Two-dimensional diagnostics of edge and divertor region of toroidal helical plasmas using a lithium beam probe

A two-dimensional neutral lithium beam probe has been designed and installed on the Compact Helical System (CHS) to study the edge and separatrix region of l=2 helical divertor configuration. A 10–20 keV beam with equivalent neutral beam current of 0.1 mA is injected. Light emission from the injected beam by electron impact excitation (LiI/670.8 nm) is collected by an eight-channel detector system using optical band-pass filters and Avalanche Photodiodes. The injection beam line is mechanically tilted to cover the area two-dimensionally. The total system has been calibrated by injecting the beam into the helium-gas-filled CHS vacuum chamber. Detailed measurements of two-dimensional structure of edge and divertor region are expected to contribute to studies of helical divertor concept and to improve understanding of the role of edge plasmas on core confinement as well.