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Description
ERO2.0 simulations of the limiter phase in the JET ITER-like wall (JET-ILW) predict nickel to erode primarily from the low-field side (LFS) midplane of the inconel 625 vacuum vessel wall due to charge-exchange neutrals. Inconel is a nickel alloy, mixed with iron and chromium. The sputtered nickel ionizes mostly in the LFS scrape-off layer and is transported by the plasma flows towards the contact point between plasma and beryllium limiters, depositing onto the limiter surfaces. Nickel is observed in post-mortem analysis of the divertor tiles [1]. Previous studies on nickel migration in the JET-ILW focus on the diverted phase of the plasma, with typical distances of 6cm from the limiter apex and 45cm from the inconel wall, neglecting the limiter phase despite the considerable time accumulated during plasma startups and shutdowns [2].
Nickel deposition into the divertor is negligible in comparison with the diverted phase, consistent with previous Be migration studies in limiter plasmas [3], during the 2011-2016 JET-ILW campaigns, with the high-field side (HFS) limited plasma adding nickel to the primarily Be deposit layer on the order of 1e17/cm² on tile 1. In the LFS limited plasma the nickel content is predicted to be 4e17/cm² on tile 1. Deposition into the divertor peaks on tile 10, where in the HFS limited plasma the deposition of nickel is on the order of 3e17/cm² and 1-2e18/cm² in the LFS limited plasma. The erosion rates for nickel in HFS and LFS limited scenarios are 8.4e19/s and 1.9e20/s respectively. The limiter configuration erosion rates are comparable to the lower end of the predicted rates in diverted plasmas [2].
Two limiter plasmas, representative of the 2011-2016 campaigns, are investigated using SOLPS-ITER, one limited by the HFS limiters and the other by the LFS limiters. SOLPS-ITER replicates the radial electron density profile as observed in experiments in both HFS and LFS limited plasmas. For the HFS limited plasma, SOLPS-ITER simulations match Te measurements from the core up to the last 3-4 cm from the radially outer edge of the grid, where Te is underpredicted by an order of magnitude. Te measurements for the LFS limited plasma are only available near the grid edge. Te at the closest measurement to the separatrix is 1.5x the predicted value.
[1] A. Widdowson et al., Nucl. Mater. Energy, 19:218, 2019
[2] P. Virtanen et al., Nucl. Mater. Energy, 42:101864, 2025
[3] S. Brezinsek et al., Nucl. Fusion, 55:063021, 2015