STEP Fusion, the UK’s flagship fusion energy programme, has presented the latest evolution of its STEP Prototype Powerplant (SPP) design at SOFT 2026, the 34th Symposium on Fusion Technology in Aix-en-Provence, unveiling new design innovations to improve the commercial viability of future fusion power plants
The presentation revealed SPP3, the third generation of the STEP prototype plant design and the latest milestone in the programme’s ongoing work to deliver a prototype fusion powerplant capable of producing net electricity and paving the way for a future commercial fleet.
Building on previous design iterations, SPP3 demonstrates how targeted improvements in key technologies and plant architecture could enhance performance, maintainability and operational availability.
The presentation focused on the ambition to increase gyrotron efficiency, the high-power microwave systems used to heat and sustain fusion plasmas.
The SPP3 design also strengthens one of STEP’s key differentiators: a spherical tokamak concept designed to support steady-state operation, rather than being intrinsically pulsed. This approach is intended to maximise electricity production and provide a more direct route to commercially attractive fusion power plants.
In addition to advances in plasma heating, STEP presented new details of its approach to maintenance and plant availability, including its vertical maintenance strategy and emerging stacked rings architecture.
These innovations can simplify access to in-vessel components, reduce maintenance outages and support the high levels of availability required from future fusion power plants.
The stacked rings concept, discussed publicly for the first time at an international conference, forms part of STEP’s wider strategy to design a powerplant that can generate electricity and be maintained quickly enough to achieve high availability and operate efficiently throughout its lifetime.
Sam Davis, head of Engineering for the Tokamak Machine at STEP Fusion, said, “This is all very hard, but we have to keep sight of the benefits. We are consciously taking on some of these technical challenges and uncertainties because they unlock steady-state operation and practical maintenance.
“And of course, we’re doing everything we can to mitigate the risks in the meantime, for example by testing everything we can.”
The SPP3 design continues STEP’s focus on delivering net electrical output, achieving fuel self-sufficiency, and creating a design that industrial partners can replicate as part of a future fleet of fusion power plants.
Presented to the international fusion community at SOFT 2026, SPP3 represents the latest step in the programme’s progression from concept design towards a commercially relevant prototype power plant.
