Plasma Cross-Section Shape

Hyperion's poloidal cross-section is strongly elongated and shaped to negative triangularity, a reversed-D that hugs the center column.

Reading the cross-section

Cut the torus vertically and you see the poloidal cross-section: the shape of the plasma in the plane that contains the machine axis. Hyperion's is tall and narrow, strongly elongated, and shaped to negative triangularity of delta -0.30, so the outboard edge is drawn inward at top and bottom into a reversed-D rather than the outward-pointing D of most tokamaks.

Elongation

Vertical elongation (kappa) increases the plasma volume and current-carrying capacity for a given minor radius, which raises confinement and the achievable current. Spherical tokamaks naturally run at high elongation because the field geometry supports it. Hyperion's tall cross-section is part of how it sustains 9.66 MA in so compact a footprint.

Triangularity

Triangularity measures how much the top and bottom of the plasma are pushed toward larger or smaller major radius. Positive triangularity points the corners outward; Hyperion uses negative triangularity, delta -0.30, pointing them inward. That choice interacts with edge stability and heat-exhaust behavior and is treated in detail on its own page.

Why the shape is engineered

The cross-section is not incidental; it is produced deliberately by the poloidal-field coils and the plasma current working together, and it must be held actively throughout a discharge. Elongation and negative triangularity together determine how much current the plasma can carry, how stable its edge is, and where heat is exhausted. Getting the shape right is therefore a prerequisite for reaching 9.66 MA and Q_sci 3.076, not a cosmetic detail, and holding it at Hyperion's compact scale is one of the tasks the shaping and control systems are designed for.

• Tall (high-elongation) poloidal cross-section
• Negative triangularity delta -0.30 (reversed-D)
• Shape set by 9.66 MA current and edge-stability goals

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.