ST40

Overview

Compact high-field spherical tokamak operating at the company's Oxfordshire campus since 2018 and the machine behind its plasma records. The spherical geometry confines plasma more efficiently per unit of magnetic field than a conventional tokamak, which is what makes a smaller, cheaper power plant plausible.

Closed out its 2025 campaign in December with three records (1 MA plasma current, highest stored energy, triple product up 30%+) and entered the $52M DOE/DESNZ upgrade shutdown that runs through most of 2026. The upgrade adds lithium-coated all-metal plasma-facing components and radiofrequency heating; the gyrotron heating system passed site acceptance testing in July 2026 and the next experimental campaign is scheduled for 2027-2028.

Key Specs