'Natural' divertor- and limiter-discharges in Heliotron E

A comparative study on edge plasma properties between the original 'natural' divertor configuration and the material limiter configuration was performed for Heliotron E currentless plasma. By insertion of a carbon rail limiter, the particle and heat fluxes to the divertor footprint were reduced to 20-50% of that in the divertor configuration. Such a reduction of influx resulted in the decrease of metal impurities sputtered from the wall surface. There were no clear differences in the edge density and heat flux profiles for NBI plasma between the limiter and divertor scrape-off. In the limiter configuration, a highly heat loaded area was observed locally on only one side of the limiter head. A perturbation field affected this local heat load. (orig.)