The development of systems for removing the heat produced by the plasma represents a challenge in terms of the choice and implementation of the materials used.
When a plasma is maintained for long periods, the components facing it have to dissipate very large quantities of heat. If it were possible to standardise the heat flux incident on the walls facing the plasma of a fusion reactor, this flux would be of the order of 0.5 MW/m2. In other words, a flux level close to that of the fuel assemblies in an EPR-type fission reactor. In fact, in fusion machines, it is impossible to distribute the power evacuated by the plasma uniformly over the entire surface of the torus walls. The zone of interaction between the plasma and the wall is therefore much smaller than the total surface area of the wall. The heat flux in the contact zone can therefore reach 10 to 20 MW/m2, i.e. around a quarter of the heat flux present at the surface of the Sun.µ
Located on the “floor” of the vacuum chamber, the ITER divertor must fulfil this function. The choice of surface material for the divertor is therefore crucial: only a very few materials are capable of providing the conditions for heat conductivity and withstanding the stresses and high temperatures, for the twenty years that ITER is expected to be in operation. These materials do exist, but they still need to be qualified and characterised in an operating tokamak environment, particularly with a view to their use on ITER.
This is the aim of the WEST support programme run by the CEA on its tokamak.
