Study of a Closed Divertor Configuration for the Three-Dimensionally Complicated Magnetic Structure in the LHD Plasma Periphery

The distribution of strike points in a closed divertor configuration with additional baffle plates installed in the toroidal ends of closed divertor components near lower/upper ports is calculated by tracing magnetic field lines from the last closed flux surface in various magnetic configurations (radial position of the magnetic axis, Rax = 3.50 ∼ 3.90 m). The calculation shows that the ratio of the number of strike points on additional plates is maximum for Rax = 3.60 m, showing that the plates are effective in this magnetic configuration. Neutral particle transport is investigated using a fully three-dimensional code EIRENE with one-dimensional plasma fluid analysis of divertor legs, where the plasma parameter profiles on the legs are obtained by an iterative calculation including interaction processes between the plasma and neutral particles. The plates raise the pressure of molecular hydrogen locally near the baffle plates to more than 0.2 Pa, which is enough for efficient particle control using vacuum pumping systems installed near the plates. The simulation proposes one possible candidate of optimized closed divertor configuration for the three-dimensionally complicated magnetic structure in the LHD plasma periphery.