Gyrokinetic Simulation of Plasma Instabilities in the DIII-D Tokamak
Fusion energy gives humankind the prospect of nearly unlimited clean energy. To this end future burning plasma experiments are presently under construction, such as the International Thermonuclear Experimental Reactor (ITER). Two potentially significant challenges for ITER are the effects of Edge Localized Modes (ELMs), and energetic particle (EP) transport. While ELMs are benign in present day experiments, extrapolations to reactor scale predict ELM energy fluxes of up to 20 MJ in fractions of a millisecond, which can drastically decrease divertor lifetimes, generate impurities, and erode first wall components. Moreover, EP transport can affect plasma profiles, beam deposition, and current drive, and can erode reactor walls. Due to the strong coupling of EPs with burning thermal plasmas, plasma confinement properties in the ignition regime are some of the most uncertain factors when extrapolating from existing tokamaks to ITER. This work presents advances in addressing the challenges these mechanisms deliver by making use of gyrokinetic simulations of the DIII-D Tokamak.
This thesis presents gyrokinetic simulations of the DIII-D tokamak, via the Gyrokinetic Toroidal Code, with axisymmetric equilibrium show that the reduction in the radial electric field shear at the top of the pedestal during ELM suppression with the $n=2$ resonant magnetic perturbations (RMPs) leads to enhanced drift-wave turbulence and extended turbulence spreading to the top of the pedestal relative to ELMing plasmas with similar RMP and pedestal parameters. The simulated turbulent transport at the top of the pedestal in ELM suppressed conditions is consistent with experimental observations of enhanced turbulence at the top of the pedestal during ELM suppression by the RMPs. These results suggest that enhanced drift-wave turbulence due to reduced $E \times B$ shear at the pedestal top can contribute to the additional transport required to prevent the pedestal growing to a width that is unstable to ELMs.
This thesis also reports verification and validation of linear simulations of Alf