New ITER divertor design using carbon insert on the tungsten plate to mitigate ELMs and secondary radiation effects on nearby components.

Significant heat loads are expected during ELMs on divertor plate in ITER and future tokamaks normal operation. Such high power loads at the strike point (SP) can cause surface vaporization, ionization, and development of secondary plasma from the divertor materials. The secondary plasma converts and redistributes the incident core plasma energy into intense photon radiation and scattered core particle fluxes from this dense secondary plasma (more than 3 orders of magnitude denser than the core plasma). In this study, we compared the power load redistribution on nearby components for two divertor designs: current ITER design with tungsten divertor (high-Z case) and tungsten divertor with carbon insert at the SP (low-Z case). We simulated the divertor response during ELMs using our integrated HEIGHTS 3D package. These include self-consistent modeling of the interaction of incoming core plasma particles with the initial solid divertor material, energy deposition processes, MHD of secondary plasma evolution, incident core particles collisions and scattering from the dense secondary plasma, secondary plasma photon radiation, and the resulting heat loads on nearby components. Our simulations showed that carbon insert at the SP can significantly reduce the overall expected damage on W dome structure, reflector plates, and prevent W vaporization and potential core plasma contamination.