Feedback | Help | Exit
Physics of Plasmas
Search:
   
 
 
 

BROWSE VOLUME

Year Range:  

BROWSE EARLY VOLUMES

November 2009

Volume 16, Issue 11,  partial issue

Journal Issue Cover Image PDF file
Issue Cover Art Image
Cover image from Pablo Luis García-Martínez and Ricardo Farengo, Phys. Plasmas 16, 112508 (2009).

Enlarge the Image | Read the Article

back to top

LETTERS

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: PDF (236 kB)

Show Abstract
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.
Show PACS
52.75.-d, 52.50.Dg, 52.58.Lq, 52.80.Yr, 52.25.Os

Geometry dependence of stellarator turbulence

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

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

Online Publication Date: 10 November 2009

Full Text: PDF (802 kB)

Show Abstract
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, ibid. 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.
Show PACS
52.55.Hc, 52.65.Tt, 52.35.Ra

Current sheet bifurcation and collapse in electron magnetohydrodynamics

A. Zocco, L. Chacón, and Andrei N. Simakov

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

Online Publication Date: 16 November 2009

Full Text: PDF (229 kB)

Show Abstract
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 delta 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.
Show PACS
52.30.Cv, 52.35.Vd

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. R. Weynants, M. Van Schoor, M. Vergote, A. Krämer-Flecken, O. Schmitz, B. Unterberg, C. Hidalgo, and TEXTOR Team

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

Online Publication Date: 18 November 2009

Full Text: PDF (1508 kB)

Show Abstract
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.
Show PACS
52.30.Cv, 52.55.Fa, 52.25.Gj, 52.35.Qz
back to top

ARTICLES

Basic Plasma Phenomena, Waves, Instabilities

Langmuir wave linear evolution in inhomogeneous nonstationary anisotropic plasma

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

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

Online Publication Date: 2 November 2009

Full Text: PDF (211 kB)

Show Abstract
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 E-tilde universally scales with the electron density N as E-tilde [proportional]N3/4 in homogeneous plasma, whereas the wavevector evolution varies depending on the wave geometry.
Show PACS
52.35.Fp, 52.25.-b

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

Full Text: PDF (396 kB)

Show Abstract
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.
Show PACS
52.30.Cv, 52.35.Ra, 52.35.Py

Plasmons with orbital angular momentum

J. T. Mendonca, S. Ali, and B. Thidé

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

Online Publication Date: 11 November 2009

Full Text: PDF (251 kB)

Show Abstract
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.
Show PACS
52.35.-g, 72.30.+q, 52.25.Fi

Destabilizing effect of density gradient on the Kelvin–Helmholtz instability

L. F. Wang, C. Xue, W. H. Ye, and Y. J. Li

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

Online Publication Date: 18 November 2009

Full Text: PDF (385 kB)

Show Abstract
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.
Show PACS
47.20.Ft, 52.35.Py, 52.57.Fg

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

Full Text: PDF (176 kB)

Show Abstract
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 theta, 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.
Show PACS
52.25.Mq

Dressed soliton in quantum dusty pair-ion plasma

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

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

Online Publication Date: 19 November 2009

Full Text: PDF (289 kB)

Show Abstract
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)].
Show PACS
52.35.Mw, 52.65.Vv

Nonlinear Phenomena, Turbulence, Transport

Anomalous transport of energetic particles in ITER relevant scenarios

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

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

Online Publication Date: 2 November 2009

Full Text: PDF (271 kB)

Show Abstract
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.
Show PACS
52.55.Pi, 52.35.Ra

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

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

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

Online Publication Date: 4 November 2009

Full Text: PDF (213 kB)

Show Abstract
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.
Show PACS
52.35.Mw, 52.35.Kt, 52.35.Fp, 52.30.Cv, 52.35.Tc, 95.30.Qd

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

Full Text: PDF (341 kB)

Show Abstract
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,2pi/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.
Show PACS
52.25.Gj, 52.35.-g, 05.40.-a, 05.70.Fh

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

Full Text: PDF (221 kB)

Show Abstract
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.
Show PACS
52.20.-j, 52.25.Tx, 52.25.Mq, 52.25.Fi, 77.22.Ej

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

Full Text: PDF (2611 kB)

Show Abstract
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.
Show PACS
52.35.Tc, 52.50.Lp, 52.65.-y, 52.40.Db, 52.25.Fi

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

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

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

Online Publication Date: 19 November 2009

Full Text: PDF (401 kB)

Show Abstract
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.
Show PACS
52.27.Ny, 52.25.Fi, 52.35.-g

Nonlinear screening effect in an ultrarelativistic degenerate electron-positron gas

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

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

Online Publication Date: 20 November 2009

Full Text: PDF (117 kB)

Show Abstract
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.
Show PACS
52.27.Ny, 52.35.Mw, 52.25.Kn, 52.25.Gj

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

Full Text: PDF (2289 kB)

Show Abstract
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 theta, where theta 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.
Show PACS
52.65.Cc, 52.35.Tc, 52.35.Mw, 52.65.Rr

Magnetically Confined Plasmas, Heating, Confinement

A closure scheme for modeling rf modifications to the fluid equations

C. C. Hegna and J. D. Callen

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

Online Publication Date: 2 November 2009

Full Text: PDF (108 kB)

Show Abstract
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.
Show PACS
52.25.Dg, 52.30.Ex, 52.35.Py, 52.55.Wq

Steady state self-induced current in tokamak

Yu. V. Gott and E. I. Yurchenko

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

Online Publication Date: 3 November 2009

Full Text: PDF (158 kB)

Show Abstract
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.
Show PACS
52.55.Fa, 52.25.Fi

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: PDF (391 kB)

Show Abstract
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.
Show PACS
52.25.Dg, 52.25.Xz, 52.30.Gz, 52.35.Ra

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

Full Text: PDF (813 kB)

Show Abstract
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.
Show PACS
52.55.Fa, 52.30.Ex, 52.58.Lq, 52.55.Ez

Variational coordinate transformation in plasma physics

Ryan White, Emila R. Solano, and R. D. Hazeltine

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

Online Publication Date: 6 November 2009

Full Text: PDF (117 kB)

Show Abstract
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.
Show PACS
52.55.Hc, 52.25.Fi, 02.30.Sa

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

Full Text: PDF (593 kB)

Show Abstract
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.
Show PACS
52.30.Cv, 52.55.Tn, 52.55.Fa

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

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

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

Online Publication Date: 11 November 2009

Full Text: PDF (1357 kB)

Show Abstract
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.
Show PACS
52.35.Ra, 52.55.Fa, 52.65.Tt, 52.70.Gw
FREE

Relaxation of spheromak configurations with open flux

Pablo Luis García-Martínez and Ricardo Farengo

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

Online Publication Date: 16 November 2009

Full Text: PDF (1536 kB)

Show Abstract
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 lambda profile (lambda=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.
Show PACS
52.35.Py, 52.65.Kj, 52.55.Hc, 52.55.Ip, 52.25.Gj, 52.30.Cv

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

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

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

Online Publication Date: 20 November 2009

Full Text: PDF (513 kB)

Show Abstract
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.
Show PACS
52.25.Fi, 52.20.Hv, 52.70.-m

Electron-cyclotron wave scattering by edge density fluctuations in ITER

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

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

Online Publication Date: 20 November 2009

Full Text: PDF (201 kB)

Show Abstract
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.
Show PACS
05.40.-a, 42.25.Fx, 52.35.Hr

Inertially Confined Plasmas, High Energy Density Plasma Science, Warm Dense Matter

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

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

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

Online Publication Date: 2 November 2009

Full Text: PDF (456 kB)

Show Abstract
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)].
Show PACS
52.70.-m, 52.57.Fg, 52.50.Jm

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

T. Ma, M. H. Key, R. J. Mason, K. U. Akli, R. L. Daskalova, R. R. Freeman, J. S. Green, K. Highbarger, P. A. Jaanimagi, J. A. King, K. L. Lancaster, S. P. Hatchett, A. J. Mackinnon, A. G. MacPhee, P. A. Norreys et al.

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

Online Publication Date: 4 November 2009

Full Text: PDF (706 kB)

Show Abstract
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 Kalpha 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.
Show PACS
52.50.Jm, 52.27.Ny, 52.40.Mj, 52.25.Fi

Enhancement of backward Raman scattering by electron-ion collisions

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

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

Online Publication Date: 4 November 2009

Full Text: PDF (259 kB)

Show Abstract
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.
Show PACS
52.35.Fp, 52.20.-j

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

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

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

Online Publication Date: 12 November 2009

Full Text: PDF (1129 kB)

Show Abstract
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.
Show PACS
52.38.Dx, 52.38.Kd, 52.65.Rr

Wall shocks in high-energy-density shock tube experiments

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

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

Online Publication Date: 13 November 2009

Full Text: PDF (311 kB)

Show Abstract
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.
Show PACS
52.35.Tc, 47.40.Rs, 52.38.Mf, 52.50.Lp, 52.40.Hf

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

S. X. Hu, P. B. Radha, J. A. Marozas, R. Betti, T. J. B. Collins, R. S. Craxton, J. A. Delettrez, D. H. Edgell, R. Epstein, V. N. Goncharov, I. V. Igumenshchev, F. J. Marshall, R. L. McCrory, D. D. Meyerhofer, S. P. Regan et al.

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

Online Publication Date: 16 November 2009

Full Text: PDF (516 kB)

Show Abstract
Neutron yields of direct-drive, low-adiabat (alpha[approximate]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 ([script-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-alpha, 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-[script-l]-mode DRACO simulation predictions. Simulations including the effect of laser-beam nonuniformities indicate that high-[script-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 sigmarms<3  µm are required.
Show PACS
52.50.Jm, 52.57.-z, 28.52.Fa, 28.52.Cx

Estimates of confinement time and energy gain for plasma liner driven magnetoinertial fusion using an analytic self-similar converging shock model

J. T. Cassibry, R. J. Cortez, S. C. Hsu, and F. D. Witherspoon

Phys. Plasmas 16, 112707 (2009) (10 pages)

Online Publication Date: 20 November 2009

Full Text: PDF (548 kB)

Show Abstract
Plasma liner driven magnetoinertial fusion (PLMIF) is a fusion energy concept that utilizes an imploding plasma liner to shock heat and compress a magnetized target plasma to fusion conditions. The fusion burn fraction is linearly proportional to the confinement (or “dwell”) time of the liner-target system at peak compression, and therefore it is important to estimate the dwell time accurately in order to assess the fusion energy yield and gain. In this work, the dwell time has been estimated using the exact solution to a self-similar converging shock model. The dwell time was found to be determined by the sum of the outgoing shock and rarefaction times through the plasma liner at peak compression, and for chosen PLMIF conditions the dwell time was on the order of 1  µs. In addition, we show that the engineering gain, i.e., the total energy extracted as electricity (from fusion plus expanded liner energy) divided by the electrical energy required to implode the liner, exceeds unity for a wide range of liner thicknesses and specific heat ratios.
Show PACS
52.58.Qv, 52.35.Tc, 52.50.Lp, 05.45.Df, 52.25.Xz

Lasers, Particle Beams, Accelerators, Radiation Generation

FREE

Onset and saturation of backward stimulated Raman scattering of laser in trapping regime in three spatial dimensions

L. Yin, B. J. Albright, H. A. Rose, K. J. Bowers, B. Bergen, D. S. Montgomery, J. L. Kline, and J. C. Fernández

Phys. Plasmas 16, 113101 (2009) (13 pages) Multimedia

Online Publication Date: 2 November 2009

Full Text: PDF (2328 kB)

Show Abstract
A suite of three-dimensional (3D) VPIC [K. J. Bowers et al., Phys. Plasmas 15, 055703 (2008)] particle-in-cell simulations of backward stimulated Raman scattering (SRS) in inertial confinement fusion hohlraum plasma has been performed on the heterogeneous multicore supercomputer, Roadrunner, presently the world's most powerful supercomputer. These calculations reveal the complex nonlinear behavior of SRS and point to a new era of “at scale” 3D modeling of SRS in solitary and multiple laser speckles. The physics governing nonlinear saturation of SRS in a laser speckle in 3D is consistent with that of prior two-dimensional (2D) studies [L. Yin et al., Phys. Rev. Lett. 99, 265004 (2007)], but with important differences arising from enhanced diffraction and side loss in 3D compared with 2D. In addition to wave front bowing of electron plasma waves (EPWs) due to trapped electron nonlinear frequency shift and amplitude-dependent damping, we find for the first time that EPW self-focusing, which evolved from trapped particle modulational instability [H. A. Rose and L. Yin, Phys. Plasmas 15, 042311 (2008)], also exhibits loss of angular coherence by formation of a filament necklace, a process not available in 2D. These processes in 2D and 3D increase the side-loss rate of trapped electrons, increase wave damping, decrease source coherence for backscattered light, and fundamentally limit how much backscatter can occur from a laser speckle. For both SRS onset and saturation, the nonlinear trapping induced physics is not captured in linear gain modeling of SRS. A simple metric is described for using single-speckle reflectivities obtained from VPIC simulations to infer the total reflectivity from the population of laser speckles of amplitude sufficient for significant trapping-induced nonlinearity to arise.
Show PACS
52.38.Bv, 52.65.-y, 52.57.-z, 52.50.Jm, 52.35.Py, 52.35.Mw

Validity of closed periodic magnetic focusing for sheet electron beams

Ding Zhao

Phys. Plasmas 16, 113102 (2009) (8 pages)

Online Publication Date: 3 November 2009

Full Text: PDF (610 kB)

Show Abstract
Theoretical analyses and numerical calculations have demonstrated that a closed periodic cusped magnetic (PCM) field can effectively confine a sheet electron beam in two transverse directions (i.e., in the wide and narrow dimensions, simultaneously) for stable long distance transport in which the sizes of the beam cross section are set by referring to the present state of the art. Moreover, the method for matching the transverse magnetic focusing force and the inner space charge force in the wide dimension of the sheet electron beam is given, and the longitudinal periodic length and the cross sectional shape of the closed PCM focusing structure can be determined. Calculations also demonstrate that the optimum focusing state can be attained by adjusting the wide dimension on the transverse section of the closed PCM structure independently. The work presented in this paper indicates that the closed PCM structure is very promising for the confinement of the sheet electron beam, and it can be helpful for guiding practical engineering design.
Show PACS
52.55.-s, 41.85.Lc, 29.27.Eg

Energy gain of free electron in pulsed electromagnetic plane wave with constant external magnetic fields

Justin Angus and Sergei Krasheninnikov

Phys. Plasmas 16, 113103 (2009) (10 pages)

Online Publication Date: 10 November 2009

Full Text: PDF (520 kB)

Show Abstract
The interactions of a relativistic free electron with a pulsed electromagnetic (EM) plane wave in the presence of constant magnetic fields are studied using the well-known constants of motion. The goal is to determine the energy gained by the electron after the wave has passed. For a constant magnetic field along the axis of the wave, a general solution for the energy gain as a function of the vector potential describing the EM plane wave is obtained. Solutions for magnetic fields transverse to the axis of the wave are sought in the limit where the cyclotron frequency is much less than the wave frequency and are examined using several different profiles for the wave amplitude. For this case, an adiabatic invariant is found that shows that there is no energy gain when an EM plane wave comes and goes with a profile that is slowly varying in time with respect to the cyclotron motion.
Show PACS
52.59.Rz, 52.40.Db

Dispersive characteristics and longitudinal resonance properties in a relativistic backward wave oscillator with the coaxial arbitrary-profile slow-wave structure

Xingjun Ge, Huihuang Zhong, Baoliang Qian, Jun Zhang, Yuwei Fan, Ting Shu, and Jinliang Liu

Phys. Plasmas 16, 113104 (2009) (10 pages)

Online Publication Date: 12 November 2009

Full Text: PDF (1408 kB)

Show Abstract
The method for calculating the dispersion relations of the slow-wave structures (SWSs) with arbitrary geometrical structures is studied in detail by using the Fourier series expansion. In addition, dispersive characteristics and longitudinal resonance properties of the SWSs with the cosinusoidal, trapezoidal, and rectangular corrugations are analyzed by numerical calculation. Based on the above discussion, a comparison on an L-band coaxial relativistic backward wave oscillator (BWO) and an L-band coaxial BWO with a coaxial extractor is investigated in detail with particle-in-cell KARAT code (V. P. Tarakanov, Berkeley Research Associates, Inc., 1992). Furthermore, experiments are carried out at the TORCH-01 accelerator under the low guiding magnetic field. At diode voltage of 647 kV, beam current of 9.3 kA, and guiding magnetic field strength of 0.75 T, the microwave is generated with power of 1.07 GW, mode of TM01, and frequency of 1.61 GHz. That is the first experimental report of the L-band BWO.
Show PACS
84.40.Fe

Guiding of 35 TW laser pulses in ablative capillary discharge waveguides

C. McGuffey, M. Levin, T. Matsuoka, V. Chvykov, G. Kalintchenko, P. Rousseau, V. Yanovsky, A. Zigler, A. Maksimchuk, and K. Krushelnick

Phys. Plasmas 16, 113105 (2009) (7 pages)

Online Publication Date: 19 November 2009

Full Text: PDF (675 kB)

Show Abstract
An ablatively driven capillary discharge plasma waveguide has been used to demonstrate guiding of 30 fs, 35 TW laser pulses over distances up to 3 cm with incident intensity in excess of 4×1018  W/cm2. The plasma density range over which good guiding was observed was 1–3×1018  cm−3. The quality of the laser spot at the exit mode was observed to be similar to that at the entrance and the transmitted energy was ~25% at input powers of 35 TW. The transmitted laser spectrum typically showed blueshifting due to ionization of carbon and hydrogen atoms in the capillary plasma by the high intensity laser pulse. The low plasma density regime in which these capillaries operate makes these devices attractive for use in single stage electron accelerators to multi-GeV energies driven by petawatt class laser systems.
Show PACS
52.38.Kd, 52.40.Fd, 29.25.Bx, 52.25.Jm

Radiation: Emission, Absorption, Transport

Application of variational method for three-color three-photon transitions in hydrogen atom implanted in Debye plasmas

S. Paul and Y. K. Ho

Phys. Plasmas 16, 113301 (2009) (10 pages)

Online Publication Date: 11 November 2009

Full Text: PDF (1699 kB)

Show Abstract
Multiphoton processes, where transparency appears, have long fascinated physicists. Plasma screening effects are investigated on three-color three-photon bound-bound transitions in hydrogen atom embedded in Debye plasmas; where photons are linearly and circularly polarized, two left circular and one right circular. All possible combinations of frequency and polarization are considered. Analytical wave functions are used for initial and final states along with the pseudostate wave functions for intermediate states. The analytical wave functions are obtained from the modified wave functions for screening Coulomb potential (Debye model) using Ritz variational method. Here, we have found three-photon transparency for lower values of Debye length. This type of phenomenon occurs due to energy level shifting in the presence of Debye plasma environments. The description of resonance enhancements and three-photon transparency is reported in the present context along with the region of resonance enhancements and three-photon transparency.
Show PACS
52.35.-g, 52.20.Hv

Low-Temperature Plasmas, Plasma Applications, Plasma Sources, Sheaths

Microwave absorption of magnetized hydrogen plasma in carbon nanotubes

Afshin Moradi

Phys. Plasmas 16, 113501 (2009) (5 pages)

Online Publication Date: 11 November 2009

Full Text: PDF (205 kB)

Show Abstract
A simple model to describe the microwave absorption of magnetized hydrogen plasma embedded inside the carbon nanotubes (CNTs), which were grown by iron-catalyzed high-pressure disproportionation (HiPco), is proposed and analyzed. By using Maxwell equations in conjunction with a general expression of the complex permittivity of magnetized hydrogen plasma in HiPco CNTs, known as the Appleton–Hartree formula, the absorption coefficients of the system for right-hand circularly wave propagation along and across the static magnetic field are obtained. The effects of the continuously changing the electron density, the collision frequency, and the cyclotron frequency on the absorption of the microwave are discussed.
Show PACS
81.07.De, 52.30.Ex, 52.50.Sw

Comparison between experiment and simulation for argon inductively coupled plasma

Fei Gao, Shu-Xia Zhao, Xiao-Song Li, and You-Nian Wang

Phys. Plasmas 16, 113502 (2009) (9 pages)

Online Publication Date: 16 November 2009

Full Text: PDF (882 kB)

Show Abstract
In order to include the nonlocal characteristics of electrons and investigate the inductively coupled plasma (ICP) resources more completely, we have developed a hybrid Monte Carlo (MC)/fluid hybrid model and calculated the axial and radial distributions of electron density, electron temperature, plasma potential, and electron energy distribution functions (EEDFs) of Ar discharge in a planar ICP. Furthermore, to make the model more practical, we still incorporate the effects of metastable atoms, whose sets of rate coefficients and density are, respectively, calculated through the electron MC part and fluid module. Besides, the corresponding Langmuir probe measurements are used to compare these data to validate the simulated results. Under all the selected discharge powers and pressures, the theoretically simulated and experimentally measured quantity profiles agree reasonably with each other, embodied in the generally identical magnitude ranges and spatial distributions. Furthermore, the interpretations about their detailed differences are given, which are based on the designs of both experimental schematic and model configuration. The analysis implements that the inclusions of electron-electron collision and a neutral density distribution into the hybrid model are likely to improve the comparison between the model predictions and experiment diagnostics. Furthermore, the evolution of plasma parameters and EEDFs with discharge conditions is discussed.
Show PACS
52.70.-m, 52.65.-y, 52.80.Pi

Parametric analysis of a magnetized cylindrical plasma

Eduardo Ahedo

Phys. Plasmas 16, 113503 (2009) (11 pages)

Online Publication Date: 19 November 2009

Full Text: PDF (275 kB)

Show Abstract
The relevant macroscopic model, the spatial structure, and the parametric regimes of a low-pressure plasma confined by a cylinder and an axial magnetic field is discussed for the small-Debye length limit, making use of asymptotic techniques. The plasma response is fully characterized by three-dimensionless parameters, related to the electron gyroradius, and the electron and ion collision mean-free-paths. There are the unmagnetized regime, the main magnetized regime, and, for a low electron-collisionality plasma, an intermediate-magnetization regime. In the magnetized regimes, electron azimuthal inertia is shown to be a dominant phenomenon in part of the quasineutral plasma region and to set up before ion radial inertia. In the main magnetized regime, the plasma structure consists of a bulk diffusive region, a thin layer governed by electron inertia, a thinner sublayer controlled by ion inertia, and the non-neutral Debye sheath. The solution of the main inertial layer yields that the electron azimuthal energy near the wall is larger than the electron thermal energy, making electron resistivity effects non-negligible. The electron Boltzmann relation is satisfied only in the very vicinity of the Debye sheath edge. Ion collisionality effects are irrelevant in the magnetized regime. Simple scaling laws for plasma production and particle and energy fluxes to the wall are derived.
Show PACS
52.30.Cv, 52.80.-s, 52.25.Jm

Laser induced fluorescence of the ferroelectric plasma source assisted hollow anode discharge

V. Vekselman, J. Gleizer, S. Yatom, D. Yarmolich, V. Tz. Gurovich, G. Bazalitski, Ya. E. Krasik, and V. Bernshtam

Phys. Plasmas 16, 113504 (2009) (9 pages)

Online Publication Date: 20 November 2009

Full Text: PDF (828 kB)

Show Abstract
Parameters of the plasma produced by a ferroelectric plasma source (FPS) assisted high-current (~1  kA), hollow anode (HA), low-pressure (10−4  Torr) Ar gas discharge were studied using a time- and space-resolved laser induced fluorescence (LIF) diagnostic technique. It was shown that the plasma filling of the HA cavity occurs due to the expansion of the plasma flows generated by the FPSs with a gradual time-dependent increase in the plasma density along the length of the HA cavity. These data were verified by the results of one-dimensional modeling of the plasma expansion in vacuum and time-dependent collisional-radiative modeling. Also, LIF diagnostics, which was tested on the saturation effect both experimentally and numerically, showed that the plasma ion temperature gradually increases during the discharge reaching ~9  eV at its end. Various phenomena (plasma kinetic instabilities, charge-exchange processes during the plasma ion interaction with the HA walls, and the model of neutral atoms ionization inside the Debay's sphere), which could be responsible for such ion temperature, were considered.
Show PACS
52.25.Os, 52.35.Qz, 52.20.Hv, 52.30.-q, 52.50.Dg, 52.70.Kz

Energy coupling to the plasma in repetitive nanosecond pulse discharges

Igor V. Adamovich, Munetake Nishihara, Inchul Choi, Mruthunjaya Uddi, and Walter R. Lempert

Phys. Plasmas 16, 113505 (2009) (13 pages)

Online Publication Date: 20 November 2009

Full Text: PDF (1020 kB)

Show Abstract
A new analytic quasi-one-dimensional model of energy coupling to nanosecond pulse discharge plasmas in plane-to-plane geometry has been developed. The use of a one-dimensional approach is based on images of repetitively pulsed nanosecond discharge plasmas in dry air demonstrating that the plasma remains diffuse and uniform on a nanosecond time scale over a wide range of pressures. The model provides analytic expressions for the time-dependent electric field and electron density in the plasma, electric field in the sheath, sheath boundary location, and coupled pulse energy. The analytic model predictions are in very good agreement with numerical calculations. The model demonstrates that (i) the energy coupled to the plasma during an individual nanosecond discharge pulse is controlled primarily by the capacitance of the dielectric layers and by the breakdown voltage and (ii) the pulse energy coupled to the plasma during a burst of nanosecond pulses decreases as a function of the pulse number in the burst. This occurs primarily because of plasma temperature rise and resultant reduction in breakdown voltage, such that the coupled pulse energy varies approximately proportionally to the number density. Analytic expression for coupled pulse energy scaling has been incorporated into the air plasma chemistry model, validated previously by comparing with atomic oxygen number density measurements in nanosecond pulse discharges. The results of kinetic modeling using the modified air plasma chemistry model are compared with time-resolved temperature measurements in a repetitively pulsed nanosecond discharge in air, by emission spectroscopy, and purely rotational coherent anti-Stokes Raman spectroscopy showing good agreement.
Show PACS
52.80.-s, 82.33.Xj, 52.25.Dg, 52.25.Mq, 52.65.-y

Dynamic and spectroscopic characteristics of atmospheric gliding arc in gas-liquid two-phase flow

X. Tu, L. Yu, J. H. Yan, K. F. Cen, and B. G. Chéron

Phys. Plasmas 16, 113506 (2009) (5 pages)

Online Publication Date: 20 November 2009

Full Text: PDF (417 kB)

Show Abstract
In this study, an atmospheric alternating-current gliding arc device in gas-liquid two-phase flow has been developed for the purpose of waste water degradation. The dynamic behavior of the gas-liquid gliding arc is investigated through the oscillations of electrical signals, while the spatial evolution of the arc column is analyzed by high speed photography. Different arc breakdown regimes are reported, and the restrike mode is identified as the typical fluctuation characteristic of the hybrid gliding arc in air-water mixture. Optical emission spectroscopy is employed to investigate the active species generated in the gas-liquid plasma. The axial evolution of the OH (309 nm) intensity is determined, while the rotational and vibrational temperatures of the OH are obtained by a comparison between the experimental and simulated spectra. The significant discrepancy between the rotational and translational temperatures has also been discussed.
Show PACS
52.50.Dg, 52.80.Mg, 52.80.Wq, 52.70.-m

Dusty Plasmas

Dust negative ion acoustic shock waves in a dusty multi-ion plasma with positive dust charging current

S. S. Duha

Phys. Plasmas 16, 113701 (2009) (5 pages)

Online Publication Date: 4 November 2009

Full Text: PDF (748 kB)

Show Abstract
Recent analysis of Mamun et al. [ Phys. Lett. A 373, 2355 (2009)], who considered electrons, light positive ions, heavy negative ions, and extremely massive (few micron size) charge fluctuating dust, has been extended by positive dust charging current, i.e., considering the charging currents for positively charged dust grains. A dusty multi-ion plasma system consisting of electrons, light positive ions, negative ions, and extremely massive (few micron size) charge fluctuating stationary dust have been considered. The electrostatic shock waves associated with negative ion dynamics and dust charge fluctuation have been investigated by employing the reductive perturbation method. It has been shown that the dust charge fluctuation is a source of dissipation and is responsible for the formation of dust negative ion acoustic (DNIA) shock structures. The basic features of such DNIA shock structures have been identified. The findings of this investigation may be useful in understanding the laboratory phenomena and space dusty plasmas.
Show PACS
52.27.Lw, 52.35.Tc, 52.35.Fp

Technique for analysis of interparticle interaction in nonideal dissipative systems with isotropic pair potentials

O. S. Vaulina and E. A. Lisin

Phys. Plasmas 16, 113702 (2009) (6 pages)

Online Publication Date: 4 November 2009

Full Text: PDF (707 kB)

Show Abstract
A new technique for determining interaction forces between the particles in nonideal dissipative systems with isotropic pair potentials is presented. This technique is based on solving of the inverse problem describing movement of dust particles by a system of Langevin equations. Numerical simulations in a wide range of the parameters typical for dusty plasma experiments were performed to verify the solutions of inverse problem.
Show PACS
52.27.Lw, 52.27.Gr, 82.70.Dd

Obliquely propagating cnoidal waves in a magnetized dusty plasma with variable dust charge

L. L. Yadav and V. K. Sayal

Phys. Plasmas 16, 113703 (2009) (8 pages)

Online Publication Date: 5 November 2009

Full Text: PDF (391 kB)

Show Abstract
We have studied obliquely propagating dust-acoustic nonlinear periodic waves, namely, dust-acoustic cnoidal waves, in a magnetized dusty plasma consisting of electrons, ions, and dust grains with variable dust charge. Using reductive perturbation method and appropriate boundary conditions for nonlinear periodic waves, we have derived Korteweg–de Vries (KdV) equation for the plasma. It is found that the contribution to the dispersion due to the deviation from plasma approximation is dominant for small angles of obliqueness, while for large angles of obliqueness, the dispersion due to magnetic force becomes important. The cnoidal wave solution of the KdV equation is obtained. It is found that the frequency of the cnoidal wave depends on its amplitude. The effects of the magnetic field, the angle of obliqueness, the density of electrons, the dust-charge variation and the ion-temperature on the characteristics of the dust-acoustic cnoidal wave are also discussed. It is found that in the limiting case the cnoidal wave solution reduces to dust-acoustic soliton solution.
Show PACS
52.27.Lw, 52.35.Fp, 52.35.Dm, 52.35.Mw

Head-on collision of ion thermal waves in a magnetized pair-ion plasma containing charged dust impurities

E. F. El-Shamy

Phys. Plasmas 16, 113704 (2009) (6 pages)

Online Publication Date: 11 November 2009

Full Text: PDF (168 kB)

Show Abstract
This article presents the first study of the head-on collision between two ion thermal waves in a two-fluid (i.e., a pair-ion) magnetized plasma consisting of positive and negative ions, as well as a fraction of stationary charged dust impurities, using the extended Poincaré–Lighthill–Kuo method. The effects of the external magnetic field, the concentration of charged dust impurities, and the positive ion to negative ion temperature ratio on the solitary wave collisions are investigated. It is found that these factors significantly modify the phase shift.
Show PACS
52.27.Lw, 52.25.Vy, 52.35.Sb, 52.20.Hv

Effect of high-voltage nanosecond pulses on complex plasmas

M. Y. Pustylnik, A. V. Ivlev, H. M. Thomas, G. E. Morfill, L. M. Vasilyak, S. P. Vetchinin, D. N. Polyakov, and V. E. Fortov

Phys. Plasmas 16, 113705 (2009) (5 pages)

Online Publication Date: 12 November 2009

Full Text: PDF (218 kB)

Show Abstract
Influence of high-voltage (1–11 kV) pulses of nanosecond (20 ns) duration on microparticles levitating in a rf plasma is studied. It is shown that the pulses produce significant influence on the plasma, causing perturbations with the relaxation time of the order of 10−4  s. This time is sufficient for the microparticle to acquire significant kinetic energy. Application of repetitive pulses leads to the vertical oscillations of the microparticles. Clusters, consisting of small number of microparticles, exhibit parametric instabilities of horizontal modes under the effect of repetitive pulses. It was shown that the parametric instability is caused by the vertical oscillations of the microparticles in the nonuniform environment of the sheath.
Show PACS
52.27.Lw, 52.40.Kh, 52.80.Pi

Dust charging effects on test charge potential in a multi-ion dusty plasma

S. Ali

Phys. Plasmas 16, 113706 (2009) (5 pages)

Online Publication Date: 18 November 2009

Full Text: PDF (138 kB)

Show Abstract
The Debye–Hückel and oscillatory wake potentials caused by a test charge are studied in a multi-ion dusty plasma, whose constituents are the Boltzmann distributed electrons and light positive ions, the heavy mobile negative ions, and static but charge fluctuating dust particles. For this purpose, fluid equations are employed to obtain the dielectric constant of the dust-negative-ion acoustic wave involving the negative ions and dust charge fluctuation effects. Theoretical and numerical investigations have revealed the modification in the Debye–Hückel and wake potentials due to the effects of dust relaxation rate, dust absorption frequency, dust grain radius, and negative ion temperature. The present results should be important to form new materials in the presence of negative ions in laboratory as well as dust coagulation/agglomeration in space dusty plasmas.
Show PACS
52.27.Lw, 52.25.Gj, 52.25.Mq, 52.35.Fp

Dust charge and ion drag forces in a high-voltage, capacitive radio frequency sheath

I. Denysenko, K. Ostrikov, and N. A. Azarenkov

Phys. Plasmas 16, 113707 (2009) (10 pages)

Online Publication Date: 18 November 2009

Full Text: PDF (260 kB)

Show Abstract
The charge of an isolated dust grain and ion drag forces on the grain in a collisionless, high-voltage, capacitive rf sheath are studied theoretically. The studies are carried out assuming that the positive ions are monoenergetic, as well as in more realistic approximation, assuming that the time-averaged energy distribution of ions impinging on the dust grain has a double-peaked hollow profile. For the nonmonoenergetic case, an analytical expression for the ion flux to the dust grain is obtained. It is studied how the dust charge and ion drag forces depend on the rf frequency, electron density at plasma-sheath boundary, electron temperature and ratio of the effective oscillation amplitude of rf current to the electron Debye length. It is shown that the dust charge and ion drag forces obtained in the monoenergetic ion approximation may differ from those calculated assuming that the ions are nonmonoenergetic. The difference increases with increasing the width of the ion energy spread in the ion distribution.
Show PACS
52.25.Vy, 52.27.Lw, 52.77.Dq, 52.80.Pi

Current driven instability in collisional dusty plasmas

B. P. Pandey, S. V. Vladimirov, and A. Samarian

Phys. Plasmas 16, 113708 (2009) (5 pages)

Online Publication Date: 18 November 2009

Full Text: PDF (115 kB)

Show Abstract
The current driven electromagnetic instability in a collisional, magnetized, dusty medium is considered in the present work. It is shown that in the presence of the magnetic field aligned current, the low-frequency waves in the medium can become unstable if the ratio of the current to the ambient field is larger than the light speed times the wave number. The growth rate of the instability depends upon the ratio of the Alfvén to the dust cyclotron frequency as well as on the ratio of the current density J to the dust charge density Zend, where Z is the number of electronic charge on the grain, e is the electron charge, and nd is the dust number density. The typical growth rate of this instability is on the order of Alfvén frequency which compares favorably with the electrostatic, cross-field current driven, Farley–Buneman instability and thus could play an important role in the Earth's ionosphere.
Show PACS
52.27.Lw, 52.20.-j, 52.35.Qz, 52.25.Fi, 52.35.Bj
back to top

BRIEF COMMUNICATIONS

On interaction of large dust grains with fusion plasma

S. I. Krasheninnikov and R. D. Smirnov

Phys. Plasmas 16, 114501 (2009) (3 pages)

Online Publication Date: 6 November 2009

Full Text: PDF (269 kB)

Show Abstract
So far the models used to study dust grain-plasma interactions in fusion plasmas neglect the effects of dust material vapor, which is always present around dust in rather hot and dense edge plasma environment in fusion devices. However, when the vapor density and/or the amount of ionized vapor atoms become large enough, they can alter the grain-plasma interactions. Somewhat similar processes occur during pellet injection in fusion plasma. In this brief communication the applicability limits of the models ignoring vapor effects in grain-plasma interactions are obtained.
Show PACS
52.27.Lw, 52.40.-w

Experimental observation of carbon dioxide reduction in exhaust gas from hydrocarbon fuel burning

Han S. Uhm and Chul H. Kim

Phys. Plasmas 16, 114502 (2009) (4 pages)

Online Publication Date: 11 November 2009

Full Text: PDF (349 kB)

Show Abstract
A high-negative voltage at the cathode initiates a dark discharge, resulting in a reduction of the carbon dioxide concentration in exhaust gas from the burning of hydrocarbon fuel. An experiment indicated that nearly 44% of the carbon dioxide in exhaust gas disappears after a high-voltage application to the cathode. The energy needed for the endothermic reaction of the carbon dioxide dissociation corresponding to this concentration reduction is provided mainly by the internal energy reduction of the discharge gas, which is nearly 20 times the electrical energy for electron emission.
Show PACS
82.33.Xj, 52.80.-s, 82.30.Lp, 82.33.Vx

Arbitrary amplitude dust ion-acoustic shock waves in a dusty plasma with positive and negative ions

A. A. Mamun, P. K. Shukla, and B. Eliasson

Phys. Plasmas 16, 114503 (2009) (4 pages)

Online Publication Date: 13 November 2009

Full Text: PDF (389 kB)

Show Abstract
Arbitrary amplitude dust ion-acoustic shock waves in a multi-ion dusty plasma (composed of electrons, light positive ions, heavy negative ions, and stationary massive dust grains) has been studied. For this purpose, the coupled Poisson and dust-charging equations, which accounts for the fluctuation of charges on static dust, have been numerically solved. The large amplitude shocks are associated with a sudden decrease in the electrostatic potential and of the dust grain charge. It is found that in the lower speed limit small amplitude shocks are formed, while in the larger speed limit large amplitude shocks are formed. It is anticipated that the profiles and amplitudes of the DIA shocks predicted here will be observed in forthcoming laboratory and space experiments.
Show PACS
52.27.Lw, 52.50.Lp, 52.35.Tc

Nonthermal effects on the Karpman–Washimi ponderomotive magnetization in Lorentzian plasmas

Hwa-Min Kim and Young-Dae Jung

Phys. Plasmas 16, 114504 (2009) (4 pages)

Online Publication Date: 13 November 2009

Full Text: PDF (622 kB)

Show Abstract
The nonthermal effects on the Karpman–Washimi ponderomotive magnetization are investigated in Lorentzian plasmas. The induced magnetization due to the nonstationary ponderomotive interaction related to the time variation of the field intensity is obtained as a function of the Debye length and spectral index. It is shown that the nonthermal character of the Lorentzian plasma suppresses the cyclotron frequency due to the ponderomotive interactions. It is also shown that the Karpman–Washimi magnetization enhances with increasing the spectral index and scaled wave number. In addition, it is found that the ponderomotive magnetizations in Lorentzian plasmas are always smaller than those in Maxwellian plasmas due to the nonthermal effects. It is also shown that the nonthermal character strongly suppresses the total energy radiated due to the Karpman–Washimi ponderomotive force in Lorentzian plasmas.
Show PACS
52.20.-j

On the role of a nonscalar electron pressure in the collisionless magnetic reconnection

M. Hosseinpour and G. Vekstein

Phys. Plasmas 16, 114505 (2009) (4 pages)

Online Publication Date: 20 November 2009

Full Text: PDF (100 kB)

Show Abstract
Collisionless tearing instability in a sheared force-free magnetic field is considered in the framework of electron magnetohydrodynamics. A rigorous analytical analysis demonstrates that the bulk inertia of electrons is the dominant reconnection mechanism in a sufficiently low-beta plasma, when the reconnection current sheet width exceeds the electron gyroradius. Otherwise a fluidlike approach fails, and fully kinetic treatment of the problem is required. A recently raised issue of the role of the electron gyroviscous cancellation in collisionless reconnection is also addressed.
Show PACS
52.30.Cv, 52.25.-b, 52.35.Py
back to top

ERRATA

FREE

Erratum: “Electrostatic and thermal fluctuations are the source of magnetic fields in unmagnetized inhomogeneous plasmas” [Phys. Plasmas 16, 082102 (2009)]

Hamid Saleem

Phys. Plasmas 16, 119901 (2009) (1 page)

Online Publication Date: 16 November 2009

Full Text: PDF (51 kB)

+
 Abstract Unavailable
Show PACS
99.10.Cd

Copyright © American Institute of Physics