In-vessel inspection of arc traces on the W7-X plasma facing components after the operation phase OP2.1

Updated distribution of arc traces across the interior walls after the operation phase 2.1 of Wendelstein 7-X (W7-X) is reported. A total of 105 new arc places were found, with 95% of them located around the stainless steel panels, diagnostic ports, and the glow discharge cleaning electrodes. Remaining 5% of the traces were found on carbon surfaces such as the graphite baffle and carbon fiber-reinforced composites divertor tiles, for the first time in W7-X. The arcing on the divertor tiles showed a retrograde motion, suggesting that the arcing must have occurred during the main plasma operations. A simple estimate of the mass loss due to arcing on the divertor area shows that ∼ 0.2-0.3 g of carbon was eroded during OP2.1. This amount turns out to be a significantly smaller amount compared to the estimated losses due to sputtering, ∼ 7.6 g/1800 s during OP1.2b (Brezinsek et al., 2021). • After the operation phase 2.1 (OP2.1) of W7-X, 105 arc places are newly recognized. • 95% of the traces are formed on non-carbon areas. • 5% recorded on carbon include linear arc traces that occurred during main operations. • Erosion of the divertor by arcing would be negligible compared to that by sputtering.