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  • 1
    Electronic Resource
    Electronic Resource
    An edge pedestal investigation for high-confinement tokamak plasmas (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 1332-1341 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model for the edge pedestal in high-confinement mode tokamak plasmas is described. Separate gradient scale lengths of the density and of the ion and electron temperatures are calculated from transport and atomic physics considerations, and a common pedestal width is calculated from either a magnetohydrodynamic pedestal β-limit or from neutral penetration considerations. Predictions of the model for a representative gas fueled tokamak model problem are discussed vis-à-vis measured values of pedestal gradient scale lengths and widths, ballooning mode limits, and scaling with operational parameters. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1461846
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  • 2
    Electronic Resource
    Electronic Resource
    An edge pedestal model based on transport and atomic physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4073-4079 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model is presented for the calculation of the characteristic scale lengths from transport considerations in the edge pedestal region of high confinement (H-mode) plasmas. The model is based on the requirements of heat and particle removal through the edge. Atomic physics effects on edge density and temperature gradient scale lengths are taken into account. An empirical fit for the width of the edge pedestal transport barrier is employed. Model problem calculations indicate that the model predicts the magnitudes and some trends of characteristic gradient scale lengths observed in current experiments. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1388175
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  • 3
    Electronic Resource
    Electronic Resource
    Neoclassical theory for rotation and impurity transport in tokamaks with neutral beam injection (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 158-166 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A self-consistent, first-principles neoclassical theory for rotation and impurity transport in tokamaks is presented. The implications of this theory for impurity transport in a tokamak are illustrated by a model problem calculation. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1324664
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  • 4
    Electronic Resource
    Electronic Resource
    Thermal instabilities in the edge transport barrier (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2452-2461 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A linear analysis of the edge transport barrier identifies localized, two-dimensional (radial-perpendicular) thermal instabilities driven by both impurity radiation and atomic (ionization/charge-exchange/elastic scattering) cooling and suppressed by conductive and convective heat transport. These instabilities are stabilized by sufficiently large values of the edge temperature gradient. Numerical calculations indicate that such instabilities would be expected for edge conditions (electron, impurity and neutral atom densities, temperatures, gradient scale lengths) typical of current tokamak experiments. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873517
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  • 5
    Electronic Resource
    Electronic Resource
    Explanation for MARFE formation and subsequent evolution into a detached symmetric plasma edge (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2673-2678 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An explanation is proposed for the experimentally observed tokamak phenomenon of a symmetric radiating edge evolving with increasing density into a multifaceted asymmetric radiation from the edge (MARFE) condition and then cooling into a detached plasma with a symmetric edge. The thermal stability impurity density limits increase with the poloidal mode number, m, of the edge plasma distribution. When the edge impurity density exceeds the m=0 mode density limit, the edge plasma evolves into a mixture of m(approximately-greater-than)0 modes which becomes more highly asymmetric as the density increases further and exceeds the density limits of successively higher modes, forcing the plasma into the remaining stable higher-m modes—the stable MARFE. If the radiative cooling of the edge is sufficient to reduce the temperature to Te∼10 eV, the various thermal modes are stabilized by the strong positive temperature dependence of the ionization cooling in the presence of neutral atoms, the impurity density limits are thereby increased, and the plasma evolves back into a stable m=0 mode. On the other hand, if the plasma becomes highly enough asymmetric before sufficient cooling takes place, nonlinear effects drive a disruptive collapse of the radial temperature distribution. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871524
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  • 6
    Electronic Resource
    Electronic Resource
    Multifaceted asymmetric radiation from the edge suppression by external edge heating (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 134-137 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A linear, fluid model stability analysis of a radiative plasma mantle reveals that the impurity density limit for the onset of multifaceted asymmetric radiation from the edge (MARFE) in tokamaks can be increased by external heating of the radiative mantle at the plasma edge. The required injected power is estimated to be a few MW for present experiments and a few tens of MW for future reactors. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872123
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  • 7
    Electronic Resource
    Electronic Resource
    The low-energy toroidal grating monochromator beamline at the synchrotron radiation source at Daresbury Laboratory : Proceedings of the 4th international conference on synchrotron radiation instrumentation (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 1274-1277 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The bending magnet beam line 1.2 low-energy toroidal grating monochromator of the synchrotron radiation source (SRS) at Daresbury Laboratory, was designed1 to deliver moderately high fluxes (∼ 5 × 1011 photons s−1), of linearly polarized, medium resolution (∼0.2 eV) radiation in the energy range 5–85 eV. The colinear optical system utilizes platinum-coated silicon-carbide mirrors to focus the broad-band radiation emergent from the SRS at the entrance slits of the three grating monochromator. A single ellipsoidal mirror is then used to doubly focus the desired narrow-band radiation at the sample position. The colinear arrangement of the optical elements ensures that the radiation at the sample point is strongly horizontally plane polarized (estimated to be of order 90%). The entire system has been the subject of detailed analyses using the raytracing program shadow,2 and standard optical theory. These calculations have been compared with experimental determinations of photon flux outputs and resolution measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143098
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  • 8
    Electronic Resource
    Electronic Resource
    Detachment and divertor temperature and density redistribution (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 525-532 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theoretical model is developed for large scale-length, one-dimensional thermal instabilities along the field lines in tokamak divertors. Calculated growth rates predict a divertor thermal instability under the conditions (low-plasma temperature and density and high-neutral densities at the divertor plate) at which detachment followed by large-scale divertor temperature and density redistributions are observed in several DIII-D [Plasma Physics and Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1986), p. 159] discharges. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1339836
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  • 9
    Electronic Resource
    Electronic Resource
    Edge pedestal deterioration in tokamak high-mode discharges (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 5199-5203 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model for calculating edge gradients in density and temperature from transport and atomic physics considerations is combined with a model for calculating the enhancement of edge transport by thermal instabilities, the onset and strength of which in turn depend on edge gradients and atomic physics. A minimum threshold value of the nonradiative power flux passing through the edge that is required to suppress transport enhancing thermal instabilities is established. When the power flux through the edge is less than this minimum threshold value, the model predicts a deterioration of the edge gradients as the neutral concentration, the impurity concentration and/or the impurity radiation emissivity in the edge plasma increase, which is consistent with experimental observations. Model problem calculations are presented to illustrate the predicted pedestal deterioration for representative experimental conditions.© 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1416879
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  • 10
    Electronic Resource
    Electronic Resource
    A numerical study of density limit mechanisms in tokamaks (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 3656-3668 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A core particle and power balance model with radiative cooling, a ballooning-mode-limit pedestal model, a "two-point" plasma divertor model with radiative and atomic recycling cooling, and a two-dimensional (2-D) neutral transport model have been combined to model the coupled plasma core-edge physics in a tokamak. This model has been applied to examine the physical mechanisms which limit the attainable core density. The first limitation is fueling rate and core penetrability. For fueling that is able to penetrate the core, the core density increases with a fueling rate up to a limit set by one of two other mechanisms. When a sufficient impurity concentration is present, the mechanism that limits the maximum density attainable in the core seems to be an impurity-driven thermal instability that produces a thermal collapse of the core plasma. At lower impurity concentrations, the buildup of plasma density in the divertor and the associated increase in atomic recycling and ionization cooling causes a collapse of the divertor plasma temperature, leading to a thermal collapse of the core plasma. An increase in core heating input power or in plasma confinement extends the point of thermal collapse to higher density. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873084
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