Linear Gyrokinetic Analysis of High Poloidal Beta Discharge on DIII-D

Linear gyrokinetic simulations performed on kinetic equilibrium reconstructions of high poloidal beta DIII-D discharges show the features of the dominant micro-turbulent instabilities. In low-k range, ITG-like and KBM-like modes co-exist outside the large radius internal transport barrier (ITB) in the low pressure gradient region (rho=0.73) as dominant modes for different k_thetas. In these simulations, the ITG-like mode is very marginal to many parameters, e.g. beta, collisionality and ion temperature scale length. Some increase in these parameters will bring a conversion of this mode to KBM-like mode, which has out-of-phase parity in the parallel part of the vector potential. The linear growth rate of the KBM-like mode is proportional to plasma beta. Ion temperature gradient is the major driving force of this instability. In the steep gradient region of ITB, the KBM-like mode can still be seen unstable and the ITG-like mode changes to an electron mode. The comparison with turbulence measurement in experiment will also be presented.