SUBJECT: | Ph.D. Dissertation Defense |

BY: | Theresa Wilks |

TIME: | Thursday, March 17, 2016, 3:00 p.m. |

PLACE: | Boggs, 3-47 |

TITLE: | Determination of the Radial Electric Field in the DIII-D Tokamak Edge Plasma |

COMMITTEE: | Dr. Weston Stacey, Co-Chair (NRE) Dr. Todd Evans, Co-Chair (General Atomics) Dr. Bojan Petrovic (NRE) Dr. Tris Utschig (NRE) Dr. Robert McGrath (GTRI) |

SUMMARY The application of a theoretical framework for calculating the radial electric field in the DIII-D tokamak is discussed. Changes in the radial electric field are correlated with changes in many important edge plasma phenomena, including rotation, the L-H transition, and ELM suppression. A self-consistent model for the radial electric field may therefore suggest a means of controlling other important parameters in the edge plasma. Implementing a methodology for calculating the radial electric field can be difficult due to the complex interrelationships among ion losses, rotation, radial ion fluxes, momentum transport, and the radial electric field. The radial electric field enters the calculations for ion orbit loss. This ion orbit loss, in turn, affects the radial ion flux both directly and indirectly through return currents, which has been shown theoretically to torque the edge plasma causing rotation. The edge rotation generates a motional radial electric field, which can influence both the edge pedestal structure and the ion orbit losses. In conjunction with validating the analytical modified Ohmâ€™s Law model for the radial electric field, modeling efforts presented in this dissertation focus on improving calculations of ion orbit losses and x-loss into the divertor region, as well as the formulation of models for fast beam ion orbit losses and the fraction of lost particles that return to the confined plasma. After rigorous implementation of the ion orbit loss model and related mechanisms into fluid equations, efforts are shifted to calculate effects from rotation on the radial electric field calculation and compared to DIII-D experimental measurements. This calculation of the radial electric field will provide a basis for future modeling of a fast, predictive calculation to characterize future tokamaks like ITER. |