Erosion and redeposition pattern on the W7-X graphite test divertor unit tile

A set of plasma-facing components was retrieved f􀂘om the W7-X vessel afcer OPl.2b campaign with an inertially cooled Test Divertor Unit (TDU) and analyzed postmortem to provide data on the plasma-surface interactions processes in the complex device geometry. In ehe present study, the lower TDU horizontal target (HT) graphite tile HMl 9TM400hTE2 exposed to the plasma du ring both OP 1.2 campaigns was examined. The surface modification of the material caused by the plasma-wall interactions was determined. The study employed several microscopy mcthods including SEM, FIB, STEM, TEM, EDX, and optical profilomecry which showed that (i) distinct erosion zone was located at the inner HT strike line position, (ii) the area covered by a pronounced deposit was located adjacent the erosion zone, (iii) the target finger substructures positioned close to the outboard side was unaltered, and (iv) significant changes to surface roughness values along the length of the plate occurred.