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

•Information on the surface changes of the divertor tile from target module 4 h.•Comparison to the distributions generated for the special target elements.•Determination of changes in the surface roughness along the length of the tile. A set of plasma-facing components was retrieved from the W7-X vessel after OP1.2b 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 the present study, the lower TDU horizontal target (HT) graphite tile HM19TM400hTE2 exposed to the plasma during 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 methods including SEM, FIB, STEM, TEM, EDX, and optical profilometry 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.