Hyperion Plasma Shape and Negative Triangularity
Hyperion runs a D-shaped plasma with negative triangularity of -0.30, a shaping choice drawn honestly in the model.
The shape of the plasma
A tokamak plasma is not round in cross-section. It is shaped by the poloidal-field coils into a D, described by two main numbers: elongation, how tall it is relative to its width, and triangularity, how much the D-shape leans. Hyperion runs negative triangularity of -0.30.
Positive versus negative
- Positive triangularity points the sharp corner of the D inward, toward the machine axis, the conventional choice.
- Negative triangularity, Hyperion's choice, leans the shape the other way, presenting a flatter face outward.
- The sign is defined in the R-Z poloidal plane, which is why the poloidal cutaway is the shape view.
Why negative
Negative triangularity can suppress the edge instabilities that otherwise dump heat onto the wall in bursts, and it can spread the exhaust load more favorably. It is an actively studied route to a better-behaved plasma edge. Choosing it is a considered design decision, and the model commits to it rather than drawing a generic D.
In the model
This is one place where model honesty is easy to check: the plasma boundary in the poloidal cutaway is drawn with genuine -0.30 triangularity, leaning the correct way, not a decorative oval. A shape callout reports the triangularity and elongation against the drawn boundary.
What holds the shape
The shape is produced entirely by coil currents. See the poloidal-field coils that set it and the divertor whose geometry follows from the same field.