In Vessel Material Migration Study using Toroidal Probe Array in LHD

Abstract

In order to study migration of sputtered materials and profiles of their re-deposition in the Large Helical Device (LHD), material probes fixed with Si specimens were installed on the private region of the torus outer first-wall in all toroidal sections (10 sections) in the experimental campaign in 2011. The material probes fixed with the Si specimens were exposed to various wall conditionings such as glow discharges cleanings (GDCs), boronization, Ti sublimation and main plasma discharges. After the campaign, the specimens surfaces were investigated with visual observation, Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). A type of visual deposition (band) pattern has been observed on the probes at almost all toroidal sections of LHD. The analysis of these patterns on the material probes informs the source and direction of material migration inside the LHD vacuum vessel. The observation and result of the experiment have been presented in this paper.