Milestones
- Magnet manufacturing2024Complete.
- Full-system testingNowCurrent milestone.
Most important updates
- 14 Apr 2026
- 20 Nov 2025
- 6 Feb 2023
Current obstacles
- Coils pushing on each otherPowering all the coils at once creates complex forces that single-coil tests can't reveal.
Physics limits
- Stronger fields mean crushing forcesMagnetic pressure grows with field squared: at 20 T it is about 160 MPa, over 1,500 atmospheres, so coil structure, not the superconductor, often sets the maximum field.
- Superconductors quit above critical limitsHTS tape carries current without loss only below a critical temperature, field and current; its capacity falls as field rises, and neutron damage lowers it further.
- A quench must dump stored energy fastIf a spot stops superconducting, the magnet's stored energy must be removed before it burns the coil. In HTS the warm zone spreads slowly, so it is hard to detect in time.
How it works
Magnets
A full superconducting magnet set
Demo4 is a complete set of high-temperature superconducting coils in a spherical-tokamak layout, tested without plasma.
Cold
Cooled to about -243 °C
The tape superconducts at around 30 K (-243 °C), much warmer than older low-temperature magnets, which cuts cooling power.
Test
Power-plant fields and forces
The coils push and pull on each other with huge forces; Demo4 checks they hold field (11.8 T in 2025) without deforming or quenching.
Update log
Tue 14 Apr
- Minor: PressPartnership
Thu 20 Nov 2025
- Major: PressTest
Mon 6 Feb 2023
- Minor: BlogHardware
About Tokamak Energy
Tokamak Energy
Spherical tokamaks, HTS magnets, ST40
UK company combining spherical tokamaks (a compact, apple-core shape) with high-temperature superconducting magnets. Its ST40 reached 100-million-degree plasma in 2022, and it also sells its magnet tech to other industries.
- ST40 reached 100 million °C in 2022, a record for a privately funded spherical tokamak.
- Building Demo4, a full set of HTS magnets in tokamak shape, to test fusion-level fields.
- Part of the US DOE Milestone-Based Fusion Development Program.
tokamakenergy.com (opens tokamakenergy.com)Company profile →
- Founded
- 200917 yrs
- Headquarters
- United Kingdom
- Status
- Private
- Valuation
- private
- Works in
- EnergyFusion
- Coverage
- 2 programs · 8 updateslatest 14 Apr 2026checked 25 Sep