Core Turbulence and Transport Dependence on Isotope Mass in Dimensionally Similar H-Mode Plasmas on DIII-D

The global energy confinement time is approximately 80% higher in low-rotation H-mode Deuterium (D) plasmas compared with dimensionally similar Hydrogen (H) plasmas, indicating an isotopic dependence that significantly exceeds that in the empirical scaling relation, τ_E~M^0.19. Correspondingly, both electron and ion thermal diffusivity are nearly twice as high in H than D across much of the radius. Long-wavelength (ion-gyroscale) turbulence characteristic differences may partially explain the large transport differences. Spatiotemporal measurements of long-wavelength density fluctuations obtained with BES demonstrate the surprising result that the turbulence amplitude is lower in H than in D plasmas, in contrast to the higher transport, however other characteristics are consistent with higher transport. The turbulence radial correlation lengths are larger in the H-plasma (2.5 cm) compared to D (1.5 cm), consistent with larger turbulent step size, and the H and D wavenumber spectra differ, suggesting different turbulence modes. Comparisons with gyrokinetic simulations will be performed to identify underlying mechanisms for the isotope dependence, and implications for D-T plasmas in ITER.