Confinement and H-Mode

Good energy confinement is what lets a compact plasma reach Q_sci 3.076; high-confinement regimes and shaping are how Hyperion aims to hold it.

Holding the heat in

Fusion gain depends on how well the plasma retains its energy: the longer heat stays in, the hotter and denser the plasma runs for a given input, and the higher the fusion output. Energy confinement time captures this. Reaching Q_sci 3.076 at 85.0 MW in a machine only 1.2 m in major radius depends on confinement being good enough to sustain fusion conditions at that scale.

High-confinement operation

Tokamaks can transition into a high-confinement regime (H-mode) in which an edge transport barrier steepens the pressure at the plasma boundary and improves overall confinement. This regime is central to reaching high gain, but its edge pressure gradient can drive edge-localized modes. Hyperion's negative-triangularity shaping is chosen partly to access good confinement while keeping those edge relaxations manageable.

Confinement as an open test

Confinement in the spherical-tokamak regime does not follow the same scaling as conventional tokamaks, and extrapolating it to Hyperion's exact parameters carries uncertainty. Whether the plasma confines as well as the design assumes, at 9.66 MA, with negative triangularity, in this compact geometry, is a first-order question the design-and-simulation program models and that the first-of-a-kind machine is built to verify.

• Confinement time sets the gain for a given machine size
• High-confinement regimes and shaping raise it
• ST-regime confinement extrapolation is an open test at FOAK

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.