Poloidal Distribution Measurement of Inward Neutral Flux in LHD

Abstract

Three emission lines of neutral helium, i.e., the λ 667.8 nm (2¹P-3¹D), λ 728.1 nm (2¹P-3¹S), and λ 706.5 nm (2³P-3³S) lines, are observed with an array of parallel lines-of-sight which covers an entire poloidal cross section of the plasma in the Large Helical Device (LHD). Their emission locations and intensities are determined from the Zeeman profiles. The electron temperature and density are evaluated from intensity ratios among the observed emission lines at each emission location and the poloidal distribution of ionization flux or its equivalent quantity, inward neutral particle flux, is derived with the help of collisional-radiative model calculations. A relatively strong neutral flux is observed at the inboard-side X-point and this result implies a high particle recycling in the inboardside divertor region. The result is consistent with the ion flux distribution onto the helically located divertor plates measured with Langmuir probes.