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Fusion Research Center

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George W. Woodruff School of Mechanical Engineering

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Now showing 1 - 10 of 27

The Effect of Ion Orbit Loss and X-Loss on the Interpretation of Ion Energy and Particle Transport in the DIII-D Edge Plasma

(Georgia Institute of Technology, 2011-10-14) Stacey, Weston M.

Calculation models are presented for treating ion orbit loss effects in interpretive fluid transport calculations for the tokamak edge pedestal. Both standard ion orbit loss of particles following trapped or passing orbits across the separatrix and the X-loss of particles that are poloidally trapped in a narrow null-Bθ region extending inward from the X-point, where they gradB and curvature drift outward, are considered. Calculations are presented for a representative DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] shot which indicate that ion orbit loss effects are significant and should be taken into account in calculations of present and future experiments.
Force Balance and Ion Particle Transport Differences in High and Low Confinement Tokamak Edge Pedestals

(Georgia Institute of Technology, 2010-11-22) Stacey, Weston M. ; Groebner, Rich J.

The various terms in the radial force balance in the edge plasma are evaluated using experimental data from the low (L) and high (H) confinement phase of a DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] discharge in order to investigate the differences in the radial force balance among the several electromagnetic and pressure gradient forces in L-mode and H-mode. The roles of cross-field toroidal momentum transport and of a radial pinch velocity in determining different radial particle fluxes in L-mode and H-mode are elucidated
The effects of rotation, electric field, and recycling neutrals on determining the edge pedestal density profile

(Georgia Institute of Technology, 2010-05-19) Stacey, Weston M.

The edge density profile is calculated from the continuity and momentum balance equations, using experimental electric field and rotation velocities and a calculated recycling neutral source, to evaluate the relative importance of these quantities in determining the observed structure of the edge density profile in a DIII-D _J. Luxon, Nucl. Fusion 42, 614 _2002__ high-confinement mode discharge.
The effect of rotation and viscous heating on the interpretation of experimental heat diffusivities in the edge pedestal

(Georgia Institute of Technology, 2010-05-17) Stacey, Weston M.

A formalism is presented for evaluating the effect of plasma rotation, via viscous heating, on the interpretation of thermal conductivities from measured temperature and density gradients in the edge pedestal. An application to a H-mode DIII-D [ J. Luxon, Nucl. Fusion 42, 614 (2002) ] discharge indicates that the effect could be significant.
Analysis of neutral particle recycling and pedestal fueling in a H-mode DIII-D discharge

(Georgia Institute of Technology, 2010-02-23) Friis, Zachary Ward ; Stacey, Weston M. ; Leonard, Anthony W. ; Rensink, M. E.

A detailed analysis of neutral atom recycling and pedestal fueling in a DIII-D _J. Luxon, Nucl. Fusion 42, 614 _2002__ high-confinement mode discharge is presented. Experimental data and two-dimensional _2D_ edge plasma fluid code calculations are employed to provide ion wall recycling and recombination neutral sources and background edge plasma parameters for a 2D edge neutral code calculation of detailed neutral density, ionization, and charge-exchange distributions throughout the edge pedestal, scrape-off layer and surrounding halo region, divertor, and private flux regions. The effectiveness of the different neutral sources for fueling the confined plasma is evaluated
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.

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.
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

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.
Rotation velocities in the plasma edge driven viscously by scrape-off layer flows

(Georgia Institute of Technology, 2009-06-25) Stacey, Weston M.

Scrape-off layer parallel flows and the viscous fluxes in the plasma edge driven thereby are calculated from neoclassical theory for a model problem representative of a present experiment, using an analytical model for elongated flux surface geometry with a Shafranov shift to provide a realistic evaluation of important poloidal dependences. The estimated effects of the viscous torques of toroidal and poloidal momentum driven by these scrape-off layer flows on rotation velocities in the edge plasma are substantial, suggesting possible explanations for various experimental observations.
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.

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.
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.

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.