Study of quasi-coherent fluctuations (QCFs) using BOUT$++$

The BOUT$++$ simulations are used to study the characteristics of quasi-coherent fluctuations (QCFs) at different pressure profiles, which are generated by VARYPED tool based on measured plasma profiles from DIII-D. The results show that QCFs can provide the necessary transport to limit and saturate the H-mode pedestal gradient. The simulations predict that (1) QCFs are localized in the pedestal region as observed in DIII-D; (2) the QCFs are near marginal unstable for ideal ballooning modes combined with drift-Alfven wave modes; (3) the frequency of the mode is around 80kHz, close to that of the measured QCF; and (4) particle transport is smaller than the heat transport. (5) Strong nonlinear interactions can be found when the amplitude of QCFs grows to a threshold value.