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  • 1
    Electronic Resource
    Electronic Resource
    Effect of convection on multifaceted asymmetric radiation from edge density limits (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3464-3467 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A previous theory for the MARFE (multifaceted asymmetric radiation from edge) edge density limit has been extended to explicitly account in the linear stability analysis for the convective radial heat flux through the plasma edge. All other edge parameters being equal and the temperature dependence of the particle and heat diffusivities being the same, the MARFE density limit increases significantly and almost linearly with the convective fraction of the radial heat flux through the plasma edge. Calculations for parameters typical of present experiments indicate that it is important to explicitly represent heat convection, as well as conduction, in MARFE density limit predictions. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874211
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  • 2
    Electronic Resource
    Electronic Resource
    The role of thermal instabilities in limiting the density in DIII-D (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4931-4941 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mechanisms which apparently govern the maximum achievable density in several DIII-D [Luxon, Anderson, Batty et al., Plasma Physics on Controlled Nuclear Fusion Research 1986 (IAEA, Vienna, 1987), Vol. 1, p. 159] shots in which different operating procedures were used in building up the density were investigated and compared with the predictions of thermal instability theory. Core MARFEs (multifaceted asymmetric radiation from the edge) followed by a H–L (high-to-low confinement mode) transition limit the density well below the Greenwald limit in continuous gas puffed lower single-null discharges with low triangularity. Similar continuous gas puff fueled discharges with higher triangularity or with pumping in the lower divertor achieve densities at or above the Greenwald value, apparently limited by confinement degradation, without the formation of core MARFEs. Pellet fueled discharges achieve densities up to twice the Greenwald value, limited by global radiative collapse. Thermal instability theory predictions of the limiting core MARFEs, confinement degradation or global radiative collapse are in good agreement with the experimental observations for the shots examined. Evidence for an important role of neutral particles in the plasma edge in core MARFE onset and in confinement degradation was identified. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1316766
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  • 3
    Electronic Resource
    Electronic Resource
    Calculation of the effects of pumping, divertor configuration and fueling on density limit in a tokamak model problem (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 850-856 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Several series of model problem calculations have been performed to investigate the predicted effect of pumping, divertor configuration and fueling on the maximum achievable density in diverted tokamaks. Density limitations due to thermal instabilities (confinement degradation and multifaceted axisymmetric radiation from the edge) and to divertor choking are considered. For gas fueling the maximum achievable density is relatively insensitive to pumping (on or off), to the divertor configuration (open or closed), or to the location of the gas injection, although the gas fueling rate required to achieve this maximum achievable density is quite sensitive to these choices. Thermal instabilities are predicted to limit the density at lower values than divertor choking. Higher-density limits are predicted for pellet injection than for gas fueling. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1340617
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  • 4
    Electronic Resource
    Electronic Resource
    International Cooperation in Magnetic Fusion (1985)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Environment and Resources 10 (1985), S. 79-107 
    Details
    ISSN: 0362-1626
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.eg.10.110185.000455
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  • 5
    Electronic Resource
    Electronic Resource
    Radial thermal stability of the radiative mantle (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1012-1021 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Sufficient conditions for the thermal stability against radial excursions of a cylindrical equilibrium temperature distribution in a plasma with a strongly radiative edge, or mantle, are established in terms of the minimum allowable ratio of the core heating power density to the edge radiation power density. A positive dependence of the thermal conductivity upon temperature is found to be stabilizing, and a divertor separatrix boundary condition for the temperature is found to be destabilizing relative to a fixed separatrix temperature condition. The stability conditions are consistent with the conditions extant in a stable radiative mantle experiment and in a stable radiative mantle simulation. Expressions are developed for a radiation edge density limit and for the maximum fraction of the plasma heating power which can be radiated from the mantle. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871812
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  • 6
    Electronic Resource
    Electronic Resource
    Deuterium atomic cross section uncertainties and molecular recycling effects in the divertor region of tokamaks (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 678-689 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: How predictions of deuterium atomic reaction rates in tokamak divertors are altered by changes in cross section data which are comparable with the uncertainty in published data is investigated. An extended neutral diffusion theory calculation, which includes D atoms and ground and excited state D2 molecules, is performed on a fixed background plasma. For the atoms, the principal relevant mechanisms are elastic scattering, charge exchange, ionization, and recombination. It is evaluated that the charge exchange and electron processes are known to an accuracy better than +/−25%, and it is concluded that this level of accuracy is sufficient for the present state of divertor calculations. Of significant concern is the fact that classical elastic cross sections which are widely used in divertor calculations differ substantially from a more accurate set of cross sections based on quantum mechanics, and that the latter produce predictions of neutral density and ionization rate which differ by orders of magnitude from predictions based on the classical cross sections. Opacity of the plasma to Lyman alpha radiation influences transport for high density plasma situations. The explicit representation of incident particles recycling as molecules is shown to significantly affect the neutral atom density and reaction rates near the divertor plate. In particular, the dissociation of even a small fraction of excited molecules significantly reduces the plasma ion population and increases the neutral atom population just in front of the plate in nearly detached plasmas. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872150
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  • 7
    Electronic Resource
    Electronic Resource
    Variational estimates of changes in neutral-plasma reaction rates (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3725-3730 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A variational estimate of the change in a neutral-plasma reaction rate due to a change in plasma properties is presented. The effect of the change in neutral distribution which would result from a change in plasma properties is taken into account in the estimate, without the need for a recomputation of the neutral distribution. The general methodology is specialized to a neutral diffusion theory model and a numerical example is presented for a representative divertor problem. Application to reduce the computational time for coupled plasma-neutral calculations is discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872566
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  • 8
    Electronic Resource
    Electronic Resource
    An interface current balance formulation of neutral atom transport theory in plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 179-189 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An interface current balance (ICB) method for neutral particle transport is presented and specialized to the calculation of neutral atom transport in background plasmas. A multigroup extension of the ICB methodology is presented which enables the direct calculation of neutral atom energy distributions and energy and momentum transport, as well as particle transport. Extension of the ICB methodology to multidimensions recovers the transmission/escape probability method. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872131
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  • 9
    Electronic Resource
    Electronic Resource
    Multi-faceted asymmetric radiation from the edge formation in DIII-D high-confinement mode discharges with continuous gas puffing (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3941-3954 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A set of continuously gas fueled DIII-D [Plasma Physics and Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1986) p. 159] high confinement mode (H-mode) shots at three neutral beam injection powers and two values of magnetic field (q95) have been analyzed to investigate the evolution of plasma edge conditions leading to the formation of X-point MARFEs (multifaceted asymmetric radiation from edge), which are followed by an H–L transition that constitutes a practical density limit for this class of shots in DIII-D. The MARFE initiation is found to be caused by a combination of a sharply increasing concentration of recycling neutrals in the plasma edge, decreasing edge inverse temperature and density gradient scale lengths, and increasing edge density. The line-average density at which MARFEs precipitates increases with increasing injection power and with decreasing q95. It is not clear whether the formation of the X-point MARFE causes or merely precedes the H–L transition. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873658
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  • 10
    Electronic Resource
    Electronic Resource
    A coupled plasma-neutrals model for divertor simulations (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1015-1026 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The integral balance, or "two-point," class of divertor plasma models is extended to explicitly represent effects associated with recycling neutrals and is coupled to a two-dimensional neutral transport model. New analytical solutions for the plasma density, velocity, and temperature distributions along the field lines are derived. The resulting divertor model is intermediate in complexity between the simple "two-point" models and the coupled two-dimensional plasma fluid–Monte Carlo or Navier Stokes neutrals models; it is suitable for coupling with core transport codes and for performing a wide range of divertor physics studies. Qualitative comparison with experiment and model problem calculations indicates that the new model produces many of the features found in divertor experiments. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872631
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