Modelling fuel retention in the W divertor during the D/H/D changeover experiment in WEST

A fuelling changeover experiment from Deuterium (D) to Hydrogen (H), and back has been performed in WEST to study the retention and removal in metallic devices with actively cooled ITER-grade tungsten divertor. The present study reports trapping-diffusion modelling of H and D in the W divertor during this session. In this model approach, the divertor is represented by multiple (radially distributed) 1D simulations. The plasma exposure conditions are calculated with soledge3x-eirene , delivering the heat and particle flux for each of the divertor bins. The material model is parametrized by reproducing a thermal desorption spectrometry experiment and an isotope exchange experiment on polycristalline tungsten. The simulated outgassing flux during the post-pulse phase of the changeover pulses are converted to H 2 , HD and D 2 partial pressure in the WEST vacuum vessel. The calculated pressure is one order of magnitude below the experimental one as only the contribution from the divertor is taken into account in this analysis. An additional source of H 2 outgassing should be taken into account to recover the dynamics of the H 2 partial pressure, especially during D plasma phases. However, the dynamics of HD and D 2 pressure drop is similar in the simulations and experiments. Finally, the analysis of the divertor H/D inventory shows that the isotope exchange is efficient near the plasma exposed surface but is limited by the D/H migration towards the bulk. • Calculating a plasma background for the D/H/D changeover experiment in WEST. • Parametrization of the W wall model by simulating TDS and isotope exchange experiment. • Simulating H/D retention and outgassing from the W ITER-like WEST divertor. • Simulating the inter-pulses pressure drop and comparing with the experimental data