General Fusion has measured electron temperatures above 12 million degrees Celsius during mechanical compression of a magnetised plasma in its Lawson Machine 26 (LM26) experimental system. The result, obtained with diagnostics developed in collaboration with the UK Atomic Energy Authority (UKAEA), establishes the first major temperature milestone of the company’s programme to investigate magnetised target fusion.
Thomson scattering diagnostics measured an electron temperature of approximately 1.1 kiloelectronvolts, equivalent to 12.6 million degrees Celsius, shortly before peak plasma compression. The associated technical paper reports 1,090 electronvolts with an uncertainty of 40 electronvolts during a specified LM26 shot. These figures describe the electron population in the plasma and provide an experimental heating measurement, without establishing net fusion energy production.
In LM26, a mechanically driven solid lithium liner collapses around magnetised plasma, reducing its volume and transferring energy that raises its density and temperature. General Fusion is investigating whether mechanical compression can produce useful fusion conditions without the superconducting magnets used in some magnetic confinement systems or the powerful lasers employed in certain inertial confinement experiments. Performance will depend on maintaining the plasma during the compression interval.
As the liner moves inward, magnetic confinement must keep the plasma sufficiently stable while it becomes denser and hotter. Radiation, interaction with surrounding material and other loss mechanisms can remove energy before the intended conditions are reached. The measured temperature therefore marks progress in compression heating, while adequate density and energy confinement remain additional requirements for a power producing system.
LM26 uses the solid liner to investigate compression physics and provide measurements for later machine designs. General Fusion’s planned commercial approach involves a liquid metal boundary, introducing additional engineering work on repeated compression, circulation of the material and management of heat between operations. These systems would have to operate together reliably before the concept could support sustained industrial generation.
The contracting liner also restricts optical access to the plasma, leaving only a short interval in which diagnostic measurements can be made. Thomson scattering uses laser light directed into the plasma and analyses the light scattered by electrons to determine temperature from its spectral characteristics. Background light produced by the experiment must be distinguished from that measurement signal to obtain usable results.
To meet those measurement constraints, UKAEA supplied a specialised polychromator that separates scattered light into wavelength ranges suitable for analysis. The diagnostic uses narrow optical views and a relatively small scattering angle adapted to LM26’s geometry. Measurements at different stages of compression enabled the researchers to trace the change in electron temperature as the plasma volume decreased.
Observations at successive times and two spatial positions allowed the team to examine the heating progression rather than relying on a single temperature measurement near maximum compression. This evidence helps distinguish the behaviour of the plasma during the compression sequence, although other instruments are needed to investigate the remaining quantities relevant to fusion performance. The combined results provide a broader account of the experiment than any one diagnostic technique.
Using absolute extreme ultraviolet diagnostics, General Fusion estimated an electron temperature of approximately 1.2 keV at peak compression, compared with the Thomson scattering result obtained just beforehand. Analysis involving neutron yield, plasma density and diagnostic reconstruction also yielded an inferred ion temperature of approximately 0.46 keV. These values concern different particle populations or measurement techniques, providing complementary evidence without being interchangeable.
Electron and ion temperatures can differ during rapid plasma heating because the two populations exchange energy over time. Fusion reactions depend directly on ion behaviour, while the measured electron temperature provides evidence of heating and aspects of energy confinement. Interpreting the results therefore requires both particle populations to be considered alongside density, confinement duration and the losses occurring during compression.
The latest result extends earlier LM26 experiments in which General Fusion measured electron heating to approximately 0.72 keV. Reaching about 1.1 keV exceeds its initial 1 keV objective and provides evidence of further heating under mechanical compression. The next target of 10 keV will require additional improvements in starting plasma conditions, compression performance and control of energy losses.
Achieving higher temperatures will still leave density and confinement time to be established at appropriate levels. These quantities are combined in the Lawson criterion, which describes the requirements for an energetically useful fusion reaction under specified assumptions. A generating installation must ultimately deliver all the necessary conditions together and account for the energy consumed by the machine and its supporting equipment.
Progress beyond individual experimental shots will also depend on achieving repeatable results from target formation and compression. Where LM26 provides measurements from selected operations, a future power system would require dependable compression hardware, cooling, energy recovery and repeated cycling of the target material. The reliability and maintenance requirements of those interconnected systems remain to be demonstrated.
UKAEA’s diagnostic contribution draws on its experience with other fusion systems but has been adapted to the restricted access and timing of LM26. The joint measurements provide evidence of plasma heating during mechanical compression, supplemented by General Fusion’s other diagnostic results. The related technical papers have been submitted for peer review and remain at that stage.
General Fusion is upgrading LM26 for further compression experiments, with 10 keV identified as the next temperature objective. Progress towards a commercial fusion plant will depend on higher plasma temperatures, sufficient density and confinement, and equipment capable of reliable repeated operation under industrial conditions.
