Abstract
The interaction processes between the burning plasma and the first wall in a fusion reactor are diverse: the first wall will be exposed to extreme thermal loads of up to several tens of megawatts per square meter during quasistationary operation, combined with repeated intense thermal shocks (with energy densities of up to several megajoules per square meter and pulse durations on a millisecond time scale). In addition to these thermal loads, the wall will be subjected to bombardment by plasma ions and neutral particles (D, T, and He) and by energetic neutrons with energies up to 14 MeV. Hopefully, ITER will not only demonstrate that thermonuclear fusion of deuterium and tritium is feasible in magnetic confinement regimes; it will also act as a first test device for plasma-facing materials (PFMs) and plasma-facing components (PFCs) under realistic synergistic loading scenarios that cover all the above-mentioned load types. In the absence of an integrated test device, material tests are being performed primarily in specialized facilities that concentrate only on the most essential material properties. New multipurpose test facilities are now available that can also focus on more complex loading scenarios and thus help to minimize the risk of an unexpected material or component failure. Thermonuclear fusion—both with magnetic and with inertial confinement—is making great progress, and the goal of scientific break-even will be reached soon. However, to achieve that end, significant technical problems, particularly in the field of high-temperature and radiation-resistant materials, must be solved. With ITER, the first nuclear reactor that burns a deuterium–tritium plasma with a fusion power gain Q ≥ 10 will start operation in the next decade. To guarantee safe operation of this rather sophisticated fusion device, new PFMs and PFCs that are qualified to withstand the harsh environments in such a tokamak reactor have been developed and are now entering the manufacturing stage.
Highlights
The plasma-facing wall of future thermonuclear fusion reactors with magnetic confinement such as ITER or DEMO must withstand harsh loading scenarios.1,2 The so-called plasma–wall interaction (PWI) processes that are crucial at the interface between the hot plasma and the wall are associated with quasistationary thermal loads up to about 20 MW m−2 combined with short, extremely strong thermal transients up to the gigawatts per square meter range during edgelocalized modes (ELMs).3–6 In addition, irradiation effects resulting from the plasma species and the 14 MeV neutrons have a strong impact on the integrity of the wall armor materials
ITER will demonstrate that thermonuclear fusion of deuterium and tritium is feasible in magnetic confinement regimes; it will act as a first test device for plasma-facing materials (PFMs) and plasma-facing components (PFCs) under realistic synergistic loading scenarios that cover all the above-mentioned load types
The first option consists of flat tiles that have been machined from a PFM and are attached to a water-cooled heat sink made from a metallic alloy with high thermal conductivity and sufficient strength to guarantee the mechanical integrity of the full PFC
Summary
The plasma-facing wall of future thermonuclear fusion reactors with magnetic confinement such as ITER or DEMO must withstand harsh loading scenarios. The so-called plasma–wall interaction (PWI) processes that are crucial at the interface between the hot plasma and the wall are associated with quasistationary thermal loads up to about 20 MW m−2 combined with short, extremely strong thermal transients up to the gigawatts per square meter range during edgelocalized modes (ELMs). In addition, irradiation effects resulting from the plasma species and the 14 MeV neutrons have a strong impact on the integrity of the wall armor materials. The plasma-facing wall of future thermonuclear fusion reactors with magnetic confinement such as ITER or DEMO must withstand harsh loading scenarios.. Depending on the selected fiber type and architecture, carbon-fiber reinforced graphite can be manufactured with thermal conductivities equal to or even better than that of copper (up to about 400 W m−1 K−1). Such an excellent thermal conductivity will degrade rapidly under the influence of energetic neutrons. In D-T-burning fusion reactors with carbon walls, tritiumcontaining hydrocarbon deposits are formed on all in-vessel components This will result in an inacceptable tritium inventory in the fusion reactor under current licensing laws and limits. The loading conditions in both scenarios are similar (especially with regard to hydrogen, helium, and neutron loads); transient thermal loads differ greatly depending on the selected ICF concept and the operational situation.
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