Vacuum-Vessel Materials
The vacuum vessel holds the plasma's high vacuum and forms a primary safety boundary; its material must be strong, weldable, and low-activation.
The boundary that must not leak
The vacuum vessel encloses the plasma volume and maintains the high vacuum the plasma needs. It is also a primary confinement boundary for the safety case, so its integrity is fundamental. The material must hold vacuum, carry structural loads, survive neutron dose, be weldable for construction and remote repair, and activate as little as possible.
Competing requirements
- Vacuum tightness with no leaks across the operating life.
- Structural strength to carry loads and off-normal events.
- Weldability for assembly and remote repair.
- Low activation to ease maintenance and waste.
Why it interacts with everything
The vessel sits between the blanket/shield inside and the cryostat and magnets outside. Its penetrations are the same ports that reduce blanket coverage; its material activation contributes to the dose fields that govern maintenance; its structure helps react magnet loads. The vessel is not an isolated shell but a shared boundary that couples plasma, blanket, magnet, and maintenance considerations.
Reference class
Reduced-activation structural steels are the reference class, chosen to balance strength, weldability, and activation. As with the blanket structure, their behavior under 14 MeV neutron damage is an open qualification item the breeder tracks rather than assumes. The vessel is designed as a lifetime safety boundary, verified against that damage over the machine's operation.
Double boundary and leak tolerance
As a primary confinement boundary, the vessel is designed with leak detection and, where warranted, a defense-in-depth arrangement so a single flaw does not directly breach containment. Weld inspectability and remote repairability are part of this, ensuring the boundary can be verified and maintained across the operating life rather than trusted blindly.
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.