Center-Post Material Selection
The center-post carries the toroidal-field current through the machine's most hostile volume: highest field, highest force, highest neutron flux, least space.
The hardest-working component
The center-post is the inboard conductor of the toroidal-field system, running up the machine axis through the narrow center stack. In a compact spherical tokamak it sits where field is highest (16.84 T region), centering force is largest, neutron flux is most intense, and radial space is smallest. No other component faces all four extremes at once.
Competing demands
The material must carry large current, react centering load, tolerate a fierce neutron flux, and fit a tight radius while leaving room for shielding and cooling. These demands conflict: more conductor leaves less room for shield; more shield leaves less room for cooling; more of anything leaves less room for the rest. The center-post is the machine's most contested volume.
- Highest toroidal field of any conductor in the machine.
- Largest centering force, reacted through the central column.
- Most intense neutron flux, driving rapid damage.
- Least radial space, shared with shield and coolant.
The consequence
Because these demands cannot all be satisfied for a long life in a compact machine, the breeder accepts a center-post with a limited lifetime and plans to replace it. Material selection is made with replacement in mind rather than trying to build a permanent part that cannot exist in this volume.
Copper-class conductor, replaceable
The center-post is typically a copper-class normal conductor rather than superconductor, chosen to survive the intense flux and to be economical to replace on its short interval. Accepting resistive heating in exchange for radiation tolerance and replaceability is a deliberate inversion of the superconducting-everywhere instinct, driven entirely by the center stack's hostility.
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.