Reduction of Core Turbulence in I-mode Plasmas at Alcator C-Mod

Core turbulent fluctuations (0.40 \textless\ r/a \textless\ 0.95) are reduced in the high confinement regime, I-mode, at Alcator C-Mod. Long wavelength density fluctuation levels are observed to decrease from L-mode levels by up to 30{\%}, while long wavelength electron temperature fluctuation levels are observed to decrease by up to 70{\%}. This reduction in core turbulence is correlated with the increases in confinement in I-mode. During some L-I transitions, density fluctuations in the core (r/a $\sim$ 0.5) and near the top of the Te pedestal (r/a $\sim$ 0.95) are both reduced prior to the reduction of low-frequency edge turbulence (r/a $\sim$ 0.99-1.0), and prior to the onset of the edge-localized weakly coherent mode (WCM) (r/a $\sim$ 0.99-1.0). This result contrasts typical observations of confinement transitions (I-mode and H-mode) where changes in edge turbulence occur prior to changes in core turbulence