Vapor Shielding Effect on DEMO Divertor

The impact of the edge-localized modes (ELMs) on the tungsten divertor erosion by taking into account the screening effect of vapor shielding is analyzed for DEMO steady-state operation condition. The evaluation of tungsten ablation, energy radiation, and absorption by divertor plate due to a single ELM impact is calculated by using a model of vapor shielding inserted in the MEMOS code. The effect of repetitive ELM impact and the tungsten melt layer formation is described by using the model of W monoblock with a compliance layer of Cu alloy between the W and EUROFER water cooling tube.

It is shown that the vapor plasma shielding results in saturation of the single ELM energy accumulated by the divertor plate and that the saturation level depends on the ELM duration. The ablation thickness can reach about 0.01 µm. The total number of ablated particles is rather critical for the shielding formation, and the lifetime of the divertor plate depends strongly on this effect.