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  • 1
    Electronic Resource
    Electronic Resource
    Investigation of physical processes limiting plasma density in high confinement mode discharges on DIII-D : 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. 1752-1760 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of experiments was conducted on the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] to investigate the physical processes which limit density in high confinement mode (H-mode) discharges. The typical H-mode to low confinement mode (L-mode) transition limit at high density near the empirical Greenwald density limit [M. Greenwald et al., Nucl. Fusion 28, 2199 (1988)] was avoided by divertor pumping, which reduced divertor neutral pressure and prevented formation of a high density, intense radiation zone (MARFE) near the X-point. It was determined that the density decay time after pellet injection was independent of density relative to the Greenwald limit and increased nonlinearly with the plasma current. Magnetohydrodynamic (MHD) activity in pellet-fueled plasmas was observed at all power levels, and often caused unacceptable confinement degradation, except when the neutral beam injected (NBI) power was ≤3 MW. Formation of MARFEs on closed field lines was avoided with low safety factor (q) operation but was observed at high q, qualitatively consistent with theory. By using pellet fueling and optimizing discharge parameters to avoid each of these limits, an operational space was accessed in which density ∼1.5×Greenwald limit was achieved for 600 ms, and good H-mode confinement was maintained for 300 ms of the density flat-top. More significantly, the density was successfully increased to the limit where a central radiative collapse was observed, the most fundamental density limit in tokamaks. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872277
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  • 2
    Electronic Resource
    Electronic Resource
    Enhanced confinement in tokamaks (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 2941-2960 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The physics of enhanced confinement regimes in tokamaks is reviewed and some directions for further enhancements are assessed. The H-mode confinement regime is examined. A number of other observations of enhanced confinement, having in common peaked density profiles, are compared to the theory of ion temperature gradient modes. Two schemes of promise in enhancing confinement, second stability and control of electric fields, are discussed. The contributions of alternate concepts to understanding tokamak transport are described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859361
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  • 3
    Electronic Resource
    Electronic Resource
    Two-stage turbulence suppression and E×B velocity shear measured at the L–H transition (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 87-91 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: At the onset of the L–H transition in the DIII-D tokamak [Plasma Physics and Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p.159], a fast (≈100 μsec) suppression of microturbulence is observed as the edge transport barrier is formed. This fast edge suppression is followed by a much slower (tens of msec), but substantial (≥50%) reduction in the relative density fluctuation level. This second turbulence suppression phase, which is observed to correlate with growing E×B velocity shear, has been localized to the plasma interior, and may explain why the observed transport reduction in the H mode has been observed to extend deep into the plasma, well beyond the edge transport barrier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860871
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  • 4
    Electronic Resource
    Electronic Resource
    Use of positrons to probe magnetic versus electrostatic turbulence : Eighth topical conference on high−temperature plasma diagnostics (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 3043-3045 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Kwon et al. have shown that runaway electron (positron) diffusion is produced by magnetic turbulence and unaffected by electrostatic turbulence. By measuring the diffusion coefficient of positrons at runaway energies (0.1–2 MeV) as a function of radius for two discrete positron energies, the radial correlation length W of the turbulence can be extracted. Then if the thermal electrons are in the weak turbulence regime, the thermal electron diffusion coefficient from magnetic fluctuations alone can be calculated and compared to values from other techniques. We propose to inject charged energetic positrons (100–2000 keV) in few millisecond bursts from radioactive sources by means of their curvature drift when trapped in toroidal field ripples. The energetic positrons will diffuse over 60–600 ms time scales. At any time the radial profile of the positrons can be sampled by injecting a small solid pellet. A fraction of all the positrons on a flux surface will annihilate in the pellet as it passes that flux surface. The time-dependent 0.511 MeV γ-ray signal then can be unfolded into the positron radial profile and the positron diffusion coefficient determined from the time evolution of those profiles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141721
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  • 5
    Electronic Resource
    Electronic Resource
    A Fusion Development Facility Based on the Spherical Torus (1998)
    Springer
    Journal of fusion energy 17 (1998), S. 183-188 
    Details
    ISSN: 1572-9591
    Keywords: Fusion development ; spherical torus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The Fusion community could soon have available an opportunity to significantly advance fusion development, an opportunity afforded by the potential of the spherical torus as a plasma confinement system. That opportunity is, in a single device at an affordable price and at a suitable site, to move sequentially through the major fusion objectives of advanced confinement physics, burning plasma and DT physics, blanket and other fusion nuclear technology development, tritium self-sufficiency, and, perhaps at the end with an upside performance outcome, a chance at net electric breakeven. Meeting this set of objectives would dramatically advance the development of fusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1021889708640
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  • 6
    Electronic Resource
    Electronic Resource
    DIII-D Program Results and Future Plans (1999)
    Springer
    Journal of fusion energy 18 (1999), S. 19-21 
    Details
    ISSN: 1572-9591
    Keywords: Tokamaks ; DIII-D
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract This paper summarizes recent research results and future plans for the DIII-D National Fusion Program. The full set of transparencies for this presentation can be found at http://fusion.gat.com/pubs-ext/presentations/Stambaugh_FPA00.pdf
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018866722997
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