Local Turbulence Suppression and Shear Flow Dynamics During $q_{min}$-Triggered Internal Transport Barriers on DIII-D

Long-wavelength turbulence ($k_\perp \rho_i < 1$) is locally suppressed simultaneously with a rapid but transient increase in local poloidal flow shear at the appearance of low-order rational $q_{min}$ surfaces in negative central shear discharges. At these events, reductions in energy transport are observed and Internal Transport Barriers (ITBs) may form. Application of off-axis ECH slows the $q$-profile evolution and increases $\rho_{qmin}$, both of which enhance turbulence measurements using a new high-sensitivity large-area (8$\times\,$8) 2D BES array. The measured transient turbulence suppression is localized to the low-order rational surface ($q_{min} = 2$, 5/2, 3, etc.). Measured poloidal flow shear transiently exceeds the turbulence decorrelation rate, which is consistent with shear suppression. The localized suppression zone propagates radially outward, nearly coincident with the low-order surface.