Edge-localized modes (ELMs) produce an intense transient heat flux on castellated divertor mono-blocks (MBs). The parallel transport of electrons and ions from the ELM burst varies due to their different velocities, which significantly influences the power load on the MBs. This study shows that two heat load phases are caused by an ELM burst. In the first phase, the horizontal surface withstands the intense heat flux because the faster electrons generate a high sheath potential drop. The leading edge of the MBs suffers a great power load from energetic ions in the second phase. This study applies a multiscale hybrid numerical approach to investigate the temporal evolution of heat flux on the poloidal gap from the ELM source in the scrape-off layer to the castellated divertor surface. Our results indicate that the power load on both the MB surface and the leading edge should be considered in the future design of castellated divertors.
Findings of pre-ELM structures through the observation of divertor heat load patterns at JET with applied n = 2 perturbation fields