Commissioning Gates vs Physics Gates
Commissioning milestones prove subsystems work; the physics gates prove the machine performs, and the two are kept distinct.
Two kinds of milestone
It is easy to confuse getting a machine running with proving it performs. The program keeps them separate. Commissioning milestones confirm that subsystems function, vacuum, cryogenics, magnet energization, first plasma. The physics gates (G1, G2, G3) confirm that the machine meets its design point and breeds tritium.
Commissioning milestones
- Vessel reaches operating vacuum
- Magnets reach operating temperature with margin
- Magnets energize and hold field
- First plasma is formed and controlled
Physics gates
- G1: confinement sufficient to reach Q_sci 3.076
- G2: 16.84 T peak field held under load
- G3: neutrons breed and are accounted as tritium
Why the distinction is enforced
A machine can pass commissioning, everything switches on, and still fall short at a physics gate, for instance if confinement is below prediction. Treating first plasma or magnet energization as if it were proof of performance would overclaim. The gates, reported against pre-registered predictions, are the real evidence; commissioning is the necessary precondition, not the demonstration itself.
How they are sequenced together
The two interleave in practice. Magnet energization is a commissioning milestone that also produces the evidence for the magnet gate G2. First plasma is a commissioning milestone that opens the ramp toward the confinement gate G1. First tritium is where fuel-loop commissioning and the fuel-loop gate G3 coincide. So each physics gate rides on a commissioning milestone, but the gate is judged on measured performance against prediction, while the commissioning milestone is judged only on the subsystem working.
Both apply to a machine not yet built. Keeping them distinct is part of how the program avoids the overclaiming that has damaged fusion, first plasma is a real milestone, but it is not gain, and it is not first tritium.