Broadband turbulence characteristics in wide pedestal quiescent H-mode on DIII-D

ELM-free high confinement operation with a wide pedestal has been achieved in DIII-D, exhibiting a spontaneous transition from the coherent edge harmonic oscillation (EHO) to the broadband MHD turbulence state by a sufficient reduction of input torque. It is thought that ExB rotational shear altered by changes in torque affects the edge turbulence state and associated radial transport, leading to the wider pedestal. Clarifying the characteristics of the turbulence is one of the important issues to understanding the mechanisms of formation of the improved pedestal condition. The broadband turbulence was typically observed in the frequency range of 0-250 kHz with Beam Emission Spectroscopy, and is composed of two components; a lower frequency band propagating in the ion diamagnetic drift direction in the lab frame and a higher frequency band in the electron diamagnetic drift direction near the top of the pedestal. The lower frequency band is found to have a long poloidal correlation length of ~10 cm, which tends to be slightly longer compared to ~9 cm in standard QH-mode phase. Temporal evolution of the broadband turbulence characteristics during the transition from standard QH-mode to wide pedestal QH-mode will be presented.