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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Computer Physics Communications 42 (1986), S. 313-331 
    ISSN: 0010-4655
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Computer Science , Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 5013-5022 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results of Landau fluid calculations of ion temperature gradient-driven turbulence in cylindrical geometry but which cover the whole plasma cross section are reported. A simple gyrofluid model is used which evolves in time equations for the ion density or vorticity, the parallel ion velocity, and the ion temperature where Landau damping is included through a linear closure relation. Adiabatic electrons and the electrostatic approximation are assumed to hold. Linear calculations indicate that the growth rates are significantly reduced in the presence of Landau damping. Nonlinear single helicity calculations serve to illustrate the spatial localization of the turbulence in the presence of Landau damping. Finally nonlinear multiple helicity calculations performed with three different values for the ratio of the central ion Larmor radius to the plasma minor radius denoted by ρ* exhibit a definite linear scaling of all the fluctuation characteristics, such as levels, scale sizes, quasilinear profile modifications, self-generated poloidal flows, and heat diffusivities, with ρ*. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 174-179 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Through the principal use of the reduced magnetohydrodynamic version of the finite aspect ratio code [L. A. Charlton et al., J. Comput. Phys. 86, 270 (1990)], an m/n=1/1 resistive kink mode was poloidally rotated with the accompanying rotational shear. It was observed that the growth rate of this unstable mode can either decrease or increase as the applied equilibrium rotation is increased to near poloidal sonic speeds. Shear in the poloidal rotation profile is stabilizing, but only if the destabilizing effects of bulk rotation can be overcome. Therefore, the mode's stability was sensitive to the location of the rotation's peak relative to the eigenmode's spatial extent. The destabilizing effects of bulk rotation are apparently a rotationally enhanced beta, and the stabilizing effects appear to be caused by exceeding a critical rotational shear spatially averaged over the eigenmode structure. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of externally imposed and self-generated poloidal flows on turbulence and magnetohydrodynamic (MHD) activity are examined in the context of the possible Electric Tokamak (ET) [Phys. Plasmas 6, 4722 (1999)] plasmas and (circularized) DIII-D-like [Fusion Technol. 8, 441 (1985)] discharges. Global gyrokinetic particle simulations and reduced MHD calculations respectively show that ion temperature gradient driven turbulence (ITGDT) and resistive internal kink MHD activity can be reduced and/or suppressed with experimentally achievable externally imposed flows for possible ET start-up plasmas. Global gyrokinetic particle simulations of ITGDT also serve to demonstrate that self-generated flows are necessary to yield experimentally relevant radial correlation lengths in the case of DIII-D-like discharges. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In recent experiments in DIII-D, comparison of specific turbulence characteristics with linear and nonlinear modeling has identified common features associated with the ion temperature gradient (ITG) mode. A low-frequency turbulence feature is observed in high-density saturated Ohmic confinement discharges, which is absent in low-density linear Ohmic confinement discharges. The feature is in a range of wavelength (k⊥ρs(approximate)0.2–0.5) and the frequency expected for the ITG mode and onset of the feature is coincident with onset of confinement saturation. The density profile is significantly broader in the high-density discharge, a known destabilizing effect on the ITG mode. Gyrokinetic stability calculations of the growth rate of the most unstable drift ballooning mode show the ITG mode to be more unstable in the high-density discharges. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2033-2043 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Shear Alfvén waves can be driven unstable by hot particles such as alpha particles in an ignited fusion device or hot ions in existing devices. Motivated by rather collisional Wendelstein 7 Advanced Stellarator (W7-AS) [Phys. Rev. Lett. 72, 1220 (1994)] beam-driven global Alfvén instability experiments, the effect of electron and ion collisions on these modes has been examined. Collisions broaden and suppress the peak associated with Landau effects. This broadening makes ion damping more important, while the electron damping is suppressed. Additional resistive effects provide increased damping for the main part of the spectrum, which can have a rather high phase velocity. Of more general interest is the fact that collisional and collisionless resistivity has a numerically stabilizing effect that is known to be important for nonlinear resistive magnetohydrodynamics (MHD). This can preclude the need for introducing and testing the sensitivity to similar ad hoc effects. Numerical and analytic results for both a particle-conserving Krook collision operator and a Lorentz (pitch angle) collision operator are compared and contrasted. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 4656-4658 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For treating Alfvén waves driven unstable by α particles, an alternative to the Oak Ridge National Laboratory gyro-Landau fluid approach is suggested. Its primary advantage is that this method can simultaneously treat fluid nonlinearities and kinetic quasilinear effects. It is argued that more perturbative approaches could overestimate the kinetic quasilinear effects. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3871-3882 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The radiation drives for plasma edge parameters are reexamined. By including the electron density gradient, the radiation drive through density fluctuations can be strongly destabilizing even in a parameter regime away from force balance. This results in the dominance of the magnitude of the radiation power (γn drive) over its derivative (γT drive) for plasma edge parameters of Ohmic tokamak discharges. This leads to instability over a range of poloidal mode numbers much broader than in the case of the γT drive and to temperature fluctuations of opposite phase to the density fluctuations. Nonlinear numerical calculations show that this opposite phase relationship persists nonlinearly. As a consequence, the fluctuations induce a heat flux that is observed to be inward, while the particle and energy fluxes that they generate are calculated to be outward. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Electric Tokamak (ET), currently under construction at the University of California–Los Angeles, is designed to rotate poloidally via a radial current induced by fast wave rf heating fast enough to bifurcate the plasma into a global "H mode" ("high confinement mode"). A global gyrokinetic code is used to explore and illustrate some of the effects on ion temperature gradient turbulence. The realistic radial electric field required to completely suppress these modes for ET parameters is demonstrated to be 〈−30 V/cm at its maximum near the half radius. The effects of both a poloidally supersonic bulk rotation threshold and the shear in this rotation near that supersonic threshold were shown to be important in reducing these modes. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2203-2209 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transport dynamics of laser-ablated neutral/plasma plumes are of significant interest for film growth by pulsed-laser deposition of materials, since the magnitude and kinetic energy of the species arriving at the deposition substrate are key processing parameters. Dynamical calculations of plume propagation in vacuum and in background gas have been performed using particle-in-cell hydrodynamics, continuum gasdynamics, and scattering models. Results from these calculations are presented and compared with experimental observations. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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