The Neutron Shield

The shield stops fusion neutrons from damaging the magnet and activating the structure. A low-neutron plant needs far less of it — a compounding advantage.

Job

Protect magnets and structure from neutrons

Cost

Takes space and adds mass, especially inboard

Kronos advantage

Low-neutron flux → thinner shield

Budget

Explicit fluence budget for the shielded center stack

The neutron shield is the layer that absorbs fusion neutrons before they reach and damage the magnets, and that limits how much the surrounding structure gets activated. In any fusion reactor it is a demanding component; in a spherical tokamak it is doubly so, because the inboard shield must fit in the cramped center stack alongside the magnet.

This is where being low-neutron compounds into a real design advantage. With a neutron fraction around 5.25% — some 25× below D–T — Kronos MetroVolt needs far less shielding, which frees precious inboard space for the conductor. The design still carries an explicit neutron-fluence budget for the shielded center stack, sized to keep the magnet within its lifetime dose.