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  • 1
    Electronic Resource
    Electronic Resource
    Drift mode calculations for the Large Helical Device (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4942-4947 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A fully kinetic assessment of the stability properties of toroidal drift modes has been obtained for a case for the Large Helical Device [A. Iiyoshi et al., Nucl. Fusion 39, 1245 (1999)]. This calculation retains the important effects in the linearized gyrokinetic equation, using the lowest-order "ballooning representation" for high toroidal mode number instabilities in the electrostatic limit. Results for toroidal drift waves destabilized by trapped particle dynamics and ion temperature gradients are presented, using three-dimensional magnetohydrodynamic equilibria reconstructed from experimental measurements. The effects of helically trapped particles and helical curvature are investigated. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1317521
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  • 2
    Electronic Resource
    Electronic Resource
    Drift mode calculations in nonaxisymmetric geometry (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 4705-4713 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A fully kinetic assessment of the stability properties of toroidal drift modes has been obtained for nonaxisymmetric (stellarator) geometry, in the electrostatic limit. This calculation is a comprehensive solution of the linearized gyrokinetic equation, using the lowest-order "ballooning representation" for high toroidal mode number instabilities, with a model collision operator. Results for toroidal drift waves destabilized by temperature gradients and/or trapped particle dynamics are presented, using three-dimensional magnetohydrodynamic equilibria generated as part of a design effort for a quasiaxisymmetric stellarator. Comparisons of these results with those obtained for typical tokamak cases indicate that the basic trends are similar. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873757
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  • 3
    Electronic Resource
    Electronic Resource
    Large orbit neoclassical transport : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1707-1713 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neoclassical transport in the presence of large ion orbits is investigated. The study is motivated by the recent experimental results that ion thermal transport levels in enhanced confinement tokamak plasmas fall below the "irreducible minimum level" predicted by standard neoclassical theory. This apparent contradiction is resolved in the present analysis by relaxing the basic neoclassical assumption that the ions orbital excursions are much smaller than the local toroidal minor radius and the equilibrium scale lengths of the system. Analytical and simulation results are in agreement with trends from experiments. The development of a general formalism for neoclassical transport theory with finite orbit width is also discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872273
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  • 4
    Electronic Resource
    Electronic Resource
    Microinstability analysis of DIII-D high-performance discharges (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 4074-4083 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The kinetic stability properties in a number of high performance discharges from the DIII-D tokamak [R. D. Stambaugh for the DIII-D Team, Plasma Physics and Controlled Nuclear Fusion Research, 1994 (International Atomic Energy Agency, Vienna, 1995), Vol. 1, p. 83] have been analyzed utilizing a comprehensive kinetic eigenvalue code. The instability considered is the toroidal drift mode [trapped-electron-ion temperature gradient (ηi) mode]. This code has been interfaced with equilibria specific to DIII-D plasmas. Experimentally measured kinetic profile data, along with motional stark effect data and external magnetic data, was used, and the corresponding magnetohydrodynamic (MHD) equilibria were computed numerically. In particular, a low confinement mode (L-mode) case, a high-li high confinement mode (H-mode) case, a very high confinement mode (VH-mode) case, and a high plasma pressure/poloidal magnetic pressure (βp) case have been analyzed. For the L-mode case, a wide region of instability was found, while for the H-mode and VH-mode and high-βp cases, only relatively narrow regions of instability were found. An assessment of the influence of velocity-shear flow on these instabilities has also been made, as well as of changes in the electron and ion temperature gradients and density gradients. While the experimental values of the sheared toroidal flow velocity are not sufficient to stabilize the instability, an increase by a factor of two to four in the flow velocity could completely stabilize this mode. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871539
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  • 5
    Electronic Resource
    Electronic Resource
    Gyrokinetic simulations in general geometry and applications to collisional damping of zonal flows : The 41st annual meeting of the division of plasma physics of the american physical society (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1857-1862 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A fully three-dimensional gyrokinetic particle code using magnetic coordinates for general geometry has been developed and applied to the investigation of zonal flows dynamics in toroidal ion-temperature-gradient turbulence. Full torus simulation results support the important conclusion that turbulence-driven zonal flows significantly reduce the turbulent transport. Linear collisionless simulations for damping of an initial poloidal flow perturbation exhibit an asymptotic residual flow. The collisional damping of this residual causes the dependence of ion thermal transport on the ion–ion collision frequency, even in regimes where the instabilities are collisionless. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874008
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  • 6
    Electronic Resource
    Electronic Resource
    On the gyrokinetic equilibrium (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 991-1000 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent developments in gyrokinetic-magnetohydrodynamics (MHD) theory and in electromagnetic gyrokinetic particle simulations raise the question of consistency between the gyrokinetic model and the fluid model. Due to the special characteristics of the guiding center coordinates, it is a nontrivial exercise to show this consistency. In this paper it is shown, in a very general setting, that the gyrokinetic theory and the fluid equations do give an equivalent description of plasma equilibrium (∂/∂t=0). The fluid continuity equation and momentum equation for equilibrium plasmas are recovered entirely from the gyrokinetic theory. However, it was Spitzer who first realized the importance of consistency between guiding-center motion and fluid equations. In particular, he studied the "apparent paradoxical result" regarding the difference between perpendicular particle flow and guiding-center flow, which will be referred to as the Spitzer paradox in this paper. By recovering the fluid equations from the gyrokinetic theory, we automatically resolve the Spitzer paradox, whose essence is how the perpendicular current and flow are microscopically generated from particles' guiding-center motion. The mathematical construction in the gyrokinetic theory which relates observable quantities in the laboratory frame to the distribution function in the guiding-center coordinates is consistent with Spitzer's original physical picture, while today's gyrokinetic-MHD theory covers a much wider range of problems in a much more general and quantitative way. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873898
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  • 7
    Electronic Resource
    Electronic Resource
    Drift mode growth rates and associated transport (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 1162-1167 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Drift mode linear growth rates and quasilinear transport are investigated using the FULL kinetic stability code [Rewoldt et al., Phys. Plasmas 5, 1815 (1998)] and a version of the Weiland transport model [Strand et al., Nucl. Fusion 38, 545 (1998)]. It is shown that the drift mode growth rates (as well as the marginal stability temperature gradient) obtained using the FULL code are dependent on the accuracy of the equilibrium employed. In particular, when an approximate equilibrium model is utilized by the FULL code, the results can differ significantly from those obtained using a more accurate numerical equilibrium. Also investigated are the effects of including full electron physics. It is shown, using both the FULL code and the Weiland model, that the nonadiabatic (e.g., trapped) electron response produces a significant increase in the linear growth rate of the ion-temperature-gradient (ITG) driven branch of the drift instability. Other consequences of the nonadiabatic electron response include a reduction in the marginal temperature gradient for the onset of the ITG mode and an additional contribution to transport due to the excitation of the Trapped Electron Mode (TEM). Physical explanations are given for the sensitivity of the mode growth rates to the equilibrium and the nonadiabatic electron response. Finally, linear growth rates for the ITG mode computed using the FULL code are compared with growth rates obtained using the Weiland model. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873360
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  • 8
    Electronic Resource
    Electronic Resource
    Gyrokinetic theory for arbitrary wavelength electromagnetic modes in tokamaks (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1035-1049 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A linear gyrokinetic system for arbitrary wavelength electromagnetic modes is developed. A wide range of modes in inhomogeneous plasmas, such as the internal kink modes, the toroidal Alfvén eigenmode (TAE) modes, and the drift modes, can be recovered from this system. The inclusion of most of the interesting physical factors into a single framework enables one to look at many familiar modes simultaneously, and thus to study the modifications of and the interactions between them in a systematic way. Especially, it is possible to investigate self-consistently the kinetic magnetohydrodynamics (MHD) phenomena entirely from the kinetic side. Phase space Lagrangian Lie perturbation methods and a newly developed computer algebra package for vector analysis in general coordinate system are utilized in the analytical derivation. In tokamak geometries, a two-dimensional finite element code has been developed and tested. In this paper, the basic theoretical formalism and some of the preliminary results are presented. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872633
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  • 9
    Electronic Resource
    Electronic Resource
    Sheared rotation effects on kinetic stability in enhanced confinement tokamak plasmas, and nonlinear dynamics of fluctuations and flows in axisymmetric plasmas : The 39th annual meeting of division of plasma physics of APS (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1815-1821 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Sheared rotation dynamics are widely believed to have significant influence on experimentally-observed confinement transitions in advanced operating modes in major tokamak experiments, such as the Tokamak Fusion Test Reactor (TFTR) [D. J. Grove and D. M. Meade, Nucl. Fusion 25, 1167 (1985)], with reversed magnetic shear regions in the plasma interior. The high-n toroidal drift modes destabilized by the combined effects of ion temperature gradients and trapped particles in toroidal geometry can be strongly affected by radially-sheared toroidal and poloidal plasma rotation. In previous work with the FULL linear microinstability code, a simplified rotation model including only toroidal rotation was employed, and results were obtained. Here, a more complete rotation model, which includes contributions from toroidal and poloidal rotation and the ion pressure gradient to the total radial electric field, is used for a proper self-consistent treatment of this key problem. Relevant advanced operating mode cases for TFTR are presented. In addition, the complementary problem of the dynamics of fluctuation-driven E×B flow is investigated by an integrated program of gyrokinetic simulation in annulus geometry and gyrofluid simulation in flux tube geometry. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872851
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  • 10
    Electronic Resource
    Electronic Resource
    Radially global gyrokinetic simulation studies of transport barriers (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1959-1966 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Improvements in tokamak transport have recently been obtained in a variety of operational modes through the formation of transport barriers, or good confinement radial zones. Here global nonlinear three-dimensional toroidal gyrokinetic simulation is used to study three effects that are linearly stabilizing and may cause the formation of transport barriers, namely, sheared toroidal rotation, reversed magnetic shear, and peaked density profiles. The effect of toroidal shear flow on ion heat diffusivity is found to be relatively weak compared to mixing-length expectations based on linear calculations. In contrast, it is found that weak or negative magnetic shear (s〈1/2) in combination with a peaked density profile relative to the temperature profile greatly suppresses ion-temperature-gradient-driven turbulence in the central region of global nonlinear simulations. Similar features are seen experimentally in reversed magnetic shear tokamak plasmas. There is some nonlocal penetration (∼20–30ρi) of the turbulence into the subcritical core region. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871992
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