The role of a series of quasi-coherent modes (QCMs) on the turbulence properties has been investigated during Type-III ELMs under HL-2A high confinement mode (H-mode) scenarios. The QCMs are essentially electrostatic and appear during the inter-ELM periods, with a frequency ranging from 20 kHz to 60 kHz. These QCMs are localized in the pedestal region and are related to the saturation of density gradient in the pedestal. Nonlinear couplings between QCMs and ambient turbulence have been observed and also verified through the envelope modulation of turbulence in density by the radial electrical field fluctuation of the modes. The presence of QCMs can increase the radial and poloidal turbulence correlation lengths, thereby modulating the turbulent transport. Experimental results show that QCMs significantly impact pedestal turbulence and transport by increasing the correlation length as well as the decorrelation time of turbulent eddies. The flow shearing rate in pedestal region is also enhanced to a level that surpasses the decorrelation frequency of turbulence, thus, the existence of QCMs has the ability to put off the ELM burst due to relative stronger stabilization of turbulence by sheared flows. The above results have demonstrated that the pedestal dynamics is largely determined by the complex interactions among QCMs, turbulence and the shear flow.
This paper investigates the role of quasi-coherent modes (QCMs) on turbulence in the pedestal region during high confinement mode (H-mode) on the HL-2A tokamak. The QCMs, which appear between edge-localized mode (ELM) events, can influence turbulence properties by increasing correlation lengths and decorrelation times. This leads to enhanced flow shearing, which can delay the onset of ELMs. The findings demonstrate the importance of understanding the complex interactions between QCMs, turbulence, and sheared flows in the pedestal region.