Preliminary results of density turbulence measurements using fast sweep reflectometry in DIII-D

Recently, the capability of the state-of-the-art density profile reflectometer on DIII-D has been expanded to determine the radial profile of electron density fluctuations. Measurement of reflectometer phase fluctuations (f ≤ ~5 MHz) associated with O-mode launch during fast RF frequency sweep operation, has allowed both the wavenumber spectrum and radial profile of n_e fluctuations to be analytically derived. The analyzed radial wavenumber range is from ~1.2 cm^-1 to ~10 cm^-1, which is limited by Bragg scattering condition. Preliminary results show that L-mode turbulence levels are small (δn/n ~ 1%) in the core (ρ < 0.6) when the normalized n_e and T_e gradients are small. However, as the gradients steadily increase with radius (ρ > 0.6), turbulence levels also steadily increase. The comparison with n_e fluctuation measurements such as BES and DBS in various plasma conditions will be presented. Further investigation of this analysis will be also presented.