Toroidal Field and Ripple

A finite number of toroidal-field coils makes the field ripple in the toroidal direction; excess ripple degrades confinement and must be held low.

The field is not perfectly smooth

The toroidal field is produced by a set of discrete coils, so the field strength ripples slightly as one moves around the torus between coils. This toroidal-field ripple is small but not zero, and it matters: ripple can trap fast particles in local magnetic wells and let them drift out before depositing their energy, degrading confinement and adding heat load.

In a spherical tokamak the return-limb geometry and the tight center column shape the ripple pattern. Keeping ripple low enough that it does not spoil confinement or dump excessive heat on the wall is a constraint on the toroidal-field coil design, alongside the peak-field and stress limits.

Coupling to fast-particle physics

The particles most sensitive to ripple are the energetic ones: fusion alphas and any beam-injected ions. Because alpha heating is part of what sustains Q_sci 3.076, ripple-induced alpha loss subtracts directly from the self-heating budget. Quantifying acceptable ripple for Hyperion is a design-and-simulation task tied to the confinement and heating gates. The design sets a ripple budget at the plasma edge and sizes the number and placement of toroidal-field coils to stay within it, trading coil count and geometry against the fast-particle loss the plasma can tolerate before its self-heating and wall loads are affected.

• Discrete coils → toroidal ripple in field strength
• Ripple can trap and eject fast particles, degrading confinement
• Alpha-particle loss from ripple erodes the self-heating budget

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. No hardware net-gain is claimed before FOAK.