UK-based Tokamak Energy has verified its new gyrotron system for its high field spherical tokamak ST40. The gyrotron team has completed site acceptance testing to verify the radio frequency (RF) heating system’s performance ahead of installation on the spherical tokamak.
The new gyrotron, built by Kyoto Fusioneering for Tokamak Energy over 18 months, 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. It also passed tests for repeatability, modulation, power control and mode purity, confirming it can consistently deliver the performance required for fusion experiments.
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. STEP (Spherical Tokamak for Energy Production) is the UK’s flagship government programme to design and build a prototype fusion power plant by 2040. The ST40 serves as a primary physical test platform for STEP. It allows engineers to test real-world magnetic configurations, plasma stability, and coil forces, drastically accelerating engineering validation cycles over software simulations alone
The gyrotron 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 (DOE) and the UK Department for Energy Security and Net Zero (DESNZ). The LEAPS (Lithium Evaporations to Advance PFCs in ST40) programme is a $52m public-private upgrade initiative funded jointly by DOE and DESNZ.
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.
Kyoto Fusioneering’s plasma heating experts are working work directly at Tokamak Energy’s Oxfordshire headquarters to support installation, commissioning, and system testing. Both companies are core participants in the FAST (Fusion by Advanced Superconducting Tokamak) project, an industrial-academic collaboration led by Starlight Engine. It aims to demonstrate net fusion power in Japan by the 2030s.
Within FAST, Tokamak Energy supplies its specialised high-temperature superconducting (HTS) magnet and tokamak design expertise, while Kyoto Fusioneering drives the plant engineering and plasma design. Kyoto Fusioneering maintains a strong corporate presence in the UK (with facilities in Reading and a major hub at the Culham Campus).
This geographical proximity aligns perfectly with Tokamak Energy’s UK-based operations and their shared involvement with public programmes such as the UK Atomic Energy Authority (UKAEA). Tokamak Energy operates a dedicated subsidiary, Tokamak Energy KK, which manages its relationship with Kyoto Fusioneering and other Japanese entities to coordinate global supply chains.
