Microturbulence in DIII-D tokamak pedestal. II. Electromagnetic instabilities

Gyrokinetic simulations have been used to identify electromagnetic microinstabilities in the H-mode pedestal region of DIII-D shot 131 997 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 maximum gradient location the most unstable mode is the kinetic ballooning mode (KBM) for the dominant poloidal wavenumber k(theta) approximate to 1 cm(-1). For shorter wavelengths the dominant instability is the trapped-electron mode (TEM). 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 while gradients remain unchanged.