On ablation of large Tungsten dust grains in edge plasma of fusion devices

Highlights: • We developed the model describing vapor shielding effects for W dust in plasmas. • Model shows reduction of evaporation rate of the grain in 10 times. • This model can also be applied for other high-Z grain material. - Abstract: The model describing vapor induced shielding effects for W dust grain evaporation in the edge plasmas is considered. It is shown that unlike the case of pellet ablation models, where it is assumed that the heat flux to pellet is due to free streaming electrons, the heat flux to W grain in edge plasma is due to electron heat conduction. By using some reasonable simplifications, tractable equations for the evaporation rate of the grain are obtained. Approximate analytical analysis of these equations, supported by numerical solutions, shows that the vapor induced screening effects can reduce the evaporation rate of the grain in edge plasmas by an order of magnitude. This model can also be applied for other high-Z grain materials (e.g. Mo)