Measurements of the Wavenumber Spectrum of Multi-scale Turbulence in the Core of DIII-D H-mode Plasmas*

The wavenumber spectrum and spectral index of multi-scale turbulence $(0.5 \leq k_\theta \rho_s \leq 6)$ in the core of L- and H-mode DIII-D plasmas have been determined by Doppler Backscattering (DBS). A comparison is made to quasi-linear spectra from the trapped gyro-Landau fluid code (TGLF) to assess the contributions of ITG and TEM/ETG turbulence to transport fluxes $(0.4 \leq r/a \leq 0.8)$. Initial results of comparisons to spectra calculated via nonlinear gyrokinetic (GYRO) simulations are also presented. In high temperature, low density plasmas, ITG-scale and intermediate-scale core turbulence is found reduced by at least an order of magnitude across the L- to H-mode transition $(T_i/T_e \geq 2)$. This reduction is attributed to the combined effects of reduced turbulence drive and increased core $E\times B$ flow shear in H-mode.