The Central-Cell First Wall

The first wall faces the plasma and takes radiation and particle flux; the low neutron fraction makes it far lighter than a D-T machine's.

The plasma-facing boundary

The first wall is the innermost material surface surrounding the central-cell plasma. It receives radiated power (bremsstrahlung and line radiation), charge-exchange neutrals, and the 5.44% neutron flux. Unlike a D-T machine, it is not backed by a thick breeding blanket — the burner does not breed its own fuel — so the wall-plus-shield structure is comparatively thin.

Loads on the wall

• Radiation flux from the hot, doubly-charged-helium plasma
• Modest neutron flux causing limited activation and damage
• Charge-exchange particle bombardment and sputtering
• Heat that is removed and recovered as waste heat

Material choice

The wall material must handle steady heat flux, resist sputtering, and keep impurities out of the plasma, since impurities raise radiation and can quench the demanding D-3He burn. Low-activation materials keep the radioactive inventory small and support hands-on maintenance. Because most power leaves as charged particles down the ends rather than as neutrons into the wall, the wall's job is dominated by radiation and particle handling rather than neutron energy capture.

First-wall specifics for the burner are part of the ongoing design study, informed by mirror-program experience and by the breeder's materials work. See materials for the selection criteria and open questions.

Because the wall does not have to survive an intense 14 MeV neutron flux, its replacement cadence is set mainly by radiation heat and sputtering rather than by neutron damage — a meaningful simplification the burner inherits from its fuel choice.