Negative-Triangularity Shaping

Delta -0.30 shapes Hyperion's edge into a reversed-D, a configuration studied for benign edge behavior without the usual heat-exhaust penalty.

What negative triangularity is

Triangularity delta describes how the plasma boundary leans at its top and bottom. In a standard tokamak the boundary points outward toward larger major radius (positive delta), giving the familiar D shape. Hyperion runs negative triangularity, delta -0.30, so the boundary leans inward toward the center column and the cross-section reads as a reversed-D.

Why choose it

Negative triangularity has been studied because it can access good confinement while suppressing or softening edge-localized modes (ELMs), the periodic edge relaxations that eject heat and particles in high-confinement plasmas. Avoiding large ELMs eases the transient heat load on plasma-facing components, which matters when the first wall also serves as the neutron window into the breeding blanket.

The trade-offs

Negative triangularity is harder to hold at high current and pressure: the shaping coils must work against the plasma's tendency toward positive delta, and the stable operating window can be narrower. Hyperion's design carries delta -0.30 as a canonical choice, and the shaping requirement feeds directly into the poloidal-field coil currents and the center-stack loads. Whether the predicted edge benefits hold at 9.66 MA is one of the confinement questions the first-of-a-kind machine is meant to test.

• delta -0.30: reversed-D edge
• Motivation: softened ELMs, manageable edge heat loads
• Trade-off: demanding shaping, narrower stable window — to be tested

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.