The UK’s MAST Upgrade fusion programme is preparing to investigate plasma temperatures of up to 60 million degrees Celsius following a major engineering milestone at UKAEA’s Culham Campus.
A newly installed 12-tonne vessel, known as a double beam box, will accommodate two additional neutral beam injectors, significantly expanding the machine’s heating capabilities.
The upgrade will increase MAST Upgrade’s neutral beam heating power from 4.4 megawatts (MW) to 8.8 MW, giving researchers greater scope to investigate the extreme plasma conditions needed to develop future fusion power plants, including the UK’s STEP prototype.
Preparing fusion plasma for higher temperatures
Achieving the conditions necessary for fusion requires heating fuel to extremely high temperatures.
MAST Upgrade currently uses neutral beam injection technology to heat its plasma, firing high-energy neutral atoms into the fuel to raise its temperature beyond 30 million degrees Celsius.
The additional injectors will provide twice the existing heating power, with plasma temperatures expected to reach approximately 60 million degrees Celsius.
Investigating these conditions will help scientists better understand the physics and technologies required to make fusion energy commercially viable.
This research will also contribute to the development of future fusion power plants, where maintaining and controlling extremely hot plasma is a fundamental challenge.
The double beam box has been designed with two internal levels to accommodate the additional injection equipment, making its installation an important step towards expanding the machine’s experimental capabilities.
Multiple upgrades support expanded research
The vessel installation is one part of a broader engineering programme at Culham, with several other modifications being undertaken to prepare MAST Upgrade for its next phase of research.
These include installing a new electron Bernstein wave (EBW) microwave heating system, alongside adapting power supply equipment previously used by the Joint European Torus (JET).
Engineers are also developing a beam line module to form and direct the neutral beams into the plasma. A cryopump is being manufactured to regulate pressure within the double beam box, while positive ion neutral injectors (PINIs) are also being installed.
The work represents a substantial engineering programme, with multiple systems needing to be completed and integrated before the upgraded machine can begin its next experiments.
Andrew Thornton, Head of MAST Upgrade Operations at UKAEA, explained: “The lift of the double beam box is a huge step forward for MAST Upgrade. By doubling our heating power, we will explore plasma conditions we simply couldn’t reach before.
“We will be able to study the stability of higher-pressure plasmas while testing how the MAST Upgrade exhaust system copes with these hotter, higher-performance plasmas.
“These are crucial questions for STEP and future fusion power plants. It’s also a great example of the engineering skill and collaboration across UKAEA’s science and engineering teams.”
2028 experiments mark next milestone
The completed double beam box, including its lid, will weigh approximately 15 tonnes and have a volume of 20 cubic metres.
Its construction uses 316L stainless steel, chosen for its strength, durability and corrosion resistance. The material is also compatible with the ultra-high vacuum conditions required inside the vessel.
UKAEA expects all major hardware to be manufactured and installed within the structure by the end of autumn 2027. Commissioning will follow, with scientific experiments scheduled to begin in 2028.
These experiments will allow researchers to explore the higher-energy plasma conditions made possible by the latest MAST Upgrade improvements, supporting the wider development of fusion power technology.
