Investigation of Multiscale Turbulence in DIII-D ITER Baseline Discharges*

The role of ion-scale (ITG/TEM) and electron-scale (high-k TEM/ETG) turbulence and their coupling in reactor-relevant conditions has been investigated in DIII-D ITER baseline discharges. Dedicated experiments used localized ECH to stimulate conditions exhibiting cross-scale coupling and a suite of turbulence diagnostics (BES, DBS, PCI) were employed to provide an ideal test bed for understanding cross-scale coupling and for validating gyrokinetic simulation. Changes in profiles which favor cross-scale coupling and possible density fluctuation signatures were documented in the wavenumber spectrum of intermediate-k (k*rho_s ~ 2.5-5.0) fluctuations measured with DBS. Ion, electron, and multiscale gyrokinetic simulations using the CGYRO code were performed using all experimental inputs. Single scale simulations reveal that low-k turbulence cannot explain experimental electron heat fluxes, but that inclusion of high-k will likely resolve this discrepancy. Comparison of simulated and measured spectra, ion and electron heat fluxes, and impurity transport will be presented as part of an ongoing effort to validate the gyrokinetic model and to understand the nature of cross-scale coupling in reactor relevant conditions.