A crucial fuel-heating technology which will be used in future fusion energy power plants will start being installed on Tokamak Energy’s high field spherical tokamak ST40 this year.
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.
Kyoto Fusioneering built the gyrotron, which will produce 1MW of Radio Frequency (RF) power, for Tokamak Energy over 18 months. It was delivered to the company’s Oxfordshire headquarters from Japan in late December 2024 ready for installation and commissioning.
The gyrotron upgrade complements a recently announced collaboration between the U.S. Department of Energy (DOE), the UK’s Department of Energy Security and Net Zero (DESNZ) and Tokamak Energy. Once the gyrotron is in operation, the partners will be able to advance the fusion science and technology needed to deliver a future pilot plant by testing lithium on the inner wall of ST40.
Dr Ross Morgan, Director of Strategic Partnerships at Tokamak Energy, said: “We’re excited to work with our partners Kyoto Fusioneering to add this important upgrade to our record-breaking fusion machine, and continue to operate ST40 to test and push new boundaries. The results from future experiments using the high-power gyrotron heating system will provide critical data to inform the design of future spherical tokamak pilot plants, on our mission to commercialise clean and limitless fusion energy in the 2030s.”
Dr Satoshi Konishi, Kyoto Fusioneering’s CEO, Chief Fusioneer, and Co-Founder, said: “We are honoured to contribute to Tokamak Energy’s ST40, which stands as a benchmark for public-private partnerships and international collaboration. This partnership, bolstered by strong UK-Japan collaboration, represents a significant step forward in the pursuit of fusion energy. Committed to delivering world-class gyrotrons and exceptional engineering support, we look forward to working together to achieve the shared goal of clean, sustainable fusion power.”
Tokamak Energy’s ST40 has reached a plasma ion temperature greater than 100 million degrees Celsius, the threshold required for commercial fusion energy and the highest ever achieved in a privately funded spherical tokamak.
Tokamak Energy recently presented the first details of its fusion energy pilot plant being designed as part of the DOE Milestone-Based Fusion Development Program, established for private firms to bring fusion towards technical and commercial viability.
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.