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Apr 1999

Volume 6, Issue 4, pp. 1043-1385

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Stimulated Raman and Brillouin scattering of polarization-smoothed and temporally smoothed laser beams

R. L. Berger, E. Lefebvre, A. B. Langdon, J. E. Rothenberg, C. H. Still, and E. A. Williams

Phys. Plasmas 6, 1043 (1999); http://dx.doi.org/10.1063/1.873713 (5 pages) | Cited 17 times

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Control of filamentation and stimulated Raman and Brillouin scattering is shown to be possible by use of both spatial and temporal smoothing schemes. The spatial smoothing is accomplished by the use of phase plates [Y. Kato and K. Mima, Appl. Phys. 329, 186 (1982)] and polarization smoothing [Lefebvre et al., Phys. Plasmas 5, 2701 (1998)] in which the plasma is irradiated with two orthogonally polarized, uncorrelated speckle patterns. The temporal smoothing considered here is smoothing by spectral dispersion [Skupsky et al., J. Appl. Phys. 66, 3456 (1989)] in which the speckle pattern changes on the laser coherence time scale. At the high instability gains relevant to laser fusion experiments, the effect of smoothing must include the competition among all three instabilities. © 1999 American Institute of Physics.
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52.38.-r Laser-plasma interactions
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.57.-z Laser inertial confinement
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back to top Basic Plasma Phenomena, Waves, Instabilities

Temporal evolution of dust grain-charge in a plasma

H. Yamaguchi and Y.-N. Nejoh

Phys. Plasmas 6, 1048 (1999); http://dx.doi.org/10.1063/1.873351 (4 pages) | Cited 7 times

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Temporal and spatial evolution of the dust-charge in a low temperature plasma is demonstrated by numerical calculation. It is shown that the dust-charge number at the steady state obtained by the present calculation is in good agreement with that derived from an experiment of a direct current glow discharge. By changing the conditions, such as plasma and dust densities and ion and electron temperatures, their effects on the dust-charge are clarified by the present model. These are useful results for understanding the charging process of micron-sized dust grains in plasmas. © 1999 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.80.Hc Glow; corona
52.25.-b Plasma properties

Propagation and damping of m=+1 and m=−1 helicon modes in an inhomogeneous plasma column

M. Krämer

Phys. Plasmas 6, 1052 (1999); http://dx.doi.org/10.1063/1.873352 (7 pages) | Cited 24 times

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The effect of the density gradient on the dispersion of the m=+1 and m=−1 helicon modes is investigated both theoretically as well as numerically. In particular, attention is focussed on the helicon wave damping that is closely related to the rf power absorption and the Poynting flux. It is shown that the propagation characteristics of the m=−1 mode changes drastically when the density gradient is sufficiently strong. This mode exhibits a cutoff that depends on the gradient scale length and the plasma parameters. In the regime where both helicon modes propagate, the excitation of the m=−1 mode is unlikely as it is strongly damped. The results give evidence that the density gradient effect is decisive for the formation of helicon discharges, which are predominantly sustained by the m=+1 mode. © 1999 American Institute of Physics.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
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.)
52.80.Pi High-frequency and RF discharges

Local approximation for the phase velocity transform

Nathan Mattor

Phys. Plasmas 6, 1059 (1999); http://dx.doi.org/10.1063/1.873353 (6 pages) | Cited 3 times

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A recent paper [N. Mattor, Phys. Plasmas 5, 1822 (1998)] introduced the phase velocity transform. This was used to derive closed fluid moment equations from a collisionless kinetic equation. Here, a local approximation for this transform is introduced, which allows much simpler calculation. A local approximation to the Hilbert transform is also given. © 1999 American Institute of Physics.
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52.25.Dg Plasma kinetic equations
02.30.Uu Integral transforms
02.30.Vv Operational calculus

Collisionless fluid equations: Lagrangian, Eulerian, and local forms

Nathan Mattor

Phys. Plasmas 6, 1065 (1999); http://dx.doi.org/10.1063/1.873381 (7 pages) | Cited 6 times

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A recent paper [N. Mattor, Phys. Plasmas 5, 1822 (1998)] derived closed fluid moment equations from a collisionless kinetic equation. These fluid equations retain the effects of linear and nonlinear wave-particle resonances, traditionally thought to require kinetic equations. This paper gives three methods to calculate this term. In the Lagrangian form, the components making up the closure term are constant along phase rays, and so can be traced from the initial time. The Eulerian form evolves the components on a constant spatial grid and so does not require explicit calculation of phase rays. The local approximation is a heuristic method of approximating global integrals based on local gradients, and offers significant simplification over the other two methods. © 1999 American Institute of Physics.
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52.25.Dg Plasma kinetic equations
05.20.Jj Statistical mechanics of classical fluids

Local transit-time damping of electrostatic wave packets

O. Skjæraasen, A. Melatos, P. A. Robinson, H. Pécseli, and J. Trulsen

Phys. Plasmas 6, 1072 (1999); http://dx.doi.org/10.1063/1.873354 (11 pages) | Cited 11 times

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The theory of local transit-time damping is generalized to coherent electrostatic wave packets with nonzero mean wave number in an unmagnetized plasma. A general analytic formula for the phase-averaged power dissipated locally within an arbitrary three-dimensional wave packet is derived to second order in the fields. This expression is evaluated explicitly for a representative one-dimensional field structure. The result agrees with independent numerical test-particle calculations to within numerical rounding errors for small to moderate field amplitudes, which justify the perturbation expansions. The resulting damping involves both Landau (resonant) and non-Landau (nonresonant) terms, the latter having been omitted in previous works. It is found that the dissipated power depends sensitively on the ratio of the particle velocity to the phase velocity of the packet, the ratio of the wavelength to the size of the packet, and the form of the particle distribution. In general, particles remove energy from some parts of the packet and deposit it in others, thus reshaping it. © 1999 American Institute of Physics.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Center manifold approach to the reduced magnetohydrodynamic bifurcations with diffusive magnetic field lines

M. Blüming, K. H. Spatschek, and R. Grauer

Phys. Plasmas 6, 1083 (1999); http://dx.doi.org/10.1063/1.873355 (10 pages)

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Bifurcations in plasmas are investigated on the basis of a reduced dissipative magnetohydrodynamic (MHD) model. In contrast to previous investigations, the diffusivity of magnetic field lines is taken into account. Making use of the center manifold theory for the first bifurcations, and Galerkin approximations for higher bifurcations, it is shown that the diffusion of magnetic field lines affects the transitions in the transients. When the mode which resembles the so-called high confinement mode becomes unstable via a Hopf bifurcation, the changes in the oscillation frequencies are calculated. It is demonstrated that over a wide range of parameter values the so called electrostatic approximation is quite good. The strength of the generated magnetic field fluctuations is calculated, and the influence of the latter on a possible magnetic braiding is estimated. © 1999 American Institute of Physics.
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05.45.-a Nonlinear dynamics and chaos
47.20.Ky Nonlinearity, bifurcation, and symmetry breaking
52.25.Gj Fluctuation and chaos phenomena
52.30.-q Plasma dynamics and flow
52.65.Kj Magnetohydrodynamic and fluid equation
back to top Nonlinear Phenomena, Turbulence, Transport

Kinetic theory of dusty plasmas. I. General approach

V. N. Tsytovich and U. de Angelis

Phys. Plasmas 6, 1093 (1999); http://dx.doi.org/10.1063/1.873356 (14 pages) | Cited 52 times

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The kinetic theory of dusty plasmas is formulated introducing the dust charge as an independent variable. The Bogoliubov–Klimontovich approach is generalized for the case where the discreetness of the dust grain distribution is described rigorously, while the electrons and ions are described by continuous kinetic equations which take into account their absorption on the highly charged dust grains. The theory is valid for dust densities larger than the critical value where the binary plasma particle collisions can be neglected with respect to the collisions with dust particles. This condition is fulfilled in most dust-plasma experiments and often in space plasmas. The discreetness in the dust distribution leads to both dust fluctuations and plasma particle fluctuations, the latter induced by the dust fluctuations. The dust charge fluctuations alter the interaction appreciably, leading to effective dust charges in interactions which depend on distance and deviate substantially from the equilibrium dust charges. New collision integrals describing the dust charge distribution and inelasticity of dust-plasma particle collisions are found and the problem of dust charging is formulated self-consistently. © 1999 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.25.Dg Plasma kinetic equations
52.20.-j Elementary processes in plasmas

Chaos in the parallel sheared plasma flow driven electromagnetic turbulence in nonuniform magnetoplasmas

Arshad M. Mirza, Tariq Rafiq, G. Murtaza, P. K. Shukla, and R. T. Faria

Phys. Plasmas 6, 1107 (1999); http://dx.doi.org/10.1063/1.873357 (6 pages) | Cited 1 time

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By employing the two-fluid model, a system of nonlinear equations for low-frequency electromagnetic waves in nonuniform collisional magnetoplasmas has been derived. The plasma contains both the equilibrium density gradient and sheared flows. In the linear limit, a local dispersion relation has been obtained and analyzed in several interesting limiting cases. It is found that equilibrium sheared plasma flows cause instabilities of Alfvén-type waves even in the absence of the density gradient. The numerical results also show a large growth rate of electromagnetic parallel velocity shear (PVS) mode compared to the electrostatic mode for some ionospheric parameters. For this case, the temporal nonlinear behavior of the relevant governing mode coupling equations is governed by six coupled equations, which are a generalization of the Lorenz–Stenflo equations and which admit chaotic trajectories. The results of this investigation should be useful for understanding the linear and nonlinear properties of electromagnetic waves that are generated by sheared plasma flows in magnetized plasmas.© 1999 American Institute of Physics.
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52.35.Ra Plasma turbulence
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.30.-q Plasma dynamics and flow
52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
back to top Magnetically Confined Plasmas, Heating, Confinement

Improved magnetohydrodynamic stability through optimization of higher order moments in cross-section shape of tokamaks

A. D. Turnbull, Y. R. Lin-Liu, R. L. Miller, T. S. Taylor, and T. N. Todd

Phys. Plasmas 6, 1113 (1999); http://dx.doi.org/10.1063/1.873380 (4 pages) | Cited 16 times

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Optimization of the higher order moments—specifically the squareness—of a tokamak cross-section can significantly enhance the stability to ideal magnetohydrodynamic ballooning and kink modes. At conventional aspect ratios, it is shown that access to the second regime of ballooning stability is facilitated by moderate squareness. In a low aspect ratio, fully bootstrap current driven spherical torus, optimization of the squareness results in an increase in β of the order of 10%, leading to a configuration stable to ballooning, axisymmetric, and ideal n ⩽ 5 kink modes at β ≃ 67%.© 1999 American Institute of Physics.
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52.30.-q Plasma dynamics and flow
52.65.Kj Magnetohydrodynamic and fluid equation
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.)
52.55.Fa Tokamaks, spherical tokamaks
52.55.Jd Magnetic mirrors, gas dynamic traps

Distributions of alpha particles escaping to the wall during sawtooth oscillations in the Tokamak Fusion Test Reactor

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

Phys. Plasmas 6, 1117 (1999); http://dx.doi.org/10.1063/1.873358 (14 pages) | Cited 6 times

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It has been observed experimentally in deuterium–tritium shots of the Tokamak Fusion Test Reactor (TFTR) [D. J. Grove and D. M. Meade, Nucl. Fusion 25, 1167 (1985)] that crashes of sawtooth oscillations may result in very inhomogeneous flux of alpha particles to the wall. To explain this phenomenon, both theoretical analysis and numerical simulation have been carried out. It is concluded that the “crash-induced prompt loss,” i.e., the orbital loss of marginally trapped particles arising because of the crash-induced orbit transformation of circulating particles, is responsible for the flux near the bottom of the vessel, whereas the crash-induced stochastic diffusion of moderately trapped particles explains the large signal near the equatorial plane of the torus. The calculated poloidal distributions of the integral alpha flux are in reasonable agreement with experimental data. The energy spectrum of the escaping particles has also been calculated, which can be used for diagnostics of the crash type. © 1999 American Institute of Physics.  
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52.25.Fi Transport properties
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.65.-y Plasma simulation
52.55.Fa Tokamaks, spherical tokamaks

A theoretical analysis on electrostatic lower-hybrid wave propagation in plasmas with magnetic ripple: Nonlinear oscillations, resonances, ray tracing, and spectral gap

João P. S. Bizarro, Jorge S. Ferreira, and Roland Nakach

Phys. Plasmas 6, 1131 (1999); http://dx.doi.org/10.1063/1.873600 (16 pages) | Cited 2 times

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See Also: Erratum

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The analytical expression for the frequency of the unperturbed radial electrostatic lower-hybrid (LH) ray oscillations is derived, which constitutes the first analytically calculable result in nonlinear LH ray dynamics. For LH current drive (CD) conditions, and after comparing the frequency of the unperturbed LH ray motion with the frequency of the ripple perturbation, it is concluded that the electrostatic LH ray dynamics is generally regular in cylindrical plasmas with magnetic ripple. It is also found analytically that including the magnetic ripple in ray-tracing calculations does not lead to a final closure of the spectral-gap problem for LHCD in circular-poloidal-cross-section tokamaks having sufficiently low electron density, in addition to a high enough aspect ratio and safety factor, in which case electrostatic LH wave propagation turns out to be independent of the latter, and the unperturbed LH ray oscillations become basically linear. This is an important null result that helps to show that the conventional ray-tracing picture widely used in LHCD modeling (that is to say, a standardly coupled LH spectrum propagating according to geometrical optics in an established tokamak equilibrium) is not to be taken as final. The analysis presented, carried out within an explicitly Hamiltonian formalism and addressing the role of resonances between the frequency of the unperturbed LH ray motion and the frequencies of the perturbations due to magnetic ripple and toroidicity, is detailed and careful, with analytical results and conclusions being supported by numerical calculations. © 1999 American Institute of Physics.
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52.50.Gj Plasma heating by particle beams
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
05.45.-a Nonlinear dynamics and chaos
42.15.Dp Wave fronts and ray tracing

What is the “beta-induced Alfvén eigenmode?”

W. W. Heidbrink, E. Ruskov, E. M. Carolipio, J. Fang, M. A. van Zeeland, and R. A. James

Phys. Plasmas 6, 1147 (1999); http://dx.doi.org/10.1063/1.873359 (15 pages) | Cited 34 times

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An instability with a lower frequency than the toroidicity-induced Alfvén eigenmode was initially identified as a beta-induced Alfvén eigenmode (BAE). Instabilities with the characteristic spectral features of this “BAE” are observed in a wide variety of tokamak plasmas, including plasmas with negative magnetic shear. These modes are destabilized by circulating beam ions and they transport circulating beam ions from the plasma core. The frequency scalings of these “BAEs” are compared to theoretical predictions for Alfvén modes, kinetic ballooning modes, ion thermal velocity modes, and energetic particle modes. None of these simple theories match the data. © 1999 American Institute of Physics.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
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.)
52.25.Fi Transport properties
52.55.Fa Tokamaks, spherical tokamaks

Drift mode growth rates and associated transport

Aaron J. Redd, Arnold H. Kritz, Glenn Bateman, Gregory Rewoldt, and W. M. Tang

Phys. Plasmas 6, 1162 (1999); http://dx.doi.org/10.1063/1.873360 (6 pages) | Cited 15 times

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Drift mode linear growth rates and quasilinear transport are investigated using the FULL kinetic stability code [Rewoldt et al., Phys. Plasmas 5, 1815 (1998)] and a version of the Weiland transport model [Strand et al., Nucl. Fusion 38, 545 (1998)]. It is shown that the drift mode growth rates (as well as the marginal stability temperature gradient) obtained using the FULL code are dependent on the accuracy of the equilibrium employed. In particular, when an approximate equilibrium model is utilized by the FULL code, the results can differ significantly from those obtained using a more accurate numerical equilibrium. Also investigated are the effects of including full electron physics. It is shown, using both the FULL code and the Weiland model, that the nonadiabatic (e.g., trapped) electron response produces a significant increase in the linear growth rate of the ion-temperature-gradient (ITG) driven branch of the drift instability. Other consequences of the nonadiabatic electron response include a reduction in the marginal temperature gradient for the onset of the ITG mode and an additional contribution to transport due to the excitation of the Trapped Electron Mode (TEM). Physical explanations are given for the sensitivity of the mode growth rates to the equilibrium and the nonadiabatic electron response. Finally, linear growth rates for the ITG mode computed using the FULL code are compared with growth rates obtained using the Weiland model. © 1999 American Institute of Physics.
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47.15.-x Laminar flows
47.60.-i Flow phenomena in quasi-one-dimensional systems
52.35.Kt Drift waves
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.25.Kn Thermodynamics of plasmas
52.65.-y Plasma simulation
52.25.Fi Transport properties
52.25.Dg Plasma kinetic equations

Formation and locking of the “slinky mode” in reversed-field pinches

Richard Fitzpatrick

Phys. Plasmas 6, 1168 (1999); http://dx.doi.org/10.1063/1.873361 (26 pages) | Cited 38 times

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The formation and breakup of the “slinky mode” in a Reversed-Field Pinch (RFP) is investigated analytically. The slinky mode is a toroidally localized, coherent interference pattern in the magnetic field, which corotates with the plasma at the reversal surface. This mode forms, via a series of bifurcations, as a result of the nonlinear coupling of multiple m = 1 core tearing modes. The slinky mode breaks up via a second series of bifurcations. However, the typical mode amplitude below which slinky breakup is triggered is much smaller than that above which slinky formation occurs. Analytic expressions for the slinky formation and breakup thresholds are obtained in all regimes of physical interest. The locking of the slinky mode to a static error field is also investigated analytically. Either the error field arrests the rotation of the plasma at the reversal surface before the formation of the slinky mode, so that the mode subsequently forms as a nonrotating mode, or the slinky mode forms as a rotating mode and subsequently locks to the error field. Analytic expressions for the locking and unlocking thresholds are obtained in all regimes of physical interest. © 1999 American Institute of Physics.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.55.Ez Theta pinch

Nonlinear coupling of rotating magnetic island triplets

R. M. Coelho, E. Lazzaro, M. F. Nave, and F. Serra

Phys. Plasmas 6, 1194 (1999); http://dx.doi.org/10.1063/1.873362 (9 pages) | Cited 8 times

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The role and mechanism of nonlinear coupling of finite size rotating magnetic islands in a tokamak are analyzed in a finite dimensional model obtained from the continuum Reduced Magnetohydrodynamic (RMHD) description of resistive tearing modes. General properties of the electrodynamic interaction of modes of different helicities are found and a phase space analysis of the effects of inertia and eddy currents in the tokamak wall is presented. The results obtained are relevant for the definition of strategies of feedback control of resistive instabilities and a possible help for the interpretation of tokamak performances linked to the onset of a spectrum of magnetic perturbations. © 1999 American Institute of Physics.
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52.30.-q Plasma dynamics and flow
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

Magnetic island deformation due to sheared flow and viscosity

C. Ren, M. S. Chu, and J. D. Callen

Phys. Plasmas 6, 1203 (1999); http://dx.doi.org/10.1063/1.873363 (5 pages) | Cited 13 times

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A partial differential equation for a two-dimensional magnetohydrodynamic (MHD) equilibrium with flow and viscosity is derived. The equation is used to describe the deformation of the magnetic island caused by the viscous drag of a sheared flow. The deformation is characterized by the phase gradient of the magnetic perturbation across a magnetic island. This phase gradient has been observed experimentally in electron cyclotron emission data from the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)]. © 1999 American Institute of Physics.
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52.30.-q Plasma dynamics and flow
02.30.Jr Partial differential equations
52.70.-m Plasma diagnostic techniques and instrumentation
52.55.Fa Tokamaks, spherical tokamaks

Stability of short wavelength tearing and twisting modes

F. L. Waelbroeck

Phys. Plasmas 6, 1208 (1999); http://dx.doi.org/10.1063/1.873364 (9 pages) | Cited 1 time

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The stability and mutual interaction of tearing and twisting modes in a torus is governed by matrices that generalize the well-known Δ′ stability index. The diagonal elements of these matrices determine the intrinsic stability of modes that reconnect the magnetic field at a single resonant surface. The off-diagonal elements indicate the strength of the coupling between the different modes. A method is presented for evaluating the elements of these matrices, in the limit of short wavelength, from the free energy driving radially extended ballooning modes. This method is applied to calculate the tearing and twisting Δ′ for a model high-beta equilibrium with circular flux surfaces. © 1999 American Institute of Physics.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Fa Tokamaks, spherical tokamaks
52.55.Jd Magnetic mirrors, gas dynamic traps
02.10.Ud Linear algebra
02.10.Xm Multilinear algebra

Effect of toroidal rotation on the localized modes in low beta circular tokamaks

L.-J. Zheng, M. S. Chu, and Liu Chen

Phys. Plasmas 6, 1217 (1999); http://dx.doi.org/10.1063/1.873365 (10 pages) | Cited 11 times

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Effects of finite toroidal rotation on the stability of radially localized ideal magnetohydrodynamic (MHD) modes are investigated analytically for low-beta, large aspect-ratio circular tokamaks. Specifically, it is found that, for the Mercier interchange mode, a finite rotation shear is generally stabilizing. For the double internal kink mode, however, finite toroidal rotation shear further enhances the ballooning destabilizing effect. © 1999 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.30.-q Plasma dynamics and flow

Global gyrokinetic simulation of tokamak transport

G. Furnish, W. Horton, Y. Kishimoto, M. LeBrun, and T. Tajima

Phys. Plasmas 6, 1227 (1999); http://dx.doi.org/10.1063/1.873366 (19 pages) | Cited 14 times

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A kinetic simulation code based on the gyrokinetic ion dynamics in global general metric (including a tokamak with circular or noncircular cross-section) has been developed. This gyrokinetic simulation is capable of examining the global and semi-global driftwave structures and their associated transport in a tokamak plasma. We investigate the property of the ion temperature gradient (ITG) or ηi(ηi ≡ ∂ ln Ti/∂ ln ni) driven drift waves in a tokamak plasma. The emergent semi-global drift wave modes give rise to thermal transport characterized by the Bohm scaling. © 1999 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties
52.65.Tt Gyrofluid and gyrokinetic simulations
52.35.Kt Drift waves

Finite-beta equilibria for Wendelstein 7-X configurations using the Princeton Iterative Equilibrium Solver code

S. Arndt, P. Merkel, D. A. Monticello, and A. H. Reiman

Phys. Plasmas 6, 1246 (1999); http://dx.doi.org/10.1063/1.873367 (7 pages) | Cited 2 times

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Fixed- and free-boundary equilibria for Wendelstein 7-X (W7-X) [W. Lotz et al., Plasma Physics and Controlled Nuclear Fusion Research 1990 (Proc. 13th Int. Conf. Washington, DC, 1990), (International Atomic Energy Agency, Vienna, 1991), Vol. 2, p. 603] configurations are calculated using the Princeton Iterative Equilibrium Solver (PIES) [A. H. Reiman et al., Comput. Phys. Commun., 43, 157 (1986)] to deal with magnetic islands and stochastic regions. Usually, these W7-X configurations require a large number of iterations for PIES convergence. Here, two methods have been successfully tested in an attempt to decrease the number of iterations needed for convergence. First, periodic sequences of different blending parameters are used. Second, the initial guess is vastly improved by using results of the Variational Moments Equilibrium Code (VMEC) [S. P. Hirshmann et al., Phys. Fluids 26, 3553 (1983)]. Use of these two methods have allowed verification of the Hamada condition and tendency of “self-healing” of islands has been observed. © 1999 American Institute of Physics.
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52.55.Jd Magnetic mirrors, gas dynamic traps
52.65.-y Plasma simulation

Modeling of magnetic island formation in magnetic reconnection experiment

T.-H. Watanabe, T. Hayashi, T. Sato, M. Yamada, and H. Ji

Phys. Plasmas 6, 1253 (1999); http://dx.doi.org/10.1063/1.873368 (5 pages) | Cited 5 times

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Formation of a magnetic island found in the Magnetic Reconnection Experiment (MRX) [M. Yamada, H. Ji, S. Hsu, et al., Phys. Plasmas 4, 1936 (1997)] is investigated by a magnetohydrodynamic (MHD) relaxation theory and a numerical simulation. In the cohelicity injection with a mean toroidal field, the growing process of the island into a spheromak-type configuration is explained by quasistatic transition of the force-free and minimum energy state to a state with larger normalized helicity. It also turns out that no magnetic island would be generated in the counterhelicity case. The MHD simulation with inhomogeneous electric resistivity agrees with experimental results, which clearly shows formation and growth of the magnetic island in a diffusion region where the reconnection takes place. © 1999 American Institute of Physics.
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52.30.-q Plasma dynamics and flow
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.Fi Transport properties
52.55.Jd Magnetic mirrors, gas dynamic traps
02.60.Cb Numerical simulation; solution of equations
back to top Inertially Confined Plasmas, Dense Plasmas, Equations of State

Saturation of stimulated Raman backscatter in strongly turbulent plasmas

D. Mourenas

Phys. Plasmas 6, 1258 (1999); http://dx.doi.org/10.1063/1.873369 (12 pages) | Cited 7 times

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The nonlinear behavior of stimulated Raman backscattering in a large, homogeneous and hot plasma slab at subcritical density is investigated analytically in the limit of moderate to strong linear and nonlinear ion acoustic damping. It is found that the Langmuir waves damping might be reduced to the collisional one, leading to a highly incoherent interaction for moderate to strong laser pump power. Scaling laws for the saturated reflectivity are obtained in the presence of parametric decay cascade and strong Langmuir turbulence, and compared to recent experimental observations. © 1999 American Institute of Physics.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.65.-y Plasma simulation
52.25.Kn Thermodynamics of plasmas
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering

Systematic trends in x-ray emission characteristics of variable-wire-number, fixed-mass, aluminum-array, Z-pinch implosions

T. W. L. Sanford, R. C. Mock, T. J. Nash, K. G. Whitney, P. E. Pulsifer, J. P. Apruzese, D. Mosher, D. L. Peterson, and M. G. Haines

Phys. Plasmas 6, 1270 (1999); http://dx.doi.org/10.1063/1.873370 (24 pages) | Cited 21 times

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Increasing the number of wires an order of magnitude from 10 to almost 200 while simultaneously fixing the total wire mass in annular aluminum-wire-array Z-pinch implosions on the 20 TW Saturn generator [Proceedings of the 6th International IEEE Pulsed Power Conference (Institute of Electrical and Electronics Engineers, Piscataway, NJ, 1987), p. 310] demonstrates two separate power-law trends in the measured x-ray characteristics as a function of the initial interwire gap (g). These trends are approximately independent of the array radius. When g decreases from ∼6 to 0.4 mm, the peak total radiated power increases by a factor of 20 and the total energy by a factor of 2. There is a more rapid increase in peak power and energy radiated as g decreases for gaps greater than ∼2 mm. This increase is related to a measured decrease in precursor plasma and to a calculated decreased sensitivity of the implosion to azimuthal asymmetries that occurs when individual wire plasmas begin to merge following their vaporization. The substantial increase in power arises from an inferred increase in plasma compression and can be correlated with an almost linear reduction in the calculated effective thickness of the plasma annulus near stagnation as g decreases. © 1999 American Institute of Physics.
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52.55.Ez Theta pinch
52.50.Lp Plasma production and heating by shock waves and compression
52.80.Qj Explosions; exploding wires
07.85.-m X- and γ-ray instruments

Nonlinear saturation of stimulated Raman scattering in laser hot spots

David A. Russell, D. F. DuBois, and Harvey A. Rose

Phys. Plasmas 6, 1294 (1999); http://dx.doi.org/10.1063/1.873371 (24 pages) | Cited 56 times

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Two-dimensional simulation studies are reported of the nonlinear development of stimulated Raman scattering (SRS) from a compact laser hot spot using a reduced model, which includes saturation by pump depletion, Langmuir wave decay cascades, Langmuir wave collapse, and ponderomotive density profile modification. The needle-like intensity distribution in a speckle arising from a random phase plate processed laser beam promotes backscatter SRS. The dependence of the saturated reflectivity and (the comparable in magnitude) absorptivity, on ion acoustic wave and Langmuir wave damping, laser power, electron density, and temperature is studied. There are regimes in which the ponderomotive potential (as well as the Ohmic dissipation) of the induced Langmuir turbulence exceeds that of the localized laser pump. The results support the conclusion that the Langmuir wave Landau damping must be determined by an electron velocity distribution modified by quasilinear and Ohmic heating to account for SRS observed at low densities and high temperatures. © 1999 American Institute of Physics.
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42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.30.Ms Speckle and moiré patterns
41.20.Jb Electromagnetic wave propagation; radiowave propagation
42.25.-p Wave optics
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