Gyrokinetic Simulations of Microturbulence in DIII-D pedestal

 

 

 

ITER operation requires control of the edge localized mode (ELM) excited by the steep pressure gradient in the pedestal of the H-mode plasmas. Comprehensive kinetic description is required to understand the ELM triggering mechanism. Here we present recent gyrokinetic simulations aimed to identify electromagnetic microinstabilities in the pedestal region of DIII-D tokamak using global gyrokinetic code GTC. It was found that dominant instability at the top of the pedestal is the ion temperature gradient mode (ITG). In the middle of a pedestal the kinetic ballooning mode (KBM) becomes the most unstable. We have demonstrated the ITG-KBM transition at the pedestal top and TEM-KBM transition in the steep pressure gradient region as plasma pressure increases. One possibility to control drastic ELM activity during H-mode operation is applying resonant magnetic perturbations (RMP). However the detailed mechanism of RMP effect is not completely clear. In our studies we address the direct effect of modified magnetic equilibrium geometry on microturbulence in DIII-D pedestal. The direct effect of RMP geometry perturbation on KBM growth rate, zonal flow generation, and turbulent transport is found to be insignificant.

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