Tokamak Energy
ST40 Spherical Fusion Reactor
LTi Metaltech, a UK expert in high-integrity welded structures and pressure vessel fabrication, was chosen by fusion pioneers Tokamak Energy to manufacture a vacuum chamber pressure vessel for the groundbreaking ST40 spherical Tokamak fusion reactor prototype.
This next-generation compact reactor, developed at a fraction of standard industry size, represents a major step forward in the pursuit of clean fusion energy. By combining high-temperature superconducting (HTS) magnets with spherical Tokamak technology, the ST40 creates the ideal conditions for nuclear fusion, reaching plasma temperatures hotter than the centre of the sun. In this environment, the isotopes deuterium and tritium fuse together, releasing vast amounts of clean energy.
With the world’s unsustainable reliance on fossil fuels and the urgent need to cut carbon emissions, fusion energy is recognised as a transformational breakthrough. It offers the potential for virtually limitless, carbon-free power - providing a sustainable solution to meet rising global energy demand and help combat the climate crisis.
The Challenge: Designing a Fusion-Ready Vacuum Vessel
For this project, LTi Metaltech was tasked with designing and manufacturing a new vacuum vessel chamber that could meet Tokamak Energy’s stringent requirements for specification, performance, and quality - all within a demanding delivery timeframe.
The engineering challenge was immense. The fabricated pressure vessel needed to withstand plasma conditions of more than 100 million°C - over seven times hotter than the centre of the sun. At the same time, it had to maintain flawless weld integrity, since the seals and joints in a nuclear fusion pressure vessel represent some of the most critical and failure-sensitive elements of the entire system.
In the nuclear fusion sector, there is simply no margin for error. Tolerances are exceptionally tight, precision is absolute, and compliance with EN 13445 European Pressure Vessel Standards is mandatory. For LTi, the challenge was to engineer a chamber that could meet these extreme demands, ensuring safety, reliability, and regulatory compliance at every stage of manufacture.
How LTi went about it
Drawing on its extensive expertise in high-integrity pressure vessel design and fabrication, LTi Metaltech transformed Tokamak Energy’s concept into reality by developing a robust stainless-steel vacuum vessel structure.
Working in full compliance with EN 13445 European Pressure Vessel Standards - which set the minimum requirements for the design, manufacture, and inspection of pressure vessels - LTi created an innovative IVC angled support fabrication design. Every stage of the project was carefully engineered to ensure that performance, safety, and compliance were built in from the outset.
To meet the extreme demands of the ST40 spherical Tokamak reactor, LTi introduced several critical design and fabrication innovations:
-
Precision weld engineering ensured structural reliability, with single-sided welds designed to include a minimum 4 mm backing gap. This was extended to 10 mm from the joint edge to prevent burn-through, enhancing long-term weld integrity.
-
Flange design enhancements incorporated raised surfaces around the flanges, improving both weld backing and component alignment during assembly.
-
Time-saving weld optimisation reduced fabrication hours by eliminating the need to grind back on certain double-sided welds, maintaining quality while increasing efficiency.
-
Structural simplification was achieved by adding preparation angles and machining square edges on coned features, streamlining manufacture without compromising performance.
-
Optimised geometry re-engineered the IVC outer wall into a cylindrical form, preventing voids from impacting the cone sections and ensuring overall stability.
These innovations delivered a vessel that combined manufacturing efficiency with uncompromising structural integrity, meeting the extreme conditions required for nuclear fusion applications.
What was the outcome?
LTi Metaltech successfully designed, developed, and delivered a high-integrity stainless-steel vacuum vessel that met Tokamak Energy’s exacting specifications, achieved exceptional quality standards, and was completed within the required timeframe.
The project demonstrated LTi’s ability to combine precision engineering, advanced welding innovation, and strict regulatory compliance to enable one of the most ambitious developments in the nuclear fusion sector. The impact of this achievement was recognised when LTi was awarded “Best Research & Development Project” at the Cotswold Life Engineering, Manufacturing & Innovation Awards 2017.
Most importantly, the project contributed directly to the successful development of the ST40 spherical Tokamak prototype, advancing the global pursuit of clean, sustainable fusion energy. By helping to overcome critical fabrication challenges, LTi reinforced its reputation as a trusted partner in delivering the high-performance pressure vessels essential to the future of carbon-free power.