First-Wall Erosion and Sputtering

Ion bombardment sputters wall atoms, eroding the surface and seeding the plasma with impurities the material choice must limit.

Two problems from one process

Energetic ions striking the wall knock out surface atoms. This erosion thins the wall over time, and the sputtered atoms enter the plasma as impurities that radiate energy and dilute the fuel. A good first-wall material erodes slowly and, if it does enter the plasma, radiates less catastrophically.

Why hard refractories help

Hard, high-binding-energy materials such as hafnium carbide resist sputtering better than soft low-Z materials. The trade is that high-Z impurities radiate strongly if they reach the plasma core, so a small amount of eroded material costs more per atom. Selection balances erosion rate against impurity penalty.

• Erosion sets first-wall lifetime and replacement cadence.
• Sputtered high-Z atoms radiate strongly if they reach the core.
• Redeposition can partially heal or can build up in unwanted places.
• Edge plasma conditions strongly modulate the erosion rate.

Lifetime, not permanence

The breeder does not assume a permanent first wall. Erosion, together with neutron damage, sets a component lifetime and a planned replacement through remote handling. Designing for replacement rather than permanence is a recurring theme across the breeder's plasma-facing and center-stack components.

Redeposition and migration

Sputtered material does not simply vanish: some redeposits nearby, partially healing the surface, while some migrates and accumulates in unintended locations, where it can trap tritium or form loosely-bound dust. Managing where eroded material ends up is part of the erosion problem, tying first-wall behavior to tritium inventory and in-vessel cleanliness.

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.