ST40 is Tokamak Energy's high-field compact spherical tokamak, the first privately funded machine to reach 100 million °C ion temperatures. It is being upgraded with lithium-coated plasma-facing components under a $52m US DOE/UK DESNZ/company partnership and supports the UK STEP programme.
New to fusion? Nuclear fusion, explained: three ways to bottle a star
Current state
| Status | Operating |
| Country | United Kingdom |
| Location | Milton Park, Oxfordshire |
| Developer | Tokamak Energy |
| Developer type | Private |
| Concept | Spherical tokamak |
| Fuel | D-D |
| Purpose | Research |
| Private funding raised | USD 335m (as of 2024-11) |
| Public funding | $52m ST40 lithium upgrade co-funded by US DOE and UK DESNZ; former DOE Milestone program awardee |
Notes
Original ST40 first-plasma date not verified in the sources reviewed (left not recorded); the upgraded ST40 had first plasma in Dec 2022 per Tokamak Energy. The ST40 upgrade is expected operational in 2027 subject to appropriations. Company has pivoted toward HTS magnets (TE Magnetics) and partnering (STEP) rather than building its own plant.
Timeline
- 2024-11 — Tokamak Energy closed a $125 million round, bringing total raised since its 2009 spin-out to $335 million. (source)
- 2024-12-05 — US DOE, UK DESNZ and Tokamak Energy agreed a $52 million upgrade of ST40 with lithium-coated plasma-facing components. (source)
- 2026-04-14 — UK Fusion Energy named Tokamak Energy Magnet Systems Partner for STEP under a £70 million contract that includes continued use of ST40. (source)
- 2026-08-18 — Tokamak Energy published its fusion pilot plant design in Nuclear Fusion while stating it will not go on to construct the plant itself. (source)
The timeline is append-only: corrections are added as new entries. Stated targets appear in the current-state table, never as milestones.
Related projects
- CTRFR-1 / Startorus No.1 (Startorus Fusion) Design · China
- JET (Joint European Torus) Shut down · United Kingdom
- Machine 4 (First Light Fusion) Cancelled · United Kingdom
- MAST Upgrade Operating · United Kingdom
- ST80-HTS (Tokamak Energy) Design · United Kingdom
- STEP Fusion (West Burton) Design · United Kingdom
See all 51 projects in the Fusion Energy Companies & Projects Tracker →
Sources
- US and UK partner with Tokamak Energy on ST40 upgrade — World Nuclear News, checked 2026-10-11
- Tokamak Energy: $125 Million Closed To Commercialize Transformative Fusion And Magnet Tech — Pulse 2.0, checked 2026-10-11
- Tokamak Energy named Magnet Systems Partner for STEP Fusion programme — Tokamak Energy (primary), checked 2026-10-11
- Tokamak Energy's 'Focus Collection' featured in Nuclear Fusion journal — Tokamak Energy (primary), checked 2026-10-11
- First plasma for Tokamak Energy's upgraded ST40 fusion device — Tokamak Energy (primary), checked 2026-10-11