A new design concept of actively cooled plasma-facing units for the divertors of fusion reactors

•A new design concept for tokamak divertor plasma-facing units eliminates sharp edges and optical hot spots.•The thermal performance is not worse than that of ITER divertor monoblocks under equivalent inter-ELM plasma irradiation.•The design performs much better against ELMs than the present ITER design.•The design is insensitive to assembly tolerances, which could mean important savings in cost and complexity. This paper sketches a new divertor design concept that solves most of the issues already identified with the actual ITER design, especially in what concerns transient heat loading. It resists ELM heat loads better than the present ITER design. This alternative design, consisting of tubes running approximately along the magnetic field direction, simultaneously eliminates sharp toroidal edges of tungsten monoblocks that will melt, and optical hot spots that could melt or vaporize in ITER if ELMs are present. Steady state, inter-ELM divertor surface temperatures will not be higher than in ITER for identical plasma irradiation conditions. The design is just as resilient as ITER’s with respect to critical heat flux in the cooling tubes. Knowing that simple tubes might not be appropriate for a divertor design in a fusion reactor, we also discuss the possibility of bonding conical tungsten “beads” to the cooling tubes. The expected differences between the simple tube model and the one with tungsten beads will be discussed.