Poloidal Field Coils

Poloidal-field coils position, elongate, and shape the plasma, holding its negative-triangularity cross-section and controlling its vertical stability.

Shaping the plasma

Poloidal-field (PF) coils are rings arranged coaxially with the machine, above, below, and around the plasma. Their fields push and pull the plasma column into position and give it its cross-sectional shape: the elongation and the negative triangularity of delta -0.30 that define Hyperion's poloidal profile. They also hold the plasma radially and control its vertical position.

Elongation and triangularity control

A tall, elongated plasma is vertically unstable: left alone it drifts up or down and is lost. The PF system provides fast feedback control to hold it, while the steady currents set the elongation and drive the boundary to negative triangularity. Because negative triangularity works against the plasma's natural tendency, the shaping coils carry demanding currents and their placement is tightly constrained by the compact geometry.

Working with the solenoid

The PF coils act together with the central solenoid, which drives the plasma current, and with the toroidal field. Coordinating all three through a discharge, ramp-up, flat-top, and shutdown, is the job of the machine's magnet control system. In a spherical tokamak the inboard PF space is scarce, so some shaping is shared with conductors in the center stack.

• Set plasma position, elongation, and triangularity
• Provide fast vertical-stability feedback
• Coordinate with the central solenoid and toroidal field

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.