A set of high frequency coherent (HFC) modes ($f=80–250\mathrm{kHz}$) 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 $n\sim 10–25$; poloidal wave numbers of $k_{\theta }\sim 0.17–0.4{\mathrm{cm}}^{-1}$; and high measured decorrelation rates (${\tau }_c^{-1}\sim {\omega }_s\sim 0.5\times {10}^6{\mathrm{s}}^{-1}$). Their appearance correlates with saturation of the pedestal pressure.

• Received 29 October 2010

DOI:https://doi.org/10.1103/PhysRevLett.107.055004