POP Nameplate
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Flickr Twitter iResearch App Facebook

Search Issue | RSS Feeds RSS
Previous Issue Next Issue

Feb 2010

Volume 17, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Phys. Plasmas 17, 023107 (2010); http://dx.doi.org/10.1063/1.3299391 (7 pages)

K. Harres, I. Alber, A. Tauschwitz, V. Bagnoud, H. Daido, M. Günther, F. Nürnberg, A. Otten, M. Schollmeier, J. Schütrumpf, M. Tampo, and M. Roth
Enlarge Image | Read More
Page 1 of 2 Pages Next Page | Jump to Page
back to top
RSS Feeds

Simultaneous measurement of core electron temperature and density fluctuations during electron cyclotron heating on DIII-D

A. E. White, L. Schmitz, W. A. Peebles, T. L. Rhodes, T. A. Carter, G. R. McKee, M. W. Shafer, G. M. Staebler, K. H. Burrell, J. C. DeBoo, and R. Prater

Phys. Plasmas 17, 020701 (2010); http://dx.doi.org/10.1063/1.3318469 (4 pages) | Cited 3 times

Online Publication Date: 18 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
New measurements show that long-wavelength (kθρs<0.5) electron temperature fluctuations can play an important role in determining electron thermal transport in low-confinement mode (L-mode) tokamak plasmas. In neutral beam-heated L-mode tokamak plasmas, electron thermal transport and the amplitude of long-wavelength electron temperature fluctuations both increase in cases where local electron cyclotron heating (ECH) is used to modify the plasma profiles. In contrast, the amplitude of simultaneously measured long-wavelength density fluctuations does not significantly increase. Linear stability analysis indicates that the ratio of the trapped electron mode (TEM) to ion temperature gradient (ITG) mode growth rates increases in the cases with ECH. The increased importance of the TEM drive relative to the ITG mode drive in the cases with ECH may be associated with the increases in electron thermal transport and electron temperature fluctuations.
Show PACS
52.55.Fa Tokamaks, spherical tokamaks
52.35.Ra Plasma turbulence
52.25.Fi Transport properties
52.70.Gw Radio-frequency and microwave measurements

Spectroscopic study of a long high-electron-density argon plasma column generated at atmospheric pressure

Shou-Zhe Li, Wen-Tong Huang, and Dezhen Wang

Phys. Plasmas 17, 020702 (2010); http://dx.doi.org/10.1063/1.3314724 (4 pages) | Cited 1 time

Online Publication Date: 22 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A stable plasma column is generated in a quartz tube using a pair of hollow electrodes driven by a sinusoidal power supply of 45 kHz at atmospheric pressure in argon. Two distinct operating modes (low-current and high-current modes) are identified through observing its discharge phenomena, measuring its electrical characteristics, and determining the gas temperatures by spectroscopic diagnosis of Q branch of UV OH spectrum. The electron density in the high-current mode is diagnosed by Stark broadening and is found to be two orders higher than that in low-current mode.
Show PACS
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.80.Tn Other gas discharges

Suprathermal electrons generated by the two-plasmon-decay instability in gas-filled Hohlraums

S. P. Regan, N. B. Meezan, L. J. Suter, D. J. Strozzi, W. L. Kruer, D. Meeker, S. H. Glenzer, W. Seka, C. Stoeckl, V. Yu. Glebov, T. C. Sangster, D. D. Meyerhofer, R. L. McCrory, E. A. Williams, O. S. Jones, et al.

Phys. Plasmas 17, 020703 (2010); http://dx.doi.org/10.1063/1.3309481 (4 pages) | Cited 12 times

Online Publication Date: 23 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
For the first time a burst of suprathermal electrons is observed from the exploding laser-entrance-hole window of gas-filled Hohlraums driven with 13.5 kJ of 351 nm laser light. The two-plasmon-decay instability appears to produce up to 20 J of hot electrons with Thot ∼ 75 keV at early times and has a sharp laser-intensity threshold between 0.3 and 0.5×1015 W/cm2. The observed threshold can be exploited to mitigate preheat by window hot electrons in ignition Hohlraums for the National Ignition Facility and achieve high-density, high-pressure conditions in indirect drive implosions.
Show PACS
52.57.−z
52.38.Ph X-ray, γ-ray, and particle generation
52.38.Kd Laser-plasma acceleration of electrons and ions
52.70.La X-ray and γ-ray measurements
back to top
RSS Feeds
back to top Basic Plasma Phenomena, Waves, Instabilities

Electron velocity shear driven instability in relativistic regime

Sita Sundar and Amita Das

Phys. Plasmas 17, 022101 (2010); http://dx.doi.org/10.1063/1.3299364 (9 pages) | Cited 1 time

Online Publication Date: 3 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The electron magnetohydrodynamics model has been generalized to incorporate relativistic effects. The model is then employed to study the instability associated with sheared electron velocity flow in the relativistic regime. The instability has features similar to the conventional velocity shear driven Kelvin–Helmholtz-like mode [ A. Das and P. Kaw, Phys. Plasmas 8, 4518 (2001) ] in the weakly relativistic regime. However, in the strongly relativistic regime the instability shows certain distinct characteristics. The threshold value of the wave number is found to be considerably higher than the inverse shear width of the equilibrium velocity profile in this regime. Thus, the unstable domain of the wave-number space is considerably wider in this case. Also the mode does not remain purely growing but acquires a real frequency even for an antisymmetric velocity profile. These features of the mode have been understood by realizing that in the strongly relativistic regime the relativistic mass factor γ0 for the equilibrium has much sharper variations than that of the velocity profile.
Show PACS
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.27.Ny Relativistic plasmas
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Alfvén continuum deformation by kinetic geodesic effect in rotating tokamak plasmas

A. G. Elfimov

Phys. Plasmas 17, 022102 (2010); http://dx.doi.org/10.1063/1.3299329 (5 pages) | Cited 5 times

Online Publication Date: 9 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Using a quasitoroidal set of coordinates with coaxial circular magnetic surfaces, Vlasov equation is solved for collisionless plasmas in drift approach and a perpendicular dielectric tensor is found for large aspect ratio tokamaks in a low frequency band. Taking into account plasma rotation and charge separation parallel electric field, it is found that an ion geodesic effect deform Alfvén wave continuum producing continuum minimum at the rational magnetic surfaces, which depends on the plasma rotation and poloidal mode numbers. In kinetic approach, the ion thermal motion defines the geodesic effect but the mode frequency also depends on electron temperature. A geodesic ion Alfvén mode predicted below the continuum minimum has a small Landau damping in plasmas with Maxwell distribution but the plasma rotation may drive instability.
Show PACS
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Tn Ideal and resistive MHD modes; kinetic modes
52.55.Fa Tokamaks, spherical tokamaks

The Alfvén resonance in pair plasmas

N. F. Cramer

Phys. Plasmas 17, 022103 (2010); http://dx.doi.org/10.1063/1.3304187 (6 pages) | Cited 1 time

Online Publication Date: 11 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The absorption of wave energy in a magnetized cold pair plasma at the analog of the Alfvén resonance is considered. Splitting of the parallel propagating wave modes due to imbalance of pair species densities is discussed. For oblique propagation of the waves, it is shown that, if the wave frequency is much less than the plasma frequency, there is an approximate resonance in the wave vector component perpendicular to the magnetic field, which may be identified as the analog of the Alfvén resonance in normal electron-ion plasmas. The wave differential equations for a nonuniform plasma also exhibit the resonance. The pair species charge imbalance plays a similar role in the Alfvén resonance process to the Hall term (or finite ion cyclotron frequency effect) in electron-ion plasmas. Wave absorption at the resonance can take place via mode conversion to the analog of the short wavelength inertial Alfvén wave, whose properties are discussed.
Show PACS
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)

Features of ion acoustic waves in collisional plasmas

J. Vranjes and S. Poedts

Phys. Plasmas 17, 022104 (2010); http://dx.doi.org/10.1063/1.3309490 (7 pages) | Cited 2 times

Online Publication Date: 11 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The effects of friction on the ion acoustic (IA) wave in fully and partially ionized plasmas are studied. In a quasineutral electron-ion plasma the friction between the two species cancels out exactly and the wave propagates without any damping. If the Poisson equation is used instead of the quasineutrality, however, the IA wave is damped and the damping is dispersive. In a partially ionized plasma, the collisions with the neutrals modify the IA wave beyond recognition. For a low density of neutrals the mode is damped. Upon increasing the neutral density, the mode becomes first evanescent and then reappears for a still larger number of neutrals. A similar behavior is obtained by varying the mode wavelength. The explanation for this behavior is given. In an inhomogeneous plasma placed in an external magnetic field, and for magnetized electrons and unmagnetized ions, the IA mode propagates in any direction and in this case the collisions make it growing on the account of the energy stored in the density gradient. The growth rate is angle dependent. A comparison with the collisionless kinetic density gradient driven IA instability is also given.
Show PACS
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.30.Ex Two-fluid and multi-fluid plasmas

Numerical modeling of Large Plasma Device Alfvén wave experiments using AstroGK

Kevin D. Nielson, Gregory G. Howes, Tomoya Tatsuno, Ryusuke Numata, and William Dorland

Phys. Plasmas 17, 022105 (2010); http://dx.doi.org/10.1063/1.3309486 (11 pages) | Cited 1 time

Online Publication Date: 22 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Collisions between counterpropagating Alfvén waves represent the fundamental building block of plasma turbulence, a phenomenon of great importance to a wide variety of fields, from space physics and astrophysics to controlled magnetic fusion. Proposed experiments to study Alfvén wave collisions on the Large Plasma Device (LAPD) [ W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)] at the University of California, Los Angeles, will benefit significantly from numerical modeling capable of reproducing not only the linear dispersive effects of kinetic and inertial Alfvén waves, but also the nonlinear evolution of the Alfvénic turbulence. This paper presents a comparison of linear simulation results using the astrophysical gyrokinetics code, AstroGK, to the measured linear properties of kinetic and inertial Alfvén waves in the LAPD plasma. Results demonstrate that: (1) finite frequency effects due to the ion cyclotron resonance do not prevent satisfactory modeling of the LAPD plasma using gyrokinetic theory; and (2) an advanced collision operator, recently implemented in AstroGK, enables the code to successfully reproduce the collisionally enhanced damping rates of linear waves measured in recent LAPD experiments. These tests justify the use of AstroGK in the modeling of LAPD Alfvén wave experiments and suggest that AstroGK will be a valuable tool in modeling the nonlinear evolution of proposed Alfvén wave collision experiments.
Show PACS
52.20.Fs Electron collisions
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.65.Tt Gyrofluid and gyrokinetic simulations
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Clustered frequency analysis of shear Alfvén modes in stellarators

D. A. Spong, E. D’Azevedo, and Y. Todo

Phys. Plasmas 17, 022106 (2010); http://dx.doi.org/10.1063/1.3313818 (12 pages) | Cited 10 times

Online Publication Date: 24 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The shear Alfvén spectrum in three-dimensional configurations, such as stellarators and rippled tokamaks, is more densely populated due to the larger number of mode couplings caused by the variation in the magnetic field in the toroidal dimension. This implies more significant computational requirements that can rapidly become prohibitive as more resolution is requested. Alfvén eigenfrequencies and mode structures are a primary point of contact between theory and experiment. A new algorithm based on the Jacobi–Davidson method is developed here and applied for a reduced magnetohydrodynamics model to several stellarator configurations. This technique focuses on finding a subset of eigenmodes clustered about a specified input frequency. This approach can be especially useful in modeling experimental observations, where the mode frequency can generally be measured with good accuracy and several different simultaneous frequency lines may be of interest. For cases considered in this paper, it can be a factor of 102–103 times faster than more conventional methods.
Show PACS
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.55.Jd Magnetic mirrors, gas dynamic traps
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Linear theory of anisotropy driven modes in a Harris neutral sheet

K. B. Quest, H. Karimabadi, and W. Daughton

Phys. Plasmas 17, 022107 (2010); http://dx.doi.org/10.1063/1.3309731 (19 pages) | Cited 5 times

Online Publication Date: 25 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
There are several sources of electron and ion anisotropies that can have a profound effect on the stability of the current sheets in the magnetosphere. A new semianalytical approach is introduced and utilized to develop the linear theory of anisotropy driven modes in a neutral sheet. This technique is intermediary between analytical models and those that solve the exact linear Vlasov equation. Its advantage is in its accuracy and speed. Both the parallel and perpendicular limits are considered, and improved stability criteria and growth rates for Weibel, anisotropic tearing, and Fried–Weibel modes are obtained. For the same anisotropy levels, electron anisotropy is much more effective in modifying the stability of the modes, but the presence of large ion anisotropy in the magnetosheath can still have a significant effect on the growth of the tearing mode. Effects of ion anisotropy are more pronounced for thicker sheets, whereas the electron anisotropy is weakly dependent on the current sheet thickness. Although the current expectation is that magnetic reconnection in the magnetosphere is associated with the formation of thin current sheets, our results suggest an interesting possibility of fast growth rates for thick sheets in the presence of sufficient electron and/or ion anisotropies.
Show PACS
94.30.cq MHD waves, plasma waves, and instabilities
94.30.cj Magnetosheath
94.30.cp Magnetic reconnection
52.35.Vd Magnetic reconnection
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.25.Dg Plasma kinetic equations
back to top Nonlinear Phenomena, Turbulence, Transport

Coaxial discharge with axial magnetic field: Demonstration that the Boltzmann relation for electrons generally does not hold in magnetized plasmas

T. M. G. Zimmermann, M. Coppins, and J. E. Allen

Phys. Plasmas 17, 022301 (2010); http://dx.doi.org/10.1063/1.3299390 (7 pages) | Cited 6 times

Online Publication Date: 3 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A one-dimensional two-fluid model is used to describe the quasineutral plasma of a discharge formed between coaxial cylinders under the influence of an axial magnetic field. The geometry treated in this paper is symmetric about the z-axis and is radially varying. The nested cylinders are necessarily different in size, leading to a potential difference between the sheath edges of the discharge plasma. This can be removed by applying a strong enough magnetic field, which also has the effect of flattening the potential profile, i.e., reducing the electric field in the plasma volume. In a previous publication [ T. M. G. Zimmermann et al., Phys. Plasmas 16, 043501 (2009) ], the authors examined the validity of the Boltzmann relation for electrons when applied to a similar geometry. When the magnetic field becomes strong enough to affect the electron flow in the radial direction, this expression breaks down. It was further discovered that certain situations require a self-consistent treatment of magnetic fields, since significant azimuthal currents can arise in such geometries. This work is applied and extended to offer a complete description of the electron density.
Show PACS
52.25.Fi Transport properties
52.55.Dy General theory and basic studies of plasma lifetime, particle and heat loss, energy balance, field structure, etc.
52.65.Kj Magnetohydrodynamic and fluid equation
52.80.-s Electric discharges

Fluctuation characteristics and transport properties of collisionless trapped electron mode turbulence

Yong Xiao, Ihor Holod, Wenlu Zhang, Scott Klasky, and Zhihong Lin

Phys. Plasmas 17, 022302 (2010); http://dx.doi.org/10.1063/1.3302504 (10 pages) | Cited 3 times

Online Publication Date: 12 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The collisionless trapped electron mode turbulence is investigated by global gyrokinetic particle simulation. The zonal flow dominated by low frequency and short wavelength acts as a very important saturation mechanism. The turbulent eddies are mostly microscopic, but with a significant portion in the mesoscale. The ion heat transport is found to be diffusive and follows the local radial profile of the turbulence intensity. However, the electron heat transport demonstrates some nondiffusive features and only follows the global profile of the turbulence intensity. The nondiffusive features of the electron heat transport is further confirmed by nonlognormal statistics of the flux-surface-averaged electron heat flux. The radial and time correlation functions are calculated to obtain the radial correlation length and autocorrelation time. Characteristic time scale analysis shows that the zonal flow shearing time and eddy turnover time are very close to the effective decorrelation time, which suggests that the trapped electrons move with the fluid eddies. The fluidlike behaviors of the trapped electrons and the persistence of the mesoscale eddies contribute to the transition of the electron turbulent transport from gyro-Bohm scaling to Bohm scaling when the device size decreases.
Show PACS
52.25.Gj Fluctuation and chaos phenomena
52.25.Fi Transport properties
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Ra Plasma turbulence
52.65.Tt Gyrofluid and gyrokinetic simulations

Nonplanar electrostatic shock waves in dense plasmas

W. Masood and H. Rizvi

Phys. Plasmas 17, 022303 (2010); http://dx.doi.org/10.1063/1.3309733 (6 pages) | Cited 3 times

Online Publication Date: 25 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Two-dimensional quantum ion acoustic shock waves (QIASWs) are studied in an unmagnetized plasma consisting of electrons and ions. In this regard, a nonplanar quantum Kadomtsev–Petviashvili–Burgers (QKPB) equation is derived using the small amplitude perturbation expansion method. Using the tangent hyperbolic method, an analytical solution of the planar QKPB equation is obtained and subsequently used as the initial profile to numerically solve the nonplanar QKPB equation. It is observed that the increasing number density (and correspondingly the quantum Bohm potential) and kinematic viscosity affect the propagation characteristics of the QIASW. The temporal evolution of the nonplanar QIASW is investigated both in Cartesian and polar planes and the results are discussed from the numerical stand point. The results of the present study may be applicable in the study of propagation of small amplitude localized electrostatic shock structures in dense astrophysical environments.
Show PACS
52.35.Tc Shock waves and discontinuities
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.25.Fi Transport properties
02.60.-x Numerical approximation and analysis
02.30.-f Function theory, analysis
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Generation of zonal flows by electrostatic drift waves in electron-positron-ion plasmas

T. D. Kaladze, M. Shad, and L. V. Tsamalashvili

Phys. Plasmas 17, 022304 (2010); http://dx.doi.org/10.1063/1.3313359 (13 pages) | Cited 2 times

Online Publication Date: 25 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Generation of large-scale zonal flows by comparatively small-scale electrostatic drift waves in electron-positron-ion plasmas is considered. The generation mechanism is based on the parametric excitation of convective cells by finite amplitude drift waves having arbitrary wavelengths (as compared with the ion Larmor radius of plasma ions at the plasma electron temperature). Temperature inhomogeneity of electrons and positrons is taken into account assuming ions to be cold. To describe the generation of zonal flow generalized Hasegawa–Mima equation containing both vector and two scalar (of different nature) nonlinearities is used. A set of coupled equations describing the nonlinear interaction of drift waves and zonal flows is deduced. Explicit expressions for the maximum growth rate as well as for the optimal spatial dimensions of the zonal flows are obtained. Enriched possibilities of zonal flow generation with different growth rates are revealed. The present theory can be used for interpretations of drift wave observations in laboratory and astrophysical plasmas.
Show PACS
52.30.-q Plasma dynamics and flow
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Kt Drift waves
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.-b Plasma properties
back to top Magnetically Confined Plasmas, Heating, Confinement

Intermittent convective transport carried by propagating electromagnetic filamentary structures in nonuniformly magnetized plasma

G. S. Xu, V. Naulin, W. Fundamenski, J. Juul Rasmussen, A. H. Nielsen, and B. N. Wan

Phys. Plasmas 17, 022501 (2010); http://dx.doi.org/10.1063/1.3302535 (22 pages) | Cited 6 times

Online Publication Date: 9 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Drift-Alfvén vortex filaments associated with electromagnetic turbulence were recently identified in reversed field pinch devices. Similar propagating filamentary structures were observed in the Earth magnetosheath, magnetospheric cusp and Saturn’s magnetosheath by spacecrafts. The characteristics of these structures closely resemble those of the so-called mesoscale coherent structures, prevailing in fusion plasmas, known as “blobs” and “edge localized mode filaments” in the boundary region, and propagating avalanchelike events in the core region. In this paper the fundamental dynamics of drift-Alfvén vortex filaments in a nonuniformly and strongly magnetized plasma are revisited. We systemize the Lagrangian-invariant-based method. Six Lagrangian invariants are employed to describe structure motion and the resultant convective transport, namely, magnetic flux, background magnetic energy, specific entropy, total energy, magnetic momentum, and angular momentum. The perpendicular vortex motions and the kinetic shear Alfvén waves are coupled through the parallel current and Ampere’s law, leading to field line bending. On the timescale of interchange motion τ⊥, a thermal expansion force in the direction of curvature radius of the magnetic field overcomes the resultant force of magnetic tension and push plasma filament to accelerate in the direction of curvature radius resulting from plasma inertial response, reacted to satisfy quasineutrality. During this process the internal energy stored in the background pressure gradient is converted into the kinetic energy of convective motion and the magnetic energy of field line bending through reversible pressure-volume work as a result of the plasma compressibility in an inhomogeneous magnetic field. On the timescale of parallel acoustic response τ∥⪢τ⊥, part of the filament’s energy is transferred into the kinetic energy of parallel flow. On the dissipation timescale τd⪢τ⊥, the kinetic energy and magnetic energy are eventually dissipated, which is accompanied by entropy production, and in this process the structure loses its coherence, but it has already traveled a distance in the radial direction. In this way the propagating filamentary structures induce intermittent convective transports of particles, heat, and momentum across the magnetic field. It is suggested that the phenomena of profile consistency, or resilience, and the underlying anomalous pinch effects of particles, heat, and momentum in the fusion plasmas can be interpreted in terms of the ballistic motion of these solitary electromagnetic filamentary structures.
Show PACS
52.35.Ra Plasma turbulence
52.25.Fi Transport properties

Drift-resistive-inertial ballooning modes in quasihelical stellarators

T. Rafiq, C. C. Hegna, J. D. Callen, and A. H. Kritz

Phys. Plasmas 17, 022502 (2010); http://dx.doi.org/10.1063/1.3291061 (11 pages) | Cited 3 times

Online Publication Date: 9 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A linear stability theory of nonideal magnetohydrodynamic (MHD) ballooning modes is investigated using a two fluid model for electron-ion plasmas. Drift-resistive-inertial ballooning mode eigenvalues and eigenfunctions are calculated for a variety of equilibria including axisymmetric shifted circular geometry (math−α model) as well as for three dimensional configurations relevant for the Helically Symmetric Stellarator (HSX) [ F. S. B. Anderson, A. F. Almagri, D. T. Anderson, et al., Fusion Technology 27, 273 (1995) ]. For typical HSX parameters, characteristic ballooning mode growth rates exceed the electron collision frequency. In this regime, electron inertial effects dominate plasma resistivity and produce an instability whose growth rate scales with the electromagnetic skin depth. However, as plasma β is increased, the resistive and inertial effects become unimportant. Under these conditions, the mode is completely stabilized by drift frequency effects, which dominate resistivity and inertia. Numerical results indicate that in the absence of drift effects, the resistive-inertial MHD modes are purely growing and persist in regimes where ideal MHD ballooning modes are stable. It is found that the magnitudes of the linear growth rates are not sensitive to the addition of a mirror term to the magnetic spectrum that spoils the quasihelical symmetry of the configuration. The eigenvalues and eigenvectors in the strong ballooning approximation are used together with a quasilinear mixing length estimate to determine particle flux and particle diffusivity. The particle diffusivity increases with rising density gradient and collisionality in a plasma with a low electron temperature. This increase in transport is consistent with the increase observed in the edge region of HSX plasmas. The magnitude of the particle diffusivity is computed to be in the range from 5 to 10 m2/s, which is consistent with the experimental measured particle diffusivity at the edge of HSX plasmas.
Show PACS
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.20.Fs Electron collisions
52.55.Jd Magnetic mirrors, gas dynamic traps
52.55.Tn Ideal and resistive MHD modes; kinetic modes
52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Stabilization of pressure-driven magnetohydrodynamic modes by separatrix in dipole plasma confinement

M. Furukawa, H. Hayashi, and Z. Yoshida

Phys. Plasmas 17, 022503 (2010); http://dx.doi.org/10.1063/1.3304238 (5 pages) | Cited 1 time

Online Publication Date: 17 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The eigenvalue problem is solved for the short-wavelength pressure-driven magnetohydrodynamic modes in configuration with closed magnetic field lines in the poloidal direction. Here we show that the magnetic separatrix (which determines the boundary of the confinement region) provides a substantial stabilizing effect by which the total volume inside the separatrix becomes stable even for very high beta values. The plasma inertia and compressibility are properly formulated to give the correct growth rate of the mode.
Show PACS
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Jd Magnetic mirrors, gas dynamic traps
52.55.Tn Ideal and resistive MHD modes; kinetic modes
94.30.cq MHD waves, plasma waves, and instabilities

Investigations of lower hybrid wave-plasma coupling by gas puffing in HT-7

B. J. Ding, M. H. Li, Y. L. Qin, W. K. Li, L. Z. Zhang, J. F. Shan, F. K. Liu, M. Wang, L. G. Meng, H. D. Xu, D. X. Wang, Y. X. Jie, Y. W. Sun, B. Shen, W. Zhang, et al.

Phys. Plasmas 17, 022504 (2010); http://dx.doi.org/10.1063/1.3301206 (7 pages) | Cited 3 times

Online Publication Date: 19 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Lower hybrid wave (LHW)-plasma coupling experiments in HT-7 [ J. K. Xie and HT-7 Group, Proceedings of the 16th International Conference on Fusion Energy, Montreal, 1996 (IAEA, Trieste, 1997), Vol. 1, p. 685 ] were carried out by means of puffing gas (CD4 and D2) just around the antenna. Both experiments show that wave-plasma coupling is improved by the gas puffing. The maximum distance between the plasma and the antenna is limited to about 8 cm due to the plasma disruption. The variation in the lined averaged density in the different channels gives a possible evidence of the mechanism of the ionization of neutral gas. The effect of the gas flow rate on the wave-plasma coupling shows that an optimized gas flow rate is necessary for good coupling, being consistent with simulation through Brambilla theory qualitatively. Experiments with puffing D2 show that the improved coupling results from the global density increase and the local gas puffing. Langmuir probe measurements indicate that the gas puffing effectively increases the density and decreases the temperature in scrape of layer. Studies show that the ionization of the puffed gas is affected by both LHW electric field and plasma temperature. Comparison of D2 and CD4 puffing shows that D2 improves coupling better with less effect on core density.
Show PACS
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.55.Fa Tokamaks, spherical tokamaks
52.70.Ds Electric and magnetic measurements
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Jm Ionization of plasmas

Fokker–Planck description of the scattering of radio frequency waves at the plasma edge

Kyriakos Hizanidis, Abhay K. Ram, Yannis Kominis, and Christos Tsironis

Phys. Plasmas 17, 022505 (2010); http://dx.doi.org/10.1063/1.3304241 (10 pages) | Cited 9 times

Online Publication Date: 22 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In magnetic fusion devices, radio frequency (rf) waves in the electron cyclotron (EC) and lower hybrid (LH) range of frequencies are being commonly used to modify the plasma current profile. In ITER, EC waves are expected to stabilize the neoclassical tearing mode (NTM) by providing current in the island region [ R. Aymar et al., Nucl. Fusion 41, 1301 (2001) ]. The appearance of NTMs severely limits the plasma pressure and leads to the degradation of plasma confinement. LH waves could be used in ITER to modify the current profile closer to the edge of the plasma. These rf waves propagate from the excitation structures to the core of the plasma through an edge region, which is characterized by turbulence—in particular, density fluctuations. These fluctuations, in the form of blobs, can modify the propagation properties of the waves by refraction. In this paper, the effect on rf due to randomly distributed blobs in the edge region is studied. The waves are represented as geometric optics rays and the refractive scattering from a distribution of blobs is formulated as a Fokker–Planck equation. The scattering can have two diffusive effects—one in real space and the other in wave vector space. The scattering can modify the trajectory of rays into the plasma and it can affect the wave vector spectrum. The refraction of EC waves, for example, could make them miss the intended target region where the NTMs occur. The broadening of the wave vector spectrum could broaden the wave generated current profile. The Fokker–Planck formalism for diffusion in real space and wave vector space is used to study the effect of density blobs on EC and LH waves in an ITER type of plasma environment. For EC waves the refractive effects become important since the distance of propagation from the edge to the core in ITER is of the order of a meter. The diffusion in wave vector space is small. For LH waves the refractive effects are insignificant but the diffusion in wave vector space is important. The theoretical model is general enough to study the effect of density blobs on all propagating cold plasma waves.
Show PACS
52.25.Gj Fluctuation and chaos phenomena
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
42.25.Gy Edge and boundary effects; reflection and refraction

Drift-kinetic simulation of neoclassical transport with impurities in tokamaks

R. A. Kolesnikov, W. X. Wang, F. L. Hinton, G. Rewoldt, and W. M. Tang

Phys. Plasmas 17, 022506 (2010); http://dx.doi.org/10.1063/1.3310839 (9 pages) | Cited 8 times

Online Publication Date: 22 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Plasmas in modern tokamak experiments contain a significant fraction of impurity ions in addition to the main deuterium background ions. A new multiple ion-species δf particle simulation capability has been developed to self-consistently study the nonlocal effects of impurities on neoclassical transport in toroidal plasmas. A new algorithm for an unlike-particle collision operator, including test-particle and conserving field-particle parts, is described. Effects of the carbon impurity on the main deuterium species heat flux as well as an ambipolar radial electric field in a National Spherical Torus Experiment (NSTX) [ M. Ono, S. M. Kaye, Y.-K. M. Peng et al., Nucl. Fusion 40, 557 (2000) ] configuration were studied. A difference between carbon poloidal rotation found from simulation and from conventional theoretical estimates has been investigated and was identified to be a nonlocal finite orbit effect. In the case of large-aspect ratio tokamak configurations with steep toroidal flow profiles, we propose a theoretical model to describe this nonlocal effect. The dominant mechanisms captured by the model are associated with ion parallel velocity modification due to steep toroidal flow and radial electric field profiles. We present simulation results for carbon poloidal velocity in NSTX. Comparisons with neoclassical theory are discussed.
Show PACS
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.25.Xz Magnetized plasmas
52.25.Dg Plasma kinetic equations

Analysis of neutral particle recycling and pedestal fueling in a H-mode DIII-D discharge

Z. W. Friis, W. M. Stacey, A. W. Leonard, and M. E. Rensink

Phys. Plasmas 17, 022507 (2010); http://dx.doi.org/10.1063/1.3305809 (11 pages) | Cited 5 times

Online Publication Date: 23 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A detailed analysis of neutral atom recycling and pedestal fueling in a DIII-D [ J. Luxon, Nucl. Fusion 42, 614 (2002) ] high-confinement mode discharge is presented. Experimental data and two-dimensional (2D) edge plasma fluid code calculations are employed to provide ion wall recycling and recombination neutral sources and background edge plasma parameters for a 2D edge neutral code calculation of detailed neutral density, ionization, and charge-exchange distributions throughout the edge pedestal, scrape-off layer and surrounding halo region, divertor, and private flux regions. The effectiveness of the different neutral sources for fueling the confined plasma is evaluated.
Show PACS
52.40.Hf Plasma-material interactions; boundary layer effects
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.25.Fi Transport properties
52.55.Fa Tokamaks, spherical tokamaks
back to top Inertially Confined Plasmas, High Energy Density Plasma Science, Warm Dense Matter

Irradiation uniformity and zooming performances for a capsule directly driven by a 32×9 laser beams configuration

M. Temporal, B. Canaud, and B. J. Le Garrec

Phys. Plasmas 17, 022701 (2010); http://dx.doi.org/10.1063/1.3309489 (7 pages) | Cited 6 times

Online Publication Date: 11 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
An inertial confinement fusion capsule directly driven by laser beams has been considered. A ray-tracing package is used to evaluate the uniformity of the energy deposition and the absorption efficiency provided by the direct irradiation of the capsule. Two distinct configurations with a single laser beam or a bundle of nine laser beams associated to 32 directions of irradiation are considered. Assuming a beam-to-beam power imbalance of 5% and a super-Gaussian spatial profile of the beams intensity, is found that the configuration using the bundles provides better irradiation uniformity. The laser beams of each bundle have been divided in two groups of four and five beams with associated different focal spots in order to increase the laser-capsule coupling efficiency. A configuration saving 16% of the laser energy and limiting the irradiation nonuniformity to less than 1% has been individuated.
Show PACS
52.57.Kk Fast ignition of compressed fusion fuels
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.50.Lp Plasma production and heating by shock waves and compression

Two-pulse driving of D+D nuclear fusion within a single Coulomb exploding nanodroplet

Isidore Last, Fabio Peano, Joshua Jortner, and Luis O. Silva

Phys. Plasmas 17, 022702 (2010); http://dx.doi.org/10.1063/1.3309482 (8 pages) | Cited 1 time

Online Publication Date: 24 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
This paper presents a computational study of D+D fusion driven by Coulomb explosion (CE) within a single, homonuclear deuterium nanodroplet, subjected to double-pulse ultraintense laser irradiation. This irradiation scheme results in the attainment (by the first weaker pulse) of a transient inhomogeneous density profile, which serves as a target for the driving (by the second superintense pulse) of nonuniform CE that triggers overrun effects and induces intrananodroplet (INTRA) D+D fusion. Scaled electron and ion dynamics simulations were utilized to explore the INTRA D+D fusion yields for double-pulse, near-infrared laser irradiation of deuterium nanodroplets. The dependence of the INTRA yield on the nanodroplet size and on the parameters of the two laser pulses was determined, establishing the conditions for the prevalence of efficient INTRA fusion. The INTRA fusion yields are amenable to experimental observation within an assembly of nanodroplets. The INTRA D+D fusion can be distinguished from the concurrent internanodroplet D+D fusion reaction occurring in the macroscopic plasma filament and outside it in terms of the different energies of the neutrons produced in these two channels.
Show PACS
36.40.Qv Stability and fragmentation of clusters
25.60.Pj Fusion reactions
34.10.+x General theories and models of atomic and molecular collisions and interactions (including statistical theories, transition state, stochastic and trajectory models, etc.)
back to top Ionospheric, Solar-System, and Astrophysical Plasmas

Energy transfer and magnetic field generation via ion-beam driven instabilities in an electron-ion plasma

Jaehong Park, Chuang Ren, Eric G. Blackman, and Xianglong Kong

Phys. Plasmas 17, 022901 (2010); http://dx.doi.org/10.1063/1.3299325 (8 pages)

Online Publication Date: 1 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Whether an efficient collisionless temperature equilibration mechanism exists for a two-temperature ion-electron plasma, with Ti>Te, is important for understanding astrophysical phenomena such as two-temperature accretion flows and collisionless shocks in supernova remnants or gamma-ray bursts. In this paper, counter-streaming ion beam-driven two-stream, Weibel (or filamentation), and oblique instabilities are studied using two-dimensional (2D) particle-in-cell (PIC) simulations as a possible plasma instability that could operate in such astrophysical objects. The PIC simulations show interplay among these instabilities and that distinct stages with different dominant modes occur during the nonlinear evolution period. Although the 2D results show stronger electron-ion coupling than the one-dimensional (1D) instabilities, it is still too weak to rule out existing two-temperature accretion solutions. The nonrelativistic quasilinear equations for the 1D Weibel plus 1D two-stream modes are numerically solved to compare the results with the 2D PIC simulations and qualitative similarities were found. The equations also show that the magnetic fields generated by the Weibel instability decay to zero in the end.
Show PACS
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.65.Rr Particle-in-cell method
95.30.Qd Magnetohydrodynamics and plasmas
98.62.Mw Infall, accretion, and accretion disks
98.58.Mj Supernova remnants

Nonlinear whistler instability driven by a beamlike distribution of resonant electrons

Martin Lampe, Glenn Joyce, Wallace M. Manheimer, and Gurudas Ganguli

Phys. Plasmas 17, 022902 (2010); http://dx.doi.org/10.1063/1.3298733 (7 pages) | Cited 4 times

Online Publication Date: 5 February 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Theory and simulation are used to study the instability of a coherent whistler parallel-propagating in a simplified model radiation belt with a background of cold electrons, as well as a ring distribution of energetic electrons. A nonlinear instability is initiated at the location z+, where the electrons are cyclotron resonant with the wave, on the side of the equator (z = 0) where the wave is propagating away from the equator. The instability propagates backward toward the equator, growing both spatially and temporally. As the instability develops, frequency falls in such a way as to keep the electrons nearly resonant with the waves over the entire region 0<z<z+. The instability causes a sharp drop in the pitch angle of the resonant electrons and eventually saturates with peak amplitude near the equator.
Show PACS
94.30.cq MHD waves, plasma waves, and instabilities
94.30.Xy Radiation belts
91.25.Mf Magnetic field reversals: process and timescale
52.65.-y Plasma simulation
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
Page 1 of 2 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close