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Feb 1999

Volume 6, Issue 2, pp. 425-635

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back to top Magnetically Confined Plasmas, Heating, Confinement

On the orbit-averaged Monte Carlo operator describing ion cyclotron resonance frequency wave–particle interaction in a tokamak

L.-G. Eriksson, M. J. Mantsinen, T. Hellsten, and J. Carlsson

Phys. Plasmas 6, 513 (1999); http://dx.doi.org/10.1063/1.873195 (6 pages) | Cited 14 times

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In a toroidal plasma the distribution function of ions interacting resonantly with waves in the ion cyclotron range of frequencies (ICRF) can be described with a three-dimensional orbit-averaged Fokker–Planck equation. This equation can be solved with a Monte Carlo method. Explicit expressions for the Monte Carlo operator describing wave–particle interaction, within the framework of quasilinear theory, are given. Furthermore, properties of the operator are discussed. © 1999 American Institute of Physics.
Show PACS
52.55.Fa Tokamaks, spherical tokamaks
52.65.Pp Monte Carlo methods
52.65.Ff Fokker-Planck and Vlasov equation
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Effect of neutrals on scrape-off-layer and divertor stability in tokamaks

D. A. D’Ippolito and J. R. Myra

Phys. Plasmas 6, 519 (1999); http://dx.doi.org/10.1063/1.873196 (11 pages) | Cited 4 times

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The influence of ion–neutral interactions (charge exchange, elastic scattering) on scrape-off-layer (SOL) stability is studied in the eikonal limit for a single-null X-point geometry typical of tokamak divertors. Instability drives due to curvature and to the ion–neutral drag effect are included in the model. The ion–neutral interaction terms are highly localized near the divertor plates; these terms are stabilizing for typical parameters and large enough to affect the SOL ballooning-interchange stability in the absence of resistivity. It is shown that the growth rate of ideal curvature-driven modes is significantly reduced by the ion–neutral interaction terms; the growth rate of resistive ballooning modes is not affected much by the neutrals, because resistivity allows the mode to disconnect from the divertor region. In both cases, the X-point geometry significantly affects the stability. An ion–neutral drag instability localized near the plates is only found in a small region of parameter space. Conditions for the existence of this instability in X-point geometry are discussed. © 1999 American Institute of Physics.
Show PACS
52.55.Fa Tokamaks, spherical tokamaks
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.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Resistive ballooning modes near the edge of toroidal configurations

Darío Correa-Restrepo

Phys. Plasmas 6, 530 (1999); http://dx.doi.org/10.1063/1.873197 (11 pages) | Cited 3 times

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The resistive ballooning mode equations are cast in a new form appropriate for evaluation near the plasma edge of toroidal (axisymmetric as well as three-dimensional) configurations, where the resistive ballooning effects outweigh the diamagnetic effects. Explicit evaluation is carried out for cylindrically symmetric plasmas and for a tokamak model with circular cross sections. Owing to the large electric resistivity of the regions considered, resistive ballooning modes with growth rates comparable to the characteristic growth rate of ideal ballooning modes are possible. A general feature is that modes with large growth rates are localized around the regions of bad curvature and become less unstable with increasing shear, while those with smaller growth rates are extended along the magnetic field lines and are insensitive to shear. © 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
52.25.Fi Transport properties

Spectroscopic analysis of normal and reversed ion flows in the DIII-D divertor

R. C. Isler, N. H. Brooks, W. P. West, A. W. Leonard, G. R. McKee, and G. D. Porter

Phys. Plasmas 6, 541 (1999); http://dx.doi.org/10.1063/1.873198 (9 pages) | Cited 20 times

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Flow velocities of C+, C2+, B+, and D+ parallel to the magnetic field in the DIII-D [J. Luxon, P. Anderson, F. Batty et al., Plasma Physics Controlled Nuclear Fusion Research, Proceedings of the 11th International Conference, Tokyo, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] divertor have been measured from Doppler shifts of spectral lines. In general, both normal flows (toward the target plate) and reversed flows (away from the target plate) are observed in the outer scrape-off layer with the reversed flows occurring near the separatrix. Following the transition from attached to partially detached conditions, normal flow velocities generally speed up while in some regions reversed flows are observed to slow down. In high density plasmas, deuteron velocities are reflected in Balmer line emission which originates mainly from atoms which have thermalized by charge exchange or which have been formed by recombination. Low-temperature areas of nearly stagnated deuteron flow have been observed. In these regions recombination should be efficient for neutralizing the divertor plasma. © 1999 American Institute of Physics.
Show PACS
52.55.Fa Tokamaks, spherical tokamaks
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.30.-q Plasma dynamics and flow
52.25.Vy Impurities in plasmas
52.55.Pi Fusion products effects (e.g., alpha-particles, etc.), fast particle effects
52.40.Hf Plasma-material interactions; boundary layer effects
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Collisionless transport parallel to the magnetic field in a toroidal plasma

R. D. Hazeltine

Phys. Plasmas 6, 550 (1999); http://dx.doi.org/10.1063/1.873199 (6 pages) | Cited 5 times

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Transport parallel to the magnetic field of a toroidal plasma confinement system is investigated through kinetic theory, with emphasis on the long mean-free path limit. The crucial differences between transport on rational and irrational (ergodic) magnetic surfaces is discussed in detail. A collisionless transport law, involving a nonlocal operator that accounts for toroidal topology, is derived for parallel heat conduction on irrational magnetic surfaces. In the rational surface case, perpendicular diffusion is included in the kinetic equation to avoid singularity; this allows a calculation of the width and amplitude of resonant temperature perturbations that will be excited by heat sources with sufficiently broad Fourier spectra. © 1999 American Institute of Physics.
Show PACS
52.25.Fi Transport properties
52.25.Dg Plasma kinetic equations
52.55.Fa Tokamaks, spherical tokamaks
52.55.Jd Magnetic mirrors, gas dynamic traps
02.40.Pc General topology

Effects of magnetic shear on electron cyclotron resonance heating in heliotron/torsatron configurations

K. Nagasaki, A. Ejiri, T. Mizuuchi, T. Obiki, H. Okada, F. Sano, H. Zushi, S. Besshou, and K. Kondo

Phys. Plasmas 6, 556 (1999); http://dx.doi.org/10.1063/1.873200 (9 pages) | Cited 10 times

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Effects of magnetic shear on electron cyclotron resonance heating (ECRH) are studied in heliotron/torsatron configurations. In such configurations, the poloidal magnetic field is comparable to the toroidal magnetic field, and varies spatially along the minor radius, making a strong magnetic shear. When high power millimeter waves are launched into a plasma, it is coupled to propagating modes at the plasma peripheral region. The existence of a transition layer between the core plasma region and the vacuum region, where the magnetic field direction is largely changed, requires accurate polarization control for good single pass absorption. The mode conversion between the propagation modes due to the magnetic shear also affects the launching conditions. The polarization control experiment by using second harmonic ECRH in Heliotron E [T. Obiki, Fusion Technol. 17, 101 (1990)] are compared with the numerical calculation in which one dimensional second order coupled equations are solved. The polarization dependence experimentally measured is in good agreement with the numerical results including the magnetic shear terms. © 1999 American Institute of Physics.
Show PACS
52.55.Jd Magnetic mirrors, gas dynamic traps
52.50.Gj Plasma heating by particle beams
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
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