First-Wall Armor Attachment

Joining brittle refractory armor to a cooled heat sink across a thermal-expansion mismatch is the fatigue-critical detail of the first wall.

The join under cycling

The first wall must move heat from a refractory surface into a coolant while surviving repeated heating and cooling. The surface material and the cooled structure expand by different amounts, so every thermal cycle strains the interface between them. This attachment is where plasma-facing components most often reach their life limit.

Approaches

• Graded interlayers that step the expansion mismatch across the join.
• Compliant bonds that accommodate strain without cracking.
• Mechanical attachment that allows differential motion.
• Segmentation so no single tile spans too large a thermal gradient.

Why segmentation helps

Breaking the wall into smaller tiles reduces the absolute expansion difference any one joint must absorb and lets damaged tiles be replaced individually. The cost is more joints and more assembly, and each tile edge is a potential heat-flux peaking site. The design balances tile size against joint count.

Honest status

Refractory-to-metal joining under fusion cycling and dose is an active materials question, not a closed one. The breeder studies candidate joints and states the fatigue and delamination risks plainly, treating the armor attachment as a lifetime-limiting detail to be qualified, not assumed.

Inspection of the bond

Because the bond is the fatigue-critical detail, its integrity must be verifiable, ideally without destroying the component. Designs favor joints that can be inspected for delamination and cracking during maintenance, so a weakening bond is caught before it fails in service. Inspectability is thus a design requirement of the attachment, not only its strength.

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.