General Fusion and UKAEA measured 1.1 keV inside LM26’s metal liner

Magnetised Target Fusion on LM26 read 1.1 keV by Thomson scattering and about 1.2 keV by AXUV

(Image courtesy of United Kingdom Atomic Energy Authority)

Professor Dennis Whyte, UKAEA’s chief executive, points back to 1969, when a UK team used the then-new Thomson scattering technique to verify 1 keV electrons in a Russian tokamak. UKAEA specialists have now helped General Fusion measure an electron temperature of 1.1 keV, or 12.6 million degrees Celsius, in its Lawson Machine 26 (LM26), a result the announcement calls a world first for the company’s Magnetised Target Fusion approach.

Measuring Magnetised Target Fusion plasma inside a metal liner

Reading the temperature inside LM26 was a significant technical challenge. The plasma is enclosed within a metal liner and compressed to a very small volume, which severely limits diagnostic access and visibility.

Despite those constraints, diagnostic specialists from UKAEA and General Fusion jointly designed and commissioned a Thomson scattering system that measured the plasma near peak compression. The technique fires a laser through the plasma and analyses how the light scatters from the particles inside it, which gives an accurate temperature reading without disturbing the plasma.

UKAEA designed and built a polychromator, one of the system’s key components, at its Diagnostic Innovation Centre of Excellence (DICE) at the Culham Campus. It cites decades of experience operating JET and MAST Upgrade behind its plasma diagnostics expertise.

Magnetised Target Fusion plasma reads above 1 keV on two diagnostics

In Magnetised Target Fusion, LM26 compresses magnetically confined plasma with a solid metal wall over milliseconds, which UKAEA’s release sets against microseconds or nanoseconds for other plasma compression technologies. General Fusion describes LM26 as the first fusion machine to reach 1 keV with low-speed compression. The Thomson scattering system read approximately 1.1 keV just prior to peak compression, while at peak compression, a deeper point at which Thomson scattering measurement is not available, General Fusion’s absolute extreme ultraviolet (AXUV) diagnostic recorded approximately 1.2 keV, or 13.7 million degrees Celsius. According to the company, the AXUV data closely aligned with the Thomson scattering heating trend.

Ion heating also reached approximately 0.46 keV during compression, up to a twofold increase above the starting ion temperature. General Fusion infers ion temperature from neutron yield and plasma density profile, and from a time-dependent reconstruction of diagnostic data.

Before this, General Fusion reported 0.72 keV, or 8.4 million degrees Celsius, in June 2026, with an uncertainty of plus or minus 0.08 keV. It described that as a more than threefold rise in electron temperature during mechanical compression, largely from compressional heating.

The 10 keV milestone and the diagnostics behind it

Whyte said hot electrons are a necessary step for proving fusion confinement concepts. General Fusion designed the LM26 programme around three technical milestones, and the 1 keV result completes the first. Upgrades are now under way to support the higher plasma compression ratios needed for the second, 10 keV, and the programme then advances toward the Lawson criterion, the combination of temperature, density and energy confinement time required for net fusion energy in the plasma. It supports the company’s goal to begin operating a first-of-a-kind plant around 2035.

Its Magnetised Target Fusion design aims to use a liquid metal wall with existing materials, and to avoid superconducting magnets and high-powered lasers.General Fusion Group Ltd has traded on Nasdaq as GFUZ since July 2026, entering public markets with approximately US$150 million in cash.

In November 2024, General Fusion named TRIUMF, UKAEA, Université de Sherbrooke and the University of Lisbon, among others, as collaborators on LM26 diagnostics. In May 2026 it announced a collaboration with General Atomics Energy Group, which is advising on the diagnostic system for the 10 keV milestone, including advanced tools to measure ion and electron temperature and density.

Both papers have been submitted for peer review, and UKAEA says it looks forward to the outcome and to publication of the paper in Review of Scientific Instruments.

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