Reduction of core turbulence in I-mode plasmas in Alcator C-Mod

In this paper, we report observations of reduced core (0.40<ρ<0. 95) fluctuations in the edge localized mode (ELM)-free high-confinement regime, I-mode, at Alcator C-Mod (Marmar et al2009 Nucl. Fusion 49 104014). Long wavelength (kθρs<0.5) density fluctuation levels are observed to decrease from L-mode levels by up to 30% in I-mode, while long wavelength (kθρs<0.3) electron temperature fluctuation levels are observed to decrease by up to 70% in I-mode. This reduction in core turbulence is correlated with the increases in confinement in I-mode compared to L-mode. As the pedestal temperature increases across the L-I transition, core density fluctuations (0.40<ρ