The Central Cell
The central cell is the long, low-field region where most of the fusion power is produced and where the confining potential well sits.
Where the burn happens
The central cell is a straight solenoidal section holding the bulk of the burning plasma. Its field is modest compared with the end plugs — the on-axis field is a fraction of the 26.49 T plug peak — because the central cell does not need to mirror-confine ions on its own. Its job is volume: it provides the length and cross-section over which D and 3He fuse.
Confined by potential, not by mirror
Central-cell ions are held axially by the ambipolar potential peaks generated at each end. The plugs raise the potential at the ends so that central-cell ions see a well and are electrostatically reflected. This lets the central cell run at high density and good confinement without an extreme local mirror ratio.
Fueling and burn
Fuel enters as deuterium and helium-3 via pellet and gas injection, and neutral beams and RF heating maintain the ion and electron temperatures. The dominant reaction is aneutronic D-3He; only 5.44% of the fusion power appears as neutrons, mostly from side D-D reactions, which sets the modest shielding requirement on the central-cell first wall.
- Long solenoidal geometry maximizes burn volume
- Low field relative to plugs — the plugs do the confining
- High-beta operation is a stability question — see beta limits
- First-wall loading is dominated by charged particles and radiation, not neutrons
Because so little energy leaves as neutrons, the central-cell first wall and blanket are far lighter than a D-T machine's, and the charged-particle power flows out the ends toward direct conversion rather than into a steam-raising blanket.