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Aug 1998

Volume 5, Issue 8, pp. 2827-3069

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Dynamics of laser produced shocks in foam–solid targets

Alessandra Benuzzi, Michel Koenig, Jyothi Krishnan, Bernard Faral, Wigen Nazarov, Mauro Temporal, Dimitri Batani, Laura Müller, Flavia Torsiello, Tom Hall, and Nicolas Grandjouan

Phys. Plasmas 5, 2827 (1998); http://dx.doi.org/10.1063/1.873031 (3 pages) | Cited 4 times

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The influence of foams on laser shocks was studied with ns laser pulses smoothed with phase zone plates and focused onto layered foam–aluminum targets. Foams of 5–200 mg/cm3 density and 60 μm thickness were used. A strong pressure increase was measured with the foam in comparison to focusing the beam directly onto aluminum due to impedance mismatch at the aluminum–foam interface. Below a particular density, the measured pressure decreased as a result of hydrodynamics effects. Results are compared with computer simulations. © 1998 American Institute of Physics.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
82.70.Rr Aerosols and foams
52.25.Kn Thermodynamics of plasmas
52.35.Tc Shock waves and discontinuities
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Fast heat pulse propagation in hot plasmas

Enzo Lazzaro and Hans Wilhelmsson

Phys. Plasmas 5, 2830 (1998); http://dx.doi.org/10.1063/1.873002 (6 pages) | Cited 6 times

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It is found that traveling wave solutions of the diffusion equation can have propagation times, related to the scale length of the perturbation, which can be considerably less than the characteristic diffusion times. This provides a possible model for the interpretation of recent experiments of fast “hot” and “cold” pulses in magnetically confined plasmas. © 1998 American Institute of Physics.
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52.25.Fi Transport properties
52.25.Kn Thermodynamics of plasmas

Heat flux driven ion turbulence

X. Garbet and R. E. Waltz

Phys. Plasmas 5, 2836 (1998); http://dx.doi.org/10.1063/1.873003 (10 pages) | Cited 71 times

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This work is an analysis of an ion turbulence in a tokamak in the case where the thermal flux is fixed and the temperature profile is allowed to fluctuate. The system exhibits some features of self-organized critical systems. In particular, avalanches are observed. Also the frequency spectrum of the thermal flux exhibits a structure similar to the one of a sand pile automaton, including a 1/f behavior. However, the time average temperature profile is found to be supercritical, i.e., the temperature gradient stays above the critical value. Moreover, the heat diffusivity is not the same for a turbulence calculated at fixed flux than at fixed temperature gradient, with the same time averaged temperature. More precisely the diffusivity at fixed temperature is found to be larger in the edge and smaller close to the heat source. © 1998 American Institute of Physics.
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52.35.Ra Plasma turbulence
52.25.Fi Transport properties
52.25.Kn Thermodynamics of plasmas
05.50.+q Lattice theory and statistics (Ising, Potts, etc.)
52.55.Fa Tokamaks, spherical tokamaks

Modulational instability of random phase plasmons in collisional plasmas

P. K. Shukla, L. Stenflo, and R. T. Faria

Phys. Plasmas 5, 2846 (1998); http://dx.doi.org/10.1063/1.873004 (3 pages) | Cited 1 time

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The modulational instability of random phase Langmuir waves in an unmagnetized collisional plasma is investigated. The growth rate of the instability is presented in several interesting limiting cases. The relevance of this investigation to space and laboratory plasmas is pointed out. © 1998 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.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.20.-j Elementary processes in plasmas

Forced magnetic field line reconnection in electron magnetohydrodynamics

K. Avinash, S. V. Bulanov, T. Esirkepov, P. Kaw, F. Pegoraro, P. V. Sasorov, and A. Sen

Phys. Plasmas 5, 2849 (1998); http://dx.doi.org/10.1063/1.873005 (12 pages) | Cited 31 times

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The forced reconnection of magnetic field lines within the framework of electron magnetohydrodynamics (EMHD) has been investigated. A broad class of solutions that describe stationary reconnection have been found. The time evolution of the plasma and of the magnetic field when perturbations are imposed from the boundary of a high conductivity plasma slab are also studied. The initial magnetic field has a null surface. Following this discussion, the so-called Taylor’s problem for EMHD in which the perturbations cause a change in the topology of the magnetic field has been solved. The plasma and the magnetic field are seen to evolve with the time scale of the linear tearing mode. Their time evolution is described by exponential dependences. Analytic and numerical simulation results of the nonlinear regime of forced magnetic reconnection in EMHD are also presented. Finally, the above results are compared with a case where the reconnection is mediated by dissipative electron viscosity effects. © 1998 American Institute of Physics.
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52.65.Kj Magnetohydrodynamic and fluid equation
52.65.-y Plasma simulation
51.20.+d Viscosity, diffusion, and thermal conductivity
52.30.-q Plasma dynamics and flow

Sudden transition to chaos in plasma wave interactions

O. López-Rebollal, J. R. Sanmartín, and E. del Río

Phys. Plasmas 5, 2861 (1998); http://dx.doi.org/10.1063/1.873006 (7 pages) | Cited 4 times

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The coherent three-wave interaction, with linear growth in the higher frequency wave and damping in the two other waves, is reconsidered; for equal dampings, the resulting three-dimensional (3-D) flow of a relative phase and just two amplitudes behaved chaotically, no matter how small the growth of the unstable wave. The general case of different dampings is studied here to test whether, and how, that hard scenario for chaos is preserved in passing from 3-D to four-dimensional flows. It is found that the wave with higher damping is partially slaved to the other damped wave; this retains a feature of the original problem (an invariant surface that meets an unstable fixed point, at zero growth rate) that gave rise to the chaotic attractor and determined its structure, and suggests that the sudden transition to chaos should appear in more complex wave interactions. © 1998 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.)
05.45.-a Nonlinear dynamics and chaos
52.30.-q Plasma dynamics and flow

Shock formation in a negative ion plasma

Q-Z. Luo, N. D’Angelo, and R. L. Merlino

Phys. Plasmas 5, 2868 (1998); http://dx.doi.org/10.1063/1.873007 (3 pages) | Cited 24 times

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An experimental investigation of the effect of negative ions on shock formation in a (collisional) Q machine plasma is described. Shock formation was observed only when the ratio of the negative ion to positive ion density, ϵ, exceeded about 0.9. © 1998 American Institute of Physics.
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52.35.Tc Shock waves and discontinuities
52.75.-d Plasma devices
52.25.Kn Thermodynamics of plasmas
52.70.-m Plasma diagnostic techniques and instrumentation

Quasilinear damping of ion Bernstein waves on the harmonic resonant layer

A. Cardinali, C. Castaldo, R. Cesario, and F. De Marco

Phys. Plasmas 5, 2871 (1998); http://dx.doi.org/10.1063/1.873008 (7 pages) | Cited 4 times

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The damping of an ion Bernstein wave (IBW) across a resonant layer of the minority species of the plasma is calculated within the framework of quasilinear theory. The model uses the analytical solution of the one-dimensional Fokker–Planck equation for the ion distribution function. A greater reduction of the damping has been found in this case compared with the one obtained with the linear model. This allows the wave to penetrate further towards the plasma core. In addition, a particle flux induced by the sharp spatial gradient of the distribution function across the resonant layer, due to the IBW field, has also been evaluated. This shows that modification of the distribution function generates a flux of particles from the outside which tends to increase the particle density in the vicinity of the resonance itself. © 1998 American Institute of Physics.
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52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.25.Kn Thermodynamics of plasmas

Mode transition and nonlinear self-oscillations in the beam-driven collisional discharge plasma

Hae June Lee and Jae Koo Lee

Phys. Plasmas 5, 2878 (1998); http://dx.doi.org/10.1063/1.873009 (7 pages) | Cited 9 times

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Nonlinear dynamics and self-oscillations in a dc beam-driven collisional discharge are investigated with particle-in-cell simulation and theoretical estimation. Three different modes, anode-glow, temperature-limited, and double-layer modes, are observed in the system. A theory for the critical voltage of mode transition between temperature-limited and anode-glow modes is in good agreement with the simulation results. The mechanism of low frequency self-oscillation in the double layer mode is examined along with period-doubling and chaotic oscillations. © 1998 American Institute of Physics.
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52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.40.Mj Particle beam interactions in plasmas
52.65.Rr Particle-in-cell method
52.80.-s Electric discharges

New mechanisms of minority ion cyclotron current drive

J. Carlsson, T. Hellsten, and J. Hedin

Phys. Plasmas 5, 2885 (1998); http://dx.doi.org/10.1063/1.873010 (8 pages) | Cited 16 times

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Minority ion cyclotron current drive is studied by solving the Fokker–Planck equation in toroidal geometry keeping the ∂/∂v∥-term in the quasilinear operator, hereby including the important effects of the finite orbit widths of the tail ions and the wave-induced spatial drift and diffusion. It has previously been found that the trapped ion current and the current carried by passing ions detrapped by wave-induced v⊥-diffusion are the two dominating contributions for high levels of coupled power. In this study yet another current-drive mechanism is presented, asymmetric detrapping by inward wave-induced radial drift, which occurs for negative k∥ and is strongest for on-axis resonance where it is the totally dominating effect for high powers. © 1998 American Institute of Physics.
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52.25.Fi Transport properties
02.30.-f Function theory, analysis

An influence of frozen-in law violation effects on the turbulent equipartition in tokamaks

Igor A. Ivonin, Vladimir P. Pavlenko, and Hans Persson

Phys. Plasmas 5, 2893 (1998); http://dx.doi.org/10.1063/1.873011 (9 pages) | Cited 1 time

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Analytical investigations and numerical simulations of the influence of frozen-in law violation effects on the turbulent equipartition (TEP) of plasma density n ∼ 1/q through the safety factor q in tokamaks are performed. Namely, the changes of the frozen-in field topology are taken into account due to strong turbulence. The found influence leads to flatter than 1/q density and temperature profiles. For a moderate level of turbulence, another reason for flat equipartition profiles was found analytically, if turbulent mixing of passing electrons takes place. This possibility arises due to conservation of the helicity (AB) integral over frozen-in field lines and produces a flat TEP density profile n ∼ AB of passing electrons (A is the vector potential of the magnetic field B). These influences have been tested in numerical experiments and the results were compared with experimental data in tokamaks. So, the numerical scaling of combined TEP profile of both trapped and passing electrons is n ∼ 1/q0.5–0.6, which is in good agreement with the experiments. © 1998 American Institute of Physics.
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52.35.Ra Plasma turbulence
52.65.-y Plasma simulation
52.25.Kn Thermodynamics of plasmas
52.55.Fa Tokamaks, spherical tokamaks

Statistical analysis of turbulent-transport suppression based on the magnetohydrodynamic approximation with electric-field effects incorporated

Akira Yoshizawa and Nobumitsu Yokoi

Phys. Plasmas 5, 2902 (1998); http://dx.doi.org/10.1063/1.873012 (10 pages) | Cited 3 times

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Suppression mechanism of turbulent thermal-energy transport is studied using the statistical method based on an extended magnetohydrodynamic (MHD) approximation. The one-fluid MHD system of equations is supplemented with effects of electric fields coming from the inhomogeneity of charge density. A Markovianized two-scale method is applied to the resulting system, and the turbulent transport rate of thermal energy is examined. In cylindrical geometry, the transport is shown to be suppressed through the combined effects of the radial electric field and the charge nonuniformity arising from its curvature. This finding is discussed in light of the formation of transport barriers observed in tokamak’s high-confinement modes and is confirmed to be consistent with observational results. © 1998 American Institute of Physics.
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52.25.Fi Transport properties
52.35.Ra Plasma turbulence
52.55.Fa Tokamaks, spherical tokamaks
52.65.Kj Magnetohydrodynamic and fluid equation
02.50.Ga Markov processes
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

A computational investigation of divertor plasma scaling laws

D. A. Knoll, Peter J. Catto, and S. I. Krasheninnikov

Phys. Plasmas 5, 2912 (1998); http://dx.doi.org/10.1063/1.873013 (9 pages)

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Usually, tokamak core scaling laws are written in terms of dimensionless geometrical quantities and parameters corresponding to Coulomb collisionality, gyro-motion, and plasma beta. However, Lackner [K. Lackner, Comments Plasma Phys. Controlled Fusion 15, 359 (1994)] observed that the temperature profiles also must be the same to obtain the same atomic physics in the divertor region of similar discharges. He obtained a scaling indicating that none of the present tokamaks could be made similar to the International Thermonuclear Experimental Reactor (ITER) [G. Janeschitz et al., J. Nucl. Mater. 220–222, 73 (1995)], but implicitly retained only two body interactions. Subsequent work [P. J. Catto et al., Phys. Plasmas 3, 3191 (1996)] demonstrated that non-two-body effects (multistep radiation, excitation, and ionization processes as well as three body recombination) cannot be ignored for plasma densities above 1019 m−3; the regime in which the ITER divertor must operate. In this reactor relevant regime, scaling law information must be obtained experimentally and by complex numerical simulations. To retain and quantify non-two-body effects on scaling laws we employ numerical simulations from a two dimensional box geometry version of the UEDGE code [D. A. Knoll et al., Phys. Plasmas 3, 293 (1996)] which includes a coupled plasma and neutral fluid description retaining non-two-body effects. Results are presented from a numerical investigation into the upstream parallel heat flux divided by upstream pressure scaling, as well as collisionality scaling, of the tokamak divertor target heat flux and ion saturation current. © 1998 American Institute of Physics.
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28.52.Av Theory, design, and computerized simulation
52.40.Hf Plasma-material interactions; boundary layer effects
52.55.Fa Tokamaks, spherical tokamaks
52.55.Pi Fusion products effects (e.g., alpha-particles, etc.), fast particle effects

Toroidally localized and nonlocalized ballooning instabilities in a stellarator

P. Cuthbert, J. L. V. Lewandowski, H. J. Gardner, M. Persson, D. B. Singleton, R. L. Dewar, N. Nakajima, and W. A. Cooper

Phys. Plasmas 5, 2921 (1998); http://dx.doi.org/10.1063/1.873014 (11 pages) | Cited 14 times

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It is shown that the coexistence of toroidally nonlocalized ideal-hydromagnetic ballooning instabilities, with a quasidiscrete spectrum, and toroidally localized ballooning instabilities with a broad continuous spectrum, as predicted by Dewar and Glasser [Phys. Fluids 26, 3038 (1983)] can be realized in a Mercier-unstable equilibrium case modeling the Large Helical Device (LHD) [A. Iiyoshi et al., Fusion Technol. 17, 148 (1990)] with a broad pressure profile. The quasidiscrete, interchange branch corresponds to extended modes that can be understood on the basis of a ripple-averaged ballooning equation, whereas the broad-continuum, ballooning branch corresponds to modes localized along a flux tube. The physical origin of the two branches is discussed. © 1998 American Institute of Physics.
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52.55.Jd Magnetic mirrors, gas dynamic traps
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.30.-q Plasma dynamics and flow
52.65.Kj Magnetohydrodynamic and fluid equation

Enhanced transport via Kirchhoff radiation

Satish Puri

Phys. Plasmas 5, 2932 (1998); http://dx.doi.org/10.1063/1.873015 (4 pages) | Cited 1 time

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Momentum transfer via Kirchhoff radiation of electrostatic electron and ion-cyclotron-harmonic waves contributes an enhanced collisionality far in excess of that given by the Fokker-Planck term in the existing neoclassical models. The resultant particle and thermal transport resembles the observed anomalous transport in ohmically heated toroidal plasmas. © 1998 American Institute of Physics.
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52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.25.Fi Transport properties
52.55.Fa Tokamaks, spherical tokamaks
52.55.Jd Magnetic mirrors, gas dynamic traps

Density profile consistency and its relation to the transport of trapped versus passing electrons in tokamaks

D. R. Baker and M. N. Rosenbluth

Phys. Plasmas 5, 2936 (1998); http://dx.doi.org/10.1063/1.873016 (6 pages) | Cited 74 times

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A formal expression for the canonical steady-state density profile in a tokamak can be obtained from the Fokker–Planck-type diffusion equation derived from the Vlasov equation in the limit of anomalous diffusion due to strong turbulence. Here we derive an explicit expression for this canonical profile for a tokamak with arbitrary cross section and aspect ratio. The resulting profile is independent of the spatial dependence of the diffusion coefficient, but does depend on the relative diffusion of trapped versus passing particles. Under conditions where only the trapped particles transport due to interactions with the turbulence the profiles are considerably flatter than if both the trapped and passing transport the same. The steepness of the calculated profile depends on the ratio of the diffusion coefficients for passing and trapped particles. The calculated profiles are compared with measured profiles from the tokamak known as DIII-D [J. L. Luxon et al., Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159]. Density profiles for a typical International Thermonuclear Experimental Reactor (ITER) [R. Aymar, Fusion Eng. Design 24, 977 (1984)] plasma are also derived. © 1998 American Institute of Physics.
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52.25.Kn Thermodynamics of plasmas
52.70.-m Plasma diagnostic techniques and instrumentation
52.35.Ra Plasma turbulence
52.25.Fi Transport properties

Locking of multiple resonant mode structures in the reversed-field pinch

A. K. Hansen, A. F. Almagri, D. J. Den Hartog, S. C. Prager, and J. S. Sarff

Phys. Plasmas 5, 2942 (1998); http://dx.doi.org/10.1063/1.873017 (5 pages) | Cited 13 times

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Locking of a rotating mode by applying a resonant magnetic perturbation having the same helicity has been observed on various devices. Experiments have been carried out on the Madison Symmetric Torus reversed-field pinch (RFP) [Dexter et al., Fusion Technol. 19, 131 (1991)] which show that an externally applied magnetic perturbation can cause locking of the dominant magnetic modes (poloidal mode number m = 1, toroidal mode numbers n = 5–10) when the perturbation is resonant with them. A perturbation which is not resonant (m = 0 or 2) produces no such effect. Thus, resonant torques may lock a stochastic magnetic structure arising from several modes, as likely exists in the RFP, as well as a distinct island as exists in tokamaks, although the details of the interaction are likely to be different. © 1998 American Institute of Physics.
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52.55.Ez Theta pinch
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Jd Magnetic mirrors, gas dynamic traps
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Linear and nonlinear dispersive Alfvén waves in two-ion plasmas

R. T. Faria, Arshad M. Mirza, P. K. Shukla, and O. A. Pokhotelov

Phys. Plasmas 5, 2947 (1998); http://dx.doi.org/10.1063/1.873018 (5 pages) | Cited 3 times

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A set of coupled nonlinear equations for dispersive Alfvén waves (DAWs) in nonuniform magnetoplasmas with two-ion species is derived by employing a multifluid model. The DAW frequency is assumed to lie between the gyrofrequencies of the light and heavy ion impurities. In the linear limit, a local dispersion relation (LDR) is derived and analyzed. The LDR admits a new type of DAW in two-ion plasmas. Furthermore, it is found that stationary solutions of the nonlinear mode coupling equations in two-ion plasmas can be represented in the form of different types of coherent vortex structures. The relevance of our investigation to space and laboratory plasmas is pointed out. © 1998 American Institute of Physics.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
02.10.-v Logic, set theory, and algebra

Prediction of Alfvén eigenmode dampings in the Joint European Torus

A. Jaun, A. Fasoli, and W. W. Heidbrink

Phys. Plasmas 5, 2952 (1998); http://dx.doi.org/10.1063/1.873019 (4 pages) | Cited 25 times

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Predictions from a gyrokinetic toroidal plasma model reproduce for the first time the evolution of Alfvén eigenmode (AE) dampings over a range of discharges. The coupling between shear-and kinetic-Alfvén waves is responsible for the main source of damping through Landau interactions and can be an order of magnitude larger than fluid predictions neglecting global kinetic effects. Strong stabilization occurs when the wave field gets localized radially by a rise in the edge magnetic shear, explaining why global AEs have never been detected in the Joint European Torus [Rebut, Bickerton, and Keen, Nucl. Fusion 25, 1011 (1985)] in the presence of an X point and suggesting how global Alfvén instabilities could be avoided in future reactors. © 1998 American Institute of Physics.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.55.Jd Magnetic mirrors, gas dynamic traps
52.25.Dg Plasma kinetic equations
52.55.Fa Tokamaks, spherical tokamaks

Feedback control of multimode magnetohydrodynamic instabilities via neutral beams

A. K. Sen

Phys. Plasmas 5, 2956 (1998); http://dx.doi.org/10.1063/1.873020 (7 pages) | Cited 5 times

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In most scenarios of confinement degradation due to MHD (magnetohydrodynamic) fluctuations in both tokamaks and reversed field pinches several MHD modes are involved. This is the motivation for the development of a multimode feedback scheme in the present paper, in contrast to the past work. The scheme is based on modal (state) feedback, where each mode is unscrambled out of the sensor signal, which is a superposition of all mode information and then individually acted upon by a unique gain and phase. Finally, all these individually processed mode signals are electronically summed and impressed on the accelerator grid of a neutral beam as a single control signal. It is shown that this process can lead to the stabilization of all unstable modes without destabilization of any stable modes, in contrast to previous feedback experiments. © 1998 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.)
52.30.-q Plasma dynamics and flow
52.25.Gj Fluctuation and chaos phenomena
52.40.Mj Particle beam interactions in plasmas
52.55.Fa Tokamaks, spherical tokamaks
52.55.Ez Theta pinch

Theory of resonance influence of sawtooth crashes on ions with large orbit width

Ya. I. Kolesnichenko, V. V. Lutsenko, R. B. White, and Yu. V. Yakovenko

Phys. Plasmas 5, 2963 (1998); http://dx.doi.org/10.1063/1.873021 (14 pages) | Cited 9 times

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The role of resonances in the sawtooth-crash-induced redistribution of fast ions is investigated. In particular, the conditions of wave-particle resonant interaction in the presence of the equilibrium electric field and the mode rotation are obtained, and effects of sawteeth on the resonant particles with arbitrary width of nonperturbed orbits are studied. It is found that resonances play the dominant role in the transport of ions having sufficiently high energy. It is shown that the resonance regions may overlap, in which case the resonant particles may constitute the main fraction of the fast ion population in the sawtooth mixing region. The behavior of the resonant particles is studied both by constructing a Poincaré map and analytically, by means of the adiabatic invariant derived in this paper and calculation of the characteristic frequencies of the particle motion. © 1998 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.)

A unified self-consistent model for calculating ion stopping power in ICF plasma

P. Wang, T. M. Mehlhorn, and J. J. MacFarlane

Phys. Plasmas 5, 2977 (1998); http://dx.doi.org/10.1063/1.873022 (11 pages) | Cited 7 times

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A new unified self-consistent ion stopping power model for use in ion-driven inertial confinement fusion (ICF) target design has been developed. This model includes sophisticated treatments for electron density distribution of an atom in plasmas and a full random phase approximation stopping function that extrapolates the zero temperature Lindhard stopping function to arbitrary temperatures. It is shown that this model provides accurate ion stopping power for cold materials, including both low-Z and high-Z elements. For finite temperature plasmas, the model accounts for the stopping effects due to electrons in ground states, excited states, resonance states, and continuum states in a self-consistent manner. There is no separation treatment for “bound” and “free” electrons. Hence, the model enables the calculations of ion stopping power to be made within a single model for a wide range of beam and target conditions relevant to ICF studies. © 1998 American Institute of Physics.
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52.58.Ei Light-ion inertial confinement
52.58.Hm Heavy-ion inertial confinement
28.52.Av Theory, design, and computerized simulation
52.20.-j Elementary processes in plasmas

Simulation of instability growth rates on the front and back of laser accelerated planar targets

S. A. Bel’kov, L. S. Mkhitarian, O. A. Vinokurov, G. G. Kochemasov, S. V. Bondarenko, D. C. Wilson, and N. M. Hoffman

Phys. Plasmas 5, 2988 (1998); http://dx.doi.org/10.1063/1.873023 (9 pages) | Cited 6 times

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The ability of an inertial confinement fusion target to achieve ignition and burn depends critically upon controlling the growth of hydrodynamic perturbations originating on the outer ablator surface and the inner deuterium–tritium (DT) ice. The MIMOZA-ND code [Sofronov et al., Voprosy Atomnoy Nauki i Tehniki 2, 3 (1990)] was used to model perturbation growth on both sides of carbon foils irradiated by 0.35 μm light at 1015 W/cm2. When an initial perturbation was applied to a laser irradiated surface, the computational instability growth rates agreed well with the existing theoretical estimates. Perturbations applied to the rear side of the target for wavelengths that are large compared to the thickness (d/Λ≪1) behave similarly to the perturbations at the ablation front. For d/Λ ≥ 1, the shorter the wave length is, the faster the decrease of the growth rate of the amplitudes at the interface (and the mass flows) as compared to the perturbations at the ablation front. This is due to the Richtmyer–Meshkov instability-induced transverse velocity component. The time of Rayleigh–Taylor instability transition to the nonlinear phase depends on the initial amplitude and is well modeled by an infinitely thin shell approximation. The transverse velocity generated by the Richtmyer–Meshkov instability causes the interaction of Λ = 10 μm and Λ = 2 μm wavelength modes to differ qualitatively when the perturbations are applied to the ablation front or to the rear side of target. © 1998 American Institute of Physics.
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28.52.Cx Fueling, heating and ignition
42.62.-b Laser applications
52.58.Ei Light-ion inertial confinement
52.58.Hm Heavy-ion inertial confinement
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.65.-y Plasma simulation

Numerical simulations of annular wire-array z-pinches in (x,y), (r,θ), and (r,z) geometries

B. M. Marder, T. W. L. Sanford, and G. O. Allshouse

Phys. Plasmas 5, 2997 (1998); http://dx.doi.org/10.1063/1.873024 (9 pages) | Cited 12 times

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The Total Immersion Particle [B. M. Marder, Math. Comput. 29, 434 (1973)] code has been used in several two-dimensional geometries to understand better the measured dynamics of annular, aluminum wire-array z-pinches. The areas investigated include the formation of the plasma sheath from current-induced individual wire explosions, the effects of wire number and symmetry on the implosion dynamics, and the dependence of the Rayleigh–Taylor instability growth on initial sheath thickness. A qualitative change in the dynamics with increasing wire number was observed, corresponding to a transition between a z-pinch composed of nonmerging, self-pinching individual wires, and one characterized by the rapid formation and subsequent implosion of a continuous plasma sheath. A sharp increase in radiated power with increasing wire number has been observed experimentally near this calculated transition. Although two-dimensional codes have correctly simulated observed power pulse durations, there are indications that three-dimensional effects are important in understanding the actual mechanism by which these pulse lengths are produced. © 1998 American Institute of Physics.
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52.55.Ez Theta pinch
52.65.-y Plasma simulation
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.40.Hf Plasma-material interactions; boundary layer effects

Magnetohydrodynamic turbulence and enhanced atomic processes in astrophysical plasmas

Steven R. Spangler

Phys. Plasmas 5, 3006 (1998); http://dx.doi.org/10.1063/1.873025 (15 pages) | Cited 3 times

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This article discusses a way in which enhanced atomic physics processes, including radiative energy losses, may occur in an astrophysical plasma containing magnetohydrodynamic turbulence. Two-dimensional (2D) magnetohydrodynamics (MHD) is adopted as a model. A major characteristic feature of 2D MHD turbulence is the development of strong current sheets on a dynamical time scale L/V0 where L is the spatial scale of the turbulent fluid and V0 is the scale of the velocity fluctuations. The current contained in the sheets will be carried by an electron drift relative to the ions. The case of a plasma containing minority atoms or ions with an excited state accessible to collisions from the tail of the electron distribution is considered. In the current carrying sheets or filaments, the electron distribution function will be perturbed such that collisional excitations will be enhanced relative to the current-free plasma. Subsequent radiative de-excitation of the atoms or ions removes energy from the turbulence. Expressions are presented for the electron drift velocity arising in 2D turbulence, the enhancement of collisional excitations of a trace atom or ion, and the energy lost to the plasma turbulence by radiative de-excitation of these atoms or ions. The mechanism would be most pronounced in plasmas for which the magnitude of the magnetic field is large, the outer scale of the turbulence is small, and the electron density and temperature are low. A brief discussion of the relevance of this mechanism to some specific astrophysical plasmas is given. © 1998 American Institute of Physics.
Show PACS
52.30.-q Plasma dynamics and flow
52.65.Kj Magnetohydrodynamic and fluid equation
52.35.Ra Plasma turbulence
95.30.Qd Magnetohydrodynamics and plasmas
52.25.Gj Fluctuation and chaos phenomena
52.20.-j Elementary processes in plasmas
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