Benchmarking Against the Spherical-Tokamak Database

Because Hyperion is a low-aspect-ratio machine, its confinement and stability estimates are weighted against the NSTX/MAST-class record, not only conventional-tokamak scalings.

The right comparison class

The breeder (Hyperion) is a spherical tokamak: aspect ratio A 2.5, major radius R0 1.2 m, strong elongation, and negative triangularity delta -0.30. Its natural comparison class is the family of spherical tokamaks — machines in the NSTX and MAST lineage — whose operating record differs from conventional tokamaks in confinement, stability, and current drive.

What the ST record informs

• Confinement at low aspect ratio, where the field-line geometry and high beta change transport.
• Stability limits, since spherical tokamaks access high normalized beta.
• The high bootstrap-current fraction that low aspect ratio favors.
• The behavior of a strongly shaped, negative-triangularity edge.

Limits of the analogy

Existing spherical tokamaks are pulsed research devices, not steady D-T breeders, and none has operated with the breeder's high-temperature-superconducting field or its blanket. The database constrains the plasma physics; it says little about integrated breeding or center-post survival. The record is explicit that the ST benchmark bounds the plasma claims and not the engineering gates.

The comparison is also asymmetric in maturity: several spherical tokamaks have logged extensive campaigns, so the plasma-physics inference rests on real operating hours, while the breeding and center-post questions have no operating analogue at all. The record keeps those two confidence levels separate rather than letting the well-supported plasma benchmark lend borrowed credibility to the unsupported engineering gates.

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