Local Turbulence Suppression and Flow Shear Dynamics During \textit{q}$_{min}$-Triggered Internal Transport Barriers

Turbulence is observed to transiently decrease locally during the formation of internal transport barriers (ITBs) following the appearance of low-order rational $q_{min}$ surfaces in negative central shear discharges on DIII-D. Simultaneously, increased poloidal flow shear is observed. To further study this phenomenon, localized 2D density fluctuation measurements of turbulence and turbulence flow were obtained over 0.3 $<$ r/a $<$ 0.7 via the high-sensitivity beam emission spectroscopy diagnostic. Both the reduction in fluctuations and the poloidal velocity shear are found to propagate radially outward at about 1 m/s. Initial observations suggest that these effects follow the $q$=2 surface. Related GYRO simulations suggest transient zonal flows form near the $q$=2 surface to trigger these ITBs. High-frequency poloidal velocity measurements will be used to examine this mechanism.