Modelling of plasma and its wall interaction for long-term tokamak operation

Metal plasma-facing materials (PFMs) are expected to be candidates for future fusion power plants from the view point of tritium retention. The purpose of this study is to develop a model including a long timescale plasma interaction with metal PFMs. As a first step, we have developed a simple zero-dimensional (0D) model, which consists of particle balance equations for the following three different particle species: (a) hydrogen plasma (elec., H⁺, H⁺ ₂ , H⁺ ₃), (b) neutral hydrogen atoms (H) and molecules (H₂) in the gas phase, and (c) the wall-stored H atoms. The model has been applied to simulate long-term operation in the limiter configuration of the QUEST tokamak. Modelling results of the long time evolution of the H atom wall inventory reasonably reproduce the experimental tendency. Although the present model is relatively simple, it is useful to understand the basic characteristics of overall plasma particle balance, the density control of the main plasma, and the H atom wall inventory for long-term tokamak operation.