Turbulence Dynamics Across the L-H Transition in DIII-D

Turbulence characteristics and the effects of sheared poloidal flows on turbulence in the pedestal region of \hbox{DIII-D} plasmas preceding and across the L-H transition are examined using high time resolution time delay estimation (TDE) as well as nonlinear analysis techniques. Density fluctuation measurements are obtained with the recently upgraded, high-sensitivity beam emission spectroscopy system (BES). Poloidal flow shear rates in \hbox{L-mode}, measured with BES and CER, are found to be roughly one quarter the measured decorrelation rates, while in \hbox{H-mode}, they are roughly four times the decorrelation rate in the pedestal region, consistent with the E$\times$B shear suppression of turbulence model for the LH transition. Furthermore, \hbox{H-mode} eddy structures have nearly double the poloidal elongation as \hbox{L-mode} turbulence structures. The evolution of this structure asymmetry as well as counter-propagating modes prior to and during the L-H transition will be investigated using biorthogonal decomposition methods.