self-consistent three-dimensional multi-fluid plasma—neutral gas—dust simulations are presented taking into account typical parameters for protoplanetary accretion disk matter like that of our early solar system. The results of the simulations show that self induced magnetic fields of 10−5 Tesla up to 10−3 Tesla can be expected in a protoplanetary accretion disk on very short time scales of a few years. Thus, shear-flow induced self-magnetization can yield a significant contribution to the magnetization of the early solar system. © 2002 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.30.Ex Two-fluid and multi-fluid plasmas
94.30.cq MHD waves, plasma waves, and instabilities

On ion injection at quasiparallel shocks

M. Scholer, H. Kucharek, and C. Kato

Phys. Plasmas 9, 4293 (2002); http://dx.doi.org/10.1063/1.1508441 (8 pages) | Cited 4 times

Online Publication Date: 19 September 2002

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A large number of numerical experiments has been performed in order to study the interaction of interstellar pickup protons and helium ions with quasiparallel collisionless shocks. The shocks are modeled by a one-dimensional hybrid simulation method which treats the ions as macroparticles and the electrons as a massless fluid. Solar wind alpha particles and pickup protons are included self-consistently. In addition, the particle splitting method is used for the solar wind ions so that the distribution function can be followed over more than 10 orders of magnitude. A large part of the pickup ion distribution is reflected; the reflection efficiency is very high, and can reach in cases where the pickup ion density is low as much as 50%–60%. The reflection efficiency is almost independent of magnetic field–shock normal angle. This indicates that magnetic mirroring is unimportant and does not lead to larger reflection efficiencies. The reflection efficiency of pickup protons rapidly decreases when the pickup ion density exceeds a few percent of the solar wind density. An addition of 25% pickup protons decreases the reflection coefficient for these ions to ∼ 10%. This represents the fact that a quasiparallel shock cannot be considered as being uncoupled from the upstream region: at high additions of pickup ions the shock structure is changed in such a way as to reflect less pickup ions. The intensity of diffuse ions upstream of a quasiparallel shock does not depend on the temperature of the core distribution. Within the framework of the present model even solar wind distributions with a hard power law tail do not produce higher intensities of diffuse ions. It is argued that this can be understood by the fact that the intrinsic self-consistency between the processes in the upstream region and at the shock transition determines the injection and reflection properties of the core solar wind distribution. © 2002 American Institute of Physics.
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95.30.Qd Magnetohydrodynamics and plasmas
52.72.+v Laboratory studies of space- and astrophysical-plasma processes
52.35.Tc Shock waves and discontinuities
52.40.Mj Particle beam interactions in plasmas
96.20.Br Origin and evolution
back to top Lasers, Particle Beams, Accelerators, Radiation Generation

Precision matched solution of the coupled beam envelope equations for a periodic quadrupole lattice with space charge

Edward P. Lee

Phys. Plasmas 9, 4301 (2002); http://dx.doi.org/10.1063/1.1502257 (8 pages) | Cited 5 times

Online Publication Date: 19 September 2002

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The coupled Kapchinskij–Vladimirskij (K–V) envelope equations for a charged particle beam transported by a periodic system of quadrupoles with self-consistent space charge force have previously been solved by various approximate methods, with accuracy ranging from 1% to 10%. A new method of solution is introduced here, which is based on a double expansion of the beam envelope functions in powers of the focal strength and either the beam’s emittance or its dimensionless perveance. This method results in accuracy better than 0.1% for typical lattice and beam parameters when carried through one consistent level of approximation higher than employed in previous work. Several useful quantities, such as the values of the undepressed tune and the beam’s perveance in the limit of vanishing emittance, are represented by very rapidly converging power series in the focal strength, with an accuracy of 0.01% or better. © 2002 American Institute of Physics.
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29.25.-t Particle sources and targets
41.75.-i Charged-particle beams
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