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Dec 2001

Volume 8, Issue 12, pp. 5073-5335

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On the nature of bursting in transport and turbulence in drift wave–zonal flow systems

M. A. Malkov, P. H. Diamond, and M. N. Rosenbluth

Phys. Plasmas 8, 5073 (2001); http://dx.doi.org/10.1063/1.1415424 (4 pages) | Cited 43 times

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The predictions of the extended predator–prey model of the coupled spectral dynamics of drift wave–zonal flow turbulence are presented. The model exhibits three possible types of time-dependent solutions, depending on system parameters, which are: (1) quasiperiodic bursting of the transport and turbulence intensity levels; (2) oscillatory relaxation to a stationary state, and in the collisionless limit; (3) an intensity pulse followed by saturation of zonal flow. These solutions are consistent with the time dependent behavior recently observed in the global gyrokinetic simulations. © 2001 American Institute of Physics.
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52.35.Kt Drift waves
52.30.-q Plasma dynamics and flow
52.25.Fi Transport properties
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.)

Electromagnetic surface waves on ultrashort pulse laser-generated plasma channels

M. J. Keskinen, R. Fernsler, H. D. Ladouceur, A. P. Baronavski, P. W. Grounds, and P. G. Girardi

Phys. Plasmas 8, 5077 (2001); http://dx.doi.org/10.1063/1.1416178 (4 pages) | Cited 4 times

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Using analytical and numerical techniques, the properties of electromagnetic surface waves on conducting plasma channels produced by ultrashort pulse lasers have been studied. Using a homogeneous slab approximation to model the conducting plasma channel, we solve for the surface wave dispersion and wave damping for both the symmetric and antisymmetric wave mode cases for both a thick and thin slab. For the dense plasma case, i.e., for wave frequencies less than the electron collision frequency, it is found that surface wave damping attenuation length can be large, on the order of the laser plasma channel propagation distance, for atmospheric pressure conditions for both the thick and thin slab approximation. In addition, it is shown that large amplitude surface waves can modify the plasma channel conductivity through nonlinear effects. © 2001 American Institute of Physics.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
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back to top Basic Plasma Phenomena, Waves, Instabilities

A new class of exact solutions of the Vlasov equation

M. Y. Yu, Zhaoyang Chen, and L. Stenflo

Phys. Plasmas 8, 5081 (2001); http://dx.doi.org/10.1063/1.1416484 (5 pages) | Cited 8 times

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A class of exact one-dimensional oscillating solutions of the Vlasov–Poisson system describing a one-component plasma in a parabolic electrostatic potential well is considered. Through a separation of variables procedure, a system of ordinary differential equations describing the moments of the velocity distribution function is obtained. The moment equations can be decoupled at any order from the higher ones without approximations. Oscillating-pattern solutions for the resulting finite and exact systems are found. © 2001 American Institute of Physics.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Sb Solitons; BGK modes
02.90.+p Other topics in mathematical methods in physics (restricted to new topics in section 02)

Scattering and extinction of ion beams in a dusty plasma device

Y. Nakamura

Phys. Plasmas 8, 5086 (2001); http://dx.doi.org/10.1063/1.1419253 (5 pages) | Cited 6 times

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Collisions of ions with charged dust grains are important for the propagation of low frequency waves such as dust acoustic waves and dust ion-acoustic waves. The collision cross-sectional area of charged dust grains depends on the velocity of an ion beam. The collision cross-sectional area of charged dust grains with beam ions is measured. It is compared with the geometrical cross-sectional area of the grain. The experiment is performed in a dusty double-plasma device with glass beads of 8.9 μm in average diameter. The ion beam current and energy are measured with a directional retarding potential analyzer. It is observed that, when dust density inside the system is increased, the beam current ratio is reduced. From the reduction of the ion beam current, the effective cross-sectional area of the dust particle is estimated as a function of the beam energy. © 2001 American Institute of Physics.
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52.40.Mj Particle beam interactions in plasmas
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.75.-d Plasma devices
52.25.Kn Thermodynamics of plasmas
52.27.Lw Dusty or complex plasmas; plasma crystals
back to top Nonlinear Phenomena, Turbulence, Transport

On the sink/source effects in two-dimensional plasma turbulence

S. A. Galkin and S. I. Krasheninnikov

Phys. Plasmas 8, 5091 (2001); http://dx.doi.org/10.1063/1.1415750 (5 pages)

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Ad hoc sinks and sources of turbulence are added in the two-dimensional (2D) magnetized plasma model to mimic excitation and damping of the modes. Depending on linear growth and damping rates and sink and source localizations, two kind of the turbulence and large scale flows evolution regimes were found: quasisteady state and dynamic. The quasisteady states with saturated averaged energy and enstrophy are characterized by strong large scale flows generated due to the inverse cascade in the nonlinear mode coupling. It is shown that for the adopted model there is not complete stabilization of high-k harmonics (microturbulence) by the generated zonal flows and convective cells. The dynamic regimes are characterized by nonvanishing energy and enstrophy fluctuations around averaged values and the energy spectrum has maximum, which corresponds to the turbulence source. The inverse cascades in these regimes are suppressed by the mode damping in the k-space sink region. © 2001 American Institute of Physics.
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52.55.Jd Magnetic mirrors, gas dynamic traps
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)

Anomalous diffusion and exit time distribution of particle tracers in plasma turbulence model

B. A. Carreras, V. E. Lynch, and G. M. Zaslavsky

Phys. Plasmas 8, 5096 (2001); http://dx.doi.org/10.1063/1.1416180 (8 pages) | Cited 59 times

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To explore the character of transport in a plasma turbulence model with avalanche transport, the motion of tracer particles has been followed. Both the time evolution of the moments of the distribution function of the tracer particle radial positions, 〈∣r(t)−r(0)∣n〉, and their finite scale Lyapunov number are used to determine the anomalous diffusion exponent, ν. The numerical results show that the transport mechanism is superdiffusive with an exponent ν close to 0.88±0.07. The distribution of the exit times of particles trapped into stochastic jets is also determined. These particles have the lowest separation rate at the low resonant surfaces. © 2001 American Institute of Physics.
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52.35.Ra Plasma turbulence
52.25.Fi Transport properties
52.25.Gj Fluctuation and chaos phenomena

Zonal and streamer structures in magnetic-curvature-driven Rayleigh–Taylor instability

Amita Das, Abhijit Sen, Sangeeta Mahajan, and Predhiman Kaw

Phys. Plasmas 8, 5104 (2001); http://dx.doi.org/10.1063/1.1416483 (9 pages) | Cited 19 times

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A detailed numerical investigation of the nonlinear evolution of the magnetic curvature-driven Rayleigh–Taylor instability is carried out. The evolution is found to follow one of two distinct paths—that leading to a saturated zonal flow pattern or growing streamer structures. For a fixed value of the density gradient and the magnetic field gradient, the parametric regimes for the occurrence of these two states is delineated in the form of a phase diagram in the D−μ space, where D is the diffusion coefficient and μ is the viscosity parameter. The bifurcation behavior is explained on the basis of a reduced quasilinear model and the final saturated state of zonal flows is understood from a phenomenological zero-dimensional model. © 2001 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.)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

One-dimensional electromagnetic solitons in a hot electron-positron plasma

Maurizio Lontano, Sergei Bulanov, and James Koga

Phys. Plasmas 8, 5113 (2001); http://dx.doi.org/10.1063/1.1416878 (8 pages) | Cited 24 times

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The set of relativistic hydrodynamic equations for a two-species plasma is derived with the aim to investigate the interaction between arbitrary amplitude electromagnetic (EM) fields and hot plasmas. The equations are then specialized in order to study the existence of solitonlike EM distributions in a one-dimensional electron-positron plasma. It is found that: (i) a nonzero temperature makes possible the existence of nondrifting soliton-like solutions, otherwise impossible in a strictly cold plasma; (ii) in an ultrarelativistic plasma, extremely large concentrations of EM energy densities can be achieved; (iii) correspondingly, the temperature profile of the background plasma develops strong nonuniformities. © 2001 American Institute of Physics.
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52.27.Ep Electron-positron plasmas
52.35.Sb Solitons; BGK modes
98.80.-k Cosmology

The nonlinear dynamics of the modulational instability of drift waves and the associated zonal flows

C. N. Lashmore-Davies, D. R. McCarthy, and A. Thyagaraja

Phys. Plasmas 8, 5121 (2001); http://dx.doi.org/10.1063/1.1416881 (13 pages) | Cited 25 times

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The linear and nonlinear dynamics of zonal flows and their interactions with drift wave turbulence is considered in the simple but illuminating generalized Charney–Hasegawa–Mima model due to Smolyakov et al. [Phys. Plasmas 7, 1349 (2000)]. Two positive definite, exact, integral invariants associated with the full generalized Charney–Hasegawa–Mima system are derived. For an initial monochromatic drift wave pump with small but finite amplitude, a modulational instability can occur, characterized by growing zonal flow and sideband perturbations (i.e., a four-wave interaction). The pump threshold for instability is readily satisfied, depending on the zonal flow wave number. The fully nonlinear Charney–Hasegawa–Mima equations are solved with a numerical scheme which is validated by demonstrating the conservation of the two exact invariants. The simulations show that the validity of the four-wave model is limited to approximately three instability growth times. The radial structure of the zonal flow can be “jet-like” or highly oscillatory depending upon the ratio of the system size to the density scale length and initial conditions. It is found that zonal flows can be dramatically reduced if the most unstable zonal flow wave number does not fit into the system. © 2001 American Institute of Physics.
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52.35.Kt Drift waves
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Ra Plasma turbulence

Cross field diffusion and transport in a nonrelativistic beam-driven magnetoplasma: Collisional kinetics

J. N. Mohanty and K. C. Baral

Phys. Plasmas 8, 5134 (2001); http://dx.doi.org/10.1063/1.1391446 (6 pages) | Cited 2 times

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Streaming or beam-driven kinetic theory is formulated for a nonrelativistic and collisional plasma diffusing across magnetic field lines, including small density and temperature gradient. Explicit formulas for modified transport coefficients are presented and their dependence on streaming parameter (V0) is discussed both qualitatively and quantitatively, while retaining the exponent in normalization intact. The dramatic results concerning the beam feature reveal that the electrical resistivity (η⊥) and thermal conductivity (K) diminish sharply with the increase in temperature for varying V0 in the limit of T+ = T− = 108 K; it approaches minimal range to resemble a rectangular hyperbola, while only the thermal conductivity (K) shows a diminishing trend with increasing (V0). The thermoelectric coefficient (λ) is almost independent of temperature, though it increases with increasing streaming. © 2001 American Institute of Physics.
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51.10.+y Kinetic and transport theory of gases
51.60.+a Magnetic properties
52.25.Fi Transport properties
52.25.Dg Plasma kinetic equations
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
back to top Magnetically Confined Plasmas, Heating, Confinement

Edge localized mode particle losses from the DIII-D tokamak

G. D. Porter, T. A. Casper, and J. M. Moller

Phys. Plasmas 8, 5140 (2001); http://dx.doi.org/10.1063/1.1412863 (11 pages) | Cited 10 times

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Particle losses associated with edge localized mode (ELM) activity on the DIII-D tokamak [J. Luxon et al., Proceedings of the 11th International Conference on Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1986, Vol. I, p. 159] are evaluated quantitatively using density profile data obtained from a Thomson scattering system. It is shown that up to 10% of the total core particle content is lost with each ELM. The particle loss varies inversely with ELM frequency. The temporally averaged ELM particle loss is shown to be about 25% of the total particle loss from the confined region under a wide variety of plasma conditions. Although this ELM loss is a small fraction of the total ion flux, it is large compared to the particle input from neutral beam heating. Hence ELM particle losses are sufficient to control the density rise associated with H-mode plasma operation with neutral beam heating. In addition to controlling the average density by enhancing the total ion flow, albeit only by 25%, it is posited that the ELMs play a role in determining the density profile in the H-mode pedestal region. © 2001 American Institute of Physics.
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52.55.Dy General theory and basic studies of plasma lifetime, particle and heat loss, energy balance, field structure, etc.
52.55.Fa Tokamaks, spherical tokamaks
52.55.Rk Power exhaust; divertors
52.40.Hf Plasma-material interactions; boundary layer effects

Convection in an asymmetrically sourced Z pinch

A. M. Rey and A. B. Hassam

Phys. Plasmas 8, 5151 (2001); http://dx.doi.org/10.1063/1.1413228 (7 pages) | Cited 3 times

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The convection of a magnetically confined plasma resulting from heat and particle sources is studied. It is assumed that the convection is low-level in that the system stays stable to ideal interchange instabilities. A Z-pinch plasma with asymmetric particle and heat sources is considered. It is found that there is no convection if there are no particle sources, independent of the distribution of the heat sources. Particle sources result in convection which in turn influences heat transport. The central temperature, however, may go up or down in response to this convection, depending on the distribution of the source function. © 2001 American Institute of Physics.
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52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.25.Fi Transport properties
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.)

A study of nonlinear properties of tearing modes

Torkil H. Jensen

Phys. Plasmas 8, 5158 (2001); http://dx.doi.org/10.1063/1.1415070 (7 pages) | Cited 1 time

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The tool used for this study is a numerical code which treats the plasma as an incompressible fluid of low resistivity and which utilizes simplifying assumptions on geometry. For a given set of “almost ideal magnetohydrodynamic (MHD) constraints” [T. H. Jensen, A. W. Leonard, R. J. La Haye, and M. S. Chu, Phys. Fluids B 3, 1650 (1991)], the code can find equilibria which satisfy these constraints when boundary conditions and external currents are specified. Thus, given an initial MHD equilibrium (without an island), and thereby its constraints, the code can be used to find external currents needed for establishing an equilibrium with the same constraints and an island of specified width. The sign of these external currents determines whether the island would grow or shrink if the external currents were removed. Thus the code can provide information on nonlinear growth or decay, but not on the time scales involved. The two main points of the paper are (i) that the stability limit and saturated island width depend not only on the quantity Δ′ [H. P. Furth, J. Killeen, and M. N. Rosenbluth, Phys. Fluids 6, 459 (1963)] but also on the constraints imposed, and (ii) that a current density gradient at the singular surface can drive a tearing mode nonlinearly to a certain island width followed by a decrease until the island vanishes. © 2001 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.)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Tn Ideal and resistive MHD modes; kinetic modes

Experimental determination of the magnetic field spectrum in the Helically Symmetric Experiment using passing particle orbits

J. N. Talmadge, V. Sakaguchi, F. S. B. Anderson, D. T. Anderson, and A. F. Almagri

Phys. Plasmas 8, 5165 (2001); http://dx.doi.org/10.1063/1.1415071 (6 pages) | Cited 17 times

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The leading terms of the magnetic field spectrum for the Helically Symmetric Experiment [Fusion Technol. 27, 273 (1995)] at low magnetic field are determined by analyzing the orbits of passing particles. The images produced by the intersection of electron orbits with a fluorescent mesh are recorded with a charge coupled device and transformed into magnetic coordinates using a neural network. To obtain the spectral components, the transformed orbits are then fit to an analytic expression that models the drift orbits of the electrons. The results confirm for the first time that quasihelical stellarators have a large effective transform that results in small excursions of particles from a magnetic surface. The drift orbits are also consistent with a very small toroidal curvature component in the spectrum. An external magnetic perturbation, nearly resonant with the transform, is shown to induce a large excursion of the particle orbit off a flux surface. © 2001 American Institute of Physics.
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52.55.-s Magnetic confinement and equilibrium
52.70.Nc Particle measurements
52.20.Dq Particle orbits

Analysis of large-scale fluctuation structures in the scrape-off layer of the Wendelstein 7-AS stellarator

O. Grulke, T. Klinger, M. Endler, and A. Piel

Phys. Plasmas 8, 5171 (2001); http://dx.doi.org/10.1063/1.1418021 (10 pages) | Cited 37 times

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Floating potential and ion saturation current fluctuations in the scrape-off layer of the Wendelstein 7-AS stellarator are investigated by using conditional averaging. If floating potential fluctuations are taken as the reference signal for the conditional averaging procedure, large-scale single-vortex structures are predominately found. If ion saturation current fluctuations are taken as the reference signal, double-vortex structures are detected. The phase shift between the two different structures is π/2. The double-vortices are interpreted as a superposition of counter rotating single-vortex potential structures. Both lead to ion saturation current fluctuations of the same sign due to E×B convection of plasma in parallel to the background plasma pressure gradient. The conditional averaging approach is directly compared to cross-correlation analysis. Both methods lead to similar physical conclusions. Lifetime and extent of structures are systematically overestimated by correlation analysis. It is demonstrated that only fluctuations with amplitudes larger than 0.5σ contribute to the detected large-scale structures. © 2001 American Institute of Physics.
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52.35.Kt Drift waves
52.35.Ra Plasma turbulence

Self-consistent treatment of stabilization of resistive wall instabilities in reversed field pinches by radio-frequency waves

V. A. Svidzinski and S. C. Prager

Phys. Plasmas 8, 5181 (2001); http://dx.doi.org/10.1063/1.1416181 (11 pages) | Cited 1 time

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Stabilization of resistive wall magnetohydrodynamic (MHD) instabilities by the force applied by injected radio-frequency (rf) waves is investigated, including the self-consistent effect of the MHD perturbation upon the rf waves in the plasma. This effect leads to the generation of Alfvénic disturbances at the frequency of the rf waves and at the wavelength (in the magnetic surface) of the MHD instability. Stabilization of the ideal external kink instability in the reversed field pinch is considered. If the self-consistent response is neglected, rf waves are confined to the thin vacuum and edge regions, and provide a restoring force which stabilizes the resistive wall instability at moderate rf wave amplitude. However, the generation of Alfvén disturbances causes the rf waves to penetrate deeply into the plasma, eliminating the stabilization.© 2001 American Institute of Physics.
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52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
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)

Guiding center particle simulation of wide-orbit neoclassical transport

A. Bergmann, A. G. Peeters, and S. D. Pinches

Phys. Plasmas 8, 5192 (2001); http://dx.doi.org/10.1063/1.1416486 (7 pages) | Cited 32 times

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The neoclassical ion transport in a tokamak plasma with circular cross section is studied with guiding center particle simulations. A Monte Carlo model of pitch-angle scattering which includes momentum conservation is employed. The model includes the whole plasma inside closed flux surfaces, but the focus is on the near-axis transport due to particles with wide orbits which lead to a different heat flux than in the standard theory. Neither of two recent theories of banana regime transport near the axis is confirmed by the simulations, nor do the numerical results for the plateau regime agree with a recent theory of wide-orbit transport in this regime. © 2001 American Institute of Physics.
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52.65.Cc Particle orbit and trajectory
52.65.Pp Monte Carlo methods
52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties

Edge pedestal deterioration in tokamak high-mode discharges

Weston M. Stacey

Phys. Plasmas 8, 5199 (2001); http://dx.doi.org/10.1063/1.1416879 (5 pages) | Cited 2 times

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A model for calculating edge gradients in density and temperature from transport and atomic physics considerations is combined with a model for calculating the enhancement of edge transport by thermal instabilities, the onset and strength of which in turn depend on edge gradients and atomic physics. A minimum threshold value of the nonradiative power flux passing through the edge that is required to suppress transport enhancing thermal instabilities is established. When the power flux through the edge is less than this minimum threshold value, the model predicts a deterioration of the edge gradients as the neutral concentration, the impurity concentration and/or the impurity radiation emissivity in the edge plasma increase, which is consistent with experimental observations. Model problem calculations are presented to illustrate the predicted pedestal deterioration for representative experimental conditions.© 2001 American Institute of Physics.
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52.25.Fi Transport properties
52.25.Vy Impurities in plasmas

Direct losses of fast particles in multiple-toroidicity stellarators

M. S. Smirnova

Phys. Plasmas 8, 5204 (2001); http://dx.doi.org/10.1063/1.1400793 (10 pages) | Cited 1 time

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Direct losses of fast ions are investigated numerically in current multiple-toroidicity stellarator configurations, in which magnetic field harmonic spectra can be described adequately by a sum of hundreds harmonics with different toroidal and poloidal mode numbers. For these configurations it is typical that amplitudes of distant harmonics with high-order N ≥ 2 toroidal mode numbers can exceed, near the plasma boundary, one-half of the amplitude of the main magnetic-field harmonic. This leads to the appearance of additional ripple wells along field lines which can trap charged particles (toroidally field ripple-trapped particles). An investigation of the role of these particles in plasma confinement in stellarators is the main goal of the paper. It is shown that a complication of the magnetic-field harmonic spectrum of a stellarator causes direct losses of transition and toroidally field ripple-trapped particles several times higher than losses of corresponding particles in rippled tokamaks. © 2001 American Institute of Physics.
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52.55.Dy General theory and basic studies of plasma lifetime, particle and heat loss, energy balance, field structure, etc.

Effect of neutral atoms on tokamak edge plasmas

T. Fülöp, Peter J. Catto, and P. Helander

Phys. Plasmas 8, 5214 (2001); http://dx.doi.org/10.1063/1.1418241 (7 pages) | Cited 7 times

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Neutral atoms can significantly influence the physics of tokamak edge plasmas, e.g., by affecting the radial electric field and plasma flow there, which may, in turn, be important for plasma confinement. Earlier work [Fülöp et al., Phys. Plasmas 5, 3969 (1998)], assuming short mean-free path neutrals and Pfirsch–Schlüter ions, has shown that the ion-neutral coupling through charge-exchange affects the neoclassical flow velocity significantly. However, the mean-free path of the neutrals is not always small in comparison with the radial scale length of densities and temperatures in the edge pedestal. It is therefore desirable to determine what happens in the limit when the neutral mean-free path is comparable with the scale length. In the present work a self-similar solution for the neutral distribution function allowing for strong temperature and density variation is used, following the analysis of Helander and Krasheninnikov [Phys. Plasmas 3, 226 (1995)]. The self-similar solution is possible if the ratio of the mean-free path to the temperature and density scale length is constant throughout the edge plasma. The resulting neutral distribution function is used to investigate the neutral effects on the ion flow and electrostatic potential as this ratio varies from much less than one to order unity.© 2001 American Institute of Physics.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.55.Fa Tokamaks, spherical tokamaks
52.25.Kn Thermodynamics of plasmas
52.20.-j Elementary processes in plasmas

Damping of relativistic electron beams by synchrotron radiation

F. Andersson, P. Helander, and L.-G. Eriksson

Phys. Plasmas 8, 5221 (2001); http://dx.doi.org/10.1063/1.1418242 (9 pages) | Cited 27 times

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Relativistic electrons emit synchrotron radiation due to their gyro- and guiding-center motions in a curved magnetic field. In this article, the kinetic theory of relativistic electron beams is developed to account for radiation reaction by including the Abraham–Lorentz reaction force in the kinetic equation. As an application of this theory, the dynamics of runaway electrons is examined and a steady-state solution is constructed describing a balance between acceleration by the electric field, pitch-angle scattering, and radiation reaction. Furthermore, it is found that a beam of relativistic electrons can be slowed down by the combined effects of pitch-angle scattering and radiation reaction. This damping can be more efficient than ordinary collisional drag, and appears to explain the decay of post-disruption runaway currents in the Joint European Torus (JET) [R. D. Gill, Nucl. Fusion 33, 1613 (1993)].© 2001 American Institute of Physics.
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41.75.Ht Relativistic electron and positron beams
52.40.Mj Particle beam interactions in plasmas
52.25.Dg Plasma kinetic equations
52.55.Fa Tokamaks, spherical tokamaks
back to top Inertially Confined Plasmas, Dense Plasmas, Equations of State

Absolutely calibrated, time-resolved measurements of soft x rays using transmission grating spectrometers at the Nike Laser Facility

J. L. Weaver, U. Feldman, J. F. Seely, G. Holland, V. Serlin, M. Klapisch, D. Columbant, and A. Mostovych

Phys. Plasmas 8, 5230 (2001); http://dx.doi.org/10.1063/1.1412862 (9 pages) | Cited 8 times

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Accurate simulation of pellet implosions for direct drive inertial confinement fusion requires benchmarking the codes with experimental data. The Naval Research Laboratory (NRL) has begun to measure the absolute intensity of radiation from laser irradiated targets to provide critical information for the radiatively preheated pellet designs developed by the Nike laser group. Two main diagnostics for this effort are two spectrometers incorporating three detection systems. While both spectrometers use 2500 lines/mm transmission gratings, one instrument is coupled to a soft x-ray streak camera and the other is coupled to both an absolutely calibrated Si photodiode array and a charge coupled device (CCD) camera. Absolute calibration of spectrometer components has been undertaken at the National Synchrotron Light Source at Brookhaven National Laboratories. Currently, the system has been used to measure the spatially integrated soft x-ray flux as a function of target material, laser power, and laser spot size. A comparison between measured and calculated flux for Au and CH targets shows reasonable agreement to one-dimensional modeling for two laser power densities. © 2001 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
52.70.La X-ray and γ-ray measurements

Polarization induced modification of thermal radiative properties of solid density plasmas produced by subpicosecond laser

F. Dorchies, P. Forget, P. Gallant, Z. Jiang, J. C. Kieffer, H. Pépin, and O. Peyrusse

Phys. Plasmas 8, 5239 (2001); http://dx.doi.org/10.1063/1.1415749 (5 pages) | Cited 4 times

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Near solid density plasmas have been obtained by the interaction of ultraintense (2×1018 W cm−2) clean laser pulses with targets composed of different thickness of Al on a Si substrate. The depth of the x-ray emission and spectral shapes were measured using x-ray spectroscopy, which simultaneously characterized the emitting plasma and the suprathermal electron distribution. Strong modifications of the plasmas thermal radiative properties have been observed, for the first time, by changing the laser polarization from S to P. This correlates with an increase of suprathermal electrons production. © 2001 American Institute of Physics.
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52.25.Kn Thermodynamics of plasmas
52.70.-m Plasma diagnostic techniques and instrumentation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Quantum-mechanical dielectric model of the electron–ion collision frequency in strong laser fields

H.-J. Kull and L. Plagne

Phys. Plasmas 8, 5244 (2001); http://dx.doi.org/10.1063/1.1416182 (13 pages) | Cited 24 times

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The electron–ion collision frequency in a strong laser field is calculated in the framework of the quantum Vlasov theory in first-order Born approximation. Using a Wigner representation of the density matrix, the collision frequency can be expressed in terms of the Lindhard dielectric function and a close correspondence between classical and quantum-mechanical approaches can be obtained. Asymptotic formulas for the high-frequency collision frequency in weak and strong electric fields are obtained and compared with complete numerical calculations. The basic strong-field behavior can be explained in terms of the cold plasma model. © 2001 American Institute of Physics.
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52.65.Ff Fokker-Planck and Vlasov equation
52.25.Mq Dielectric properties
52.25.Fi Transport properties
52.20.-j Elementary processes in plasmas

Hot-spot dynamics and deceleration-phase Rayleigh–Taylor instability of imploding inertial confinement fusion capsules

R. Betti, M. Umansky, V. Lobatchev, V. N. Goncharov, and R. L. McCrory

Phys. Plasmas 8, 5257 (2001); http://dx.doi.org/10.1063/1.1412006 (11 pages) | Cited 19 times

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A model for the deceleration phase of imploding inertial confinement fusion capsules is derived by solving the conservation equations for the hot spot. It is found that heat flux leaving the hot spot goes back in the form of internal energy and pdV work of the material ablated off the inner shell surface. Though the hot-spot temperature is reduced by the heat conduction losses, the hot-spot density increases due to the ablated material in such a way that the hot-spot pressure is approximately independent of heat conduction. For direct-drive National Ignition Facility-like capsules, the ablation velocity off the shell inner surface is of the order of tens μm/ns, the deceleration of the order of thousands μm/ns2, and the density-gradient scale length of the order a few μm. Using the well-established theory of the ablative Rayleigh–Taylor instability, it is shown that the growth rates of the deceleration phase instability are significantly reduced by the finite ablative flow and the unstable spectrum exhibits a cutoff for mode numbers of about l ≈ 90. © 2001 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.)
52.38.-r Laser-plasma interactions
47.20.-k Flow instabilities
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