Situated at the bottom of the vacuum vessel, the divertor extracts heat and ash produced by the fusion reaction, minimizes plasma contamination, and protects the surrounding walls from thermal and neutronic loads.
Each of the divertor's 54 "cassette assemblies" has a supporting structure in stainless steel and three plasma-facing components: the inner and outer vertical targets and the dome. The cassette assemblies also host a number of diagnostic components for plasma control and physics evaluation and optimization.
The inner and outer vertical targets are positioned at the intersection of magnetic field lines where particle bombardment will be particularly intense in ITER. As the high-energy plasma particles strike the vertical targets, their kinetic energy is transformed into heat and the heat is removed by active water cooling.
The heat flux sustained by the ITER divertor vertical targets is estimated at 10 MWm² (steady state) and 20 MWm² (slow transients). Tungsten, with the highest melting point of all the metals, has been chosen as the armour material following an international R&D effort, encouraging experimental results, and successful prototype testing.
The fifty four 10-tonne cassette assemblies of the ITER divertor will be installed—and also replaced at least once during the machine's lifetime—by sophisticated remote handling techniques.