Radial Correlation Length of Density Fluctuations in DIII-D Plasmas

The radial correlation length (L$_{r})$ of density fluctuations, which is directly related to the radial scale length of the fluctuations, is an important quantity for understanding turbulent transport in tokamak plasmas. In DIII-D, recent upgrades of the UCLA correlation reflectometer system allow high spatial resolution L$_{r}$ measurement in both low and high density gradient regions. Initial observations is presented, including: (1) In the OH plasma core, L$_{r }$decreases as major radius increases, but inferred radial fluctuation scale length $k_{r}$\textit{$\rho $}$_{s}$ (\textit{$\rho $}$_{s}$ is the ion gyroradius using T$_{e}$ and $k_{r}=2/L_{r}$ for a Gaussian radial correlation length) increases outwards; (2) In the plasma core, $k_{r}$\textit{$\rho $}$_{s}$ of the L-mode, QH-mode, and hybrid steady-state H-mode are comparable, and more than 2-3 times bigger than those in OH plasmas; (3) In both L- and QH-mode core, little change was observed in L$_{r}$ as plasma rotation is varied significantly by NB torque change. Initial results from H-mode edge pedestal will also be presented.