LHD Helical Divertor and lts Performance in the First Experiments

Full toroidal divertor has been installed and used in the third campaign of the LHD experiments. The divertor has a three dimensional helical structure with carbon target plates. An element consists of a graphite armor tile and a copper heat sink, which is mechanically fixed to a stainless steel (SS) cooling tube. It is actively cooled by pressurized water. After installation, significant decrease has been observed for iron impurity radiations and bolometric radiation in the central region, which indicates that the plasma wall interaction is dominated at the divertor region. Effect of active cooling has been verified during a long pulse discharge. Neutral gas pressure at the divertor region is as low as 4 x 10-3 Pa during a long pulse NBI discharge, which suggests that careful design of a closed divertor is necessary in future to realize a good particle control capability.