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Oct 2001

Volume 8, Issue 10, pp. 4267-4703

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Curvature effects on the dynamics of tearing modes in tokamaks

Hinrich Lütjens, Jean-François Luciani, and Xavier Garbet

Phys. Plasmas 8, 4267 (2001); http://dx.doi.org/10.1063/1.1399056 (4 pages) | Cited 30 times

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The curvature effects on the dynamics of magnetic island evolution in tokamaks are investigated both theoretically and numerically. By taking into account perpendicular and parallel heat diffusion, a new dispersion relation is derived for tearing modes that match the linear and nonlinear results. This evolution equation allows a quantitative description over the whole range of island sizes. It predicts a nonlinear instability, i.e., growing magnetic islands in linearly stable magnetic configurations. All these predictions are in excellent agreement with full tridimensional linear and nonlinear magnetohydrodynamic (MHD) computations with the latest version of XTOR [K. Lerbinger and J. F. Luciani, J. Comput. Phys. 97, 444 (1991)]. These results have important consequences on the onset of neoclassical tearing modes because they predict a resistive MHD threshold. © 2001 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.Fi Transport properties

Dynamics of periodic ion holes in a forced beam–plasma experiment

C. Franck, T. Klinger, A. Piel, and H. Schamel

Phys. Plasmas 8, 4271 (2001); http://dx.doi.org/10.1063/1.1403395 (4 pages) | Cited 14 times

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Experimental observation of the propagation of periodic ion phase space vortices is reported. Density fluctuation measurements in a double plasma device show an apparently spontaneous acceleration of these periodic structures from ion thermal to ion acoustic velocity. A nonlinear kinetic description explains this as a transition from a new type of nonlinear electrostatic mode (periodic ion holes) to an ion acoustic mode which is caused by trapped particle scattering. © 2001 American Institute of Physics.
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52.40.Mj Particle beam interactions in plasmas
52.35.We Plasma vorticity
52.25.Gj Fluctuation and chaos phenomena
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back to top Basic Plasma Phenomena, Waves, Instabilities

Ion acoustic waves in one- and two-negative ion species plasmas

Ryuta Ichiki, Masako Shindo, Shinji Yoshimura, Tsuguhiro Watanabe, and Yoshinobu Kawai

Phys. Plasmas 8, 4275 (2001); http://dx.doi.org/10.1063/1.1396843 (9 pages) | Cited 15 times

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Ion acoustic waves in multi-ion plasmas including two negative ion species are investigated both numerically and experimentally. Numerically, the kinetic dispersion relation in two-negative ion plasmas is investigated. There are three modes of the ion acoustic waves in two-negative ion plasmas. In an Ar+–F−–SF6− plasma, only one of the three modes is dominant, regardless of the values of the electron and the ion temperatures. In a Xe+–F−–SF6− plasma, on the other hand, two modes can be important for a certain range of the electron–ion temperature ratio. The results also imply the possibility of the coexistence of the fast mode and the slow mode in one-negative ion plasmas. Experimentally, ion acoustic waves are observed in an Ar+–F−–SF6− plasma and are found to show a mode transition that agrees with the theoretical prediction for one of the three ion acoustic modes. © 2001 American Institute of Physics.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Radiative proton-capture nuclear processes in metallic hydrogen

Setsuo Ichimaru

Phys. Plasmas 8, 4284 (2001); http://dx.doi.org/10.1063/1.1398281 (8 pages) | Cited 1 time

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Protons being the lightest nuclei, metallic hydrogen may exhibit the features of quantum liquids most relevant to enormous enhancement of nuclear reactions; thermonuclear and pycnonuclear rates and associated enhancement factors of radiative proton captures of high-Z nuclei as well as of deuterons are evaluated. Atomic states of high-Z impurities are determined in a way consistent with the equations of state and screening characteristics of the metallic hydrogen. Rates of pycnonuclear p-d reactions are prodigiously high at densities ⩾20 g/cm3, pressures ⩾1 Gbar, and temperatures ⩾950 K near the conditions of solidification. It is also predicted that proton captures of nuclei such as C, N, O, and F may take place at considerable rates, owing to strong screening by K-shell electrons, if the densities ⩾60–80 g/cm3, the pressures ⩾7–12 Gbar, and the temperatures just above solidification. The possibilities and significance of pycnonuclear p-d fusion experiments are specifically remarked. © 2001 American Institute of Physics.
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25.10.+s Nuclear reactions involving few-nucleon systems
25.40.Lw Radiative capture
52.27.Gr Strongly-coupled plasmas
64.90.+b Other topics in equations of state, phase equilibria, and phase transitions (restricted to new topics in section 64)

Modeling of diamagnetic stabilization of ideal magnetohydrodynamic instabilities associated with the transport barrier

G. T. A. Huysmans, S. E. Sharapov, A. B. Mikhailovskii, and W. Kerner

Phys. Plasmas 8, 4292 (2001); http://dx.doi.org/10.1063/1.1398573 (14 pages) | Cited 36 times

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A new code, MISHKA-D (Drift MHD), has been developed as an extension of the ideal magnetohydrodynamics (MHD) code MISHKA-1 in order to investigate the finite gyroradius stabilizing effect of ion diamagnetic drift frequency, ω∗i, on linear ideal MHD eigenmodes in tokamaks in general toroidal geometry. The MISHKA-D code gives a self-consistent computation of both stable and unstable eigenmodes with eigenvalues ∣γ∣ ≅ ω∗i in plasmas with strong radial variation in the ion diamagnetic frequency. Test results of the MISHKA-D code show good agreement with the analytically obtained ω∗i spectrum and stability limits of the internal kink mode, n/m = 1/1, used as a benchmark case. Finite-n ballooning and low-n kink (peeling) modes in the edge transport barrier just inside the separatrix are studied for high confinement mode (H-mode) plasmas with the ω∗i effect included. The ion diamagnetic stabilization of the ballooning modes is found to be most effective for narrow edge pedestals. For low enough plasma density the ω∗i stabilization can lead to a second zone of ballooning stability, in which all the ballooning modes are stable for any value of the pressure gradient. For internal transport barriers typical of the Joint European Torus [JET, P. H. Rebut et al., Proceedings of the 10th International Conference, Plasma Physics and Controlled Nuclear Fusion, London (International Atomic Energy Agency, Vienna, 1985), Vol. I, p. 11] optimized shear discharges, the stabilizing influence of ion diamagnetic frequency on the n = 1 global pressure driven disruptive mode is studied. A strong radial variation of ω∗i is found to significantly decrease the stabilizing ω∗i effect on the n = 1 mode, in comparison with the case of constant ω∗i estimated at the foot of the internal transport barrier. © 2001 American Institute of Physics.
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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.Fi Transport properties

Linear stability and mode structure of drift tearing modes

D. Grasso, M. Ottaviani, and F. Porcelli

Phys. Plasmas 8, 4306 (2001); http://dx.doi.org/10.1063/1.1399327 (12 pages) | Cited 18 times

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Ion viscosity and particle diffusivity effects on the linear stability and mode structure of drift-tearing modes are investigated. If only resistivity and diamagnetic effects are taken into account, the drift-tearing mode can exist only as a propagating wave packet, which is resolved numerically as an initial value problem. Ion viscosity, particle diffusivity, as well as finite electron compressibility, also considered in this paper, lead to radially localized modes. The mode growth rate is reduced by ion viscosity, but is increased by particle diffusivity. The instability threshold is not modified. The analysis is based on the analytic and numerical solutions of a reduced three-field fluid model. © 2001 American Institute of Physics.
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52.35.Kt Drift waves
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.)
52.25.Fi Transport properties

Effect of dust charge fluctuation on the Alfvén wave propagation in a magnetized dusty plasma

Md. Khurshed Alam, Bilkis Ara Begum, and A. Roy Chowdhury

Phys. Plasmas 8, 4318 (2001); http://dx.doi.org/10.1063/1.1389300 (7 pages) | Cited 4 times

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Growth rates of propagating waves in a magnetized dusty plasma are studied for various values of natural decay rate for the presence of dust charge fluctuation in the case of hot ions and electrons and for a weak magnetic field. The dispersion relation is obtained for the waves that propagate through low-frequency plasma with velocity, VA = B0/(μominio)1/2. Consistency of the results with previous work [Alam et al., Astrophys. Space Sci. 259, 15 (1998)] is discussed and the physical situation is also seen to be the situation considered in Varma et al. [Phys. Rev. E 47, 3612 (1993)] and Melandsø et al. [Planet Space Sci. 41, 321 (1993)]. At last, numerical estimates of the growth rate as a function of the attachment frequency, the decay rate for its various range of values have been done and are displayed graphically. © 2001 American Institute of Physics.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.90.+z Other topics in physics of plasmas and electric discharges (restricted to new topics in section 52)
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)

Boundary conditions for a Gaussian wave beam

E. Poli, A. G. Peeters, and G. V. Pereverzev

Phys. Plasmas 8, 4325 (2001); http://dx.doi.org/10.1063/1.1401116 (6 pages) | Cited 1 time

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The beam tracing technique allows the description of short-wavelength wave beams by means of a set of ordinary differential equations, in which the effects of diffraction (neglected by the standard geometrical-optics procedure) are taken into account. The propagation of the beam is expressed in terms of a central ray and a set of parameters connected with the curvature of the wave front and the amplitude profile. Two crucial issues for the applicability of this technique to situations of experimental interest are the beam reflection from a mirror and the possibility of following the beam in its vacuum–plasma crossing. These problems are investigated in the paper. The parameters of the incident beam are regarded as known quantities and their values after reflection or inside the plasma are obtained. © 2001 American Institute of Physics.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
42.15.Dp Wave fronts and ray tracing

Three designs for a magnetic trap that will simultaneously confine neutral atoms and a non-neutral plasma

Daniel H. E. Dubin

Phys. Plasmas 8, 4331 (2001); http://dx.doi.org/10.1063/1.1403355 (9 pages) | Cited 9 times

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Three trap designs are proposed for the simultaneous confinement of neutral atoms and a non-neutral plasma in close proximity. One design uses axially symmetric static magnetic fields with a magnetic minimum in a ring around the trap axis. Axial symmetry is required for confinement of the rotating non-neutral plasma, and the magnetic minimum traps the neutral atoms. The second design uses a rotating axially asymmetric magnetic field superimposed on a cusp field to create a time-averaged magnetic minimum (a “TOP” trap). The rotating asymmetry acts as a magnetic “rotating wall” to help confine the non-neutral plasma. In the third design, a cylindrically symmetric high-order multipole field traps the neutral atoms, which are made to rotate about the trap axis in order to avoid the magnetic null at the trap center. These designs may be useful for the production and confinement of cold antihydrogen. © 2001 American Institute of Physics.
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37.20.+j Atomic and molecular beam sources and techniques
52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps
back to top Nonlinear Phenomena, Turbulence, Transport

Fluid description of electron temperature gradient driven drift modes

R. Singh, Varun Tangri, H. Nordman, and J. Weiland

Phys. Plasmas 8, 4340 (2001); http://dx.doi.org/10.1063/1.1386803 (11 pages) | Cited 11 times

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The electron temperature gradient (ETG) driven drift mode is studied using an advanced fluid model retaining effects of nonadiabatic ions, Debye shielding and the electron diamagnetic heat flow. The derived eigenmode equation is solved analytically in the strong ballooning limit. Both the toroidal and the slab branch of the ETG mode are included and the fluid growth rates are compared with gyrokinetic results. The role of nonadiabatic ion response is found to have a stabilizing effect on ETG-mode in the lower-hybrid regime. Strong stabilization is also found due to Debye shielding effect for λDe2/ρe2>1. In particular, it is shown that nonadiabatic ion response can result in inward flows of particles for peaked density profiles. © 2001 American Institute of Physics.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.Dg Plasma kinetic equations
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.25.-b Plasma properties

Decay instability and Kolmogorov spectra of ion-drift waves in low-β dusty plasmas

Oleg G. Onishchenko, Oleg A. Pokhotelov, Roald Z. Sagdeev, Vladimir P. Pavlenko, Lennart Stenflo, and Padma K. Shukla

Phys. Plasmas 8, 4351 (2001); http://dx.doi.org/10.1063/1.1398084 (6 pages) | Cited 4 times

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The interaction of nonlinear ion-drift waves in a low β, that is me/mi≪β≪1, dusty plasma is investigated. The matrix elements of the three-wave interactions in an inhomogeneous plasma with uniform ion temperature are derived. The decay instability growth rates and weakly turbulent plasma wave spectra of the ion-drift waves are evaluated and analyzed. © 2001 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.35.Kt Drift waves
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.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Ra Plasma turbulence

A fluid-kinetic model for the two plasmon decay instability

A. C. Machacek and J. S. Wark

Phys. Plasmas 8, 4357 (2001); http://dx.doi.org/10.1063/1.1399324 (10 pages) | Cited 1 time

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A solution for the gain rates and plasmon frequencies of the two plasmon decay instability is obtained using a fluid-kinetic model. This work is of relevance to high temperature, short-pulse laser plasma interactions where appreciable instability is expected in regions of plasma where the phase velocity of the electrostatic waves may not be assumed to be much larger than the thermal velocity of the electrons. The model is evaluated by comparing its results for the stimulated Raman scattering process with a fully kinetic treatment. © 2001 American Institute of Physics.
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52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Oblique solitons in a cold magnetized plasma

J. F. McKenzie and T. B. Doyle

Phys. Plasmas 8, 4367 (2001); http://dx.doi.org/10.1063/1.1394777 (8 pages) | Cited 12 times

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A fully nonlinear theory for stationary waves, propagating obliquely to the ambient magnetic field in a cold plasma, has been developed. Soliton solutions, representing both compressions and rarefactions in the magnetic field, exist for sub-fast flow conditions and in certain cones of magnetic obliquity. The soliton is explicitly characterized, in terms of the wave speed and its obliquity, by a parameter m (the “soliton number”). Compressive (“bright”) solitons are found to have a maximum attainable compression amplitude of three, corresponding to the condition m = 1. Rarefactive (“dark”) solitons attain complete rarefaction when m = 4. The properties of these stationary waves are described both in terms of magnetic hodographs, and of a spatial structure equation, whose equilibrium points yield the maximum compression and rarefaction at the center of the waves. An analytic solution, in terms of elementary transcendental functions, is also presented and highlights the role played by the soliton number m in determining the speed, strength and width of the solitons. © 2001 American Institute of Physics.
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52.30.-q Plasma dynamics and flow
back to top Magnetically Confined Plasmas, Heating, Confinement

Local magnetic shear and drift waves in stellarators

M. Nadeem, T. Rafiq, and M. Persson

Phys. Plasmas 8, 4375 (2001); http://dx.doi.org/10.1063/1.1396842 (11 pages) | Cited 19 times

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A study of the effect of local magnetic shear on the drift wave stability is presented. The eigenvalue problem for the drift wave equation is solved numerically in fully three-dimensional stellarator plasma using the ballooning mode formalism. It is found that negative local magnetic shear has a stabilizing effect on the drift wave instability and positive local shear is destabilizing. This is in agreement with the effect of negative global magnetic shear in tokamaks and also agrees with the simple estimates. As a consequence the highly unstable modes found on a specific magnetic surface are localized in the region of positive local magnetic shear. © 2001 American Institute of Physics.
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52.55.Jd Magnetic mirrors, gas dynamic traps
52.35.Kt Drift waves
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.)

Measurements of C V flows from thermal charge-exchange excitation in divertor plasmas

B. Zaniol, R. C. Isler, N. H. Brooks, W. P. West, and R. E. Olson

Phys. Plasmas 8, 4386 (2001); http://dx.doi.org/10.1063/1.1395569 (4 pages) | Cited 2 times

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Certain transitions of C IV (C3+) from n = 7 to n = 6 (≈7226 Å) and from n = 6 to n = 5 (≈4660 Å) sometimes appear much brighter in tokamak divertors than expected for electron-impact excitation from the ground state. This situation occurs because of charge exchange between C V (C4+) and recycling thermal deuterium atoms in the n = 2 level. As a result, it is possible to extend parallel flow measurements of carbon, which have previously been performed on C II–C IV ions using Doppler shift spectroscopy, to include flows of the He-like C V ions. The work described here includes modeling of the spectral features, correlation of state populations with classical Monte Carlo trajectory (CTMC) predictions, and applications to flow measurements in the DIII-D divertor [Plasma Physics Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159; Proceedings of the 18th IEEE/NPSS Symposium on Fusion Engineering, Albuquerque (Institute of Electrical and Electronic Engineers, Piscataway, 1999), p. 515]. © 2001 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.25.Vy Impurities in plasmas
52.55.Rk Power exhaust; divertors
52.25.Fi Transport properties

Neoclassical poloidal plasma rotation in tokamaks during radio frequency heating

Caigen Liu and Boris Weyssow

Phys. Plasmas 8, 4390 (2001); http://dx.doi.org/10.1063/1.1398284 (13 pages) | Cited 3 times

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A neoclassical theory of poloidal rotation in tokamaks is developed for rf-heated plasmas. It is based on a moment expansion but, in contrast to the usual neoclassical theory, which takes into account the strong deformation of the local equilibrium distribution function due to rf heating. This distribution function is the solution, in the banana regime, of the drift kinetic equation, which includes both collisional diffusion and quasilinear rf diffusion operators. The set of closed, self-consistent transport and rotation equations is obtained in a form similar to its usual neoclassical counterpart. The parallel components of the generalized stress tensors are calculated. This allows us to solve the transport equations for the poloidal rotation that is obtained in explicit form. Modifications of the poloidal rotation due to the rf heating are also discussed. © 2001 American Institute of Physics.
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52.30.-q Plasma dynamics and flow
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties
52.20.-j Elementary processes in plasmas
52.25.Dg Plasma kinetic equations

Alcator C-Mod predictive modeling

Alexei Pankin, Glenn Bateman, Arnold Kritz, Martin Greenwald, Joseph Snipes, and Thomas Fredian

Phys. Plasmas 8, 4403 (2001); http://dx.doi.org/10.1063/1.1399057 (11 pages) | Cited 1 time

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Predictive simulations for the Alcator C-mod tokamak [I. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] are carried out using the BALDUR integrated modeling code [C. E. Singer et al., Comput. Phys. Commun. 49, 275 (1988)]. The results are obtained for temperature and density profiles using the Multi-Mode transport model [G. Bateman et al., Phys. Plasmas 5, 1793 (1998)] as well as the mixed-Bohm/gyro-Bohm transport model [M. Erba et al., Plasma Phys. Controlled Fusion 39, 261 (1997)]. The simulated discharges are characterized by very high plasma density in both low and high modes of confinement. The predicted profiles for each of the transport models match the experimental data about equally well in spite of the fact that the two models have different dimensionless scalings. Average relative rms deviations are less than 8% for the electron density profiles and 16% for the electron and ion temperature profiles. © 2001 American Institute of Physics.
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52.25.Fi Transport properties
52.65.-y Plasma simulation
52.35.Kt Drift waves
52.55.Fa Tokamaks, spherical tokamaks

Kinetic stability of electrostatic plasma modes in a dipolar magnetic field

Andrei N. Simakov, Peter J. Catto, and R. J. Hastie

Phys. Plasmas 8, 4414 (2001); http://dx.doi.org/10.1063/1.1399058 (13 pages) | Cited 19 times

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An axially symmetric plasma immersed in a poloidal magnetic field with closed lines is considered. Low-frequency electrostatic modes are studied kinetically for an “intermediate collisionality” ordering, in which the particle collision frequency is much smaller than the transit or bounce frequency, but much larger than the mode, magnetic drift, and diamagnetic drift frequencies. This ordering is appropriate for the Levitated Dipole Experiment (LDX) [J. Kesner et al., 17th IAEA Fusion Energy Conference, Yokahama, Japan (IAEA, Vienna, 1999)] and some other closed field line devices. “High-frequency” magnetohydrodynamic-like and “low-frequency” entropy modes are found and stability boundaries are determined. Collisional effects are considered and the corresponding ion gyro-relaxation effects are evaluated. These effects introduce dissipation (or inverse dissipation) and are shown to modify the stability picture considerably, while leaving large stability regions in the d, η parametric space, where η is the ratio of the gradients of temperature and density and d is the ratio of the diamagnetic and magnetic drift frequencies. © 2001 American Institute of Physics.
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52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Dg Plasma kinetic equations
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Stabilization of the resistive wall mode by flowing metal walls

M. V. Umansky, R. Betti, and J. P. Freidberg

Phys. Plasmas 8, 4427 (2001); http://dx.doi.org/10.1063/1.1399328 (8 pages) | Cited 10 times

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The effect of flowing metal walls on the resistive wall instabilities is analyzed for a general cylindrically symmetric diffusive pinch configuration. Two types of liquid metal flow are analyzed: a uniform flow which is poloidally symmetric, and a two-stream flow consisting of two opposite streams splitting at the top and merging at the bottom. It is found in both configurations that when the liquid wall flow velocity exceeds a critical value, the resistive wall mode is stabilized. However, for the two-stream flow the critical velocity is several times smaller than that for the uniform flow. Still in a realistic experiment one needs a flow velocity of a few tens m/s to stabilize the resistive wall mode. © 2001 American Institute of Physics.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.30.-q Plasma dynamics and flow
52.35.Dm Sound waves
52.55.Fa Tokamaks, spherical tokamaks

Shear-Alfvén waves in gyrokinetic plasmas

W. W. Lee, J. L. V. Lewandowski, T. S. Hahm, and Z. Lin

Phys. Plasmas 8, 4435 (2001); http://dx.doi.org/10.1063/1.1400124 (6 pages) | Cited 40 times

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It is found that the thermal fluctuation level of the shear-Alfvén waves in a gyrokinetic plasma is dependent on plasma β( ≡ cs2/vA2), where cs is the ion acoustic speed and vA is the Alfvén velocity. This unique thermodynamic property based on the fluctuation–dissipation theorem is verified in this paper using a new gyrokinetic particle simulation scheme, which splits the particle distribution function into the equilibrium part as well as the adiabatic and nonadiabatic parts. The numerical implication of this property is discussed. © 2001 American Institute of Physics.
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52.25.Gj Fluctuation and chaos phenomena
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.65.Rr Particle-in-cell method
52.65.Tt Gyrofluid and gyrokinetic simulations

Equilibrium and stability properties of self-organized electron spiral toroids

C. Chen, R. Pakter, and D. C. Seward

Phys. Plasmas 8, 4441 (2001); http://dx.doi.org/10.1063/1.1400792 (9 pages) | Cited 2 times

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A cold-fluid model for a self-organized electron spiral toroid (EST) is presented. In the present model, the electrons are assumed to undergo energetic spiral motion along a hollow torus with a fixed ion background, the electron mean free path is assumed to be long compared with the torus size, and the minor radius of the EST is assumed to be small compared with the major radius. Using this model, the equilibrium and stability properties of the electron flow in the self-organized EST are analyzed. It is found that a class of self-organized EST equilibria exists with or without an externally applied toroidal magnetic field. It is shown that in the absence of any applied toroidal magnetic field, the EST equilibria are stable at high electron densities (i.e., at high toroidal self-magnetic fields), although they are unstable at low electron densities (i.e., at low toroidal self-magnetic fields). © 2001 American Institute of Physics.
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41.75.Fr Electron and positron beams
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
52.55.Jd Magnetic mirrors, gas dynamic traps

Momentum confinement in DIII-D shots with impurities

W. M. Stacey and M. Murakami

Phys. Plasmas 8, 4450 (2001); http://dx.doi.org/10.1063/1.1401115 (5 pages) | Cited 4 times

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A neoclassical momentum transport model, consisting of gyroviscous and convective components, is applied to the analysis of momentum confinement in DIII-D [Luxon, Anderson, Batty et al., Plasma Physics and Controlled Nuclear Fusion Research 1986 (IAEA, Vienna, 1987), Vol. 1, p. 159] experiments with significant impurity content. Good agreement between predicted and measured central rotation speeds and momentum confinement times is obtained, for L-mode (low-mode) discharges with and without neon injection and for an ELMing (edge-localized modes) H-mode (high-mode) discharge. The observed improvement in momentum confinement time with increasing neon impurity content in the L-mode shots can be accounted for by a neoclassical inward convective momentum flux that increases with impurity content. © 2001 American Institute of Physics.
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52.25.Fi Transport properties
52.25.Vy Impurities in plasmas

Recurrence in plasma edge turbulence

M. S. Baptista, I. L. Caldas, M. V. A. P. Heller, A. A. Ferreira, R. D. Bengtson, and J. Stöckel

Phys. Plasmas 8, 4455 (2001); http://dx.doi.org/10.1063/1.1401117 (8 pages) | Cited 10 times

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Common statistics of turbulent electrostatic fluctuations observed at the plasma edge and scrape-off layer are analyzed in three tokamak devices that have different configurations. The statistics of experimental data collected using fixed sampling time is the same than the statistics of the time for which the oscillation return to a specified reference interval of values. This observation, in addition to the finding of power-scaling laws for some average quantities with respect to either the sampling time or the size of the reference interval, suggests that turbulence on tokamaks have recurrent characteristics, typical of a recurrent chaotic low-dimensional system. Furthermore, the first Poincaré recurrence time and other dynamical tools are used to simulate the mentioned fluctuation statistical properties. © 2001 American Institute of Physics.
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05.45.Tp Time series analysis
52.35.Ra Plasma turbulence
05.45.Ac Low-dimensional chaos
05.45.Gg Control of chaos, applications of chaos

Nonlinear stability of field-reversed configurations with self-generated toroidal field

Y. A. Omelchenko, M. J. Schaffer, and P. B. Parks

Phys. Plasmas 8, 4463 (2001); http://dx.doi.org/10.1063/1.1401119 (7 pages) | Cited 10 times

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The field-reversed configuration (FRC) is a high-beta compact toroidal plasma confinement scheme in which the external poloidal field is reversed on the geometric axis by azimuthal (toroidal) plasma current. A quasineutral, hybrid, particle-in-cell (PIC) approach [Y. A. Omelchenko and R. N. Sudan, Phys. Plasmas 2, 2773 (1995)] is applied to study long-term nonlinear stability of computational FRC equilibria to a number of toroidal modes, including the most disruptive tilt mode. In particular, a self-generated toroidal magnetic field is found to be an important factor in mitigating the instability and preventing the confinement disruption. This is shown to be a unique FRC property resulting from the Hall effect in the regions of vanishing poloidal magnetic field. The instability-driven toroidal field stabilizes kink formation by increasing the magnetic field energy without destabilizing curvature-driven plasma motion. Finally, the tilt instability saturates due to nonlinear, finite Larmor radius (FLR) effects and plasma relaxation to a quasisteady kinetic state. During this transition the FRC is shown to dissipate a substantial amount of initially trapped flux and plasma energy. These effects are demonstrated for kinetic and fluid-like, spherical and prolate FRCs. © 2001 American Institute of Physics.
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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
52.65.Rr Particle-in-cell method

Spectroscopic determinations of carbon fluxes, sources, and shielding in the DIII-D divertors

R. C. Isler, R. J. Colchin, N. H. Brooks, T. E. Evans, W. P. West, and D. G. Whyte

Phys. Plasmas 8, 4470 (2001); http://dx.doi.org/10.1063/1.1403416 (13 pages) | Cited 12 times

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The most important mechanisms for eroding plasma-facing components (PFCs) and introducing carbon into tokamak divertors are believed to be physical sputtering, chemical sputtering, sublimation, and radiation enhance sublimation (RES). The relative importance of these processes has been investigated by analyzing the spectral emission rates and the effective temperatures of CI, CD, and C2 under several operating conditions in the DIII-D tokamak [Plasma Physics Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159; Proceedings of the 18th IEEE/NPSS Symposium on Fusion Engineering, Albuquerque (Institute of Electrical and Electronic Engineers, Piscataway, 1999), p. 515]. Discrimination of chemical sputtering from physical sputtering is accomplished by quantitatively relating the fraction of CI influxes expected from dissociation of hydrocarbons to the measured CD and C2 influxes. Characteristics of sublimation are studied from carbon test samples heated to surface temperatures exceeding 2000 K. The shielding efficiency of carbon produced at the divertor target is assessed from comparison of fluxes of neutral atoms and ions; approximately 95% of the primary influx appears to be redeposited before being transported far enough upstream to fuel the core plasma. © 2001 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Vy Impurities in plasmas
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