Pedestal Density Fluctuations During Quiescent and ELMing H-mode Plasmas

Spatially resolved density fluctuation characteristics have been measured in the pedestal region of quasi-steady-state Type~I ELMing plasmas and ELM-free quiescent H-mode (QH) plasmas using 2D beam emission spectroscopy measurements. During Type~I ELMing plasmas, these fluctuations are modulated with the ELM cycles. Two distinct frequency bands (20-200~kHz and 250-450~kHz) are observed propagating in opposite directions. In QH-mode plasmas, discrete and coherent modes are observed in the pedestal region of particular discharges at relatively high-pedestal pressure. These modes appear from 50-250~kHz, peaking in amplitude around 150~kHz, with a uniform frequency separation of about 10~kHz. Observed characteristics of these modes will be compared with those from ELITE calculations of theoretically predicted pressure-gradient limiting instabilities, such as kinetic ballooning modes.