Neutron Shielding

Shielding protects the magnets, structure, and people from 14 MeV neutrons, but in a spherical tokamak the inboard side has almost no room for it.

Why shielding is needed

Fast neutrons damage superconductors, activate structure, and are a radiological hazard. Between the breeding blanket and the sensitive components, magnets, vessel, and the outside world, sit shielding layers that slow and absorb the neutrons that are not captured for breeding. Shielding is what lets the magnets and structure reach their intended life in an intense neutron field.

The inboard problem

On the outboard side there is room to stack adequate shielding. On the inboard side, in a spherical tokamak, the center stack already occupies nearly all the space, leaving almost none for shielding between the plasma and the center post. This is the direct cause of the center post's limited lifetime: it is exposed to the neutron flux with minimal protection because the geometry cannot spare the room.

A managed compromise

Hyperion accepts this as a defining trade of the configuration. Where shielding fits, it protects long-life components; where it does not, the affected parts, chiefly the center post, are designed to be replaced. Balancing shielding thickness against breeding coverage and machine compactness, and predicting the resulting doses and damage, is part of the neutronics and design-and-simulation program that precedes construction.

• Protects magnets and structure from fast-neutron damage
• Inboard space is nearly all consumed by the center stack
• Where shielding cannot fit, components are made replaceable

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.