Global gyrokinetic simulation of turbulence driven by kinetic ballooning mode

Nonlinear evolution of the kinetic ballooning mode (KBM) is investigated by extending the global toroidal gyrokinetic simulation code (GKNET) to an electromagnetic regime. It is found that the saturation process of KBM, which is unstable at high normalized pressure beta, is significantly different from the ion temperature gradient (ITG) mode, which is unstable at low beta. The KBMs get saturated by producing zonal flows and zonal magnetic fields. The production of zonal flow is weak in the initial saturation phase of KBM, which is in contrast to the ITG mode which produces strong zonal flows in the initial saturation phase. However, strong zonal flows are produced in the subsequent evolution of KBM, and a quasisteady state of KBM turbulence is established. In addition to the zonal flows, some low toroidal number modes, which are linearly stable against the KBM, dominate the KBM turbulence. The strong zonal magnetic field is also produced by the KBM. These zonal modes regulate the KBM turbulence.