DALTON

The nuclear fusion experiment ITER aims to demonstrate that a tokamak is able to produce 10 times more energy than it needs to run. A tokamak confines, heats and fuses a plasma of hydrogen isotopes (the fusion fuel mixture, D/T) in fusion products (He and neutron). Part of the fusion products (He) and the D/T fusion fuel are exhausted towards the divertor, an assembly of plasma facing components (PFC) made of tungsten (W). For a successful operation of ITER, a detailed understanding of the interaction of W with deuterium (D) and tritium (T) is needed, especially because T is a scarce and radioactive element. W interactions with D/T/He impacts fusion reactors on the long and short time scales. On the long time scale because D/T/He interactions lead to damages in W, a nuclear safety issue. On the short time scale, because the interaction of the D/T fuel with the surface defines the recycling coefficient, a central parameter that translates the fraction of fuel that returns to the plasma after impinging the PFC. Because multi-scale simulations of fusion plasma are computationally expensive, the recycling coefficient is usually considered to be constant. However, recent simulations have shown that, depending on the local edge-plasma conditions, recycling coefficient can vary widely and could drive instabilities such as plasma detachment or/and re-attachment. In the last ten years several laboratory and tokamak experiments have demonstrated that surface processes at W PFC are important, especially in presence of natural or injected impurities. Therefore, it appears that reaching a better understanding of D/T recycling from W in presence of impurities is timely. In the DALTON project, we propose to combine tools and methods from fundamental experimental Physics and theoretical Chemistry to better understand the role of natural (oxygen, O) and injected (nitrogen, N) impurities on recycling of the D/T fuel on W.