Blanket Coverage and Penetrations
Every hole for heating, diagnostics, or maintenance is a place the blanket cannot breed — coverage gaps are why net TBR falls below the target.
The geometry tax on breeding
A blanket breeds tritium only where it exists. Real machines must pierce the blanket for heating systems, diagnostics, pumping, and maintenance access. Each penetration removes breeding volume and lets neutrons escape without capture, so coverage — the fraction of the plasma the blanket actually surrounds — is a first-order driver of net tritium breeding.
Coverage versus access
There is a direct tension: the more completely the blanket wraps the plasma, the higher the breeding, but the machine still needs ports to heat, diagnose, and maintain the plasma. A compact spherical tokamak with a crowded center stack has less room to spare, sharpening the trade. Coverage is optimized, not maximized, against these needs.
- Heating and current-drive ports reduce coverage.
- Diagnostic and pumping penetrations remove breeding volume.
- Maintenance access competes with blanket completeness.
- The compact center stack tightens every one of these trades.
The reconciliation, stated plainly
Coverage gaps are a principal reason a local TBR target of 1.8 does not translate directly into net self-sufficiency. The breeder counts realistic coverage and penetration losses in its honest assessment and treats closing the local-to-net gap as open work rather than a solved result.
Local shielding at ports
Where the blanket must be pierced, local shielding and re-entrant blanket geometry around the port recover some breeding and limit neutron streaming past the gap. These fixes reclaim part of the coverage lost to a penetration, but never all of it, which is why penetration count and placement are minimized from the start.
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.