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Fusion Research Center

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Now showing 1 - 10 of 84
  • Item
    Effect on the divertor and scrape-off layer plasma properties of the distribution of power and particle influxes from the core
    (Georgia Institute of Technology, 2009-03-25) Stacey, Weston M. ; George W. Woodruff School of Mechanical Engineering ; Fusion Research Center
    Calculations of the profiles along the field lines within the divertor and scrape-off layer (SOL) of differences in the plasma ion density, temperature, parallel current, parallel flow velocity, and electrostatic potential, which result from using different poloidal distributions of the particle and heat influxes crossing the separatrix from the core plasma into the SOL, are presented and discussed vis-à-vis experimental observations. The calculations show that the stronger outboard than inboard particle and heat fluxes into the SOL caused by the geometric compression/expansion of flux surfaces predicted by magnetohydrodynamic equilibrium calculations lead to a prediction of higher plasma temperature at the outboard divertor than at the inboard divertor, a result that is consistent with experimental observation and that confirms a previous prediction (made without accounting for drifts) of a possible cause of the observed in-out divertor power asymmetry. The calculations also illustrate the effect of the poloidal distribution of particle and power influx into the SOL on the flow velocity, parallel current, and electrostatic potential distributions in the SOL and divertor.
  • Item
    Edge Pedestal Structure and Transport Interpretation in DIII-D (In the absence of or in between ELMs)
    (Georgia Institute of Technology, 2008) Stacey, Weston M. ; Groebner, Rich J. ; Fusion Research Center ; General Atomics
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    Comparison of the Theoretical and Experimental Heat Diffusivities in the DIII-D Edge plasma
    (Georgia Institute of Technology, 2008) Stacey, Weston M. ; Fusion Research Center
    Predictions of theoretical models for ion and electron heat diffusivity have been compared against experimentally inferred values of the heat diffusivity profile in the edge plasma of two H-mode and one L-mode discharge in DIII-D [J. Luxon, Nucl. Fusion, 42, 614 (2002)]. Various widely used theoretical models based on neoclassical, ion temperature gradient modes, drift Alfven modes and radiative thermal instability modes for ion transport, and based on paleoclassical, electron temperature gradient modes, trapped electron modes, and drift resistive ballooning modes for electron transport were investigated.
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    Rotation velocities and radial electric field in the plasma edge
    (Georgia Institute of Technology, 2005-10) Stacey, Weston M. ; Fusion Research Center
    The toroidal and poloidal rotation and related radial electric field observed in the edge (and core) of tokamak plasmas are of interest for several reasons, not least of which is what they reveal about radial momentum transport, but also because of their apparent role in the L-H transition and the edge pedestal. It was recently shown that if the heat transport coefficients and rotation velocities are taken from experiment, then the particle, momentum and energy balance equations and the conductive heat conduction relation are sufficient to determine the observed edge pedestal profile structure in the density and temperature profiles in several DIII-D discharges. Thus, it would seem that understanding the edge pedestal structure is a matter of understanding the edge rotation profiles. We present a practical computational model for the rotation and the radial electric field profiles in the plasma edge that is based on momentum and particle balance, includes both convective (including anomalous) and neoclassical gyroviscous momentum transport, and incorporates atomic physics effects associated with recycling neutrals.
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    Representation of the plasma fluid equations in "Miller equilibrium" analytical flux surface geometry
    (Georgia Institute of Technology, 2009-08-03) Stacey, Weston M. ; Bae, Cheonho ; George W. Woodruff School of Mechanical Engineering ; Fusion Research Center
    The plasma fluid equations are represented explicitly in the magnetic flux surface coordinate system resulting from the analytical “Miller equilibrium” solution of the Grad–Shafranov equation. The magnetic geometry is characterized by the elongation, triangularity, and location of the displaced major radius of the flux surface. The resulting fluid equations can be solved directly without the necessity of first solving the Grad–Shafranov equation numerically to define the flux surface coordinates.
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    Investigation of transport in the DIII-D edge pedestal
    (Georgia Institute of Technology, 2004-04) Stacey, Weston M. ; George W. Woodruff School of Mechanical Engineering ; Fusion Research Center
    A comparison of various heat conduction theories with data from several DIII-D [Luxon, Nucl. Fusion, 42, 614, 2002] shots indicates: 1) that neoclassical theory is in somewhat better agreement with experiment than is ion temperature gradient mode theory for the ion thermal conductivity in the edge pedestal, although both are in reasonable agreement with experiment for most discharges; and 2) that electron temperature gradient theory (k┴cs ≤ ωpe) is in much better agreement with experiment than is electron drift wave theory (k┴cs ≤ Ωi) for the electron thermal conductivity. New theoretical expressions derived from momentum balance are presented for: 1) a ‘diffusive-pinch’ particle flux, 2) an experimental determination of the momentum transfer frequency, and 3) the density gradient scale length. Neither atomic physics nor convection can account for the measured momentum transfer frequencies, but neoclassical gyroviscosity predictions are of the correct magnitude.
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    Interpretation 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. ; George W. Woodruff School of Mechanical Engineering ; Fusion Research Center
    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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    Non-Diffusive Transport in the Tokamak Edge Pedestal
    (Georgia Institute of Technology, 2012) Stacey, Weston M. ; Groebner, Rich J. ; Evans, T. E. ; George W. Woodruff School of Mechanical Engineering ; Fusion Research Center ; General Atomics
    There are (at least) two classical mechanisms for non-diffusive transport in the edge plasma: i) particle “pinch” velocities due to forces such as VxB, and Er; and ii) outward drifts due to ion-orbit loss and X-transport. A theoretical development for the treatment of these non-diffusive transport mechanisms within the context of fluid theory is assembled and applied to several DIII-D discharges in order to investigate the importance of these non-diffusive transport mechanisms in the edge pedestal. Several interesting insights emerge from this investigation.
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    An investigation of some effects of drifts and magnetic field direction in the scrape-off layer and divertor of tokamak plasmas
    (Georgia Institute of Technology, 2009-04-03) Stacey, Weston M. ; George W. Woodruff School of Mechanical Engineering ; Fusion Research Center
    Various effects of particle drifts in the scrape-off layer (SOL) and divertor of tokamaks have been calculated. The predictions are consistent with several experimentally observed phenomena, e.g., the double reversal of parallel ion velocity in the SOL and the enhanced core penetration of argon injected into the divertor when the grad-B ion drift is into, rather than away from, the divertor. Other interesting phenomena, such as the structure of the parallel current flowing in the SOL and the reversal of the sign of the electrostatic potential in the SOL when the toroidal field direction is reversed, are also predicted.
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    Role of Fusion in the Sustainable Expansion of Nuclear Power
    (Georgia Institute of Technology, 2011-11-29) Stacey, Weston M. ; George W. Woodruff School of Mechanical Engineering ; Fusion Research Center ; Georgia Institute of Technology. Nuclear and Radiological Engineering Program