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November 2009

Volume 16, Issue 11, partial issue

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Counter-facing plasma focus system as a repetitive and/or long-pulse high energy density plasma source

Yutaka Aoyama ,
Mitsuo Nakajima ,
and Kazuhiko Horioka

Phys. Plasmas 16, 110701 (2009) (4 pages)

Online Publication Date: 3 November 2009

Full Text: Read Online | Download PDF (236 KB)

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A plasma focus system composed of a pair of counter-facing coaxial plasma guns is proposed as a long-pulse and/or repetitive high energy density plasma source. A proof-of-concept experiment demonstrated that with an assist of breakdown and outer electrode connections, current sheets evolved into a configuration for stable plasma confinement at the center of the electrodes. The current sheets could successively compress and confine the high energy density plasma every half period of the discharge current, enabling highly repetitive light emissions in extreme ultraviolet region with time durations in at least ten microseconds.
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52.75.-d Plasma devices
52.50.Dg Plasma sources
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.80.Yr Discharges for spectral sources (including inductively coupled plasma)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Geometry dependence of stellarator turbulence

H. Mynick ,
P. Xanthopoulos ,
and A. Boozer

Phys. Plasmas 16, 110702 (2009) (4 pages)

Online Publication Date: 10 November 2009

Full Text: Read Online | Download PDF (802 KB)

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Using the nonlinear gyrokinetic code package GENE/GIST [ F. Jenko, W. Dorland, M. Kotschenreuther, and B. N. Rogers, Phys. Plasmas 7, 1904 (2000) ; P. Xanthopoulos, W. A. Cooper, F. Jenko, Yu. Turkin, A. Runov, and J. Geiger, Phys. Plasmas 16, 082303 (2009) ], we study the turbulent transport in a broad family of stellarator designs, to understand the geometry dependence of the microturbulence. By using a set of flux tubes on a given flux surface, we construct a picture of the two-dimensional structure of the microturbulence over that surface and relate this to relevant geometric quantities, such as the curvature, local shear, and effective potential in the Schrödinger-like equation governing linear drift modes.
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52.55.Jd Magnetic mirrors, gas dynamic traps
52.65.Tt Gyrofluid and gyrokinetic simulations
52.35.Ra Plasma turbulence

Current sheet bifurcation and collapse in electron magnetohydrodynamics

A. Zocco ,
L. Chacón ,
and Andrei Simakov

Phys. Plasmas 16, 110703 (2009) (4 pages)

Online Publication Date: 16 November 2009

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Inertial effects in nonlinear magnetic reconnection are studied within the context of two-dimensional electron magnetohydrodynamics with resistive and viscous dissipation. Families of nonlinear solutions for relevant current sheet parameters are predicted and confirmed numerically in all regimes of interest. Electron inertia becomes important for current sheet thicknesses δ below the inertial length de. In this case, in the absence of electron viscosity, the sheet thickness experiences a nonlinear collapse to arbitrarily small scales. Viscosity regularizes solutions at small scales. The transition between resistive and viscous regimes features a hysteresis bifurcation that describes suitable current sheet solutions and reconnection rates. Away from transition, the nonlinear reconnection rate is found not to be explicitly dependent on the electron inertia or dissipation coefficients.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Vd Magnetic reconnection

Long-distance correlation and zonal flow structures induced by mean E×B shear flows in the biasing H-mode at TEXTOR

Y. Xu ,
S. Jachmich ,
R. Weynants ,
M. Van Schoor ,
M. Vergote ,
A. Krämer-Flecken ,
O. Schmitz ,
B. Unterberg ,
and C. Hidalgo

Phys. Plasmas 16, 110704 (2009) (4 pages)

Online Publication Date: 18 November 2009

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Long-distance toroidal correlations of potential and density fluctuations have been investigated at the TEXTOR tokamak [ H. Soltwisch et al., Plasma Phys. Controlled Fusion 26, 23 (1984) ] in edge electrode-biasing experiments. During the biasing-induced H-mode, the dc E×B shear flow triggers a zonal flow structure and hence long-distance correlation in potential fluctuations, whereas for density fluctuations there is nearly no correlation. These results indicate an intimate interaction between the mean and zonal flows, and the significance of long range correlations in improved-confinement regimes.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Fa Tokamaks, spherical tokamaks
52.25.Gj Fluctuation and chaos phenomena
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
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back to top Basic Plasma Phenomena, Waves, Instabilities

Langmuir wave linear evolution in inhomogeneous nonstationary anisotropic plasma

I. Dodin ,
V. Geyko ,
and N. Fisch

Phys. Plasmas 16, 112101 (2009) (9 pages)

Online Publication Date: 2 November 2009

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A hydrodynamic equation describing the linear evolution of a nondissipative Langmuir wave in inhomogeneous nonstationary anisotropic plasma without magnetic field is derived in the geometrical optics approximation. The continuity equation for the wave action density, anticipated from general principles, is then confirmed ab initio, and the conditions for the action conservation are formulated. Given those, the wave field math universally scales with the electron density N as math∝N3/4 in homogeneous plasma, whereas the wavevector evolution varies depending on the wave geometry.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.25.-b Plasma properties

Fast reconnection in high-Lundquist-number plasmas due to the plasmoid Instability

A. Bhattacharjee ,
Yi-Min Huang ,
H. Yang ,
and B. Rogers

Phys. Plasmas 16, 112102 (2009) (5 pages)

Online Publication Date: 11 November 2009

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Thin current sheets in systems of large size that exceed a critical value of the Lundquist number are unstable to a super-Alfvénic tearing instability, referred to hereafter as the plasmoid instability. The scaling of the growth rate of the most rapidly growing plasmoid instability with respect to the Lundquist number is shown to follow from the classical dispersion relation for tearing modes. As a result of this instability, the system realizes a nonlinear reconnection rate that appears to be weakly dependent on the Lundquist number, and larger than the Sweet–Parker rate by nearly an order of magnitude (for the range of Lundquist numbers considered). This regime of fast reconnection is realizable in a dynamic and highly unstable thin current sheet, without requiring the current sheet to be turbulent.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Ra Plasma turbulence
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Plasmons with orbital angular momentum

J. Mendonca ,
S. Ali ,
and B. Thidé

Phys. Plasmas 16, 112103 (2009) (5 pages)

Online Publication Date: 11 November 2009

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Electron plasma waves carrying orbital angular momentum are investigated in an unmagnetized collisionless plasma composed of inertial electrons and static ions. For this purpose, the usual plasmon dispersion relation is employed to derive an approximate paraxial equation. The latter is analyzed with a Gaussian beam solution. For a finite angular momentum associated with the plasmon, Laguerre–Gaussian (LG) solutions are employed for solving the electrostatic potential problem which gives approximate solution and is valid for plasmon beams in the paraxial approximation. The LG potential determines the electric field components and energy flux of plasmons with finite angular momentum. Numerical illustrations show that the radial and angular mode numbers strongly modify the profiles of the LG potential.
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52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
72.30.+q High-frequency effects; plasma effects
52.25.Fi Transport properties

Destabilizing effect of density gradient on the Kelvin–Helmholtz instability

L. Wang ,
C. Xue ,
W. Ye ,
and Y. Li

Phys. Plasmas 16, 112104 (2009) (6 pages)

Online Publication Date: 18 November 2009

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In this paper, we derive explicit analytic formulas for the linear growth rate and frequency of the Kelvin–Helmholtz instability in fluids with the density gradient. The analytic formulas are in excellent agreement with the results of two-dimensional numerical simulation. We found that the density gradient effect enforces (destabilizes) the Kelvin–Helmholtz instability by increasing its linear growth rate in the direction normal to the perturbed interface. The frequency is reduced (stabilized) by the density gradient effect, i.e., the density gradient decreases the transmission of the perturbation in the direction along to the perturbed interface. In most cases, the combined effect of density and velocity gradients stabilizes the Kelvin–Helmholtz instability.
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47.20.Ft Instability of shear flows (e.g., Kelvin-Helmholtz)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.57.Fg Implosion symmetry and hydrodynamic instability (Rayleigh-Taylor, Richtmyer-Meshkov, imprint, etc.)

Fitting the dielectric response of collisionless plasmas by continued fractions

August Wierling

Phys. Plasmas 16, 112105 (2009) (6 pages)

Online Publication Date: 18 November 2009

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An approximation scheme for the dielectric response of thermal collisionless plasmas at arbitrary degeneracy is presented. A T-fraction representation is obtained from the known expansions of the real part of the dielectric function for small and large arguments. The partial numerators and denominators of the continued fraction are generated by a modified QD algorithm. For several typical values of the degeneracy parameter θ, extensive tables for the expansion coefficients and the partial numerators and denominators are given, allowing for an easy implementation of the fitting function. Also, an error analysis is performed.
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52.25.Mq Dielectric properties

Dressed soliton in quantum dusty pair-ion plasma

Prasanta Chatterjee ,
Kaushik Roy ,
S. Muniandy ,
and C. Wong

Phys. Plasmas 16, 112106 (2009) (6 pages)

Online Publication Date: 19 November 2009

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Nonlinear propagation of a quantum ion-acoustic dressed soliton is studied in a dusty pair-ion plasma. The Korteweg–de Vries (KdV) equation is derived using reductive perturbation technique. A higher order inhomogeneous differential equation is obtained for the higher order correction. The expression for a dressed soliton is calculated using a renormalization method. The expressions for higher order correction are determined using a series solution technique developed by Chatterjee et al. [Phys. Plasmas 16, 072102 (2009)] .
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.65.Vv Perturbative methods
back to top Nonlinear Phenomena, Turbulence, Transport

Anomalous transport of energetic particles in ITER relevant scenarios

M. Albergante ,
J. Graves ,
A. Fasoli ,
F. Jenko ,
and T. Dannert

Phys. Plasmas 16, 112301 (2009) (8 pages)

Online Publication Date: 2 November 2009

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The anomalous transport of energetic ions in the presence of turbulent fields is investigated. Nonlinear simulations of a steady-state ITER [ R. Aymar et al., Nucl. Fusion 41, 1301 (2001) ] scenario have been carried out using the gyrokinetic turbulence code GENE [ F. Jenko et al., Phys. Plasmas 7, 1904 (2000) ], modeling the suprathermal particles as high temperature Maxwellian distributions in the passive tracer limit. Velocity space analysis shows that single particle diffusivities of ions above the critical energy are significantly larger than their neoclassical counterpart.
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52.55.Pi Fusion products effects (e.g., alpha-particles, etc.), fast particle effects
52.35.Ra Plasma turbulence

Coupled nonlinear drift and ion acoustic waves in dense dissipative electron-positron-ion magnetoplasmas

W. Masood ,
S. Karim ,
H. Shah ,
and M. Siddiq

Phys. Plasmas 16, 112302 (2009) (7 pages)

Online Publication Date: 4 November 2009

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Linear and nonlinear propagation characteristics of drift ion acoustic waves are investigated in an inhomogeneous electron-positron-ion (e-p-i) quantum magnetoplasma with neutrals in the background using the well known quantum hydrodynamic model. In this regard, Korteweg–de Vries–Burgers (KdVB) and Kadomtsev–Petviashvili–Burgers (KPB) equations are obtained. Furthermore, the solutions of KdVB and KPB equations are presented by using the tangent hyperbolic (tanh) method. The variation in the shock profile with the quantum Bohm potential, collision frequency, and the ratio of drift to shock velocity in the comoving frame, v*/u, is also investigated. It is found that increasing the positron concentration and collision frequency decreases the strength of the shock. It is also shown that when the localized structure propagates with velocity greater than the diamagnetic drift velocity (i.e., u>v*), the shock strength decreases. However, the shock strength is observed to increase when the localized structure propagates with velocity less than that of drift velocity (i.e., u<v*). The relevance of the present investigation with regard to dense astrophysical environments is also pointed out.
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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.Kt Drift waves
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Tc Shock waves and discontinuities
95.30.Qd Magnetohydrodynamics and plasmas

Size scaling effects on the particle density fluctuations in confined plasmas

Federico Vázquez
and Ferenc Márkus

Phys. Plasmas 16, 112303 (2009) (6 pages)

Online Publication Date: 10 November 2009

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In this paper, memory and nonlocal effects on fluctuating mass diffusion are addressed in the context of fusion plasmas. Nonlocal effects are included by considering a diffusivity coefficient depending on the size of the container in the transverse direction to the applied magnetic field. It is obtained by resorting to the general formulation of the extended version of irreversible thermodynamics in terms of the higher order dissipative fluxes. The developed model describes two different types of the particle density time correlation function. Both have been observed in tokamak and nontokamak devices. These two kinds of time correlation function characterize the wave and the diffusive transport mechanisms of particle density perturbations. A transition between them is found, which is controlled by the size of the container. A phase diagram in the {L,2π/k} space describes the relation between the dynamics of particle density fluctuations and the size L of the system together with the oscillating mode k of the correlation function.
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52.25.Gj Fluctuation and chaos phenomena
52.35.−g
05.40.−a
05.70.Fh Phase transitions: general studies

Nonlinear stopping power for ions moving in magnetized two-component plasmas

Zhang-Hu Hu ,
Yuan-Hong Song ,
Gui-Qiu Wang ,
and You-Nian Wang

Phys. Plasmas 16, 112304 (2009) (6 pages)

Online Publication Date: 12 November 2009

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Energy losses of test particles in magnetized two-component plasmas are investigated by means of particle-in-cell (PIC) simulations, taking into account the dynamic polarization effects of both the plasma ions and electrons. The influences of the magnetic field, the angle between the test particle velocity and magnetic field, and certain plasma parameters on the nonlinear stopping power are studied. Comparisons are made between the PIC simulations and the linearized dielectric theory to show the nonlinear effects on the stopping power. Simulation results show that the dynamic polarization effects of the plasma ions become significant and contribute mainly to the nonlinear stopping power for low particle velocities and strong magnetic field. The nonlinear effects are found to enhance the stopping power in low particle velocity regions.
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52.20.-j Elementary processes in plasmas
52.25.Tx Emission, absorption, and scattering of particles
52.25.Mq Dielectric properties
52.25.Fi Transport properties
77.22.Ej Polarization and depolarization

Effects of trapped electrons on electromagnetic fields in an oblique shock wave

Mieko Toida
and Kenta Shikii

Phys. Plasmas 16, 112305 (2009) (9 pages)

Online Publication Date: 18 November 2009

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A magnetosonic shock wave propagating obliquely to an external magnetic field can trap electrons and accelerate them to ultrarelativistic energies. The effect of trapped electrons on electromagnetic fields in a shock wave is studied by theory and particle simulations. The expressions for field strengths are analytically obtained, including the number of trapped electrons nt as a factor. It is shown that as nt increases, the magnitude of F increases, where F is the integral of the parallel electric field, E∥ = (E⋅B)/B, along B. Theoretical analysis also suggests that the increase in F causes the electrons to be trapped deeper and accelerated to higher kinetic energies. These theoretical predictions are verified with relativistic electromagnetic particle simulations.
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52.35.Tc Shock waves and discontinuities
52.50.Lp Plasma production and heating by shock waves and compression
52.65.-y Plasma simulation
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.25.Fi Transport properties

Stochastic analysis of pitch angle scattering of charged particles by transverse magnetic waves

Don Lemons ,
Kaijun Liu ,
Dan Winske ,
and S. Gary

Phys. Plasmas 16, 112306 (2009) (11 pages)

Online Publication Date: 19 November 2009

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This paper describes a theory of the velocity space scattering of charged particles in a static magnetic field composed of a uniform background field and a sum of transverse, circularly polarized, magnetic waves. When that sum has many terms the autocorrelation time required for particle orbits to become effectively randomized is small compared with the time required for the particle velocity distribution to change significantly. In this regime the deterministic equations of motion can be transformed into stochastic differential equations of motion. The resulting stochastic velocity space scattering is described, in part, by a pitch angle diffusion rate that is a function of initial pitch angle and properties of the wave spectrum. Numerical solutions of the deterministic equations of motion agree with the theory at all pitch angles, for wave energy densities up to and above the energy density of the uniform field, and for different wave spectral shapes.
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52.27.Ny Relativistic plasmas
52.25.Fi Transport properties
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams

Nonlinear screening effect in an ultrarelativistic degenerate electron-positron gas

N. Tsintsadze ,
A. Rasheed ,
H. Shah ,
and G. Murtaza

Phys. Plasmas 16, 112307 (2009) (6 pages)

Online Publication Date: 20 November 2009

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Nonlinear screening process in an ultrarelativistic degenerate electron-positron gas has been investigated by deriving a generalized nonlinear Poisson equation for the electrostatic potential. In the simple one-dimensional case, the nonlinear Poisson equation leads to Debye-like (Coulomb-like) solutions at distances larger (less) than the characteristic length. When the electrostatic energy is larger than the thermal energy, this nonlinear Poisson equation converts into the relativistic Thomas–Fermi equation whose asymptotic solution in three dimensions shows that the potential field goes to zero at infinity much more slowly than the Debye potential. The possibility of the formation of a bound state in electron-positron plasma is also indicated. Further, it is investigated that the strong spatial fluctuations of the potential field may reduce the screening length and that the root mean square of this spatial fluctuating potential goes to zero for large r rather slowly as compared to the case of the Debye potential.
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52.27.Ny Relativistic plasmas
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.Kn Thermodynamics of plasmas
52.25.Gj Fluctuation and chaos phenomena

The effect of parallel electric field in shock waves on the acceleration of relativistic ions, electrons, and positrons

Seiichi Takahashi ,
Hiromasa Kawai ,
Yukiharu Ohsawa ,
Shunsuke Usami ,
Charles Chiu ,
and Wendell Horton

Phys. Plasmas 16, 112308 (2009) (10 pages)

Online Publication Date: 20 November 2009

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The effect of an electric field E∥ parallel to the magnetic field B on particle acceleration in shock waves is studied. With test particle calculations, for which the electromagnetic fields of shock waves are obtained from one-dimensional, fully kinetic, electromagnetic, particle simulations, the motions of relativistic ions, electrons, and positrons are analyzed. In these simulations, the shock speed vsh is taken to be close to c cos θ, where θ is the angle between the external magnetic field and wave normal, and thus strong particle acceleration takes place. Test particle motions calculated in two different methods are compared: In the first method the total electric field E is used in the equation of motion, while in the second method E∥ is omitted. The comparison confirms that in the acceleration of relativistic ions E∥ is unimportant for high-energy particles. For the acceleration of electrons and positrons, however, E∥ is essential.
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52.65.Cc Particle orbit and trajectory
52.35.Tc Shock waves and discontinuities
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.65.Rr Particle-in-cell method
back to top Magnetically Confined Plasmas, Heating, Confinement

A closure scheme for modeling rf modifications to the fluid equations

C. Hegna
and J. Callen

Phys. Plasmas 16, 112501 (2009) (6 pages)

Online Publication Date: 2 November 2009

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A procedure to include the effects of externally applied rf sources in a comprehensive fluid model is outlined. The fluid equations are derived from moments of a kinetic equation that includes the effects of an rf source. In general, this source produces additional terms in each of the fluid equations. A complete derivation requires the specification of the closure moments; calculations for the stress tensors and heat fluxes that are altered by the presence of the rf are required. By treating the rf induced modification as producing a small distortion away from the background Maxwellian distribution function, a procedure for calculating the closure moments can be formulated. Using a Chapman–Enskog-like procedure, a kinetic equation for the kinetic distortion can be derived that includes the rf-induced contributions to the fluid equations as sources.
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52.25.Dg Plasma kinetic equations
52.30.Ex Two-fluid and multi-fluid plasmas
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Wq Current drive; helicity injection

Steady state self-induced current in tokamak

Yu. Gott
and E. Yurchenko

Phys. Plasmas 16, 112502 (2009) (5 pages)

Online Publication Date: 3 November 2009

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A model, which may make it possible to self-consistently calculate the self-driven current in tokamaks taking into account asymmetry and bootstrap currents, is presented. It is shown that the described self-driven current can provide steady-state tokamak operation without the seed current produced with the help of additional methods. The total self-consistent, self-driven current does not depend on magnetic field magnitude and is proportional to the square root from plasma pressure. The experimental data obtained in the National Spherical Torus Experiment are satisfactorily described by this model.
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52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties

Linearized model collision operators for multiple ion species plasmas and gyrokinetic entropy balance equations

H. Sugama ,
T.-H. Watanabe ,
and M. Nunami

Phys. Plasmas 16, 112503 (2009) (16 pages)

Online Publication Date: 4 November 2009

Full Text: Read Online | Download PDF (391 KB)

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Linearized model collision operators for multiple ion species plasmas are presented that conserve particles, momentum, and energy and satisfy adjointness relations and Boltzmann’s H-theorem even for collisions between different particle species with unequal temperatures. The model collision operators are also written in the gyrophase-averaged form that can be applied to the gyrokinetic equation. Balance equations for the turbulent entropy density, the energy of electromagnetic fluctuations, the turbulent transport fluxes of particle and heat, and the collisional dissipation are derived from the gyrokinetic equation including the collision term and Maxwell equations. It is shown that, in the steady turbulence, the entropy produced by the turbulent transport fluxes is dissipated in part by collisions in the nonzonal-mode region and in part by those in the zonal-mode region after the nonlinear entropy transfer from nonzonal to zonal modes.
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52.25.Dg Plasma kinetic equations
52.25.Xz Magnetized plasmas
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Ra Plasma turbulence

Dynamically stable, self-similarly evolving, and self-organized states of high beta tokamak and reversed pinch plasmas and advanced active control

Yoshiomi Kondoh
and Toshinobu Fukasawa

Phys. Plasmas 16, 112504 (2009) (11 pages)

Online Publication Date: 6 November 2009

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Generalized simultaneous eigenvalue equations derived from a generalized theory of self-organization are applied to a set of simultaneous equations for two-fluid model plasmas. An advanced active control by using theoretical time constants is proposed by predicting quantities to be controlled. Typical high beta numerical configurations are presented for the ultra low q tokamak plasmas and the reversed-field pinch (RFP) ones in cylindrical geometry by solving the set of simultaneous eigenvalue equations. Improved confinement with no detectable saw-teeth oscillations in tokamak experiments is reasonably explained by the shortest time constant of ion flow. The shortest time constant of poloidal ion flow is shown to be a reasonable mechanism for suppression of magnetic fluctuations by pulsed poloidal current drives in RFP experiments. The bifurcation from basic eigenmodes to mixed ones deduced from stability conditions for eigenvalues is shown to be a good candidate for the experimental bifurcation from standard RFP plasmas to their improved confinement regimes.
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52.55.Fa Tokamaks, spherical tokamaks
52.30.Ex Two-fluid and multi-fluid plasmas
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.55.Ez Theta pinch

Variational coordinate transformation in plasma physics

Ryan White ,
Emila Solano ,
and R. Hazeltine

Phys. Plasmas 16, 112505 (2009) (6 pages)

Online Publication Date: 6 November 2009

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It is well-known from scaling arguments that action-based field theories do not possess localized solutions in spaces of more than one dimension. The same scaling argument, modified to account for external forces, is applied to magnetic plasma confinement in an axisymmetric torus. It yields an integral solvability condition of some interest.
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52.55.Jd Magnetic mirrors, gas dynamic traps
52.25.Fi Transport properties
02.30.Sa Functional analysis

Hollow current profile scenarios for advanced tokamak reactor operations

P.-A. Gourdain
and J.-N. Leboeuf

Phys. Plasmas 16, 112506 (2009) (6 pages)

Online Publication Date: 10 November 2009

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Advanced tokamak scenarios are a possible approach to boosting reactor performances. Such schemes usually trigger current holes, a particular magnetohydrodynamics equilibrium where no current or pressure gradients exist in the core of the plasma. While such equilibria have large bootstrap fractions, flat pressure profiles in the plasma core may not be optimal for a reactor. However, moderate modifications of the equilibrium current profile can lead to diamagnetism where most of the pressure gradient is now balanced by poloidal currents and the toroidal magnetic field. In this paper, we consider the properties of diamagnetic current holes, also called “dual equilibria,” and demonstrate that fusion throughput can be significantly increased in such scenarios. Their stability is investigated using the DCON code. Plasmas with a beta peak of 30% and an average beta of 6% are found stable to both fixed and free-boundary modes with toroidal mode numbers n = 1–4, as well as Mercier and high-n ballooning modes. This is not surprising as these scenarios have a normal beta close to 3.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Tn Ideal and resistive MHD modes; kinetic modes
52.55.Fa Tokamaks, spherical tokamaks

Electron gyroscale fluctuation measurements in National Spherical Torus Experiment H-mode plasmas

D. Smith ,
S. Kaye ,
W. Lee ,
E. Mazzucato ,
H. Park ,
R. Bell ,
C. Domier ,
B. LeBlanc ,
F. Levinton ,
N. Luhmann ,
J. Menard ,
and H. Yuh

Phys. Plasmas 16, 112507 (2009) (8 pages)

Online Publication Date: 11 November 2009

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A collective scattering system has measured electron gyroscale fluctuations in National Spherical Torus Experiment [ M. Ono et al., Nucl. Fusion 40, 557 (2000) ] H-mode plasmas to investigate electron temperature gradient (ETG) turbulence. Observations and results pertaining to fluctuation measurements in ETG-stable regimes, the toroidal field scaling of fluctuation amplitudes, the relation between fluctuation amplitudes and transport quantities, and fluctuation magnitudes and k-spectra are presented. Collectively, the measurements provide insight and guidance for understanding ETG turbulence and anomalous electron thermal transport.
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52.35.Ra Plasma turbulence
52.55.Fa Tokamaks, spherical tokamaks
52.65.Tt Gyrofluid and gyrokinetic simulations
52.70.Gw Radio-frequency and microwave measurements

Relaxation of spheromak configurations with open flux

Pablo García-Martínez
and Ricardo Farengo

Phys. Plasmas 16, 112508 (2009) (9 pages)

Online Publication Date: 16 November 2009

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The relaxation of several kink unstable equilibria with open flux representative of spheromaks sustained by dc helicity injection is studied by means of three-dimensional, resistive magnetohydrodynamic simulations. No external driving is applied, but the initial conditions are chosen to reproduce the current profiles existing in a gun driven spheromak, which has a high current density in the open flux region and a low current density in the closed flux region. The growth and nonlinear saturation of various unstable modes, the dynamo action which converts toroidal flux into poloidal flux, and the evolution of the λ profile (λ = μ0J⋅B/B2) are studied. An initial condition is found which results in a dynamo that produces enough poloidal flux to compensate the resistive losses occurred during a characteristic time of the instability. The flux amplification factor around which this case oscillates is consistent with existing experimental data. During the relaxation, the central open flux tube develops a helical distortion and the closed flux surfaces are destroyed. After the relaxation event, close flux surfaces form again but the final profiles are not fully relaxed and the central open flux tube remains distorted. The effect of the Lundquist number on the evolution and its impact on the required level of fluctuations are evaluated. Finally, the dynamics of the system for different current levels in the open flux region is studied.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.65.Kj Magnetohydrodynamic and fluid equation
52.55.Jd Magnetic mirrors, gas dynamic traps
52.55.Ip Spheromaks
52.25.Gj Fluctuation and chaos phenomena
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Ion flow measurements and plasma current analysis in the Irvine Field Reversed Configuration

W. Harris ,
E. Trask ,
T. Roche ,
E. Garate ,
W. Heidbrink ,
and R. McWilliams

Phys. Plasmas 16, 112509 (2009) (10 pages)

Online Publication Date: 20 November 2009

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Measurements of the Doppler shift of impurity lines indicate that there is an ion flow of ∼ 7 km/s in the Irvine Field Reversed Configuration. A charge-exchange neutral particle analyzer shows the peak energy is below the 20 eV minimum detectable energy threshold, which is in agreement with the spectroscopic data. By evaluating the collision times between the impurities and hydrogen, the dominant plasma ion species, it is concluded that the ions rotate with an angular frequency of ∼ 4×104 rad/s. Estimates of the ion current in the laboratory frame indicate it is one to two orders of magnitude larger than the measured plasma current of 15 kA. Electron drifts are expected to cancel most of the ion current based on the measured magnetic fields and calculated electric fields.
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52.25.Fi Transport properties
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.70.-m Plasma diagnostic techniques and instrumentation

Electron-cyclotron wave scattering by edge density fluctuations in ITER

Christos Tsironis ,
Arthur Peeters ,
Heinz Isliker ,
Dafni Strintzi ,
Ioanna Chatziantonaki ,
and Loukas Vlahos

Phys. Plasmas 16, 112510 (2009) (4 pages)

Online Publication Date: 20 November 2009

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The effect of edge turbulence on the electron-cyclotron wave propagation in ITER is investigated with emphasis on wave scattering, beam broadening, and its influence on localized heating and current drive. A wave used for electron-cyclotron current drive (ECCD) must cross the edge of the plasma, where density fluctuations can be large enough to bring on wave scattering. The scattering angle due to the density fluctuations is small, but the beam propagates over a distance of several meters up to the resonance layer and even small angle scattering leads to a deviation of several centimeters at the deposition location. Since the localization of ECCD is crucial for the control of neoclassical tearing modes, this issue is of great importance to the ITER design. The wave scattering process is described on the basis of a Fokker–Planck equation, where the diffusion coefficient is calculated analytically as well as computed numerically using a ray tracing code.
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05.40.−a
42.25.Fx Diffraction and scattering
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
back to top Inertially Confined Plasmas, High Energy Density Plasma Science, Warm Dense Matter

Spherical Rayleigh–Taylor growth of three-dimensional broadband perturbations on OMEGA

V. Smalyuk ,
S. Hu ,
J. Hager ,
J. Delettrez ,
D. Meyerhofer ,
T. Sangster ,
and D. Shvarts

Phys. Plasmas 16, 112701 (2009) (6 pages)

Online Publication Date: 2 November 2009

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Spherical Rayleigh–Taylor (RT) growth experiments of three-dimensional (3D) broadband nonuniformities were conducted in the acceleration phase of spherical implosions on OMEGA [ T. R. Boehly et al., Opt. Commun. 133, 495 (1997) ]. The targets consisted of 20- and 24-μm-thick plastic spherical shells having diagnostic openings for backlighter x rays to image shell modulations. Experiments were conducted with square laser pulses at a low drive intensity of ∼ 2×1014 W/cm2, high drive intensity of ∼ 1×1015 W/cm2, and a shaped pulse consisting of a low-intensity foot and high-intensity drive part (peak intensity of ∼ 1×1015 W/cm2). In low-intensity experiments, large RT growth was measured, resulting in shells being broken up by 3D modulations at the end of the drive. In the high-intensity experiments, no RT growth of the 3D modulations was detected. In the shaped-pulse experiments, perturbations grew during the low-intensity part of the drive and were stabilized later during the high-intensity part of the drive. The measured RT growth stabilization with the high-intensity drive was similar to previous observations in planar geometry [ V. A. Smalyuk et al., Phys. Rev. Lett. 101, 025002 (2008) ].
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52.70.-m Plasma diagnostic techniques and instrumentation
52.57.Fg Implosion symmetry and hydrodynamic instability (Rayleigh-Taylor, Richtmyer-Meshkov, imprint, etc.)
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Transport of energy by ultraintense laser-generated electrons in nail-wire targets

T. Ma ,
M. Key ,
R. Mason ,
K. Akli ,
R. Daskalova ,
R. Freeman ,
J. Green ,
K. Highbarger ,
P. Jaanimagi ,
J. King ,
K. Lancaster ,
S. Hatchett ,
A. Mackinnon ,
A. MacPhee ,
P. Norreys ,
P. Patel ,
R. Stephens ,
W. Theobald ,
L. Van Woerkom ,
M. Wei ,
S. Wilks ,
and F. Beg

Phys. Plasmas 16, 112702 (2009) (8 pages)

Online Publication Date: 4 November 2009

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Nail-wire targets (20 μm diameter copper wires with 80 μm hemispherical head) were used to investigate energy transport by relativistic fast electrons generated in intense laser-plasma interactions. The targets were irradiated using the 300 J, 1 ps, and 2×1020 W⋅cm−2 Vulcan laser at the Rutherford Appleton Laboratory. A spherically bent crystal imager, a highly ordered pyrolytic graphite spectrometer, and single photon counting charge-coupled device gave absolute Cu Kα measurements. Results show a concentration of energy deposition in the head and an approximately exponential fall-off along the wire with about 60 μm 1/e decay length due to resistive inhibition. The coupling efficiency to the wire was 3.3±1.7% with an average hot electron temperature of 620±125 keV. Extreme ultraviolet images (68 and 256 eV) indicate additional heating of a thin surface layer of the wire. Modeling using the hybrid E-PLAS code has been compared with the experimental data, showing evidence of resistive heating, magnetic trapping, and surface transport.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.27.Ny Relativistic plasmas
52.40.Mj Particle beam interactions in plasmas
52.25.Fi Transport properties

Enhancement of backward Raman scattering by electron-ion collisions

Z. Liu ,
Shao-ping Zhu ,
L. Cao ,
C. Zheng ,
X. He ,
and Yugang Wang

Phys. Plasmas 16, 112703 (2009) (4 pages)

Online Publication Date: 4 November 2009

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The propagation of light waves in an underdense plasma is studied using one-dimensional Vlasov–Maxwell numerical simulation. It is found that the backward stimulated Raman scattering will be enhanced by electron-ion collisions. With appropriate electron-ion collision rate the Langmuir waves, driven via SRS, can be made to propagate for a long distance.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.20.-j Elementary processes in plasmas

Hot electron generation forming a steep interface in superintense laser-matter interaction

R. Mishra ,
Y. Sentoku ,
and A. Kemp

Phys. Plasmas 16, 112704 (2009) (9 pages)

Online Publication Date: 12 November 2009

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Superintense laser light (>1020 W/cm2) is able to sweep the preplasma over short times and compress the preplasma density gradient typically generated by the prepulse of today’s high-intensity, high energy laser systems. Hot electron generation at steep plasma density gradients has been studied in a previous paper [ A. J. Kemp, Y. Sentoku, and M. Tabak, Phys. Rev. Lett. 101, 075004 (2008) ], which identified a mode of hot electron acceleration that is characterized by the formation of low-density shelf in front of the target. In this paper, we deal with laser incidence on slab target in one-dimensional situation and follow the formation of a steep interface and hot electron acceleration up to later stages of the interaction. We find that a novel mode of absorption appears during which the coupling efficiency drops, while a large number of sub-MeV hot electrons is produced at the interface. These dc-ponderomotive electrons play a dominant role in the bulk heating of solid density targets. We propose an analytical model to describe this absorption mode, explain electron energy spectra, and identify the parameter regime where it appears.
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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
52.65.Rr Particle-in-cell method

Wall shocks in high-energy-density shock tube experiments

F. Doss ,
H. Robey ,
R. Drake ,
and C. Kuranz

Phys. Plasmas 16, 112705 (2009) (6 pages)

Online Publication Date: 13 November 2009

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The radiative precursor of a sufficiently fast shock has been observed to drive the vaporization of shock tube material ahead of the shock. The resulting expansion drives a converging blast wave into the gas volume of the tube. The effects of this wall shock may be observed and correlated with primary shock parameters. We demonstrate this process in experiments performed on the Omega Laser Facility, launching shocks propagating through xenon with speeds above 100 km/s driven by ablation pressures of approximately 50 Mbars. Wall shocks in laser experiments, in which the principal shock waves themselves should not be radiative, are also reported—in which the wall shocks have been launched by some other early energy source.
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52.35.Tc Shock waves and discontinuities
47.40.Rs Detonation waves
52.38.Mf Laser ablation
52.50.Lp Plasma production and heating by shock waves and compression
52.40.Hf Plasma-material interactions; boundary layer effects

Neutron yield study of direct-drive, low-adiabat cryogenic D2 implosions on OMEGA laser system

S. Hu ,
P. Radha ,
J. Marozas ,
R. Betti ,
T. Collins ,
R. Craxton ,
J. Delettrez ,
D. Edgell ,
R. Epstein ,
V. Goncharov ,
I. Igumenshchev ,
F. Marshall ,
R. McCrory ,
D. Meyerhofer ,
S. Regan ,
T. Sangster ,
S. Skupsky ,
V. Smalyuk ,
Y. Elbaz ,
and D. Shvarts

Phys. Plasmas 16, 112706 (2009) (11 pages)

Online Publication Date: 16 November 2009

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Neutron yields of direct-drive, low-adiabat (α ≈ 2 to 3) cryogenic D2 target implosions on the OMEGA laser system [ T. R. Boehly et al., Opt. Commun. 133, 495 (1997) ] have been systematically investigated using the two-dimensional (2D) radiation hydrodynamics code DRACO [ P. B. Radha et al., Phys. Plasmas 12, 056307 (2005) ]. Low-mode (ℓ ≤ 12) perturbations, including initial target offset, ice-layer roughness, and laser-beam power imbalance, were found to be the primary source of yield reduction for thin-shell (5 μm), low-α, cryogenic targets. The 2D simulations of thin-shell implosions track experimental measurements for different target conditions and peak laser intensities ranging from 2.5×1014–6×1014 W/cm2. Simulations indicate that the fusion yield is sensitive to the relative phases between the target offset and the ice-layer perturbations. The results provide a reasonable good guide to understanding the yield degradation in direct-drive, low-adiabat, cryogenic, thin-shell-target implosions. Thick-shell (10 μm) implosions generally give lower yield over clean than low-ℓ-mode DRACO simulation predictions. Simulations including the effect of laser-beam nonuniformities indicate that high-ℓ-mode perturbations caused by laser imprinting further degrade the neutron yield of thick-shell implosions. To study ICF compression physics, these results suggest a target specification with a ≤ 30 μm offset and ice-roughness of σrms<3 μm are required.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.57.-z Laser inertial confinement
28.52.Fa Materials
28.52.Cx Fueling, heating and ignition