Neoclassical effect on strike point patterns in local island divertor configuration of LHD

Abstract

Monte Carlo simulation based on test particle representation is carried out in order to investigate the neoclassical effect on a strike point pattern of ions on the local island divertor (LID) head in the Large Helical Device configuration. According to collisionality, the particle orbits mainly contributing the particle flux from the core region to the LID head vary; in the present paper we call it the neoclassical effect on the edge transport phenomena. The pattern on the LID head is numerically observed by tracing the guiding centre orbits of the test particles under the effects of Coulomb collision and anomalous diffusion. We find that the strike point patterns on the LID head are varied according to collisionality. For the case of λmfp/Lc > 1, the pattern is characterized by the passing particle orbits along the field lines of the island separatrix, where λmfp is the mean free path and Lc ≈ 250 m is the connection length given as a length along a field line connecting the core region to the LID head. On the other hand, for the case of λmfp/Lc ≪ 1, the particles intensively strike the edge of the LID head, and the pattern is given by the trapped particle orbits. The trapped particle orbits mainly contribute the particle flux from the core region through the inside of the island, and finally the particles arrive at the edge of the LID head.