Plasma-Facing Materials

The surfaces facing the plasma must survive heat, particle bombardment, and neutron damage while adding as little impurity to the plasma as possible.

The frontline surfaces

Plasma-facing materials line the first wall and the divertor, the surfaces in direct view of the plasma. They endure steady and transient heat, bombardment by escaping ions and neutrals, sputtering erosion, and 14 MeV neutron damage. Their behavior sets component lifetimes and influences plasma purity, since eroded material can enter and radiate from the core.

Competing requirements

A good plasma-facing material resists erosion, tolerates high heat flux, does not retain much tritium, and, if eroded, produces impurities that radiate little in the core. High-atomic-number materials tolerate heat well but radiate strongly if they reach the core, while low-atomic-number materials are more forgiving to the plasma but erode faster. Divertor targets and first-wall armor may use different materials for these reasons.

Neutrons and tritium retention

Beyond surface effects, neutron irradiation changes these materials in bulk, embrittling them and altering thermal properties over time. Tritium retention in the walls is a safety and inventory concern, since trapped tritium is both a loss and a hazard. Selecting and qualifying plasma-facing materials under combined heat and fusion-neutron loading is an open materials question that the design-and-simulation program and the first-of-a-kind machine will advance.

• Survive heat, particle flux, erosion, and neutron damage
• Minimize core-radiating impurities and tritium retention
• Material qualification under fusion neutrons is an open question

This page describes a design and simulation study, not a built machine. Construction begins Q2 2027; first-of-a-kind first tritium is targeted near 2030.