General Fusion reports electron temperatures exceeding 1 keV

General Fusion announced it has achieved compressional plasma heating that produced electron temperatures exceeding 1 keV, measured using Thomson scattering in collaboration with the U.K. Atomic Energy Authority.

The 1 keV threshold is regarded as a key milestone, because it demonstrates the ability to produce and control fusion-relevant plasma temperatures. It was first reported on the Soviet T3 tokamak, announced in 1968 and independently verified by U.K. physicists using Thomson scattering the following year. While not the first fusion company to achieve this threshold, it is a first for General Fusion's unique magnetized target fusion approach, which uses low-speed compression.

Temperature measurements: Thomson scattering requires shining a laser through the plasma and analyzing how the light scatters from the particles inside it, allowing for an accurate measurement without disturbing the plasma.

General Fusion measured electron temperatures of approximately 1.1 keV just prior to peak compression using Thomson scattering in collaboration with the UKAEA, the company said. It has submitted a paper on this achievement for peer review.

The UKAEA said it was a "significant technical challenge" to apply Thomson scattering to the machine, which has a design that severely limits diagnostic access and visibility.

"Despite these constraints, diagnostic specialists from UKAEA and General Fusion jointly designed and commissioned a Thomson scattering system that successfully measured the plasma near peak compression conditions," the agency said.

General Fusion used a polychromator designed by the UKAEA at its newly established Diagnostic Innovation Center of Excellence facility, which develops advanced measurement technology for fusion systems.

The company also conducted absolute extreme ultraviolet diagnostics, the results of which it said closely aligned with the Thomson scattering trend and measured electron temperatures of approximately 1.2 keV during peak compression to verify the results. A separate paper containing those results also has been submitted.

Neutron yield and plasma density profile measurements, as well as time-dependent reconstruction of diagnostic data, also were used to infer ion heating of approximately 0.46 keV.

"Taken all together, we saw plasma temperature, density, and magnetic field all increase as expected-a consistent, corroborated picture of a plasma that stayed stable and got hot through low-speed compression alone," the company said.

Fusion approach: General Fusion's demonstration machine, Lawson Machine 26 (LM26), uses magnetized target fusion to heat magnetically confined plasma through compression on the order of milliseconds, which is considered low speed, using an electromagnetic theta-pinch to implode a solid lithium liner. This approach does not require superconducting magnets or high-power lasers.

LM26 was assembled in 2024 and achieved first plasma and first plasma compression in 2025.

According to General Fusion, LM26 is undergoing upgrades to reach the program's next milestone, which is compressional heating to 10 keV followed by advancing toward the Lawson criterion.

While LM26 does not test these elements, General Fusion plans to use a liquid lithium wall surrounding the fusion chamber to breed fuel, protect the machine from neutron damage, and act as a heat exchanger to enable energy conversion. A rotating chamber of pistons will compress the liquid metal around the plasma, compressing it to achieve fusion conditions.

The company's goal is to achieve net fusion energy by 2028 and a fusion plant by 2035.

The 1 keV club: Research devices using multiple fusion approaches have achieved electron temperatures of 1 keV or higher, but only a handful of private fusion companies have reported the milestone.

In 2023, Tokamak Energy published a paper reporting electron temperatures greater than 1 keV in its spherical tokamak, and Helion reported 1 keV electron temperatures using a pulsed magneto-inertial fusion approach in its seventh prototype device. In 2024, Zap Energy announced it had reached 1-3 keV plasma electron temperatures using its sheared-flow-stabilized Z-pinch approach and published the results in Physical Review Letters.

They said it: "Achieving a plasma electron temperature of over 1 keV marks an important milestone for General Fusion, since achieving hot electrons is a necessary step for proving fusion confinement concepts. This achievement reflects the tangible progress being made by General Fusion and others across a diverse set of fusion approaches in the private sector, while the collaboration with UKAEA, contributing its specialist expertise, highlights the value of robust public-private partnerships in broadly advancing fusion and sharing scientific results," said UKAEA CEO Dennis Whyte.

"Reaching more than 1 keV on LM26, alongside confirmed ion heating and corroborating AXUV data, is an important step forward for General Fusion and a meaningful validation of the approach we have spent more than two decades developing. It shows that we are delivering against the technical roadmap we set out for LM26 and gives us greater confidence as we advance toward our next target of 10 keV, the Lawson criterion and practical and economical fusion power at commercial scale," said General Fusion CEO Greg Twinney.