Phys. Plasmas (1994-Present) - Physics of Plasmas

Select this Article

Pycnonuclear reactions in dense astrophysical and fusion plasmas

Setsuo Ichimaru and Hikaru Kitamura

Phys. Plasmas 6, 2649 (1999); http://dx.doi.org/10.1063/1.873221 (23 pages) | Cited 15 times

Show Abstract

Rates of pycnonuclear reactions in ultradense fluids and solids are evaluated by taking account of recent progress in quantum-statistical formulations of the equations of state and phase transitions in dense matter. New theoretical results are summarized for the reaction rates and the enhancement factors, obtained through systematic studies of the screening effects by relativistic and nonrelativistic electrons, as well as of the thermodynamic properties of dense matter resulting from internuclear cohesion in electron-screened Coulombic fluids and solids; the results prove to be a significant improvement over those in a previous review [S. Ichimaru, Rev. Mod. Phys. 65, 255 (1993)]. On the basis of these theoretical developments, coupled with renovated experiments in ultrahigh-pressure metal physics, outstanding issues of nuclear reactions in stellar and planetary interiors and in terrestrial settings are explored, with inertial-confinement-fusion experiments, and for a novel scheme of fusion studies in dense liquid-metallic proton–deuteron mixtures. © 1999 American Institute of Physics.

+

Show PACS

52.20.-j	Elementary processes in plasmas
52.58.-c	Other confinement methods
95.30.Qd	Magnetohydrodynamics and plasmas
25.45.-z	2H-induced reactions
52.25.Kn	Thermodynamics of plasmas
52.27.Ny	Relativistic plasmas
97.10.Cv	Stellar structure, interiors, evolution, nucleosynthesis, ages
28.52.Av	Theory, design, and computerized simulation
52.58.Ei	Light-ion inertial confinement

Select this Article

Direct measurements of two-dimensional velocity profiles in direct current glow discharge dusty plasmas

Edward Thomas

Phys. Plasmas 6, 2672 (1999); http://dx.doi.org/10.1063/1.873544 (4 pages) | Cited 20 times

Full Text: | Download PDF

+

Show Abstract

The letter details the first application of particle image velocimetry (PIV) techniques to dusty plasmas. Using PIV, two-dimensional velocity profiles are measured in dusty plasmas of silica particles that are suspended in the anode spot of an argon dc glow discharge plasma. This letter discusses the initial results of these studies and the potential applications of PIV techniques to dusty plasma studies. © 1999 American Institute of Physics.

+

Show PACS

52.27.Lw	Dusty or complex plasmas; plasma crystals
52.25.Fi	Transport properties
52.80.Hc	Glow; corona
52.70.Nc	Particle measurements

Select this Article

Compressional Alfvén cross–field surface waves in inhomogeneous dusty plasmas

N. F. Cramer, S. V. Vladimirov, K. N. Ostrikov, and M. Y. Yu

Phys. Plasmas 6, 2676 (1999); http://dx.doi.org/10.1063/1.873222 (5 pages) | Cited 2 times

Full Text: | Download PDF

+

Show Abstract

Compressional Alfvén surface waves in an inhomogeneous dusty plasma are studied. The inhomogeneity is modeled by two distinct regions of dusty plasmas with different ion densities. The stationary external magnetic field is along the interface between the two plasmas. The dispersion properties of cross-field surface waves, impossible in dust-free plasmas, are obtained for the constant dust charge case. The existence of the surface waves is due to an imbalance in the electron and ion Hall currents in a dusty plasma. © 1999 American Institute of Physics.

+

Show PACS

52.27.Lw	Dusty or complex plasmas; plasma crystals
52.35.Bj	Magnetohydrodynamic waves (e.g., Alfven waves)

Select this Article

The energy injection into waves with a zero group velocity

M. E. Dieckmann, S. C. Chapman, A. Ynnerman, and G. Rowlands

Phys. Plasmas 6, 2681 (1999); http://dx.doi.org/10.1063/1.873223 (12 pages) | Cited 4 times

Full Text: | Download PDF

+

Show Abstract

The frequency maxima of electron cyclotron harmonic (ECH) waves provide strong responses to sounding in various plasma regimes in the solar system. The frequency maxima correspond to waves for which the group velocity and thus the energy propagation velocity in the plasma frame of reference is zero. A particle-in-cell (PIC) code is employed to show that the propagation of wave energy at a non-zero velocity, necessary to couple energy from a stationary antenna to the plasma, is accomplished by propagating wave precursors. The undamped waves at the frequency maxima of the ECH branches are nonpropagating hence the waves remain localized. It is demonstrated that the nonpropagating waves, built up by the wave precursors, are standing waves. The standing wave generation is followed from the linear to nonlinear regimes. For nonlinear emission amplitudes the emission causes a plasma density depletion close to the antenna. The depletion is shown to trigger a modulational instability in which the ECH wave collapses. The generated nonlinear standing wave also develops an electromagnetic component which couples the electrostatic ECH waves to the fast extraordinary wave. © 1999 American Institute of Physics.

+

Show PACS

52.35.-g	Waves, oscillations, and instabilities in plasmas and intense beams
52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.40.Fd	Plasma interactions with antennas; plasma-filled waveguides
52.25.Kn	Thermodynamics of plasmas

Select this Article

Dust–dust and dust-plasma interactions of monolayer plasma crystals

H. Schollmeyer, A. Melzer, A. Homann, and A. Piel

Phys. Plasmas 6, 2693 (1999); http://dx.doi.org/10.1063/1.873224 (6 pages) | Cited 25 times

Full Text: | Download PDF

+

Show Abstract

The horizontal and vertical oscillation modes of monolayer plasma crystal are investigated and are related to dust–dust and dust-plasma interactions. It is found that the dust particles in the plasma sheath excited by a biased wire show parametric resonances. This parametric resonance is identified as the reason for the observed “sublimation” transition of the plasma crystal from a solid to a gaslike state. © 1999 American Institute of Physics.

+

Show PACS

52.27.Lw	Dusty or complex plasmas; plasma crystals
52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Qz	Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.25.Kn	Thermodynamics of plasmas

Select this Article

Theory of asymmetry-induced transport in a non-neutral plasma

D. L. Eggleston and T. M. O’Neil

Phys. Plasmas 6, 2699 (1999); http://dx.doi.org/10.1063/1.873225 (6 pages) | Cited 25 times

Full Text: | Download PDF

+

Show Abstract

Radial transport produced by static nonaxisymmetric fields is thought to limit the confinement of non-neutral plasmas and experiments with applied asymmetries have verified that such fields do produce transport. A theoretical model of such transport is presented which is appropriate for long, thin plasmas. The theory allows for asymmetries with nonzero frequency and includes the linear collective response to applied wall voltages. For the regime where the effective collision frequency is large, the asymmetry-induced radial particle flux is derived from the drift kinetic/Poisson equations including collisions. For low collision frequencies a heuristic derivation is given. In both regimes the resulting transport is dominated by particles that move in resonance with the asymmetry. Possible applications of the theory to several experiments are discussed. © 1999 American Institute of Physics.

+

Show PACS

52.27.Jt	Nonneutral plasmas
52.25.Fi	Transport properties

Select this Article

Numerical computation of collisionless drift Alfvén turbulence

Frank Jenko and Bruce D. Scott

Phys. Plasmas 6, 2705 (1999); http://dx.doi.org/10.1063/1.873226 (9 pages) | Cited 22 times

Full Text: | Download PDF

+

Show Abstract

An electromagnetic hybrid model of drift-kinetic electrons and cold ions in three-dimensional sheared slab geometry is constructed to treat collisionless drift Alfvén turbulence in tokamak edge plasmas. The basic nonlinear equations are solved numerically using explicit finite-difference methods on a phase-space grid rather than an ensemble of “superparticles.” Basic properties of the turbulent fluctuations such as amplitude and phase distributions, amplitude correlations, and energy spectra are investigated. The resulting turbulent particle transport by magnetic flutter is negligible compared to that by E×B convection. However, the intrinsic dynamics of the turbulence remains electromagnetic due to the influence of kinetic shear Alfvén waves and magnetic flutter. Comparisons with a companion Landau-fluid model are more successful than in similar studies of ion temperature gradient turbulence. © 1999 American Institute of Physics.

+

Show PACS

52.35.Ra	Plasma turbulence
52.35.Kt	Drift waves
52.25.Dg	Plasma kinetic equations
52.40.Hf	Plasma-material interactions; boundary layer effects
52.55.Fa	Tokamaks, spherical tokamaks
52.25.Gj	Fluctuation and chaos phenomena
52.35.Bj	Magnetohydrodynamic waves (e.g., Alfven waves)
52.25.Kn	Thermodynamics of plasmas
02.70.Bf	Finite-difference methods

Select this Article

Renormalization-group analysis on the scaling of the randomly-stirred magnetohydrodynamic plasmas

Chang-Bae Kim and Taek-Jin Yang

Phys. Plasmas 6, 2714 (1999); http://dx.doi.org/10.1063/1.873227 (7 pages) | Cited 8 times

Full Text: | Download PDF

+

Show Abstract

Similar to the neutral fluids [M. Lesieur, Turbulence in Fluids (Kluwer, Dordrecht, 1990), p. 137], two-dimensional magnetohydrodynamic (MHD) plasmas appear to obey the power-law behavior in terms of the size of the eddy. Scaling behavior of the randomly stirred MHD plasma is studied through the renormalization-group (RG) method. Generating functional is constructed and, from the power counting, the primitively divergent vertex functions are identified up to one-loop order. They are regularized by proper renormalizations of the viscosity, the resistivity and the size of the fluctuation. Scaling solution is shown to exist at the fixed point of the RG equation. The dependence of the power exponent of the energy spectrum on the driving Gaussian noise is derived. © 1999 American Institute of Physics.

+

Show PACS

52.30.-q	Plasma dynamics and flow
52.65.Kj	Magnetohydrodynamic and fluid equation
52.35.Ra	Plasma turbulence
02.20.-a	Group theory
02.30.-f	Function theory, analysis
05.40.Ca	Noise

Select this Article

Quasipotential analysis for deriving the multidimensional Sagdeev potential equation in multicomponent plasma

Rajkumar Roychoudhury, G. C. Das, and Jnanjyoti Sarma

Phys. Plasmas 6, 2721 (1999); http://dx.doi.org/10.1063/1.873228 (6 pages) | Cited 21 times

Full Text: | Download PDF

+

Show Abstract

The exact multidimensional Sagdeev potential is derived in a multicomponent plasma consisting of negative ions wherein a fraction of electrons is trapped in the potential well developed in the plasma. More precisely, the Sagdeev potential equation revisits the results stemming from the Kadomtsev–Petviashvili (K–P) equation deduceable by applying the reductive perturbation technique in plasma-acoustic wave dynamics. In the study we show that the multidimensional Sagdeev potential derived here yields the formation and propagation of solitons, as well as double layers in plasma, by using a new approach known as the tanh-method to solve out the soliton phenomena. It is seen that different ordering in ϕ, the electrical potential, yields different solitary wave solutions that agree with earlier observations. © 1999 American Institute of Physics.

+

Show PACS

52.27.Jt	Nonneutral plasmas
52.35.Sb	Solitons; BGK modes
52.40.Hf	Plasma-material interactions; boundary layer effects

Select this Article

The geometry and symmetries of magnetohydrodynamic turbulence: Anomalies of spatial periodicity

David C. Montgomery and Jason W. Bates

Phys. Plasmas 6, 2727 (1999); http://dx.doi.org/10.1063/1.873229 (7 pages) | Cited 8 times

Full Text: | Download PDF

+

Show Abstract

It has become common to formulate theories and computations of magnetohydrodynamic turbulent effects in rectangular periodic boundary conditions, proceeding by analogy with what is seen as a useful framework for Navier–Stokes fluid turbulence. It is shown here that because of certain features of Maxwell’s equations for electrodynamics, it is inconsistent to invoke three-dimensional, rectangular, periodic boundary conditions and symmetry at the same time that the displacement current is neglected. The difficulty does not arise in the two-dimensional case. In three dimensions, the difficulty can be remedied by a reformulation in cylindrical geometry, imposing symmetry in the azimuthal and axial directions, but not in the radial one; a geometry that is closer to laboratory possibilities than the wholly three-dimensional periodic assumption. The reformulation seems particularly necessary in cases with a net flux of magnetic field and/or electric currents through the system. These cases no longer seem discontinuous from those without net magnetic fluxes or currents. The price paid is a loss of some possibilities for dimensional analysis and identification of similarity variables. © 1999 American Institute of Physics.

+

Show PACS

47.65.-d	Magnetohydrodynamics and electrohydrodynamics
47.27.-i	Turbulent flows
47.10.-g	General theory in fluid dynamics

Select this Article

Formalism for multi-fluid equilibria with flow

Loren C. Steinhauer

Phys. Plasmas 6, 2734 (1999); http://dx.doi.org/10.1063/1.873230 (8 pages) | Cited 36 times

Full Text: | Download PDF

+

Show Abstract

A formalism is developed for flowing multifluid equilibria. In the standard reduced case (massless electrons, quasineutrality) this system simplifies to a pair of second-order partial differential equations for the magnetic and ion flow stream functions plus a Bernoulli equation giving the density. Each species has its own characteristic surfaces, which are the drift surfaces, and three arbitrary surface functions associated with each species. In the case of minimum energy equilibria, the surface functions are no longer arbitrary. The flowing equilibrium system is a generalization of the familiar Grad–Shafranov system for magnetostatic equilibria. © 1999 American Institute of Physics.

+

Show PACS

47.55.Kf	Particle-laden flows
02.30.Jr	Partial differential equations
02.60.Lj	Ordinary and partial differential equations; boundary value problems
52.30.-q	Plasma dynamics and flow
52.65.Kj	Magnetohydrodynamic and fluid equation

Select this Article

Analytic modeling of axisymmetric disruption halo currents

D. A. Humphreys and A. G. Kellman

Phys. Plasmas 6, 2742 (1999); http://dx.doi.org/10.1063/1.873231 (15 pages) | Cited 26 times

Full Text: | Download PDF

+

Show Abstract

Currents which can flow in plasma facing components during disruptions pose a challenge to the design of next generation tokamaks. Induced toroidal eddy currents and both induced and conducted poloidal “halo” currents can produce design-limiting electromagnetic loads. While induction of toroidal and poloidal currents in passive structures is a well-understood phenomenon, the driving terms and scalings for poloidal currents flowing on open field lines during disruptions are less well established. A model of halo current evolution is presented in which the current is induced in the halo by decay of the plasma current and change in enclosed toroidal flux while being convected into the halo from the core by plasma motion. Fundamental physical processes and scalings are described in a simplified analytic version of the model. The peak axisymmetric halo current is found to depend on halo and core plasma characteristics during the current quench, including machine and plasma dimensions, resistivities, safety factor, and vertical stability growth rate. Two extreme regimes in poloidal halo current amplitude are identified depending on the minimum halo safety factor reached during the disruption. A “type I” disruption is characterized by a minimum safety factor that remains relatively high (typically 2–3, comparable to the predisruption safety factor), and a relatively low poloidal halo current. A “type II” disruption is characterized by a minimum safety factor comparable to unity and a relatively high poloidal halo current. Model predictions for these two regimes are found to agree well with halo current measurements from vertical displacement event disruptions in DIII-D [T. S. Taylor, K. H. Burrell, D. R. Baker, G. L. Jackson, R. J. La Haye, M. A. Mahdavi, R. Prater, T. C. Simonen, and A. D. Turnbull, “Results from the DIII-D Scientific Research Program,” in Proceedings of the 17th IAEA Fusion Energy Conference, Yokohama, 1998, to be published in a Special Edition of Nuclear Fusion (1999)]. © 1999 American Institute of Physics.

+

Show PACS

52.55.Fa	Tokamaks, spherical tokamaks
52.25.Fi	Transport properties

Select this Article

Effects of finite feedback loop gain and bandwidth on stabilization of magnetohydrodynamic instabilities by an “intelligent shell”

T. H. Jensen and A. M. Garofalo

Phys. Plasmas 6, 2757 (1999); http://dx.doi.org/10.1063/1.873232 (5 pages) | Cited 4 times

Full Text: | Download PDF

+

Show Abstract

The “intelligent shell” [C. M. Bishop, Plasma Phys. Contr. Fusion 31, 1179 (1989)] utilizes a feedback system intended to make a resistive wall appear perfectly conducting to a plasma. It can thus be used for stabilizing modes of the plasma which are unstable when the plasma is surrounded by a resistive wall, but stable if the wall were perfectly conducting. Several concepts of magnetic confinement, such as reversed field pinches, spheromaks, and tokamaks may benefit from an intelligent shell. The paper addresses the question of the dependency of the stabilizing effect on the gain and bandwidth of the feedback circuits (assumed linear). A simple model for the phenomena involved is made and solved numerically for certain parameter values. A characteristic time of the model is a resistive time τ of the wall; the calculations suggest that an upper cutoff frequency of ∼ 50/τ and sufficient gain provides a stabilization similar to that of ideal circuits with infinite bandwidth and gain. Under laboratory circumstances with τ ∼ 10⁻³ s it is thus practical to obtain mass produced components which make the circuits as effective as ideal circuits. © 1999 American Institute of Physics.

+

Show PACS

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.)
52.35.Qz	Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.55.Ez	Theta pinch
52.55.Fa	Tokamaks, spherical tokamaks
52.55.Jd	Magnetic mirrors, gas dynamic traps
84.30.Le	Amplifiers
84.30.Bv	Circuit theory

Select this Article

Stable plasma response to a dynamic magnetic excitation

C. Riconda, M. De Benedetti, and M. Ottaviani

Phys. Plasmas 6, 2762 (1999); http://dx.doi.org/10.1063/1.873233 (9 pages) | Cited 3 times

Full Text: | Download PDF

+

Show Abstract

The asymptotic linear response of the plasma to a finite frequency external magnetic perturbation is analyzed by using the reduced magnetohydrodynamics (MHD) resistive equation with antenna boundary conditions. Different regimes are identified depending on the parameter ω/η^1/3k^2/3, where ω is the difference between the antenna frequency and the rotation frequency at the rational surface normalized to the poloidal Alfvén time, and η is the normalized resistivity (the inverse of the Lundquist number). The solution for ψ (magnetic flux function) at the rational surface that interpolates the known constant-ψ regime, ω≪η^1/3k^2/3, and the ideal regime, ω≫η^1/3k^2/3, is found. In the ideal regime the presence of Alfvén resonances prevents reconnection and island formation at the rational surface. The results of recent experiments in the Joint European Torus JET [P. H. Rebut et al., Nucl. Fusion 25, 1011 (1985)], where the external magnetic field perturbations are produced by the saddle coil system are also presented. These show the presence of a resonant response of the MHD stable plasma when the antenna frequency approaches the rotation frequency of the corresponding rational surface. © 1999 American Institute of Physics.

+

Show PACS

52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Fa	Tokamaks, spherical tokamaks

Select this Article

A numerical study of rotating magnetic fields as a current drive for field reversed configurations

Richard D. Milroy

Phys. Plasmas 6, 2771 (1999); http://dx.doi.org/10.1063/1.873234 (10 pages) | Cited 33 times

Full Text: | Download PDF

+

Show Abstract

A fixed ion model has been developed to study the use of a Rotating Magnetic Field (RMF) as a current drive mechanism in a Field Reversed Configuration (FRC). This model is used to investigate the physics of RMF current drive in a parameter range of interest to two experiments at the University of Washington. Empirical expressions are found to characterize the critical RMF magnitude required for full penetration and the rate of RMF penetration. It is shown that in the presence of a strong anisotropic plasma resistivity, the direction and magnitude of the axial bias field can have a strong influence on the penetration of an RMF. Calculations that include the effects of realistic RMF antennae at finite radius are used to find the effects of coil spacing and positioning. © 1999 American Institute of Physics.

+

Show PACS

52.55.Ez	Theta pinch
52.25.Fi	Transport properties

Select this Article

Determination of the vacuum field resulting from the perturbation of a toroidally symmetric plasma

C. V. Atanasiu, A. H. Boozer, L. E. Zakharov, A. A. Subbotin, and G. I. Miron

Phys. Plasmas 6, 2781 (1999); http://dx.doi.org/10.1063/1.873235 (10 pages) | Cited 3 times

Full Text: | Download PDF

+

Show Abstract

By using the concept of a surface current, the description and calculation of the stability of modes and the plasma response function are greatly simplified. A robustly accurate and effective method is presented to determine these surface currents, considering that the perturbation is given by toroidally coupled tearing modes. A new form of the normal component of the magnetic field perturbation ( math

_n), excited by a tearing mode with toroidal coupling, has been derived in terms of the solution of a hypergeometric differential equation, which is also appropriate in the large toroidal mode number (N) limit. Examples of calculations are given for different plasma cross-sectional shapes, including separatrix configurations. © 1999 American Institute of Physics.

+

Show PACS

52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Fa	Tokamaks, spherical tokamaks
52.55.Jd	Magnetic mirrors, gas dynamic traps

Select this Article

Modeling of particle and energy transport in the edge plasma of Alcator C-Mod

M. V. Umansky, S. I. Krasheninnikov, B. LaBombard, B. Lipschultz, and J. L. Terry

Phys. Plasmas 6, 2791 (1999); http://dx.doi.org/10.1063/1.873236 (6 pages) | Cited 21 times

Full Text: | Download PDF

+

Show Abstract

In the present study recycling and transport in the edge plasma of Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] is modeled and analyzed with the multi-fluid code UEDGE [T. D. Rognlien et al., J. Nucl. Mater. 196–198, 347 (1992)]. Matching the experimental plasma density profiles in the scrape-off layer (SOL) requires a spatially dependent effective anomalous diffusion coefficient D_⊥ growing rapidly towards the wall. The midplane pressure of neutral gas, P_mid, is a key parameter that reflects the magnitude of anomalous transport of plasma from the core. Recycling of plasma on the main chamber wall appears to be quite significant, especially in the case of high P_mid ∼ 0.3 mTorr when the main wall provides ∼ 70% of recycling neutrals in the main chamber. In the upper SOL (well above the x point) draining of particles by the poloidal flow is weak and thus the particle balance is predominantly radial. For the radial heat transport it is found that energy flux carried by radial plasma convection and by charge-exchange (CX) neutrals is quite significant in SOL. In the high P_mid case, heat conduction by CX neutrals along with radial heat convection by plasma carries most of the power flux ( ∼ 75%) across the last closed flux surface. Even in the low P_mid case, heat conduction by CX neutrals dominates the radial heat flux far out in the SOL. © 1999 American Institute of Physics.

+

Show PACS

52.40.Hf	Plasma-material interactions; boundary layer effects
52.55.Fa	Tokamaks, spherical tokamaks
52.25.Fi	Transport properties
52.20.Hv	Atomic, molecular, ion, and heavy-particle collisions

Select this Article FREE

Diamagnetic stabilization of ideal ballooning modes in the edge pedestal

B. N. Rogers and J. F. Drake

Phys. Plasmas 6, 2797 (1999); http://dx.doi.org/10.1063/1.873237 (5 pages) | Cited 43 times

Full Text: | Download PDF

+

Show Abstract

The stability of the tokamak edge pedestal to ballooning modes is addressed using three-dimensional simulations of the Braginskii equations and simple analytic models. The effects of ion diamagnetic drift and the finite radial localization of the pedestal pressure gradient are found to be strongly stabilizing when δ<δ_R, where δ is the pedestal half-width and δ_R ∼ ρi2/3R^1/3 in the center of the pedestal. In this limit, conventional ballooning modes within the pedestal region become stable, and a stability condition is obtained in the two fluid system α/α_c<(4/3)δ_R/δ (stable) which is much less stringent than that predicted by local magnetohydrodynamic (MHD) theory (α/α_c<1). Given α ∼ q²Rβ/δ, this condition implies a stability limit on the pedestal β: β<β_c, where β_c = (4α_c/3q²)δ_R/R. This limit is due the onset of an ideal pressure driven “surface” instability that depends only on the pressure drop across the pedestal. Near marginal conditions, this mode has a poloidal wavenumber k_θ ∼ 1/δ_R, a radial envelope ∼ δ_R(>δ), and real frequency ω ∼ c_s/ math

+

Show PACS

52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Fa	Tokamaks, spherical tokamaks
52.25.-b	Plasma properties
52.65.-y	Plasma simulation

Select this Article

Fast particle finite orbit width and Larmor radius effects on low-n toroidicity induced Alfvén eigenmode excitation

N. N Gorelenkov, C. Z. Cheng, and G. Y. Fu

Phys. Plasmas 6, 2802 (1999); http://dx.doi.org/10.1063/1.873545 (6 pages) | Cited 28 times

Full Text: | Download PDF

+

Show Abstract

The effects of finite drift orbit width (FOW) and Larmor radius (FLR) of fast particles on the stability of low-n toroidicity-induced Alfvén eigenmodes (TAE) are studied. The formulation is based on the solution of the low frequency gyrokinetic equation (ω≪ω_c, where ω_c is particle cyclotron frequency). A quadratic form has been derived in terms of invariant variables; energy E, magnetic moment μ, and toroidal angular momentum P_φ. The growth rate of the TAE is computed perturbatively using numerical averaging over the fast particle drift orbit. This new computational capability improves the NOVA-K code [G. Y. Fu, C. Z. Cheng, and K. L. Wong, Phys. Fluids B 5, 4040 (1994)] which included FOW effects in the growth rate calculation based on small radial orbit width approximation. The new NOVA-K version has been benchmarked for different regimes of particle TAE excitation. It is shown that both FOW and FLR effects are typically stabilizing; the TAE growth rate can be reduced by as much as a factor of 2 for tokamak fusion test reactor supershots [D. J. Grove and D. M. Meade, Nucl. Fusion 25, 1167 (1985)]. However, FOW may be destabilizing for the global modes, which are localized at the plasma edge. © 1999 American Institute of Physics.

+

Show PACS

52.35.Bj	Magnetohydrodynamic waves (e.g., Alfven waves)
52.55.Fa	Tokamaks, spherical tokamaks

Select this Article

On transport, in particular of impurities, in a stochastic magnetic field

M. Z. Tokar’

Phys. Plasmas 6, 2808 (1999); http://dx.doi.org/10.1063/1.873238 (8 pages) | Cited 20 times

Full Text: | Download PDF

+

Show Abstract

The transport coefficients in a stochastic magnetic field are computed by taking into account analytical relationships for the distribution of plasma parameters along divergent lines of force. In the case of impurities, in contrast to what was believed before, stochastization primarily influences their convection but not their diffusive motion. At the plasma periphery, this convection is mainly caused by friction with the flow of background particles sustained by recycling and is directed toward the plasma boundary. This leads to an enhancement of the impurity exhaust, which provides a plausible explanation for the plasma decontamination observed in tokamaks with peripheral stochastic layers. © 1999 American Institute of Physics.

+

Show PACS

52.25.Fi	Transport properties
52.25.Vy	Impurities in plasmas
52.55.Fa	Tokamaks, spherical tokamaks

Select this Article

Self-consistent plasma-neutral modeling in tokamak plasmas with a large-area toroidal belt limiter

D. S. Gray, M. Baelmans, J. A. Boedo, D. Reiter, and R. W. Conn

Phys. Plasmas 6, 2816 (1999); http://dx.doi.org/10.1063/1.873239 (10 pages) | Cited 9 times

Full Text: | Download PDF

+

Show Abstract

Plasma-neutral phenomena in the edge plasma and scrape-off layer of the Torus Experiment for Technology Oriented Research [G.H. Wolf and the TEXTOR Team, J. Nucl. Mater. 122&123, 1124 (1984)] with the toroidal belt Advanced Limiter Test (ALT-II) [D.M. Goebel et al., J. Nucl. Mater. 162–164, 115 (1989)] are simulated using the code package B2-EIRENE [D. Reiter et al., Plasma Phys. Controlled Fusion 33, 1579 (1991)]. Spatially-constant, anomalous radial transport coefficients (D,V,χ) are used for fitting measured electron temperature and density profiles. Primary neutral fluxes are determined by plasma fluxes to material surfaces, and Dα emissions are predicted from them. Comparison of the predicted Dα emission with measurements indicates a critical need, in predictive modeling, for a self-consistent model of fluxes to material surfaces that are parallel to the magnetic field. Appropriate factors are calculated for deducing D⁺ source rates from Dα emissions measured in various locations, taking into account molecular processes and spatially varying plasma parameters; values range from 17 to 28 ions/photon. Ion fluxes lost to pumps or the wall must be explicitly re-introduced as neutral fluxes at the outer boundary. © 1999 American Institute of Physics.

+

Show PACS

52.55.Fa	Tokamaks, spherical tokamaks
52.40.Hf	Plasma-material interactions; boundary layer effects
52.25.Fi	Transport properties

Select this Article

Neoclassical simulations of fusion alpha particles in pellet charge exchange experiments on the Tokamak Fusion Test Reactor

M. H. Redi, S. H. Batha, R. V. Budny, D. S. Darrow, F. M. Levinton, D. C. McCune, S. S. Medley, M. P. Petrov, S. von Goeler, R. B. White, M. C. Zarnstorff, and S. J. Zweben

Phys. Plasmas 6, 2826 (1999); http://dx.doi.org/10.1063/1.873717 (8 pages) | Cited 5 times

Full Text: | Download PDF

+

Show Abstract

Neoclassical simulations of alpha particle density profiles in high fusion power plasmas on the Tokamak Fusion Test Reactor [Phys. Plasmas 5, 1577 (1998)] are found to be in good agreement with measurements of the alpha distribution function made with a sensitive active neutral particle diagnostic. The calculations are carried out in Hamiltonian magnetic coordinates with a fast, particle-following Monte Carlo code which includes the neoclassical transport processes, a recent first-principles model for stochastic ripple loss and collisional effects. New calculations show that monotonic shear alpha particles are virtually unaffected by toroidal field ripple. The calculations show that in reversed shear the confinement domain is not empty for trapped alphas at birth and allow an estimate of the actual alpha particle densities measured with the pellet charge exchange diagnostic. © 1999 American Institute of Physics.

+

Show PACS

52.55.Fa	Tokamaks, spherical tokamaks
52.55.Pi	Fusion products effects (e.g., alpha-particles, etc.), fast particle effects
52.25.Fi	Transport properties
52.70.Nc	Particle measurements
52.65.Pp	Monte Carlo methods