Investigation of the fast ion driven kinetic ballooning mode in FIRE mode discharge through gyrokinetic simulations

Abstract The fast ion relevant mode shown in a previous study (Kim et al 2024 Nucl. Fusion 64 066013) is further investigated via gyrokinetic simulations in the present work. This mode is identified as a kinetic ballooning mode (KBM) based on its mode structure, polarization, parametric dependence, dominant energy flux component, and mode frequency. In addition, we find that the presence of fast ions is essential for the destabilization of this KBM. The mode is destabilized by fast ion pressure and its gradient, with a threshold present, indicating that the fast ion relevant mode is a fast ion driven KBM. Energy transfer analysis shows that the fast ion driven KBM transfers energy directly to the zonal potential energy, increasing the zonal flow and zonal field. However, this mode can also increase both fast ion and electron transport by increasing the fluctuation quantities, such as ene…