Modeling of sources and transport of impurity ions and their interaction with material surfaces in powder-dropping experiments*

In powder-dropping experiments, a stream of dust particles containing boron nitride, pure boron, or other materials is continuously injected into tokamak edge plasma [1]. This is potentially a powerful tool for real-time wall conditioning and edge plasma radiation control. We are undertaking modeling of impurity particles dynamics and their interaction with plasma facing material surfaces in powder-dropping experiments as a sequence of several processes. First, to capture dynamics of injected dust particles, the DUSTT code is used, which allows modeling of physical processes for individual dust grains, including ablation. As dust particles are ablated, they produce a localized impurity ion source; impurity ion transport is modeled with the UEDGE code solving fluid equations for impurity ions and the background plasma. Interaction of plasma and impurity ions with material surfaces is modeled with the F-TRIDYN code which follows evolution of surface morphology. For boron powder injection, of particular interest is the thickness of the steady state layer of boron atoms on the surface, which is the result of dynamic balancing between deposition and sputtering. [1] Bortolon et al., to be submitted to Nucl. Mater. & Energy.