The UK Atomic Energy Authority (UKAEA) said on 6 August 2026 that its MAST Upgrade fusion machine at Culham Campus in Oxfordshire completed its fifth series of experiments, run through 2025 and 2026, producing more than 1,100 fusion plasmas. The authority reported the highest plasma pressure achieved in the machine without the plasma destabilising.

The team said it suppressed instabilities known as Edge Localised Modes using Quasi-Continuous Exhaust mode and Resonant Magnetic Perturbations, and also accessed Quiescent H-mode and I-mode regimes. It described a technique using light measurements to detect tiny plasma position imbalances in real time, and found that injecting small amounts of nitrogen at the plasma edge spread exhaust heat as light, lowering peak heat flux.

James Harrison, Head of MAST Upgrade Science at UKAEA, said the results shape future power plant design. UKAEA said enhancements planned for that year included two new neutral beam injectors and an Electron Bernstein Wave system adding 1.6 MW of heating, with the programme expected to conclude in 2027 and a sixth campaign planned for 2028.