Investigation of Carbon Films on Material Probes in the Vicinity of Local Island Divertor in the Large Helical Device

Abstract

Two sets of material probes were installed in LHD in the vicinity of the Local Island Divertor (LID) head made of carbon fiber composite. One set of the material probes faced the LID head, while the other set was placed in a shallow line of sight to the head. Carbon films on the former and the later sets of probes are expected to be formed by the deposition of physically sputtered carbon atoms and chemically sputtered hydrocarbon, respectively, during the LID discharges. Surface morphology and thickness of the films, and the amount of retained hydrogen in the films were investigated, and hydrogen concentration in the probes was estimated. The hydrogen concentration in the carbon films on the probes placed in a shallow line of sight of the head was significantly large with the atomic ratio of H/C = 0.6-1.1.