High-frequency coherent edge fluctuations in a high-pedestal-pressure quiescent H-mode plasma

A set of high frequency coherent (HFC) modes (f=80-250 kHz) is observed with beam emission spectroscopy measurements of density fluctuations in the pedestal of a strongly shaped quiescent H-mode plasma on DIII-D, with characteristics predicted for kinetic ballooning modes (KBM): propagation in the ion-diamagnetic drift direction; a frequency near 0.2-0.3 times the ion-diamagnetic frequency; inferred toroidal mode numbers of n～10-25; poloidal wave numbers of k(θ)～0.17-0.4 cm(-1); and high measured decorrelation rates (τ(c)(-1)～ω(s)～0.5×10(6) s(-1)). Their appearance correlates with saturation of the pedestal pressure.