Hyperion Poloidal-Field Coils
The poloidal-field coils shape and position the plasma, setting its elongation, its negative triangularity, and its vertical stability.
Shaping the plasma
The poloidal-field coils, or PF coils, are the rings that circle the machine horizontally at various heights. Their field runs in the poloidal plane, and their job is to control the plasma's position and cross-sectional shape. Where the TF coils confine, the PF coils sculpt.
What they set
- Vertical and radial position of the plasma column.
- Elongation, how tall the D-shaped cross-section is.
- Triangularity, the -0.30 negative value that leans the D inward on Hyperion.
- Vertical stability feedback, since an elongated plasma tends to drift up or down.
Negative triangularity
Hyperion's plasma runs negative triangularity, meaning the D-shape points its flat side outward rather than inward. This shaping can improve edge stability and heat handling, and it is a deliberate design choice carried through the model: the poloidal cutaway draws the plasma with its -0.30 triangularity so the shape is honest. The PF coil currents are what hold that shape.
In the model
The PF coil set is selectable ring by ring. Each ring shows its position in the R-Z plane, and the plasma boundary it helps produce is drawn alongside. This is the clearest place to see how coil currents translate into plasma shape, because moving between the coils and the boundary is a single glance in the poloidal view.
Relation to current drive
The innermost stacked coils form the central solenoid, treated separately because its job is inducing plasma current, not shaping. See the central solenoid and plasma shape.