Pedestal Instability Characteristics in ELM-Mitigated and ELM-Suppressed H-Mode Plasmas on DIII-D*

Mitigating or suppressing Edge Localized Modes in H-mode plasmas will be essential for the survivability of reactor divertor components. Simultaneously, a high-pressure pedestal that controls impurity influx is required for sufficient fusion performance, placing unique demands on pedestal transport properties. Quasi-steady ELM-mitigated or suppressed pedestals, as obtained in RMP ELM-suppressed and Enhanced D-Alpha (EDA) plasmas, have unique pedestal instability features. To better characterize these instabilities, a high-radial resolution (DR~0.3-0.5 cm, DZ~1 cm, f=2 MHz), 2D (12-radial x 5-poloidal channels) low-to-intermediate wavenumber density fluctuation diagnostic, Charge eXchange Imaging [1], has been deployed at DIII-D to complement wider-field low-wavenumber measurements obtained with Beam Emission Spectroscopy and other fluctuation diagnostics. Increased broadband turbulence (10-100 kHz) is observed near and inside the pedestal as I-coil current (even parity, n=3) rises in RMP-ELM suppressed discharges, while a quasi-coherent instability (25-60 kHz) is characterized in higher density EDA-like plasmas that peaks in amplitude near r~0.96 in the steep pressure gradient region of the pedestal. The 2D features of these fluctuations and their role in driving pedestal transport and maintaining the ELM-mitigated state will be assessed.