Non-Inductive Current Drive

External current drive tops up what bootstrap cannot supply; it is powerful but power-hungry, so the design minimizes the driven fraction.

Filling the gap

Bootstrap current rarely supplies the entire plasma current at exactly the right profile. The remainder must be driven non-inductively — by injecting momentum or wave power that pushes current in a chosen direction. Neutral beams and radio-frequency waves are the usual tools; both deposit current where the profile needs shaping.

For a steady-state foundry this is essential: inductive (transformer) drive is inherently pulsed and cannot sustain 9.66 MA indefinitely. Non-inductive drive lets the current continue as long as the machine runs. But every watt of drive power counts against the gain budget, so the design wants the driven fraction as small as possible on top of a large bootstrap fraction.

The efficiency question

Current-drive efficiency — amps of plasma current per watt of injected power — depends on density, temperature, and where in the plasma the current is deposited. Achieving both a favorable efficiency and a current profile that stays MHD-stable is a coupled optimization. The specific drive mix and efficiency for Hyperion are design-and-simulation results, and their sensitivity feeds directly into the confinement gate. A less efficient drive, or a larger required driven fraction because bootstrap falls short, both raise the injected power that sits in the denominator of the gain — so current-drive performance is not a side detail but a direct lever on whether Q_sci 3.076 is reached.

• Sustains current where bootstrap falls short
• Enables steady operation that inductive drive cannot
• Drive power subtracts from gain — minimize the driven fraction

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.