Elemental analysis of divertor marker tiles exposed during the 2018 (C3), 2019 (C4) and 2020 (C5) WEST campaigns

Erosion marker tiles mounted in the lower divertor of WEST were exposed during Phase 1 of plasma operations to evaluate poloidal erosion and re-deposition profiles on the tiles. Previous analyses performed to the exposed tiles have shown distinct erosion- or deposition-dominated patterns on them. Afterwards, core-drilled disks cut from the tiles were sent to different laboratories for further and detailed analysis. The present work relates the main results achieved from five characteristic regions of the tiles after completion of the C3, C4, and C5 experimental campaigns on WEST. SIMS and complementary IBA measurements were carried out and the corresponding elemental depth profiles strongly agree, confirming the main earlier conclusions. Deposits are composed of 2H, B, C, O, Mo and W, mainly. Low amounts of Cr, Fe, Ni and Cu were identified as additional metallic impurities. The research confirmed the locations of thin deposition zones nearby the inner and outer divertor limits: at the inner region, the deposition of B and C is particularly enhanced after C4 and C5. Strong erosion zones are located at the inner and outer strike point (ISP and OSP, respectively) areas: only a small erosion occurred after C3, which evolved after C4; nevertheless, the deposition of B and C is enhanced at the OSP edge after C5 nearby the thin deposition zone. Thick deposits appear in the neighborhood of ISP, towards the high field side, and evolve significantly after C4. The amount of O follows the deposition of B. Low retained amounts of 2H were quantified.