First-Wall Heat Flux
The wall must handle steady radiated power plus transients without exceeding material limits — the reason a very-high-melting-point refractory is studied.
Steady and transient loads
The first wall sees a steady heat flux from plasma radiation and particle bombardment, punctuated by transients during off-normal events. The material and its cooling must keep surface temperature and thermal stress within limits at both. With 85.0 MW of fusion power in a compact machine, power density on plasma-facing surfaces is significant.
Why melting point is not the whole story
A high melting point gives margin against reaching the melt, but the operational limit is usually thermal stress and fatigue well below melting. Repeated heating and cooling drives crack initiation in brittle carbides. The design manages peak surface temperature, temperature gradient into the coolant, and cycle count together.
- Steady radiated and conducted flux sets baseline temperature.
- Transients set the peak the material must survive without cracking.
- Thermal gradient to coolant drives stress and fatigue.
- Negative triangularity is chosen partly to ease exhaust and edge loads.
Coupling to shape
The -0.30 triangularity plasma shape is chosen partly because it can spread and reduce edge power loading compared with some alternatives. Heat-flux handling is thus a plasma-shape decision as much as a materials decision, and the two are designed together rather than in isolation.
Cycle count matters
Beyond peak flux, the number of heating-and-cooling cycles drives thermal fatigue at the armor and its attachment. A wall that survives a single worst transient can still fail after many moderate ones, so the design tracks cyclic loading and fatigue life, not just the instantaneous heat-flux limit, when sizing the first wall.
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.