LOCAL ISLAND DIVERTOR EXPERIMENTS ON CHS

A local island divertor (LLD) was installed on the Compact Helical Sys tem (CHS) to demonstrate the principle of LLD and to study its effects on the edge plasma. The particle flow was observed to be guided to th e back side of the externally created magnetic island along field line s, and pumped out by a cryogenic pump with high pumping efficiency. As a result, a factor of about 2 reduction in the average core density w as seen compared with non-LID discharges at the same gas puff rate. In addition to the demonstration of these fundamental divertor functions , we observed a modest improvement of energy confinement, which could be due to the edge plasma control by the local island divertor.