Speaker
Description
A major issue for next step devices is the control of plasma wall interaction, both for keeping the material erosion compatible sufficient lifetime of the components as well as for mitigating core contamination by high Z impurities and consequently the reduction of plasma performances. In this respect, WEST experiments supported by numerical modeling are particularly relevant to progress in the physical understanding of the complex interplay between erosion patterns, impurity migration and efficiency of plasma screening. In this contribution we will present modeling and experimental results concerning deuterium high-fluence experimental campaign which was conducted in the WEST tokamak. In 2023, the ITER-grade actively-cooled divertor has been exposed to ITER-relevant (1.0 x 1027 part.m-2) particle fluences by repeating the same attached plasma scenario (divertor Te ~ 20 eV), with a total cumulated plasma time of 10790 s. Impurities sources have been monitored by visible spectroscopy, showing high content of boron and carbon all along the campaign especially on the high-field side where deposited layers are observed. Using visible spectroscopy data (for WI 4009 Å radiance) and flush-mounted Langmuir probe measurements (to obtain ne and Te dependent local S/XB coefficients) one can estimate tungsten gross erosion flux up to 1.5 × 1019 part.m−2.s−1, leading to around 0.7 μm of net erosion near the outer strike point, assuming the high fluence campaign plasma time and relatively low 75% prompt redeposition rates. These estimations are in contrast with recent results from post-mortem analysis indicating higher values (around 7 μm of net erosion on the inner strike point) after both, foregoing and high-fluence campaign. To investigate the observed erosion and redeposition patterns, several background plasma models have been simulated with SOLEDGE3X-EIRENE, constrained by experimental measurements, with and without the inclusion of drifts. Plasma backgrounds are simulated with proxy light impurity (O) with various concentrations (1 to 3%) to match experimental conditions (particle flux and electron temperature at the edge). The impact of drifts is important to reproduce flux asymmetries between inner and outer sides and target plasma parameters. W erosion and migration is then computed with ERO2.0 using such plasma backgrounds. The simulated erosion depth at both strike-points is barely the same with and without drifts and for each used oxygen concentration (around 4 to 9 µm), consistently with post-mortem measurements. The far inner redeposition area is observed only when background plasma models are computed with drifts are taken into account.