Refractory Material Selection

First-wall and divertor materials are chosen against melting point, thermal conductivity, erosion, and neutron-damage response — no single material wins every axis.

A multi-axis trade

No plasma-facing material is best on every metric. Selection weighs melting point, thermal conductivity, sputtering resistance, fracture toughness, activation, and how properties evolve under neutron damage. The breeder studies refractory candidates — hafnium carbide for the first wall and tungsten-class materials for the divertor — because the environment rewards high-temperature capability.

The tensions

High melting point often comes with brittleness. High thermal conductivity eases heat handling but may cost erosion resistance. Low activation is desirable for waste and maintenance but constrains alloy choice. The design does not pretend these tensions vanish; it picks candidates and states the open qualification questions for each.

Neutron damage changes the answer

A material that looks ideal fresh can degrade under fast-neutron fluence — swelling, embrittlement, and conductivity loss. Selection therefore weighs end-of-life properties, not just start-of-life. This is why materials qualification against a representative 14 MeV spectrum is a program in its own right.

The selection is documented as a study with named candidates and named uncertainties, not as a closed decision.

End-of-life, not start-of-life

Selection weighs how each candidate behaves after accumulated neutron damage, not only when fresh, because swelling, embrittlement, and conductivity loss can reorder the ranking over a component's life. A material that wins on paper when new can lose once irradiation response is included, which is why qualification data ultimately decide the choice.

This page documents a design and simulation study, not a built machine. Construction begins Q2 2027; first-of-a-kind first tritium is targeted near 2030. Figures are computed, reproducible targets, not measurements.