The gyrotron team has successfully completed site acceptance testing to verify the radio frequency (RF) heating system’s performance ahead of installation on its record-breaking spherical tokamak.

The new gyrotron will generate high-power electromagnetic waves for controlling and heating a hydrogen plasma many times hotter than the centre of the sun. It will also be used to start up and drive plasma current.

During testing, the gyrotron demonstrated reliable 1 MW operation at both 104 GHz and 137 GHz, with pulse lengths of up to two seconds. Built by Kyoto Fusioneering for Tokamak Energy over 18 months, it also passed tests for repeatability, modulation, power control and mode purity, confirming it can consistently deliver the performance required for fusion experiments.

Through this project, the company is building valuable expertise in the integration and operation of high-power RF systems – a key technology for the next generation of fusion devices.

The focus now shifts to preparing the launcher, mirror polariser, transmission line and control systems ahead of installation and commissioning on ST40.

Once operational, the gyrotron will provide additional heating and current drive to ST40, supporting higher plasma performance and an experimental campaign exploring plasma heating, current drive, startup and ramp-up scenarios.

The project forms part of the company’s work with UK Fusion Energy (UKFE), helping build knowledge and capability for the UK’s STEP programme – a spherical tokamak design.

It will also play a key role in LEAPS, the company’s ST40 upgrade programme focussed on lithium systems supported by the US Department of Energy and the UK Department for Energy Security and Net Zero.

How does a gyrotron work?

A beam of electrons travels through a strong magnetic field which accelerates them to the point where they emit microwave radiation. This is directed through a waveguide to the plasma of fusion fuels – isotopes of hydrogen.

The frequency of the microwaves is tuned to match the cyclotron resonance frequency of the electrons in the plasma (104GHz or 137GHz in the case of ST40). When the microwaves interact with the plasma, they transfer energy to the electrons, which heats and drives the plasma.

A gyrotron, which uses Electron Cyclotron Resonance Heating (ECRH), solves one of the key challenges for a spherical tokamak – limited space for a central solenoid, which would otherwise be required to induce the plasma current. A gyrotron means the central solenoid can be reduced in size.

A big advantage over neutral beam heating is that gyrotrons can be positioned away from the device itself, whereas neutral beam heating needs to be very close.

On ST40, Tokamak Energy plans to use both its current neutral beam heating and gyrotron heating simultaneously. This will build greater understanding of how a gyrotron works, the control systems needed and the best balance between the two forms of heating.

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The year 2023 was officially the hottest ever. The EU’s climate service primarily attributes the record temperatures, almost 1.5C higher than the long-term average, to humans burning fossil fuels.

Alarming Copernicus Climate Change Service data also saw a new daily global temperature record set on more than 200 days of the year. Fossil fuels are changing our planet, ruining lives and wiping out livelihoods.

Energy demand is set to increase by 40% by 2035, so what next? These new figures are a stark reminder of the urgent need to both decarbonise today and invest in the technologies that can unlock the energy transition of tomorrow.

A complete energy transition cannot be achieved without fusion power – a transformative, global source of near limitless, clean, safe energy. Fusion energy, the power of the sun and stars, has the unique ability to support and sustain a long-term, permanent transition by ensuring future clean energy supplies are resilient, flexible and safe for our communities.

Furthermore, fusion offers reliable electricity and industrial heat to decarbonise essential heavy industries such as metal and fertiliser production with no harmful emissions.

Recent progress has shown fusion is no longer fantasy. Collaboration by the public and private sectors, national strategies and ambitious power plant programmes in the UK and U.S. are being boosted by advances in artificial intelligence and machine learning.

The best supercomputers are so powerful they can simulate what is happening inside a fusion device, accelerating power plant designs at rates impossible to replicate using present day physical devices. It is the power of AI that will break barriers and accelerate the path to commercial fusion in time to make a difference.

It has the potential to knock years off timelines and cut costs, and this will only gather momentum with better technology, training and computing power. This is just the beginning.

Digital twin

A tokamak digital twin is invaluable in optimising and validating experimental scenarios and developing plasma control systems at a much faster rate than contemporary machines can handle.

Take Oxford-based Tokamak Energy’s current operating device, ST40, which reached plasma temperatures of 100 million degrees Celsius in 2022 as part of the company’s mission to deliver commercial fusion in the 2030s. That is six times hotter than the centre of the sun. It can run plasma pulses up to 20 times a day when operational for approximately one third of the year, either side of upgrades and routine maintenance.

Crucially, these experiments produce real, measurable, publishable, verifiable results in the real world. Once you have that, digital twin simulations become really valuable.

Running a pulse in a digital twin takes only a second, creating a virtually unlimited space for exploration and scientific discovery. When combined with rapid advances in superconductor magnet technology, used to confine and control the plasma, and materials research, AI has huge potential to cram years and cut costs of fusion development. How else can we avoid breaching key international climate targets?

“Artificial intelligence can help us solve some of the greatest challenges of our time,” Prime Minister Rishi Sunak said when setting out his national vision at the Royal Society in the Autumn. Arguably the greatest and most urgent scientific and engineering challenge of them all is delivering fusion energy to the grid, and AI will provide the breakthrough the world needs.

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