Center-Post Current and Lifetime

The center post carries the toroidal-field current through the tightest, least shielded region; it runs hot, highly stressed, and life-limited (~0.01 fpy note).

The most loaded component

In a spherical tokamak the toroidal-field conductor must pass through the narrow central hole. This center post carries very large current, generates the 16.84 T peak field at its surface, and sits closest to the plasma with the least room for shielding. It is simultaneously the enabler of the compact ST and its most stressed part.

Three loads stack on the center post: electromagnetic (the field it produces exerts large forces on its own conductor), thermal (resistive and nuclear heating in a tight space), and neutron damage (the inboard neutron flux with minimal shielding). Together these give the center post a limited operational lifetime, noted at roughly 0.01 full-power years before it must be replaced.

An honest, designed-around limit

A ~0.01 fpy center-post life is short, and the program states it plainly rather than burying it. The machine is designed for center-post replacement as a routine maintenance operation, which shapes the remote-maintenance plan and the duty cycle. The physics point here is simple: the compactness that gives the ST its advantage is paid for at the center post, and that bill is real.

• Carries the toroidal-field current at the field peak (16.84 T)
• Electromagnetic, thermal, and neutron loads stack in a tight, unshielded space
• Limited lifetime (~0.01 fpy) — designed for routine replacement

This page describes a design-and-simulation study, not a built machine. Construction begins Q2 2027; first-of-a-kind first tritium is targeted near 2030. No hardware net-gain is claimed before FOAK.