X-ray Fluorescence analysis of global tungsten transport inside DIII-D tokamak during tungsten-coated, V-shaped Small Angle Slot divertor campaign*

After the DIII-D Small Angle Slot, V-shaped, W-clad divertor (SAS-VW) campaign, tungsten (W) deposition (<10 nm) was measured on tiles outside of the divertor. Handheld X-ray fluorescence (XRF) analyzers were used to quantify the tungsten and other metallic species, that sputter or melt off of surface tiles and structural materials. XRF has been used to identify alloys, detect trace impurities (ppm), determine coating thicknesses, and other applications requiring bulk analysis. Post-campaign measurements were taken at various different toroidal and poloidal locations (including those just outside of SAS-VW) and compared with pre-campaign calibrations. Although low W deposition outside of the divertor was observed, larger W deposition ratios in relation to iron (Fe) and nickel (Ni) were evaluated at the uppermost and bottommost center post tiles. Grinding paper proved successful in removing all measurable tungsten and the majority of Fe and Ni from exposed tiles. Laser-based coordinate measuring machine (CMM) data was used to assess tile-to-tile misalignment based on post-mortem observations of large W erosion on tile edges. CMM data was also used to investigate tungsten deposition from the W-clad divertor tile to nearby V-tiles.