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  • 1
    Electronic Resource
    Electronic Resource
    Comparisons and physics basis of tokamak transport models and turbulence simulations (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 969-983 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The predictions of gyrokinetic and gyrofluid simulations of ion-temperature-gradient (ITG) instability and turbulence in tokamak plasmas as well as some tokamak plasma thermal transport models, which have been widely used for predicting the performance of the proposed International Thermonuclear Experimental Reactor (ITER) tokamak [Plasma Physics and Controlled Nuclear Fusion Research, 1996 (International Atomic Energy Agency, Vienna, 1997), Vol. 1, p. 3], are compared. These comparisons provide information on effects of differences in the physics content of the various models and on the fusion-relevant figures of merit of plasma performance predicted by the models. Many of the comparisons are undertaken for a simplified plasma model and geometry which is an idealization of the plasma conditions and geometry in a Doublet III-D [Plasma Physics and Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] high confinement (H-mode) experiment. Most of the models show good agreements in their predictions and assumptions for the linear growth rates and frequencies. There are some differences associated with different equilibria. However, there are significant differences in the transport levels between the models. The causes of some of the differences are examined in some detail, with particular attention to numerical convergence in the turbulence simulations (with respect to simulation mesh size, system size and, for particle-based simulations, the particle number). The implications for predictions of fusion plasma performance are also discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873896
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  • 2
    Electronic Resource
    Electronic Resource
    Gyrokinetic simulation of internal kink modes (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 4257-4268 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Internal disruption in a tokamak has been simulated using a three-dimensional magneto-inductive gyrokinetic particle code. The code operates in both the standard gyrokinetic mode (total-f code) and the fully nonlinear characteristic mode (δf code). The latter is a quiet low noise algorithm. The computational model represents a straight tokamak with periodic boundary conditions in the toroidal direction and a square cross section with perfectly conducting walls in the poloidal direction. The linear mode structure of an unstable m=1 (poloidal) and n=1 (toroidal) kinetic internal kink mode is clearly observed, especially in the δf code. The width of the current layer around the x-point, where magnetic reconnection occurs, is found to be close to the collisionless electron skin depth, indicating the importance of electron inertia. Both codes give very similar nonlinear results, in which full reconnection in the Alfvén time scale is observed along with the electrostatic potential structures created during this phase. The resulting E×B drift from the potential dominates the nonlinear phase after the full reconnection. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871051
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  • 3
    Electronic Resource
    Electronic Resource
    Comparison of turbulence measurements from DIII-D low-mode and high-performance plasmas to turbulence simulations and models : Review,Tutorial and Invited Papers from the 43rd Annual Meeting of the APS Division of Plasma Physics (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 2141-2148 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measured turbulence characteristics (correlation lengths, spectra, etc.) in low-confinement (L-mode) and high-performance plasmas in the DIII-D tokamak [Luxon et al., Proceedings Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] show many similarities with the characteristics determined from turbulence simulations. Radial correlation lengths Δr of density fluctuations from L-mode discharges are found to be numerically similar to the ion poloidal gyroradius ρθ,s, or 5–10 times the ion gyroradius ρs over the radial region 0.2〈r/a〈1.0. Comparison of these correlation lengths to ion temperature gradient gyrokinetic simulations (the UCLA-University of Alberta, Canada UCAN code [Sydora et al., Plasma Phys. Controlled Fusion 38, A281 (1996)]) shows that without zonal flows simulation values of Δr are very long, spanning much of the 65 cm minor radius. With zonal flows included, these decrease to near the measured values in both magnitude and radial behavior. In order to determine if Δr scaled as ρθ,s or 5–10 times ρs, an experiment was performed which modified ρθs while keeping other plasma parameters approximately fixed. It was found that the experimental Δr did not scale as ρθ,s, which was similar to low-resolution UCAN simulations. Finally, both experimental measurements and gyrokinetic simulations indicate a significant reduction in the radial correlation length from high-performance quiescent double barrier discharges, as compared to normal L-mode, consistent with reduced transport in these high-performance plasmas. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1464544
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  • 4
    Electronic Resource
    Electronic Resource
    Electron distribution function in laser heated plasmas (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 550-556 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new electron distribution function has been found in laser heated homogeneous plasmas by an analytical solution to the kinetic equation and by particle simulations. The basic kinetic model describes inverse bremsstrahlung absorption and electron–electron collisions. The non-Maxwellian distribution function is comprised of a super-Gaussian bulk of slow electrons and a Maxwellian tail of energetic particles. The tails are heated due to electron–electron collisions and energy redistribution between superthermal particles and light absorbing slow electrons from the bulk of the distribution function. A practical fit is proposed to the new electron distribution function. Changes to the linear Landau damping of electron plasma waves are discussed. The first evidence for the existence of non-Maxwellian distribution functions has been found in the interpretation, which includes the new distribution function, of the Thomson scattering spectra in gold plasmas [Glenzer et al., Phys. Rev. Lett. 82, 97 (1999)]. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1334611
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of externally imposed and self-generated flows on turbulence and magnetohydrodynamic activity in tokamak plasmas : 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. 1795-1801 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.874000
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  • 6
    Electronic Resource
    Electronic Resource
    Recent progress toward high performance above the Greenwald density limit in impurity seeded discharges in limiter and divertor tokamaks : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2188-2198 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An overview is given of recent advances toward the realization of high density, high confinement plasmas with radiating mantles in limiter and divertor tokamaks worldwide. Radiatively improved mode discharges on the Torus Experiment for Technology Oriented Research 94 (TEXTOR-94) [Proceedings of the 16th IEEE Symposium on Fusion Engineering, 1995 (Institute for Electrical and Electronics Engineers, Piscataway, NJ, 1995), p. 470] have recently been obtained at trans-Greenwald densities (up to n¯/nGW=1.4) with high confinement mode free of edge localized modes (ELM-free H-mode) confinement quality. Experiments in DIII-D [J. Luxon et al., Proceedings of the 11th IAEA Conference on Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Association, Vienna, 1987), Vol. 1, p. 159] divertor plasmas with a low confinement mode edge have confirmed the dramatic changes in confinement observed with impurity seeding on TEXTOR-94. Recent experiment with impurity seeding on the Joint European Torus [Rebut et al., Fusion Eng. Des. 22, 7 (1993)], and the Japanese Atomic Energy Research Institute Tokamak 60 Upgrade [Horiike et al., Fusion Eng. Des. 16, 285 (1991); Hosogane et al., Proceedings of the 16th IAEA Conference on Plasma Physics and Controlled Nuclear Fusion Research Montreal, 1987 (International Atomic Energy Association, Vienna, 1987), Vol. 3, p. 555] have extended high confinement in ELMy H-mode plasmas to higher densities. Finally, recent progress in the physical understanding of radiating mantle plasmas is summarized. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1364513
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  • 7
    Electronic Resource
    Electronic Resource
    Impurity-induced turbulence suppression and reduced transport in the DIII-D tokamak : 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. 1870-1877 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Long wavelength turbulence as well as heat and momentum transport are significantly reduced in the DIII-D tokamak [Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] as a result of neon seeding of a low confinement mode negative central shear discharge. Correspondingly, the energy confinement time increases by up to 80%. Fully saturated turbulence measurements near ρ=0.7 (ρ=r/a) in the wave number range 0.1≤k⊥ρs≤0.6, obtained with beam emission spectroscopy, exhibit a significant reduction of fluctuation power after neon injection. Fluctuation measurements obtained with far infrared scattering also show a reduction of turbulence in the core, while the Langmuir probe array measures reduced particle flux in the edge and scrape-off layer. Gyrokinetic linear stability simulations of these plasmas are qualitatively consistent, showing a reduction in the growth rate of ion temperature gradient driven modes for 0〈k⊥ρs≤1.4, and nonlinear gyrokinetic simulations show a reduced saturated density fluctuation amplitude. The measured ωE×B shearing rate increased at ρ=0.7, suggesting that impurity-induced growth rate reduction is acting synergistically with ωE×B shear to decrease turbulence and reduce anomalous transport. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874010
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  • 8
    Electronic Resource
    Electronic Resource
    Three-dimensional gyrokinetic particle simulation of low-frequency drift instabilities (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1455-1460 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonlinear behavior of drift-wave fluctuations driven unstable by trapped particles and pressure gradients is studied using three-dimensional gyrokinetic plasma simulation methods. In the linear stages of instability, the growth rates and the radial and poloidal ballooning mode structures agree reasonably well with theory. Saturation of the unstable modes occurs principally through quasilinear profile modification and mode coupling. Results of the growth and saturation phase of the instability are compared with a bounce-averaged electron drift model. The resultant anomalous particle and energy diffusion are estimated using the saturated mode spectrum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859468
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  • 9
    Electronic Resource
    Electronic Resource
    Particle simulations of current-driven drift waves in shearless and sheared magnetic fields (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 4147-4160 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonlinear behavior of the collisionless current-driven drift instability in shearless and sheared magnetic fields is studied by means of particle simulation. Electrostatic models with guiding center electrons and full dynamic ions are used in both two-and-one-half and three dimensions. The electron current (J(parallel)), in the direction parallel to the magnetic field but perpendicular to the density gradient in the x direction, is maintained throughout the simulation. Instability thresholds, growth rates, real frequency spectra, and mode structures observed in the simulation are in good agreement with theory. Saturation of the unstable modes occurs by a flattening of the electron distribution function in x-v(parallel) space. The measured potential saturation levels and final distribution functions are consistent with a quasilinear plateau theory for both shearless and sheared magnetic field configurations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865706
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  • 10
    Electronic Resource
    Electronic Resource
    Particle simulation of the resistive g mode in a sheared magnetic field (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 255-260 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The linear and nonlinear evolution of the interchange instability of a resistive plasma (the resistive g mode) in a sheared magnetic field is studied using electrostatic particle simulation methods. Both the fast and slow interchange mode regimes are considered. In both cases the linear growth rates of the modes scale well with the theoretical values. The saturation of the instabilities is caused primarily by convective mixing of pressure over the width of the eigenmode. The saturation levels predicted by mixing length theory are in reasonable agreement with the simulation results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865193
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