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Mar 2008

Volume 15, Issue 3, Articles (03xxxx)

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Phys. Plasmas 15, 032902 (2008); http://dx.doi.org/10.1063/1.2884715 (9 pages)

M. Ugai
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Breakdown of electrostatic predictions for the nonlinear dispersion relation of a stimulated Raman scattering driven plasma wave

Didier Bénisti, David J. Strozzi, and Laurent Gremillet

Phys. Plasmas 15, 030701 (2008); http://dx.doi.org/10.1063/1.2888515 (4 pages) | Cited 16 times

Online Publication Date: 17 March 2008

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The kinetic nonlinear dispersion relation, and frequency shift δωsrs, of a plasma wave driven by stimulated Raman scattering are presented. Our theoretical calculations are fully electromagnetic, and use an adiabatic expression for the electron susceptibility which accounts for the change in phase velocity as the wave grows. When kλD≳0.35 (k being the plasma wave number and λD the Debye length), δωsrs is significantly larger than could be inferred by assuming that the wave is freely propagating. Our theory is in excellent agreement with 1D Eulerian Vlasov–Maxwell simulations when 0.3 ≤ kλD ≤ 0.58, and allows discussion of previously proposed mechanisms for Raman saturation. In particular, we find that no “loss of resonance” of the plasma wave would limit the Raman growth rate, and that saturation through a phase detuning between the plasma wave and the laser drive is mitigated by wave number shifts.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
52.25.Dg Plasma kinetic equations
52.65.Ff Fokker-Planck and Vlasov equation

A model for the efficient coupling between intense lasers and subwavelength grating targets

W.-M. Wang, Z.-M. Sheng, and J. Zhang

Phys. Plasmas 15, 030702 (2008); http://dx.doi.org/10.1063/1.2898456 (4 pages) | Cited 12 times

Online Publication Date: 28 March 2008

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The interaction of an ultrashort intense laser pulse with a subwavelength rectangular grating target is studied by an analytical model and particle-in-cell simulations. Such interaction excites strong periodic charge separation at the grating surface. With the presence of formed electrostatic fields, the laser field can intensively heat electrons, causing near 100% light absorption. Its dependence on grating parameters is given. At low or moderate laser intensity, there are optimized sizes of grating gibbous cells and grooves as well as groove depths at which absorption maximums are found. At high intensity, the absorption is weakly affected by groove sizes and depths.
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52.38.-r Laser-plasma interactions
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.65.Rr Particle-in-cell method

The remarkable similarity between the scaling of kurtosis with squared skewness for TORPEX density fluctuations and sea-surface temperature fluctuations

John A. Krommes

Phys. Plasmas 15, 030703 (2008); http://dx.doi.org/10.1063/1.2894560 (4 pages) | Cited 9 times

Online Publication Date: 28 March 2008

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The striking similarity between the statistics of plasma density fluctuations in the TORPEX device [ Labit et al., Phys. Rev. Lett. 98, 255002 (2007) ] and sea-surface temperature fluctuations [ Sura and Sardeshmukh, J. Phys. Oceanogr. 38, 638 (2007) ] (SS) is discussed. A nonlinear Langevin theory due to SS is generalized to include linear wave propagation. An interpretation of the nonlinear Langevin equation based on statistical closure theory is proposed.
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52.25.Gj Fluctuation and chaos phenomena
92.10.af Thermohaline convection

Double planar wire array as a compact plasma radiation source

V. L. Kantsyrev, L. I. Rudakov, A. S. Safronova, A. A. Esaulov, A. S. Chuvatin, C. A. Coverdale, C. Deeney, K. M. Williamson, M. F. Yilmaz, I. Shrestha, N. D. Ouart, and G. C. Osborne

Phys. Plasmas 15, 030704 (2008); http://dx.doi.org/10.1063/1.2896577 (4 pages) | Cited 14 times

Online Publication Date: 31 March 2008

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Magnetically compressed plasmas initiated by a double planar wire array (DPWA) are efficient radiation sources. The two rows in a DPWA implode independently and then merge together at stagnation producing soft x-ray yields and powers of up to 11.5 kJ/cm and more than 0.4 TW/cm, higher than other planar arrays or low wire-number cylindrical arrays on the 1 MA Zebra generator. DPWA, where precursors form in two stages, produce a shaped radiation pulse and radiate more energy in the main burst than estimates of implosion kinetic energy. High radiation efficiency, compact size (as small as 3–5 mm wide), and pulse shaping show that the DPWA is a potential candidate for ICF and radiation physics research.
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52.59.Qy Wire array Z-pinches
52.58.Lq Z-pinches, plasma focus, and other pinch devices
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back to top Basic Plasma Phenomena, Waves, Instabilities

Properties of asymmetric magnetic reconnection

J. Birn, J. E. Borovsky, and M. Hesse

Phys. Plasmas 15, 032101 (2008); http://dx.doi.org/10.1063/1.2888491 (13 pages) | Cited 17 times

Online Publication Date: 12 March 2008

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Properties of magnetic reconnection are investigated in two-dimensional, resistive magnetohydrodynamic (MHD) simulations of current sheets separating plasmas with different magnetic field strengths and densities. Specific emphasis is on the influence of the external parameters on the reconnection rate. The effect of the dissipation in the resistive MHD model is separated from this influence by evaluating resistivity dependence together with the dependence on the background parameters. Two scenarios are considered, which may be distinguished as driven and nondriven reconnection. In either scenario, the maximum reconnection rate (electric field) is found to depend on appropriate hybrid expressions based on a magnetic field strength and an Alfvén speed derived from the characteristic values in the two inflow regions. The scaling compares favorably with an analytic formula derived recently by Cassak and Shay [Phys. Plasmas 14, 102114 (2007) ] applied to the regime of fast reconnection. An investigation of the energy flow and conversion in the vicinity of the reconnection site revealed a significant role of enthalpy flux generation, in addition to the expected conversion of Poynting flux to kinetic energy flux. This enthalpy flux generation results from Ohmic heating as well as adiabatic, that is, compressional heating. The latter is found more important when the magnetic field strengths in the two inflow regions are comparable in magnitude.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Vd Magnetic reconnection
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)

Excitation of the l = 2 diocotron mode with a resistive load

G. Bettega, F. Cavaliere, B. Paroli, R. Pozzoli, M. Romé, and M. Cavenago

Phys. Plasmas 15, 032102 (2008); http://dx.doi.org/10.1063/1.2890773 (5 pages) | Cited 3 times

Online Publication Date: 14 March 2008

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The resistive wall instability of the l = 2 diocotron mode in a pure electron plasma has been investigated with a systematic variation of the parameters of the external impedance connected to a pair of sectored electrodes. The measured growth rate is well described by a linear perturbation theory of the two-dimensional drift-Poisson system.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

The boundary effects of the shock wave dispersion in discharges

A. Markhotok, S. Popovic, and L. Vuskovic

Phys. Plasmas 15, 032103 (2008); http://dx.doi.org/10.1063/1.2889421 (5 pages) | Cited 1 time

Online Publication Date: 18 March 2008

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Interaction of shock waves with a weakly ionized gas generated by discharges has been studied. An additional thermal mechanism of the shock wave dispersion on the boundary between a neutral gas and discharge has been proposed [A. Markhotok, S. Popovic, and L. Vuskovic, Proceedings of the 15th International Conference on Atomic Processes in Plasmas, March 19–22, 2007 (NIST, Gaitersburg, MD, 2007)] . This mechanism can explain a whole set of thermal features of the shock wave-plasma interaction, including acceleration of the shock wave, broadening or splitting of the deflection signals and its consecutive restoration. Application has been made in the case of a shock wave interacting with a laser induced plasma. The experimental observations support well the results of calculation based on this model.
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52.35.Tc Shock waves and discontinuities
52.50.Lp Plasma production and heating by shock waves and compression
52.80.-s Electric discharges
52.25.Kn Thermodynamics of plasmas

Transition from drift to interchange instabilities in an open magnetic field line configuration

F. M. Poli, P. Ricci, A. Fasoli, and M. Podestà

Phys. Plasmas 15, 032104 (2008); http://dx.doi.org/10.1063/1.2899303 (10 pages) | Cited 21 times

Online Publication Date: 26 March 2008

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The transition from a regime dominated by drift instabilities to a regime dominated by pure interchange instabilities is investigated and characterized in the simple magnetized toroidal device TORPEX [TORoidal Plasma EXperiment, A. Fasoli et al., Phys. of Plasmas 13, 055906 (2006)] . The magnetic field lines are helical, with a dominant toroidal component and a smaller vertical component. Instabilities with a drift character are observed in the favorable curvature region, on the high field side with respect to the maximum of the background density profile. For a limited range of values of the vertical field they coexist with interchange instabilities in the unfavorable curvature region, on the plasma low field side. With increasing vertical magnetic field magnitude, a gradual transition between the two regimes is observed on the low field side, controlled by the value of the field line connection length. The observed transition follows the predictions of a two-fluid linear model.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.55.Jd Magnetic mirrors, gas dynamic traps
52.30.Ex Two-fluid and multi-fluid plasmas
52.35.Kt Drift waves
52.25.Xz Magnetized plasmas

Spatially autoresonant stimulated Raman scattering in nonuniform plasmas

O. Yaakobi, L. Friedland, R. R. Lindberg, A. E. Charman, G. Penn, and J. S. Wurtele

Phys. Plasmas 15, 032105 (2008); http://dx.doi.org/10.1063/1.2884717 (6 pages) | Cited 4 times

Online Publication Date: 28 March 2008

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New solutions to the coupled three-wave equations in a nonuniform plasma medium are presented that include both space and time dependence of the waves. By including the dominant nonlinear frequency shift of the material wave, it is shown that if the driving waves are sufficiently strong (in relation to the medium gradient), a nonlinearly phase-locked solution develops that is characteristic of autoresonance. In this case, the material (electrostatic) wave develops into a front starting at the linear resonance point and moving with the wave group velocity in a manner such that the intensity increases linearly with the propagation distance. The forms of the other two (electromagnetic) waves follow naturally from the Manley–Rowe relations.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering

Effect of the radial boundary condition on Alfvén wave dynamics in reduced magnetohydrodynamics

R. E. Denton, B. Rogers, W. Lotko, and A. V. Streltsov

Phys. Plasmas 15, 032106 (2008); http://dx.doi.org/10.1063/1.2898409 (7 pages) | Cited 2 times

Online Publication Date: 28 March 2008

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The effects of different boundary conditions on Alfvén wave dynamics in reduced magnetohydrodynamics are described. If one assumes that the derivative or the second derivative of the electrostatic potential Φ is zero at one of the radial (across the magnetic field) boundaries, radially localized (guided) Alfvén wave solutions are possible, but if Φ is set to zero (grounded) at both boundaries, the solutions consistent with the boundary condition exhibit radial propagation of energy. To confirm the ideas discussed, numerical tests were done in slab geometry with a density gradient across the magnetic field.
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47.35.Tv Magnetohydrodynamic waves
47.65.-d Magnetohydrodynamics and electrohydrodynamics

A novel antiproton radial diagnostic based on octupole induced ballistic loss

G. B. Andresen, W. Bertsche, P. D. Bowe, C. C. Bray, E. Butler, C. L. Cesar, S. Chapman, M. Charlton, J. Fajans, M. C. Fujiwara, R. Funakoshi, D. R. Gill, J. S. Hangst, W. N. Hardy, R. S. Hayano, et al.

Phys. Plasmas 15, 032107 (2008); http://dx.doi.org/10.1063/1.2899305 (8 pages) | Cited 2 times

Online Publication Date: 31 March 2008

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We report results from a novel diagnostic that probes the outer radial profile of trapped antiproton clouds. The diagnostic allows us to determine the profile by monitoring the time history of antiproton losses that occur as an octupole field in the antiproton confinement region is increased. We show several examples of how this diagnostic helps us to understand the radial dynamics of antiprotons in normal and nested Penning–Malmberg traps. Better understanding of these dynamics may aid current attempts to trap antihydrogen atoms.
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37.10.Gh Atom traps and guides
29.40.-n Radiation detectors
36.10.Gv Mesonic, hyperonic and antiprotonic atoms and molecules

Critical loss radius in a Penning trap subject to multipole fields

J. Fajans, N. Madsen, and F. Robicheaux

Phys. Plasmas 15, 032108 (2008); http://dx.doi.org/10.1063/1.2899306 (6 pages) | Cited 6 times

Online Publication Date: 31 March 2008

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When particles in a Penning trap are subject to a magnetic multipole field, those beyond a critical radius will be lost. The critical radius depends on the history by which the field is applied, and can be much smaller if the particles are injected into a preexisting multipole than if the particles are subject to a ramped multipole. Both cases are relevant to ongoing experiments designed to trap antihydrogen.
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29.25.-t Particle sources and targets
52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps
back to top Nonlinear Phenomena, Turbulence, Transport

Magnetic reconnection with electron viscosity in electron magnetohydrodynamics

Huishan Cai and Ding Li

Phys. Plasmas 15, 032301 (2008); http://dx.doi.org/10.1063/1.2876622 (6 pages) | Cited 3 times

Online Publication Date: 4 March 2008

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The general dispersion relation of collisionless reconnection instability due to electron viscosity μe in the whistler frequency is derived. In the framework of electron magnetohydrodynamics (EMHD), the evolution of magnetic reconnection instability is studied, and the linear growth rates are obtained. The scaling laws of the reconnection instability growth rate with respect to the electron viscosity in constant-ψ (used in the tearing mode) and low-k regimes are obtained, respectively, and compare with those obtained in standard magnetohydrodynamic theory. In the constant-ψ regime for “tearing-mode-like” instability, the growth rate is proportional to μe1/4, while in the low-k regime, it is proportional to μe1/8.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Plasmon turbulence spectra with the filamentation patterns in a laser plasma

X. L. Liu, S. Q. Liu, and X. S. Yang

Phys. Plasmas 15, 032302 (2008); http://dx.doi.org/10.1063/1.2842363 (7 pages) | Cited 1 time

Online Publication Date: 4 March 2008

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The instantaneous spectra of the transverse, Langmuir, and ion-sound plasmons near the critical surface in a laser-plasma are numerically obtained from the complete Zakharov equations under the condition of the nonstatic limit. They are used to discuss the filamentation process in the strong Langmuir turbulence. From the turbulence spectra, the energy flux flow from small k space to large k space can be identified. The higher incident laser intensity associated with a quicker filamentation process can also be identified.
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52.35.Ra Plasma turbulence
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Dm Sound waves
52.65.-y Plasma simulation

Dynamics of Langmuir wave decay in two dimensions

L. F. Ziebell, R. Gaelzer, and P. H. Yoon

Phys. Plasmas 15, 032303 (2008); http://dx.doi.org/10.1063/1.2844740 (11 pages) | Cited 12 times

Online Publication Date: 4 March 2008

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The present paper reports on the first two-dimensional (2D) self-consistent solution of weak turbulence equations describing the evolution of electron-beam-plasma interaction in which quasilinear as well as nonlinear three-wave decay processes are taken into account. It is found that the 2D Langmuir wave decay processes lead to the formation of a quasicircular ring spectrum in wave number space. It is also seen that the 2D ring-spectrum of Langmuir turbulence leads to a tendency to isotropic heating of the electrons. These findings contain some important ramifications. First, in the literature, isotropization of energetic electrons, detected in the solar wind for instance, is usually attributed to pitch-angle scattering. The present finding constitutes an alternative mechanism, whose efficiency for other parametric regimes has to be investigated. Second, when projected onto the one-dimensional (1D) space, the 2D ring spectrum may give a false impression of Langmuir waves inverse cascading to longer wavelength regime, when in reality, the wavelength of the turbulence does not change at all but only the wave propagation angle changes. Although the present analysis excludes the induced scattering, which is another process potentially responsible for the inverse cascade, the present finding at least calls for an investigation into the relative efficacy of the inverse-cascading process in 1D vs 2D.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Ra Plasma turbulence
52.40.Mj Particle beam interactions in plasmas
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Transport of perpendicular edge momentum by drift-interchange turbulence and blobs

J. R. Myra, D. A. Russell, and D. A. D’Ippolito

Phys. Plasmas 15, 032304 (2008); http://dx.doi.org/10.1063/1.2889419 (13 pages) | Cited 20 times

Online Publication Date: 14 March 2008

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Turbulence in the vicinity of the last closed surface transports plasma momentum away from the core region toward the wall, and hence provides a momentum “source” that can induce net core plasma rotation as well as sheared flows in the edge. Here, numerical simulations of this process for the binormal (approximately poloidal) component of momentum are described that use a minimal two-dimensional model, in the plane perpendicular to the magnetic field, incorporating directionality (drift-waves), radial transport (Reynolds stress and blobs), and dissipation (sheath loss terms). A zonally averaged momentum conservation law is used to advance the zonal flows. The net momentum transferred to the core is shown to be influenced by a number of physical effects: dissipation, the competition between momentum transport by Reynolds stress and passive convection by particles, intermittency (the role of blobs carrying momentum), and velocity shear regulation of turbulence. It is shown that the edge momentum source adjusts to match the rate of momentum transfer into the core, keeping the edge velocity shear nearly constant. The simulation results are also compared with the predictions of quasilinear theory.
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52.35.Ra Plasma turbulence
52.35.Kt Drift waves
52.55.Fa Tokamaks, spherical tokamaks
52.65.Kj Magnetohydrodynamic and fluid equation

Magnetic field dependence of asymmetry-induced transport: A new approach

D. L. Eggleston and J. M. Williams

Phys. Plasmas 15, 032305 (2008); http://dx.doi.org/10.1063/1.2888500 (6 pages) | Cited 1 time

Online Publication Date: 14 March 2008

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A new technique is used to experimentally study the dependence of asymmetry-induced radial particle flux Γ on an axial magnetic field B in a modified Malmberg–Penning trap. This dependence is complicated by the fact that B enters the physics in at least two places: in the asymmetry-induced first order radial drift velocity vr = Eθ/B and in the zeroth order azimuthal drift velocity vθ = Er/B. To separate these, it is assumed that the latter always enters the physics in the combination ω−lωR, where ωR(r) = vθ/r is the column rotation frequency and ω and l are the asymmetry frequency and azimuthal mode number, respectively. Points where ω−lωR = 0 are then selected from a Γ versus r versus ω data set, thus insuring that any function of this combination is constant. When the selected flux is plotted versus the density gradient ∇n, a roughly linear dependence is observed, showing that the assumption is valid and that the diffusive contribution to the transport has been isolated. The slope of a least-squares fitted line then gives the diffusion coefficient D0 for the selected flux. Varying the magnetic field, it is found that D0∝B−1.33±0.05. This does not match the scaling predicted by resonant particle transport theory.
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52.25.Fi Transport properties
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma

Collision and average velocity effects on the ratchet pinch

M. Vlad, F. Spineanu, and S. Benkadda

Phys. Plasmas 15, 032306 (2008); http://dx.doi.org/10.1063/1.2889432 (9 pages) | Cited 4 times

Online Publication Date: 14 March 2008

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A ratchet-type average velocity VR appears for test particles moving in a stochastic potential and a magnetic field that is space dependent. This model is developed by including particle collisions and an average velocity. We show that these components of the motion can destroy the ratchet velocity but they also can produce significant increase of VR, depending on the parameters. The amplification of the ratchet pinch is a nonlinear effect that appears in the presence of trajectory eddying.
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52.35.Ra Plasma turbulence
52.25.Fi Transport properties
52.20.Dq Particle orbits
52.55.-s Magnetic confinement and equilibrium

“Maximum” entropy production in self-organized plasma boundary layer: A thermodynamic discussion about turbulent heat transport

Z. Yoshida and S. M. Mahajan

Phys. Plasmas 15, 032307 (2008); http://dx.doi.org/10.1063/1.2890189 (6 pages) | Cited 6 times

Online Publication Date: 24 March 2008

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A thermodynamic model of a plasma boundary layer, characterized by enhanced temperature contrasts and “maximum entropy production,” is proposed. The system shows bifurcation if the heat flux entering through the inner boundary exceeds a critical value. The state with a larger temperature contrast (larger entropy production) sustains a self-organized flow. An inverse cascade of energy is proposed as the underlying physical mechanism for the realization of such a heat engine.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.35.Ra Plasma turbulence
52.25.Kn Thermodynamics of plasmas
47.27.T- Turbulent transport processes

Nonlinear dynamics of plasma oscillations modeled by an anharmonic oscillator

H. G. Enjieu Kadji, B. R. Nana Nbendjo, J. B. Chabi Orou, and P. K. Talla

Phys. Plasmas 15, 032308 (2008); http://dx.doi.org/10.1063/1.2841032 (13 pages) | Cited 2 times

Online Publication Date: 25 March 2008

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This paper considers nonlinear dynamics of plasma oscillations modeled by an anharmonic oscillator. These plasma oscillations are described by a nonlinear differential equation of the form math+ε(1+x2)math+x+κx2+δx3 = F cos Ωt. The amplitudes of the forced harmonic, superharmonic, and subharmonic oscillatory states are obtained using the harmonic balance technique and the multiple time scales method. Admissible values of the amplitude of the external strength are derived. Bifurcation sequences displayed by the model for each type of oscillatory states are performed numerically through the fourth-order Runge–Kutta scheme.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
02.60.Lj Ordinary and partial differential equations; boundary value problems

The structure of weak shocks in quantum plasmas

Vitaly Bychkov, Mikhail Modestov, and Mattias Marklund

Phys. Plasmas 15, 032309 (2008); http://dx.doi.org/10.1063/1.2894565 (6 pages) | Cited 7 times

Online Publication Date: 26 March 2008

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The structure of a weak shock in a quantum plasma is studied, taking into account both dissipation terms due to thermal conduction and dispersive quantum terms due to the Bohm potential. Unlike quantum systems without dissipations, even a small thermal conduction may lead to a stationary shock structure. In the limit of zero quantum effects, the monotonic Burgers solution for the weak shock is recovered. Still, even small quantum terms make the structure nonmonotonic with the shock driving a train of oscillations into the initial plasma. The oscillations propagate together with the shock. The oscillations become stronger as the role of Bohm potential increases in comparison with thermal conduction. The results could be of importance for laser-plasma interactions, such as inertial confinement fusion plasmas, and in astrophysical environments, as well as in condensed matter systems.
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52.35.Tc Shock waves and discontinuities

Ion-acoustic shocks in quantum electron-positron-ion plasmas

K. Roy, A. P. Misra, and P. Chatterjee

Phys. Plasmas 15, 032310 (2008); http://dx.doi.org/10.1063/1.2896231 (7 pages) | Cited 33 times

Online Publication Date: 28 March 2008

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Nonlinear propagation of quantum ion-acoustic waves (QIAWs) in a dense quantum plasma whose constituents are electrons, positrons, and positive ions is investigated using a quantum hydrodynamic model. The standard reductive perturbation technique is used to derive the Korteweg–de Vries–Burger (KdVB) equation for QIAWs. It is shown by numerical simulation that the KdVB equation has either oscillatory or monotonic shock wave solutions depending on the system parameters H proportional to quantum diffraction, μi the effect of ion kinematic viscosity, and μ the equilibrium electron to ion density ratio. The results may have relevance in dense astrophysical plasmas (such as neutron stars) as well as in intense laser solid density plasma experiments where the particle density is about 1025−1028 m−3.
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52.35.Tc Shock waves and discontinuities
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.65.-y Plasma simulation
52.27.Ep Electron-positron plasmas

Theory of charged particle heating by low-frequency Alfvén waves

Zehua Guo, Chris Crabtree, and Liu Chen

Phys. Plasmas 15, 032311 (2008); http://dx.doi.org/10.1063/1.2899326 (8 pages) | Cited 2 times

Online Publication Date: 31 March 2008

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The heating of charged particles by a linearly polarized and obliquely propagating shear Alfvén wave (SAW) at frequencies a fraction of the charged particle cyclotron frequency is demonstrated both analytically and numerically. Applying Lie perturbation theory, with the wave amplitude as the perturbation parameter, the resonance conditions in the laboratory frame are systematically derived. At the lowest order, one recovers the well-known linear cyclotron resonance condition k∥v∥−ω−nΩ = 0, where v∥ is the particle velocity parallel to the background magnetic field, k∥ is the parallel wave number, ω is the wave frequency, Ω is the gyrofrequency, and n is any integer. At higher orders, however, one discovers a novel nonlinear cyclotron resonance condition given by k∥v∥−ω−nΩ/2 = 0. Analytical predictions on the locations of fixed points, widths of resonances, and resonance overlapping criteria for global stochasticity are also found to agree with those given by computed Poincaré surfaces of section.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.50.-b Plasma production and heating
back to top Magnetically Confined Plasmas, Heating, Confinement

Observation and modeling of fast trapped ion losses due to neoclassical tearing modes

Emanuele Poli, Manuel García-Muñoz, Hans-Ulrich Fahrbach, Sibylle Günter, and ASDEX Upgrade Team

Phys. Plasmas 15, 032501 (2008); http://dx.doi.org/10.1063/1.2890771 (8 pages) | Cited 6 times

Online Publication Date: 17 March 2008

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Losses of trapped fast ions in the presence of low-frequency modes are observed in the ASDEX Upgrade tokamak [Fusion Science and Technology 44, 569 (2003) , Special Issue on ASDEX Upgrade] during ion-cyclotron heated discharges by means of a new fast-ion-losses detector. The expulsion is explained in terms of the magnetic drift induced by the perturbation field when the ratio between the bounce frequency and the toroidal precession frequency equals the toroidal mode number.
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52.55.Fa Tokamaks, spherical tokamaks
52.80.-s Electric discharges
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

NIMROD resistive magnetohydrodynamic simulations of spheromak physics

E. B. Hooper, B. I. Cohen, H. S. McLean, R. D. Wood, C. A. Romero-Talamás, and C. R. Sovinec

Phys. Plasmas 15, 032502 (2008); http://dx.doi.org/10.1063/1.2890772 (17 pages) | Cited 4 times

Online Publication Date: 26 March 2008

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The physics of spheromak plasmas is addressed by time-dependent, three-dimensional, resistive magnetohydrodynamic simulations with the NIMROD code [ C. R. Sovinec et al., J. Comput. Phys. 195, 355 (2004) ]. Included in some detail are the formation of a spheromak driven electrostatically by a coaxial plasma gun with a flux-conserver geometry and power systems that accurately model the sustained spheromak physics experiment [ R. D. Wood et al., Nucl. Fusion 45, 1582 (2005) ]. The controlled decay of the spheromak plasma over several milliseconds is also modeled as the programmable current and voltage relax, resulting in simulations of entire experimental pulses. Reconnection phenomena and the effects of current profile evolution on the growth of symmetry-breaking toroidal modes are diagnosed; these in turn affect the quality of magnetic surfaces and the energy confinement. The sensitivity of the simulation results addresses variations in both physical and numerical parameters, including spatial resolution. There are significant points of agreement between the simulations and the observed experimental behavior, e.g., in the evolution of the magnetics and the sensitivity of the energy confinement to the presence of symmetry-breaking magnetic fluctuations.
Show PACS
52.65.Kj Magnetohydrodynamic and fluid equation
52.35.Vd Magnetic reconnection
52.55.Tn Ideal and resistive MHD modes; kinetic modes
52.55.Ip Spheromaks
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
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