Triangularity (δ)

How D-shaped or reverse-D the plasma is; negative triangularity can suppress edge instabilities.

Triangularity δ measures how the plasma's corners are pulled in or out relative to a pure ellipse. Positive δ gives the familiar D-shape; negative δ points the corners the other way.

HYPERION adopts negative triangularity, δ = -0.30, a configuration that can suppress edge-localised modes while maintaining good confinement — a deliberate stability choice.