Britain and America are linking two fusion supercomputers across the Atlantic
What happened
On 14 September 2026, at a summit held at Mansion House in London, the UK and the United States signed two agreements aimed at speeding up the development of fusion power. The headline piece is a plan to connect two supercomputers on opposite sides of the Atlantic. On the British side is SUNRISE, run by the UK Atomic Energy Authority. It is the UK's first artificial intelligence supercomputer built specifically for fusion research, backed by £45 million of government money. On the American side is STELLAR-AI, run by the US Department of Energy's Princeton Plasma Physics Laboratory, with support from Princeton University. The two organisations signed a Joint Declaration of Intent to explore linking them together, in a partnership they are calling the SUNRISE–STELLAR-AI Federation. It builds on a memorandum of understanding the two labs signed in June. The idea is that researchers would be able to train AI models on data from both countries' experiments. That includes the MAST Upgrade machine in Oxfordshire and the NSTX-U machine in New Jersey. The aim is to build better tools for designing future fusion power stations, including what engineers call digital twins: highly detailed computer models of a machine that can be tested and adjusted before anything is built in metal. A second agreement commits the two governments to working more closely on how fusion should be regulated.
Why this matters
Fusion is the process that powers the Sun. It joins light atoms together and releases enormous amounts of energy. If it can be made to work reliably on Earth, it would produce very large amounts of electricity without the carbon emissions of coal and gas, and without the long-lived high-level waste of conventional nuclear power. The catch is that nobody has yet built a fusion power station that puts more energy into the grid than it takes to run. It is one of the hardest engineering problems humans have ever attempted. That is where the computing comes in. Fusion involves controlling a gas hotter than the centre of the Sun, held in place by magnetic fields, in a state that changes from moment to moment. There is far more data than any team of physicists could work through by hand, and the behaviour is too complex to model with simple equations. The practical argument for joining the two machines is straightforward. Each lab has decades of experimental data the other does not. Training AI models on both is likely to produce better results than training on either alone. There is also a UK jobs angle. The government says the fusion sector is expected to support over 10,000 UK jobs by 2030.
What the evidence actually says
It is worth reading announcements like this carefully, because the language of international agreements can sound more concrete than it is. What was signed is a Joint Declaration of Intent to explore linking the two systems. That is a commitment to work on it seriously. It is not a switch being flipped this week. Connecting two national supercomputers involves real questions about security, data sharing and who is allowed to see what, and those questions have not been answered yet. The scientists involved are candid about why they are doing it. Jonathan Menard, Chief Scientist at Princeton Plasma Physics Laboratory, said: 'No single laboratory or nation will design [a fusion power plant] alone.' Joe Milnes, Executive Director for Engineering and Computing at UKAEA, said: 'Fusion needs partnerships. The US and UK are two global leaders in fusion research.' Rob Akers, UKAEA's Director of Computing Programmes, framed the benefit simply: 'Together, we can learn faster and extract maximum insight.' And Shantenu Jha, Head of Computational Sciences at PPPL, described the goal as turning 'a collection of supercomputers into a single engine for fusion discovery'. On timescales, honesty is important. Fusion electricity is not expected on the grid in the next few years. Most serious projections place commercial fusion power in the 2040s at the earliest, and there is genuine disagreement among experts about whether even that is optimistic. Anyone who tells you fusion will solve the energy bills problem this decade is overselling it.
Practical advice
This is a story about long-term science rather than something you need to act on. But there are a couple of sensible ways to think about it. If you are choosing subjects at school or thinking about a career, this is one of the areas where the UK genuinely is a world leader. Fusion needs physicists, but it also needs engineers, materials scientists, software developers, data specialists, welders, electricians and project managers. The jobs are concentrated around Oxfordshire and West Cumbria, with the STEP programme based in Nottinghamshire. If you follow energy news, treat fusion announcements with the same care you would treat a new medicine in an early trial. Promising early results are genuinely exciting, and also a long way from something you can use. And if you are thinking about your own energy bills, the things that make a difference now are the unglamorous ones: insulation, draught-proofing, and checking whether you are eligible for support such as the Warm Home Discount. Fusion is for your grandchildren's bills, not yours.
What to know
On 14 September 2026, the UK Atomic Energy Authority and the US Princeton Plasma Physics Laboratory signed a Joint Declaration of Intent to explore linking their fusion AI supercomputers, SUNRISE and STELLAR-AI. The aim is to train artificial intelligence on experimental data from both countries, and to build detailed computer models of future fusion power stations before they are built. A second agreement commits the two governments to closer co-operation on regulating fusion. SUNRISE was backed by £45 million of UK government funding. The sector is expected to support more than 10,000 UK jobs by 2030. This is a declaration of intent, not a finished link, and fusion electricity is still widely expected to be decades away. Sources: GOV.UK / UK Atomic Energy Authority, 'UK and US fusion supercomputers to be linked across Atlantic', 14 September 2026, https://www.gov.uk/government/news/uk-and-us-fusion-supercomputers-to-be-linked-across-atlantic. New Civil Engineer, 'UK and US governments sign two agreements to boost use of AI for commercial nuclear fusion', 14 September 2026, https://www.newcivilengineer.com/latest/uk-and-us-governments-sign-two-agreements-to-boost-use-of-ai-for-commercial-nuclear-fusion-14-09-2026/. Unite.AI, 'UKAEA and PPPL Agree to Explore Linking Fusion AI Supercomputers', September 2026, https://www.unite.ai/ukaea-and-pppl-agree-to-explore-linking-fusion-ai-supercomputers/. This article is for general information and does not replace advice from a doctor, pharmacist or other qualified healthcare professional.
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