The L- to H-mode transition and momentum confinement in Alcator C-Mod plasmas

Abstract

Using a spatially-resolving x-ray spectrometer system, toroidal impurity rotation in Alcator C-Mod plasmas was measured. The propagation of the rotational velocity from the edge to the core of the plasma column was measured during the L- to H-mode transition. Momentum transport was measured in both Ohmic and ICRF-heated discharges, which produced EDA and ELM-free H-modes. The momentum transport was modeled by a simplified diffusion model, in which momentum diffusivity was substantially higher than neoclassically predicted values.