The First Wall

The first wall is the plasma-facing surface that both protects the structure behind it and passes the 14 MeV neutron flux into the breeding blanket.

Where plasma meets machine

The first wall is the innermost solid surface facing the plasma. It intercepts heat, escaping particles, and radiation, and it is the window through which 14 MeV fusion neutrons cross from the plasma into the breeding blanket behind it. It protects the vacuum vessel and blanket structure while surviving one of the harshest environments in any engineered system.

Two competing jobs

The first wall must be robust against heat and particle bombardment, which favors thick, refractory armor. But it must also be nearly transparent to neutrons, since every neutron stopped in the wall is one not available for breeding tritium and helium-3. The design threads this by keeping the wall thin where it can and choosing materials that shield the plasma's heat without unduly absorbing or moderating neutrons.

Loads and lifetime

The first wall sees steady heat flux, transient loads from edge events, sputtering that erodes its surface and can contaminate the plasma, and neutron damage that degrades the material over time. Negative-triangularity shaping is chosen partly to soften edge transients on this surface. Like other close-in components, the first wall is designed for inspection and replacement, and its material behavior under fusion neutrons is an active design-and-simulation question.

• Plasma-facing surface protecting vessel and blanket
• Must survive heat and particles yet pass neutrons
• Erosion and neutron damage make it a serviceable component

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.