Turbulence wavenumber spectra and comparisons to theory using an optimized Doppler backscattering system in DIII-D*

Measurement of turbulent wavenumber spectra provides a tool to both characterize the plasma turbulence as well as test simulations and theory. The recently validated UCLA Doppler backscattering (DBS) system enables previously inaccessible measurements (for DBS on DIII-D) of higher wavenumber density fluctuations associated with turbulent transport. DBS as a plasma diagnostic measures wavenumber-resolved density turbulence fluctuation levels, ñ, localized E×B velocity, radial electric field, and plasma flows. The new DBS system has demonstrated measurements of k_ñ up to 20 cm^-1 or k_ñρ_s ≤ 10. This wavenumber range is relevant to a broad range of instabilities of interest including KBM, ITG, MTM, TEM, and ETG. The measurement locations are in the radial range ρ = 0.5–1.0. These measurements produce spectral shapes (power vs fluctuation frequency) that, when obtained as a function of the wavenumber, allow us to characterize the potential turbulence instability modes. These experimental measurements can be further investigated and compared with the theoretical predictions from linear and/or non-linear simulation codes.