Study of SOL/Divertor Plasmas in JFT-2M

Abstract

Experimental efforts on JFT-2M have been devoted to understanding the scrape-off-layer (SOL)/divertor plasmas and to investigating power and particle control by boundary plasma modification. Starting in 1985, an open divertor configuration was adopted for the first decade of the JFT-2M experiments. The characteristics of SOL/divertor plasmas such as in/out asymmetry for divertor plasmas, heat and particle diffusivities, and SOL current during an edge-localized-mode event were identified. The power and particle flux was successfully handled by active control methods such as local pumping, boundary plasma ergodization, divertor biasing, electron cyclotron wave edge heating, and fueling optimization. In 1995, to improve the power and particle control capability of the divertor, the JFT-2M divertor was modified to have a closed configuration, which demonstrated the baffling effects with its narrower divertor throat. A dense and cold divertor state (nediv = 4 × 1019 m-3 and Tediv = 4 eV), compatible with improved confinement modes (e.g., H-mode), was realized with strong gas puffing in a closed configuration. Edge plasma fluctuations related to the H-mode physics were identified by an electrostatic probe and magnetic measurements. These are reviewed in this paper.