The Central Solenoid

The central solenoid is the transformer that induces and ramps Hyperion's plasma current before non-inductive drive and bootstrap current take over.

The machine's transformer

A tokamak drives its plasma current inductively: a changing current in a central solenoid acts as the primary winding of a transformer, and the plasma ring is the single-turn secondary. Ramping the solenoid induces the toroidal electric field that breaks down the gas and drives Hyperion's plasma current toward its 9.66 MA target.

The spherical-tokamak squeeze

The solenoid needs volume on the machine axis, and that is precisely where a spherical tokamak has least room, the center stack is already crowded with toroidal-field return legs. This tension limits how much inductive flux the solenoid can supply, which is one reason STs lean heavily on non-inductive current drive and bootstrap current to sustain the plasma after startup.

Startup and hand-off

In a typical discharge the solenoid provides the flux to initiate and ramp the current, then neutral-beam and RF current drive, together with self-generated bootstrap current, carry the plasma through flat-top. Designing the hand-off so that 9.66 MA is reached and sustained without exhausting the limited solenoid flux is a core operating problem for the compact machine, and it is exercised extensively in simulation before first plasma.

• Inductive primary that starts and ramps plasma current
• Constrained by scarce center-stack volume in an ST
• Hands off to non-inductive drive and bootstrap current

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.