Characterization of Geodesic Acoustic Modes and a Lower-Frequency Zonal Flow Feature in DIII-D with BES

The spatiotemporal characteristics of geodesic acoustic mode (GAM) and lower-frequency zonal flows are examined and compared with theoretical predications as a function of safety factor, $q$ and elongation. High time resolution poloidal turbulence flow velocities are determined from multi-point beam emission spectroscopy (BES) data using time-delay-estimation analysis. Localized 2D measurements of density fluctuation are obtained in L-mode plasmas over 0.6$