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Sep 2007

Volume 14, Issue 9, Articles (09xxxx)

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Nonequilibrium gyrokinetic fluctuation theory and sampling noise in gyrokinetic particle-in-cell simulations

John A. Krommes

Phys. Plasmas 14, 090501 (2007); http://dx.doi.org/10.1063/1.2759879 (26 pages) | Cited 8 times

Online Publication Date: 6 September 2007

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The present state of the theory of fluctuations in gyrokinetic (GK) plasmas and especially its application to sampling noise in GK particle-in-cell (PIC) simulations is reviewed. Topics addressed include the Δf method, the fluctuation-dissipation theorem for both classical and GK many-body plasmas, the Klimontovich formalism, sampling noise in PIC simulations, statistical closure for partial differential equations, the theoretical foundations of spectral balance in the presence of arbitrary noise sources, and the derivation of Kadomtsev-type equations from the general formalism.
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52.25.Gj Fluctuation and chaos phenomena
52.65.Rr Particle-in-cell method
52.65.Tt Gyrofluid and gyrokinetic simulations
02.30.Jr Partial differential equations
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Dust structures in cryogenic gas discharges

S. N. Antipov, E. I. Asinovskii, V. E. Fortov, A. V. Kirillin, V. V. Markovets, O. F. Petrov, and V. I. Platonov

Phys. Plasmas 14, 090701 (2007); http://dx.doi.org/10.1063/1.2769964 (4 pages) | Cited 5 times

Online Publication Date: 18 September 2007

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Results are given of experimental investigations of dust structures of monodisperse particles in a low-pressure dc glow discharge at temperatures of liquid nitrogen (T = 77 K) and liquid helium (T = 4.2 K). It is found that the cooling of discharge at invariant discharge current and neutral gas density causes a decrease in the interparticle spacing in structures and an increase in the kinetic energy of dust particles. The forming of a superdense dust structure with free boundaries is observed for the first time at 4.2 K.
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52.80.Hc Glow; corona
52.27.Lw Dusty or complex plasmas; plasma crystals
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back to top Basic Plasma Phenomena, Waves, Instabilities

Two-stream instability, wave energy, and the energy principle

C. N. Lashmore-Davies

Phys. Plasmas 14, 092101 (2007); http://dx.doi.org/10.1063/1.2768016 (5 pages) | Cited 5 times

Online Publication Date: 4 September 2007

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A generalized Poynting theorem for a system of uniform electron beams is obtained. Two examples of the two-stream instability with beams of equal density are used to discuss the relation between negative wave energy and negative potential energy, which arises in the energy principle of ideal magnetohydrodynamics. In the first example, v10>v20, while in the second example, v20 = −v10, where v10,20 are the equilibrium beam velocities. Both cases can be interpreted in terms of the energy density arising from the generalized Poynting theorem. The first instability is due to the coupling of negative and positive energy waves at a frequency k(v10+v20)/2. The second instability is due to the coupling of the same two perturbations, but at zero frequency. In this case, there is no oscillatory (wave) energy, but the beam electrons still make a negative contribution to the total energy.
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47.65.-d Magnetohydrodynamics and electrohydrodynamics
47.35.Tv Magnetohydrodynamic waves
47.20.-k Flow instabilities

Dominance of second Bessel peak in relativistic electromagnetic ion cyclotron instabilities driven by fusion-produced fast ions

K. R. Chen, H. K. Chen, and S. H. Lee

Phys. Plasmas 14, 092102 (2007); http://dx.doi.org/10.1063/1.2769290 (8 pages) | Cited 2 times

Online Publication Date: 5 September 2007

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Relativistic electromagnetic ion cyclotron instabilities driven by fusion-produced fast ions in magnetized plasmas can have two peaks in their growth rate spectrum. The wave numbers of these two peaks are close to the first and second peaks, respectively, of the Bessel function that is in the resonance driving term. The driving of the second Bessel and growth rate peak occurring at a higher wave number is weaker than that of the first peak. Surprisingly, as in contrast to conventional wisdom, the second peak can dominate near the instability threshold. For the higher energy of fusion-produced fast ion such as 14.7 MeV, the slow ion temperature is required to be higher for overcoming the threshold to drive a cubic instability, which is determined by an Alfvénic condition. This cubic instability is due to the coupling of the first-order slow ion resonance and second-order fast ion resonance. This finite temperature effect is on the slow ion resonance and increases with wave number and thus the threshold is first satisfied near the second peak. Therefore, the second peak appears earlier in the instability spectrum and dominates near the threshold. The cubic instability has a much larger frequency mismatch than a coupled quadratic instability; a larger frequency mismatch indicates more fast ion energy to loss before the nonlinear saturation of the instability. When the slow ion temperature or density is about twice that of the threshold, the second peak has transited from the cubic to the coupled quadratic instability while the first peak remains as the cubic instability, in contrast to the previous 3.02 MeV proton case.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.27.Ny Relativistic plasmas
52.25.Xz Magnetized plasmas
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

A new derivation of the plasma susceptibility tensor for a hot magnetized plasma without infinite sums of products of Bessel functions

Hong Qin, Cynthia K. Phillips, and Ronald C. Davidson

Phys. Plasmas 14, 092103 (2007); http://dx.doi.org/10.1063/1.2769968 (8 pages) | Cited 5 times

Online Publication Date: 5 September 2007

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The susceptibility tensor of a hot, magnetized plasma is conventionally expressed in terms of infinite sums of products of Bessel functions. For applications where the particle’s gyroradius is larger than the wavelength, such as alpha particle dynamics interacting with lower-hybrid waves, and the focusing of charged particle beams using a solenoidal field, the infinite sums converge slowly. In this paper, a new derivation of the plasma susceptibility tensor is presented which exploits a symmetry in the particle’s orbit to simplify the integration along the unperturbed trajectories. As a consequence, the infinite sums appearing in the conventional expression are replaced by definite double integrals over one gyroperiod, and the cyclotron resonances of all orders are captured by a single term. Furthermore, the double integrals can be carried out and expressed in terms of Bessel functions of complex order, in agreement with expressions deduced previously using the Newburger sum rule. From this new formulation, it is straightforward to derive the asymptotic form of the full hot plasma susceptibility tensor for a gyrotropic but otherwise arbitrary plasma distribution in the large gyroradius limit. These results are of more general importance in the numerical evaluation of the plasma susceptibility tensor. Instead of using the infinite sums occurring in the conventional expression, it is only necessary to evaluate the Bessel functions once according to the new expression, which has significant advantages, especially when the particle’s gyroradius is large and the conventional infinite sums converge slowly. Depending on the size of the gyroradius, the computational saving enabled by this representation can be several orders-of-magnitude.
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52.55.-s Magnetic confinement and equilibrium
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)

Effect of burst ions on the excitation of ion-acoustic solitons in a drifting plasma

De-long Xiao, J. X. Ma, Yi-ren Li, Yang-fang Li, and M. Y. Yu

Phys. Plasmas 14, 092104 (2007); http://dx.doi.org/10.1063/1.2771134 (8 pages) | Cited 5 times

Online Publication Date: 14 September 2007

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The characteristics of fast burst ions and ion-acoustic solitons in a drifting plasma, as well as their interaction, are investigated experimentally. It is shown that the soliton evolves from the normal fast ion-beam mode excited locally in the presheath region of an excitation grid. The burst ions are created by applying a positive ramp voltage to the grid. Adjusting the rise time and amplitude of the ramp signal can lead to significant changes in the average speed of the burst ions, resulting in strong interaction (inverse Landau damping) between the burst ions and the soliton. The resonance conditions for solitons propagating along and against the plasma flow are shown to be different, since the soliton speed depends on the propagation direction.
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52.35.Sb Solitons; BGK modes
52.35.Kt Drift waves
52.30.-q Plasma dynamics and flow

Antenna impedance measurements in a magnetized plasma. I. Spherical antenna

David D. Blackwell, David N. Walker, Sarah J. Messer, and William E. Amatucci

Phys. Plasmas 14, 092105 (2007); http://dx.doi.org/10.1063/1.2779284 (5 pages) | Cited 3 times

Online Publication Date: 17 September 2007

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The input impedance of a metal sphere immersed in a magnetized plasma is measured with a network analyzer at frequencies up to 1 GHz. The experiments were done in the Space Physics Simulation Chamber at the Naval Research Laboratory. The hot-filament argon plasma was varied between weakly (ωce<ωpe) and strongly (ωce>ωpe) magnetized plasma with electron densities in the range 107–1010 cm−3. It is observed that the lower-frequency resonance of the impedance characteristic previously associated with series sheath resonance ωsh in the unmagnetized plasma occurs at a hybrid sheath frequency of ωr2 = ωsh2+κωce2, where κ is a constant 0.5<κ<1. As seen in previous experiments, the higher frequency resonance associated with the electron plasma frequency ωpe in the unmagnetized plasma is relocated to the upper hybrid frequency ωuh2 = ωpe2+ωce2. As with the unmagnetized plasma, the maximum power deposition occurs at the lower frequency resonance ωr.
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52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.40.Kh Plasma sheaths
52.65.-y Plasma simulation
52.25.Xz Magnetized plasmas

Antenna impedance measurements in a magnetized plasma. II. Dipole antenna

David D. Blackwell, David N. Walker, Sarah J. Messer, and William E. Amatucci

Phys. Plasmas 14, 092106 (2007); http://dx.doi.org/10.1063/1.2779285 (8 pages) | Cited 3 times

Online Publication Date: 17 September 2007

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This paper presents experimental impedance measurements of a dipole antenna immersed in a magnetized plasma. The impedance was derived from the magnitude and phase of the reflected power using a network analyzer over a frequency range of 1 MHz–1 GHz. The plasma density was varied between 107 and 1010 cm−3 in weakly (ωce<ωpe) and strongly (ωce>ωpe) magnetized plasmas in the Space Physics Simulation Chamber at the Naval Research Laboratory. Over this range of plasma conditions the wavelength in the plasma varies from the short dipole limit (λ≫L) to the long dipole limit (λ ∼ L). As with previous impedance measurements, there are two resonant frequencies observed as frequencies where the impedance of the antenna is real. Measurements have indicated that in the short dipole limit the majority of the power deposition takes place at the lower resonance frequency which lies between the cyclotron frequency and the upper hybrid frequency. These measured curves agree very well with the analytic theory for a short dipole in a magnetoplasma. In the long dipole regime, in addition to the short dipole effects still being present, there is resonant energy deposition which peaks at much higher frequencies and correlates to 1/2 and 3/2 wavelength dipole resonances. The wavelengths in the plasma predicted by these resonances are consistent with the antenna radiating R and L-waves.
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84.40.Ba Antennas: theory, components and accessories
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.25.Xz Magnetized plasmas

Hamiltonian theory of adiabatic motion of relativistic charged particles

Xin Tao, Anthony A. Chan, and Alain J. Brizard

Phys. Plasmas 14, 092107 (2007); http://dx.doi.org/10.1063/1.2773702 (9 pages) | Cited 10 times

Online Publication Date: 18 September 2007

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A general Hamiltonian theory for the adiabatic motion of relativistic charged particles confined by slowly varying background electromagnetic fields is presented based on a unified Lie-transform perturbation analysis in extended phase space (which includes energy and time as independent coordinates) for all three adiabatic invariants. First, the guiding-center equations of motion for a relativistic particle are derived from the particle Lagrangian. Covariant aspects of the resulting relativistic guiding-center equations of motion are discussed and contrasted with previous works. Next, the second and third invariants for the bounce motion and drift motion, respectively, are obtained by successively removing the bounce phase and the drift phase from the guiding-center Lagrangian. First-order corrections to the second and third adiabatic invariants for a relativistic particle are derived. These results simplify and generalize previous works to all three adiabatic motions of relativistic magnetically trapped particles.
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45.20.Jj Lagrangian and Hamiltonian mechanics
52.27.Ny Relativistic plasmas
94.05.-a Space plasma physics

Nonlinear dispersion of resonance extraordinary wave in a plasma with strong magnetic field

V. B. Krasovitskiy, V. A. Turikov, and V. I. Sotnikov

Phys. Plasmas 14, 092108 (2007); http://dx.doi.org/10.1063/1.2768514 (10 pages) | Cited 4 times

Online Publication Date: 20 September 2007

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In this paper, the efficiency of electron acceleration by a short, powerful laser pulse propagating across an external magnetic field is investigated. Conditions for the decay of a laser pulse with frequency close to the upper hybrid resonance frequency are analyzed. It is also shown that a laser pulse propagating as an extraordinary wave in cold, magnetized, low-density plasma takes the form of a nonlinear wave with the modulated amplitude (envelope soliton). Finally, simulation results on the interaction of an electromagnetic pulse with a semi-infinite plasma, obtained with the help of an electromagnetic relativistic PIC code, are discussed and a comparison with the obtained theoretical results is presented.
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52.38.Kd Laser-plasma acceleration of electrons and ions

Linear stability analysis of force-free equilibria close to Taylor relaxed states

E. Tassi, R. J. Hastie, and F. Porcelli

Phys. Plasmas 14, 092109 (2007); http://dx.doi.org/10.1063/1.2769324 (14 pages) | Cited 5 times

Online Publication Date: 20 September 2007

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The linear stability of a class of force-free equilibria in cylindrical geometry is investigated. The class consists of cylindrically symmetric force-free equilibria for which the ratio μ between the parallel current density and the magnetic field is a step function of the radius. It is suggested that plasmas in reversed field pinches could be roughly represented by such equilibria as a consequence of a small departure from an initial force-free state with constant μ, the latter being reached after a relaxation process according to the classical theory proposed by Taylor [Phys. Rev. Lett. 33, 1139 (1974) ]. A fully analytical derivation of the tearing stability parameter Δ′ for such class of equilibria is given. It is then shown with one explicit example how the presence of a downward step of relatively small height can destabilize the innermost resonant mode, which would otherwise be stable if μ were constant. A possible implication of this mechanism for the formation of cyclic quasisingle helicity states observed in reversed field pinches is proposed. Considerations on the ideal stability of the class of equilibria under investigation are also given.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.25.Fi Transport properties
52.55.Ez Theta pinch
52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps

Gyrokinetic simulations of collisionless magnetic reconnection

B. N. Rogers, S. Kobayashi, P. Ricci, W. Dorland, J. Drake, and T. Tatsuno

Phys. Plasmas 14, 092110 (2007); http://dx.doi.org/10.1063/1.2774003 (10 pages) | Cited 10 times

Online Publication Date: 20 September 2007

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Linear and nonlinear gyrokinetic simulations of collisionless magnetic reconnection in the presence of a strong guide field are presented. A periodic slab system is considered with a sinusoidally varying reconnecting magnetic field component. The linear growth rates of the tearing mode in both the large and small Δ′ regimes are compared to kinetic and fluid theory calculations. In the nonlinear regime, focusing on the limit of large Δ′, the nonlinear reconnection rates in the gyrokinetic simulations are found to be comparable to those obtained from a two-fluid model. In contrast to the fluid system, however, for Ti⪢Te and very small initial perturbation amplitudes, the reconnection in the gyrokinetic system saturates in the early nonlinear phase. This saturation can be overcome if the simulation is seeded initially with sufficient random noise.
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52.35.Vd Magnetic reconnection
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.Tt Gyrofluid and gyrokinetic simulations
52.25.Dg Plasma kinetic equations

Electrostatic Landau pole for κ-velocity distributions

Francesco Valentini and Roberto D’Agosta

Phys. Plasmas 14, 092111 (2007); http://dx.doi.org/10.1063/1.2776897 (9 pages) | Cited 6 times

Online Publication Date: 27 September 2007

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In this paper, the analytical solution of the linear electrostatic Vlasov dispersion relation is obtained for non-Maxwellian equilibrium distributions of particle velocities (κ distributions). The unphysical singularities for certain values of the parameter κ, recovered by several authors in solving the Landau integral, are discussed in detail, and a way to cancel these singularities and get the correct solution for Langmuir waves is proposed. The solution of the electrostatic dispersion relation presented in this paper provides a theoretical prediction for the oscillation frequency and the damping rate of Langmuir waves, for real values of κ>1/2 and in particular in the range 1/2<κ ⩽ 3/2, where previous analytical solutions fail. Velocity distributions with small values of κ have been frequently observed in solar wind plasmas; therefore, the results presented in this paper are relevant in the interpretation of the solar wind experimental data. Eulerian Vlasov numerical simulations have been performed to substantiate the analytical results; the numerical results are in very good agreement with the theoretical predictions.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.20.-j Elementary processes in plasmas
52.25.Dg Plasma kinetic equations
52.65.-y Plasma simulation
back to top Nonlinear Phenomena, Turbulence, Transport

E×B advection of trace ions in tokamak microturbulence

T. Hauff and F. Jenko

Phys. Plasmas 14, 092301 (2007); http://dx.doi.org/10.1063/1.2768025 (11 pages) | Cited 18 times

Online Publication Date: 5 September 2007

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The E×B advection of trace ions in realistic tokamak microturbulence (as described by nonlinear gyrokinetics) is investigated. In order to understand the consequences of effects such as large gyroradii, fluctuation anisotropies, zonal flows, or poloidal drifts, they are first studied in the framework of a model that is based on self-created stochastic potentials. Direct numerical simulations are performed, and a semi-analytical model is presented that provides qualitative as well as quantitative insight into the nature of passive tracer transport. One finds that the resulting diffusivities may be larger than expected as long as the gyroradii do not exceed the turbulence correlation length(s) and the poloidal drift velocities are sufficiently small.
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52.35.Ra Plasma turbulence
52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties

One-dimensional Vlasov simulation of parallel electric fields in two-electron population plasma

K. Saharia and K. S. Goswami

Phys. Plasmas 14, 092302 (2007); http://dx.doi.org/10.1063/1.2770002 (5 pages) | Cited 1 time

Online Publication Date: 5 September 2007

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One-dimensional Vlasov simulation in electron current carrying multicomponent plasma seeded with a density depression is presented. Considering two electron populations [one is sufficiently hot ( ∼ keV) and the other is cold along with cold background ions], the formation of weak double layers is investigated. Simulation results show that in this numerical setting, formation of such double layers needs the majority of the hot electrons.
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52.25.Fi Transport properties
52.25.Dg Plasma kinetic equations
52.65.Ff Fokker-Planck and Vlasov equation
52.27.Cm Multicomponent and negative-ion plasmas
52.40.Kh Plasma sheaths

Critical temperature gradient length signatures in heat wave propagation across internal transport barriers in the Joint European Torus

Alessandro Casati, P. Mantica, D. Van Eester, N. Hawkes, F. Imbeaux, E. Joffrin, A. Marinoni, F. Ryter, A. Salmi, T. Tala, P. De Vries, and JET EFDA contributors

Phys. Plasmas 14, 092303 (2007); http://dx.doi.org/10.1063/1.2772618 (11 pages) | Cited 3 times

Online Publication Date: 18 September 2007

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New results on electron heat wave propagation using ion cyclotron resonance heating power modulation in the Joint European Torus (JET) [ P. H. Rebut et al., Nucl. Fusion 25, 1011 (1985) ] plasmas characterized by internal transport barriers (ITBs) are presented. The heat wave generated outside the ITB, and traveling across it, always experiences a strong damping in the ITB layer, demonstrating a low level of transport and loss of stiffness. In some cases, however, the heat wave is strongly inflated in the region just outside the ITB, showing features of convective-like behavior. In other cases, a second maximum in the perturbation amplitude is generated close to the ITB foot. Such peculiar types of behavior can be explained on the basis of the existence of a critical temperature gradient length for the onset of turbulent transport. Convective-like features appear close to the threshold (i.e., just outside the ITB foot) when the value of the threshold is sufficiently high, with a good match with the theoretical predictions for the trapped electron mode threshold. The appearance of a second maximum is due to the oscillation of the temperature profile across the threshold in the case of a weak ITB. Simulations with an empirical critical gradient length model and with the theory based GLF23 [ R. E. Waltz et al., Phys. Plasmas, 4, 2482 (1997) ] model are presented. The difference with respect to previous results of cold pulse propagation across JET ITBs is also discussed.
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52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.55.Jd Magnetic mirrors, gas dynamic traps
52.25.Fi Transport properties
52.35.Ra Plasma turbulence

Existence and stability of alternative ion-acoustic solitary wave solution of the combined MKdV-KdV-ZK equation in a magnetized nonthermal plasma consisting of warm adiabatic ions

Jayasree Das, Anup Bandyopadhyay, and K. P. Das

Phys. Plasmas 14, 092304 (2007); http://dx.doi.org/10.1063/1.2772615 (10 pages) | Cited 5 times

Online Publication Date: 24 September 2007

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The purpose of this paper is to present the recent work of Das et al. [J. Plasma Phys. 72, 587 (2006) ] on the existence and stability of the alternative solitary wave solution of fixed width of the combined MKdV-KdV-ZK (Modified Korteweg-de Vries-Korteweg-de Vries-Zakharov-Kuznetsov) equation for the ion-acoustic wave in a magnetized nonthermal plasma consisting of warm adiabatic ions in a more generalized form. Here we derive the alternative solitary wave solution of variable width instead of fixed width of the combined MKdV-KdV-ZK equation along with the condition for its existence and find that this solution assumes the sech profile of the MKdV-ZK (Modified Korteweg-de Vries-Zakharov-Kuznetsov) equation, when the coefficient of the nonlinear term of the KdV-ZK (Korteweg-de Vries-Zakharov-Kuznetsov) equation tends to zero. The three-dimensional stability analysis of the alternative solitary wave solution of variable width of the combined MKdV-KdV-ZK equation shows that the instability condition and the first order growth rate of instability are exactly the same as those of the solitary wave solution (the sech profile) of the MKdV-ZK equation, when the coefficient of the nonlinear term of the KdV-ZK equation tends to zero.
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52.35.Dm Sound waves
52.35.Sb Solitons; BGK modes
52.35.We Plasma vorticity

Anisotropic form of third-order moments and relationship to the cascade rate in axisymmetric magnetohydrodynamic turbulence

J. J. Podesta, M. A. Forman, and C. W. Smith

Phys. Plasmas 14, 092305 (2007); http://dx.doi.org/10.1063/1.2783224 (7 pages) | Cited 13 times

Online Publication Date: 25 September 2007

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Laws governing the behavior of statistical third-order moments in the inertial range are among the few rigorous results in the theory of statistically homogeneous incompressible magnetohydrodynamic turbulence. These fundamental laws apply to both isotropic and anisotropic turbulence. Assuming that the turbulence is stationary in time and statistically axisymmetric under proper rotations about the direction of the mean magnetic field, it is shown that the general mathematical form of the tensor quantities appearing in these laws is constrained by symmetry to have a particular form. Using these forms, the general solutions of the law for the vector and pseudovector third-order moments F and FC are obtained in the limit of large kinetic Reynolds number and large magnetic Reynolds number. The physical meaning of the different terms in F and FC are investigated and a method for obtaining the cascade rates of energy ϵ and cross-helicity ϵC from experimental data is described. The results show that the measurement of the cascade rates goes hand-in-hand with the measurement of the spatial anisotropy of the third-order moments F and FC. The theory developed here can be applied to measure the turbulent cascade rates of energy and cross-helicity in laboratory plasma experiments, numerical simulations, and the solar wind.
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47.65.-d Magnetohydrodynamics and electrohydrodynamics
47.27.-i Turbulent flows
02.10.Ud Linear algebra
back to top Magnetically Confined Plasmas, Heating, Confinement

Magnetohydrodynamics modelling of H-mode plasma response to external resonant magnetic perturbations

E. Nardon, M. Bécoulet, G. Huysmans, and O. Czarny

Phys. Plasmas 14, 092501 (2007); http://dx.doi.org/10.1063/1.2759889 (10 pages) | Cited 21 times

Online Publication Date: 4 September 2007

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The response of an H-mode plasma to Resonant Magnetic Perturbations (RMPs) generated by so-called “I-coils” in DIII-D experiments on type I edge localized modes suppression is modelled using the nonlinear reduced magnetohydrodynamics (with zero-β, i.e. zero plasma temperature, in the version used here) code JOREK in X-point geometry. JOREK self-consistently advances in time the magnetic flux, vorticity, and plasma density in the presence of the RMPs. Without any toroidal rotation, the magnetic response from the plasma does not significantly modify the islands widths. A radial convective math×math plasma transport is observed to occur in the presence of the RMPs. The possibility that this mechanism could explain the enhanced density transport observed experimentally in DIII-D is discussed. Simulations with a rigid-body-like rotation at a fixed velocity shows evidence of a screening of the RMPs. The extension of our results to realistic parameters is discussed.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Self-consistent electron transport in tokamaks

R. Gatto and I. Chavdarovski

Phys. Plasmas 14, 092502 (2007); http://dx.doi.org/10.1063/1.2768940 (14 pages) | Cited 2 times

Online Publication Date: 6 September 2007

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Electron particle, momentum, and energy fluxes in axisymmetric toroidal devices are derived from a version of the action-angle collision operator that includes both diffusion and drag in action-space [ D. A. Hitchcock, R. D. Hazeltine, and S. M. Mahajan, Phys. Fluids 26, 2603 (1983) ; H. E. Mynick, J. Plasma Phys. 39, 303 (1988) ]. A general result of the theory is that any contribution to transport originating directly from the toroidal frequency of the particle motion is constrained to be zero when the electron temperature is equal to the ion temperature. In particular, this constraint applies to those components of the particle and energy fluxes that are proportional to the magnetic shear, independent of the underlying turbulence and of whether the particles are trapped or untrapped. All the total fluxes describing collisionless transport of passing electrons in steady-state magnetic turbulence contain contributions proportional to the conventional thermodynamic drives, which are always outward, and contributions proportional to the magnetic shear, which have both magnitude and sign dependent on the ion-electron temperature ratio. The turbulent generalization of Ohm’s law includes a hyper-resistive term, which flattens the current density profile on a fast time scale, and a turbulent electric field, which can have both signs depending on the electron-ion temperature ratio.
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52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Ra Plasma turbulence
52.55.Fa Tokamaks, spherical tokamaks

Hall magnetohydrodynamics simulations of end-shorting induced rotation in field-reversed configurations

A. I. D. Macnab, R. D. Milroy, C. C. Kim, and C. R. Sovinec

Phys. Plasmas 14, 092503 (2007); http://dx.doi.org/10.1063/1.2768017 (6 pages) | Cited 8 times

Online Publication Date: 11 September 2007

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End-shorting of the open field lines that surround a field-reversed configuration (FRC) is believed to contribute to its observed rotation. In this study, nonlinear extended magnetohydrodynamics (MHD) simulations were performed that detail the end-shorting process and the resulting spin-up of the FRC. The tangential component of the electric field ET is set to zero at the axial boundaries in an extended MHD model that includes the Hall and ∇Pe terms. This shorting of the electric field leads to the generation of toroidal fields on the open field lines, which apply a torque leading to a rotation of the ions on the open field lines. The FRC then gains angular momentum through a viscous transfer from the open field line region. In addition, it is shown that spin-up is still induced when insulating boundaries are assumed.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.-y Plasma simulation
52.58.Lq Z-pinches, plasma focus, and other pinch devices

Finite Larmor radius effects on the coupled trapped electron and ion temperature gradient modes

I. Sandberg, H. Isliker, and V. P. Pavlenko

Phys. Plasmas 14, 092504 (2007); http://dx.doi.org/10.1063/1.2768938 (7 pages) | Cited 1 time

Online Publication Date: 13 September 2007

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The properties of the coupled trapped electron and toroidal ion temperature gradient modes are investigated using the standard reactive fluid model and taking rigorously into account the effects attributed to the ion polarization drift and to the drifts associated with the lowest-order finite ion Larmor radius effects. In the flat density regime, where the coupling between the modes is relatively weak, the properties of the unstable modes are slightly modified through these effects. For the peak density regions, where the coupling of the modes is rather strong, these second-order drifts determine the spectra of the unstable modes near the marginal conditions.
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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.)
52.35.Ra Plasma turbulence
back to top Inertially Confined Plasmas, Dense Plasmas, Equations of State

The effect of resonance absorption in OMEGA direct-drive designs and experiments

I. V. Igumenshchev, V. N. Goncharov, W. Seka, D. Edgell, and T. R. Boehly

Phys. Plasmas 14, 092701 (2007); http://dx.doi.org/10.1063/1.2768515 (10 pages) | Cited 3 times

Online Publication Date: 7 September 2007

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Resonance absorption enhances the early time laser absorption in direct-drive inertial confinement fusion implosions, affecting the performance of imploding capsules. In this paper, resonance absorption is studied both theoretically and experimentally for a λ = 351-nm laser. Simulations demonstrate an important contribution of the resonance absorption during both the short laser picket ( ∼ 100 ps) and the first 200–300 ps in the long laser pulse. It is shown that for the conditions relevant to the direct-drive implosions on the OMEGA Laser System [ T. R. Boehly et al., Opt. Commun. 133, 495 (1997) ], the early time enhancement of laser absorption can be up to 20% for drive intensities of 1014–1015 W/cm2. Planar reflection light experiments on OMEGA were conducted to validate the theoretical results. There is a generally good agreement between simulation and experimental results. As an additional diagnostic of resonance absorption, shock-timing experiments employing OMEGA drive beams of different polarization are proposed.
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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.)
52.65.-y Plasma simulation
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)

Strongly enhanced laser absorption and electron acceleration via resonant excitation of surface plasma waves

M. Raynaud, J. Kupersztych, C. Riconda, J. C. Adam, and A. Héron

Phys. Plasmas 14, 092702 (2007); http://dx.doi.org/10.1063/1.2755969 (9 pages) | Cited 14 times

Online Publication Date: 20 September 2007

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Two-dimensional (2D) particle-in-cell numerical simulations of the interaction between a high-intensity short-pulse p-polarized laser beam and an overdense plasma are presented. It is shown that, under appropriate physical conditions, a surface plasma wave can be resonantly excited by a short-pulse laser wave, leading to strong relativistic electron acceleration together with a dramatic increase, up to 70%, of light absorption by the plasma. Purely 2D effects contribute to enhancement of electron acceleration. It is also found that the angular distribution of the hot electrons is drastically affected by the surface wave. The subsequent ion dynamics is shown to be significantly modified by the surface plasma wave excitation.
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52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.38.Kd Laser-plasma acceleration of electrons and ions
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.65.Rr Particle-in-cell method
52.27.Ny Relativistic plasmas
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Laser generated proton beam focusing and high temperature isochoric heating of solid matter

R. A. Snavely, B. Zhang, K. Akli, Z. Chen, R. R. Freeman, P. Gu, S. P. Hatchett, D. Hey, J. Hill, M. H. Key, Y. Izawa, J. King, Y. Kitagawa, R. Kodama, A. B. Langdon, et al.

Phys. Plasmas 14, 092703 (2007); http://dx.doi.org/10.1063/1.2774001 (5 pages) | Cited 11 times

Online Publication Date: 21 September 2007

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The results of laser-driven proton beam focusing and heating with a high energy (170 J) short pulse are reported. Thin hemispherical aluminum shells are illuminated with the Gekko petawatt laser using 1 μm light at intensities of ∼ 3×1018 W/cm2 and measured heating of thin Al slabs. The heating pattern is inferred by imaging visible and extreme-ultraviolet light Planckian emission from the rear surface. When Al slabs 100 μm thick were placed at distances spanning the proton focus beam waist, the highest temperatures were produced at 0.94× the hemisphere radius beyond the equatorial plane. Isochoric heating temperatures reached 81 eV in 15 μm thick foils. The heating with a three-dimensional Monte Carlo model of proton transport with self-consistent heating and proton stopping in hot plasma was modeled.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
41.85.-p Beam optics
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