Engineering estimates of impurity fluxes on the ITER port plugs

Abstract

Predictions of impurity fluxes are required for design analysis of the ITER optical diagnostics. In the present paper a simplified model is proposed for calculation of the neutral impurity fluxes on the recessed surfaces which are not in direct contact with plasma. The method is based on the Monte-Carlo simulation of the neutral particles transport in prescribed and fixed plasma background. The plasma parameters are projected from experimental observations, scalings and ITER modelling results. Blobs are approximated as stationary hot species. Results of 2D simulations with toroidally uniform wall and of the ‘2.5D model’ are presented. In this latter the 3D geometry of ports is implemented, but details of the incident ion flux distribution on the first wall panels are neglected. The calculated worst case gross deposition rate of Be in the middle of the port plug faces reaches almost 0.1 nm s−1. At the same time, the obtained Be erosion to deposition ratio at those locations is always larger than 5, indicating high probability of net erosion conditions there.