Materials and Plasma Facing Components for Thermonuclear Fusion Applications

Thermonuclear fusion is one of the options being considered for producing large-scale carbon-free energy in the future. The design of fusion devices requires cutting-edge technological advancements in many fields. This article provides an overview of the engineering of components responsible for dissipating the energy generated in fusion devices. For fusion reactions to occur, the fuel (hydrogen isotopes) must be heated to a temperature of tens of millions of degrees, at which the matter is in a plasma state. The core of fusion devices consists of a vacuum chamber in the center of which the plasma is confined. This confinement is achieved by magnetic fields in the most advanced configurations currently in use, such as tokamaks or stellarators. The components making up the chamber, known as plasma-facing components, must dissipate the power generated at the heart of the plasma, whether it comes from plasma heating systems or from the fusion reactions themselves. Plasma-facing components must therefore be actively cooled by a pressurized coolant. They consist of a plasma-facing material assembled onto a “heat sink” material in contact with the coolant. This article will focus on a key component, the divertor, which concentrates the highest thermal loads in the vacuum chamber. In the first section, the operating conditions of plasma-facing components—which make their design a major challenge for next-generation fusion machines—are described: operation under vacuum (10 ^–6 Pa) and intense magnetic fields (several teslas), high heat fluxes to be removed (up to 10–20 MW/m ² ), extreme surface temperatures (> 1,000 °C locally), intensive cycling, interactions with plasma particles…Few materials are capable of withstanding these constraints. They are reviewed along with their strengths and weaknesses, particularly with regard to tungsten, a material currently considered the most promising for applications in future fusion reactors. The main concepts for plasma-facing components are then presented, along with the design rules to be followed. Their use in fusion machines is put into perspective, allowing for an assessment of the progress made from the first generations of components in the 1980s to the components currently being designed for ITER, an international project aimed at demonstrating the scientific and technological feasibility of fusion as an energy source, currently under construction at the Cadarache site in France. The specific testing methods used to qualify the concepts selected for use in a fusion environment are also described in the article. In conclusion, the major challenges regarding long-term technological development for future fusion reactors are addressed.