Hyperion First Wall
The first wall is the plasma-facing surface that takes the heat and particle flux and shields the breeding blanket behind it.
The plasma-facing surface
The first wall is exactly what its name says: the first solid surface the plasma sees. It lines the inside of the vacuum chamber and stands between the burning plasma and the breeding blanket. Everything the plasma throws off, heat, neutrons, and stray particles, hits the first wall first.
What it must survive
- Intense surface heat flux from radiation and escaping particles.
- A 14.1 MeV neutron flux from deuterium-tritium fusion passing through it into the blanket.
- Sputtering and erosion from plasma-surface interaction.
- Thermal cycling as the machine pulses.
A thin, sacrificial layer
The first wall is deliberately thin so it does not absorb the neutrons the blanket needs for breeding, yet it must be robust enough to handle the surface load. This is a real tension in the design: too thick and it steals neutrons from the tritium breeding ratio of 1.8, too thin and it cannot survive. In the model the first wall is drawn as the innermost shell in the cutaway, just millimeters ahead of the blanket.
In the model
The first wall is selectable as a shell; its thickness callout appears at the cut face when the section plane is active. Because it is defined in millimeters against a machine measured in meters, the scale reference is important here to appreciate how thin it really is.
Relation to the blanket and divertor
The first wall handles the general chamber surface; the concentrated exhaust load is taken by the divertor. See the breeding blanket immediately behind it and the divertor that handles the exhaust.