Plasma-facing materials and first wall

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The first wall and divertor are the surfaces that face the plasma directly, and they must survive heat fluxes comparable to a rocket nozzle while being bombarded by 14.1 MeV neutrons that displace atoms in the lattice and transmute the material itself. Damage is measured in displacements per atom; published assessments put a power-plant first wall in the range of tens of dpa per operating period, with damage rates above roughly 15 dpa per year under power-plant conditions. ITER's updated 2024 baseline changed the first wall material from beryllium to tungsten, a decision driven by plasma-facing performance and licensing considerations rather than by any experimental failure of beryllium. No material has yet been qualified at power-plant neutron fluence, because no facility has produced that fluence: dedicated fusion-spectrum irradiation sources such as IFMIF-DONES are intended to fill the gap and are not yet delivering high-dose data. This is the least glamorous and possibly the most binding of the engineering gaps.

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