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ItemInterpretation of particle pinches and diffusion coefficients in the edge pedestal of DIII-D H-mode plasmas(Georgia Institute of Technology, 2009-10-15) Stacey, Weston M. ; Groebner, Rich J.A procedure is described for evaluating particle pinches to be used in interpreting particle diffusion coefficients from measured density and temperature profiles in the edge pedestal of tokamak plasmas. Application to the interpretation of two DIII-D [ J. Luxon, Nucl. Fusion 42, 614 (2002) ]. discharges yields new information about particle pinches and particle diffusion coefficient profiles in the edge pedestal.
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ItemInterpretation of edge pedestal rotation measurements in DIII-D(Georgia Institute of Technology, 2008-01-25) Stacey, Weston M. ; Groebner, Rich J.A novel methodology for inferring experimental toroidal angular momentum transfer rates from measured toroidal rotation velocities and other measured quantities has been developed and applied to analyze rotation measurements in the DIII-D J. Luxon, Nucl. Fusion 42, 6149 2002 edge pedestal. The experimentally inferred values have been compared with predictions based on atomic physics processes and on neoclassical toroidal viscosity. The poloidal rotation velocities have been calculated from poloidal momentum balance using neoclassical parallel viscosity and a novel retention of all terms in the poloidal momentum balance, and compared with measured values in the DIII-D edge pedestal.
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ItemExperimentally inferred thermal diffusivities in the edge pedestal between edge-localized modes in DIII-D(Georgia Institute of Technology, 2007-12-11) Stacey, Weston M. ; Groebner, Rich J.Using temperature and density profiles averaged over the same subinterval of several successive inter-edge-localized-mode (ELM) periods, the ion and electron thermal diffusivities in the edge pedestal were inferred between ELMs for two DIII-D [ J. Luxon, Nucl. Fusion 42, 614 (2002) ] discharges. The inference procedure took into account the effects of plasma reheating and density buildup between ELMs, radiation and atomic physics cooling, neutral beam heating and ion-electron equilibration, and recycling neutral and beam ionization particle sources in determining the conductive heat flux profiles used to infer the thermal diffusivities in the edge pedestal. Comparison of the inferred thermal diffusivities with theoretical formulas based on various transport mechanisms was inconclusive insofar as identifying likely transport mechanisms.
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ItemThermal transport analysis of the edge region in the low and high confinement stages of a DIII-D discharge(Georgia Institute of Technology, 2007-01-04) Stacey, Weston M. ; Groebner, Rich J.The ion and electron thermal diffusivities have been inferred from measured density and temperature profiles in the edge of a DIII-D [ J. Luxon, Nucl. Fusion 42, 614 (2002) ] discharge with a low confinement (L-mode) stage followed by a high confinement (H-mode) stage free of edge localized modes. Conductive heat flux profiles used to construct the inferred thermal diffusivities were calculated taking into account heat convection, radiation, atomic physics effects of recycling neutrals, ion-electron equilibration, and neutral beam heating. The inferred thermal diffusivities were compared with theoretical predictions.
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ItemThermal Transport in the DIII-D Edge Pedestal(Georgia Institute of Technology, 2006) Stacey, Weston M. ; Groebner, Rich J.A new procedure for inferring χ[subscript i,e] in the plasma edge from experimental data and integrated modeling code calculations has been developed which takes into account atomic physics and radiation effects and convective as well as conductive heat flux profiles. Application to DIII-D shots indicates that the sharp temperature gradient pedestal region may be caused as much, if not more, by an increase (with radius) of the conductive heat flux as by a decrease of the thermal transport coefficient. Inferred χ[subscript i,e][superscript exp] are compared with theoretical predictions.
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ItemApplication of a particle, momentum and energy balance model to calculate the structure of the edge pedestal in DIII-D(Georgia Institute of Technology, 2005-04) Stacey, Weston M. ; Groebner, Rich J.A calculation of edge density and temperature profiles based on "classical" physics - particle, momentum and energy balance, heat conduction closure relations, neutral particle transport - yielded a pedestal structure that is qualitatively and quantitatively similar to that found experimentally in five DIII-D [J. Luxon, Nucl. Fusion,42, 614 (2002)] discharges, when experimental radial electric field and rotation profiles and experimentally inferred heat transport coefficients were used. The principal cause of the density pedestal was a peaking of the inward pinch velocity just inside the separatrix caused by the negative well in the experimental electric field, and the secondary cause was a peaking of the radial particle flux caused by the ionization of incoming neutrals. There is some evidence that this peaking of the radial particle flux just inside the separatrix may also be responsible in part for the negative electric field in that location.
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ItemA framework for the development and testing of an edge pedestal model: formulation and initial comparison with DIII-D data(Georgia Institute of Technology, 2003-06) Stacey, Weston M. ; Groebner, Rich J.A framework has been formulated for the further development and testing of a predictive edge pedestal model. This framework combines models for the interaction of the various physical phenomena acting in the edge pedestal—transport, neutral fueling penetration, atomic physics cooling, MHD (magnetohydrodynamic) stability limit, edge density limit—to determine the pedestal widths and gradient scale lengths. Predictive models for some of these specific phenomena have been compared with DIII-D [ J. L. Luxon, Nucl. Fusion, 42, 614, 2002] measurements. It was found that a neutral penetration model for the density width and a MHD model for the maximum pedestal pressure for stability against ideal pressure-driven surface modes were roughly consistent with experimental observation, but that in both cases some refinements are needed. The major impediments to implementation of a predictive edge pedestal model within the framework of this paper are the lack of knowledge of transport coefficients in the pedestal and the unavailability of an usable characterization of the state-of-the-art MHD stability-limit surface in the space of edge parameters. Efforts to remedy these and other deficiencies and to establish a predictive model for the calculation of density, temperature and pressure widths and gradients in the edge pedestal are suggested.