Reversed rotation of limit cycle oscillation and dynamics of low-intermediate-high confinement transition

The dynamics of the confinement transition from L mode to H mode (LH) is investigated in detail theoretically via the extended three-wave coupling model describing the interaction of turbulence and zonal flow (ZF) for the first time. Thereinto, turbulence is divided into a positive-frequency (PF) wave and a negative-frequency (NF) one, and the gradient of pressure is added as the auxiliary energy for the system. The LH confinement transition is observed for a sufficiently high input energy. Moreover, it is found that the rotation direction of the limit cycle oscillation (LCO) of PF wave and pressure gradient is reversed during the transition. The mechanism is illustrated by exploring the wave phases. The results presented here provide a new insight into the analysis of the LH transition, which is helpful for the experiments on the fusion devices.