On October 8, 2026, Canada's General Fusion announced that its Lawson Machine 26 (LM26) fusion demonstration device had pushed a metal liner inward to compress plasma and raised the electron temperature above 1 keV. In laser measurements conducted jointly with the UK Atomic Energy Authority (UKAEA), it recorded about 1.1 keV (roughly 12 million °C by the company's conversion). That exceeds the roughly 0.72 keV reported in June and means LM26 has met its first temperature target. However, the 12-million-degree figure is an electron temperature, and it must be distinguished from the temperature of the fuel ions that actually undergo fusion, and from the energy balance of the machine as a whole. The two published papers confirm that compression can heat the plasma, but they also reveal challenges that arise when compressing more strongly.
A Fusion Approach That Compresses Plasma With Metal Reaches 1 keV
LM26 surrounds plasma with a solid lithium liner that has an initial diameter of 1.76 m. A liner is a cylindrical component placed inside a vessel. When current flows through external coils, the resulting magnetic field pushes the liner inward and compresses the plasma inside. As the plasma's volume shrinks, its density and temperature rise. In this experiment, it took about 3 milliseconds from the start of compression for the electron temperature to reach its peak.
General Fusion calls this approach "magnetized target fusion." A plasma confined by a magnetic field is formed in advance, and the metal surrounding it is squeezed inward to heat it. The design does not rely on superconducting magnets or high-power lasers for heating and compression, but it does not dispense with magnetic fields. The stability of the plasma is also adjusted by current flowing along the central axis, and the heating analysis takes into account "ohmic heating," which is produced by the plasma's internal electrical resistance. This is not simply a machine that crushes plasma with the force of metal. The paper describing the device and its heating mechanism positions compression as the primary heating method.
Three milliseconds is an instant by everyday standards, but it counts as "slow" compared with approaches that compress fuel over microseconds or nanoseconds. What General Fusion and UKAEA, in their joint announcement, describe as a world first is reaching 1 keV through this slow compression. The temperature of 1 keV itself is not a record high in fusion research. UKAEA also notes the history of a Russian tokamak that verified an electron temperature of 1 keV in 1969.
In its June 22 announcement, General Fusion had reported an electron temperature of 0.72±0.08 keV. This time, heating above 1 keV was also confirmed using a different measurement technique. The company's development approach of sustaining the plasma during compression and raising its temperature while limiting heat loss has advanced to a new stage in a large-scale demonstration machine.
Electrons and Ions at Different Temperatures: What Three Measurements Show
In the compression experiment "LMC-12," which recorded the highest temperature this time, both the electron temperature and the deuterium ion temperature were examined. Electrons and ions move separately in plasma, so their temperatures do not always match. Because it is the atomic nuclei that undergo fusion, it is necessary to confirm the temperature of the fuel ions, not only how far the electrons were heated.
The figure of more than 1 keV achieved by LM26 refers to electron temperature; the deuterium ion temperature estimated in the same LMC-12 experiment was 0.459±0.033 keV.
| Target / method | Reported temperature | Radial compression ratio at measurement | What the measurement represents |
|---|---|---|---|
| Electrons, Thomson scattering | 1.090±0.040 keV | 2.35 | Measured from scattered laser light |
| Electrons, soft X-ray AXUV diagnostic | 1.180±0.065 keV | 2.75 | Estimated from the ratio of filtered radiation signals |
| Deuterium ions, neutron diagnostics | 0.459±0.033 keV | 2.6 | Estimated from neutron yield and plasma density distribution |
The table extracts LMC-12 measurements from the Thomson scattering paper dated October 6, 2026, and the compressional heating paper. The original eV values and their uncertainties have each been divided by 1,000 to unify them in keV. The radial compression ratio is the liner's radius before compression divided by its radius at the time of measurement. Because the three measurements differ in when and where they were observed, it is not possible to simply calculate an electron-to-ion temperature ratio or to compare them as results measured simultaneously at the same location.
A thomson scattering measurement system designed jointly with UKAEA played an important role in measuring the electron temperature this time. Laser light is shone on the plasma, and the electron temperature is derived from the wavelength distribution of light scattered by electrons. An explanation from the National Institute for Fusion Science also describes how the wavelength of the scattered light relates to the speed of the electrons. In LM26, the path of the laser light narrows as the metal liner moves inward. The team therefore set up a configuration capable of measuring at two locations and eight points in time, and captured an electron temperature above 1 keV just before the optical path was blocked.
However, the peak temperature of about 1.180 keV was not measured directly by Thomson scattering. Temperatures at the later stage of compression were tracked with the AXUV diagnostic, which detects soft X-rays. The trends in temperature rise broadly agreed between Thomson scattering and the AXUV diagnostic, but the two observe different locations and rely on different measurement principles. Clearly stating these measurement limitations and cross-checking multiple diagnostics is an important point in evaluating this result. Note also that although the approach does not use high-power lasers for heating or compression, lasers are used to measure the temperature.
Meanwhile, the ion temperature was estimated using a reaction-rate formula based on the number of neutrons produced by fusion reactions and the plasma's density distribution. This calculation assumes that the ion velocity distribution follows a Maxwell distribution, which corresponds to thermal equilibrium. It is therefore not a figure measured directly in the way the electron temperature was. Ion heating was also confirmed, but the fact that the electron temperature exceeded 1 keV does not mean that the entire fuel reached the same temperature.
The measurement paper co-authored by P. Carle and others with UKAEA's M. Maslov, and the heating paper by S. J. Howard and others, had both been submitted for peer review at the time of publication. UKAEA's participation in the measurements is a factor in judging the reliability of the results, but peer review has not been completed, nor has independent replication been carried out on another device.
Why Temperature Dropped Sharply in the Later Stage of Compression
In LMC-12, the electron temperature peaked when the radial compression ratio reached 2.75, and then fell sharply. Stronger compression did not cause the temperature to keep rising accordingly. In connection with this phenomenon, the heating paper mentions that the plasma's internal electrical resistance increased and the plasma current began to decay.
To sustain the plasma into the later stage of compression, it is necessary to suppress instabilities arising in the magnetic field and plasma flow, reduce the admixture of impurities, and also control the effect of magnetic flux diffusing into the liner. For example, impurities cause radiative cooling and increased electrical resistance. Flux diffusion also impairs the plasma's ability to retain particles and heat. The authors cite multiple factors and do not explain the temperature drop this time by a single cause.
To put the advantages of slow compression to use in power generation, the relationship between the time required for compression and the time the plasma can retain heat needs to be improved. According to the paper, when the energy confinement time becomes shorter than the time remaining until compression is complete, the temperature will soon fall. Strengthening the compressing force and achieving a sufficiently hot, dense state before heat escapes are separate challenges.
The next target is 10 keV. According to General Fusion's announcement, modifications to achieve larger compression ratios have already begun. The heating paper describes a plan to change the compression section to a conically converging geometry so as to compress more strongly in a similar amount of time. In addition to upgrading the power supplies used to create and compress the plasma, the company plans to add gas injection valves to adjust fuel supply and to update the diagnostic systems. Extending the temperature record further will require improving the device so that the plasma can be sustained under stronger compression and that state can be measured accurately.
From Solid Lithium Demonstration to a Power Plant Using Liquid Metal
In LM26's compression experiments, the spent solid liner and central axis are removed and replaced with new components. The vacuum is then re-established and the diagnostic instruments reinstalled before the next experiment proceeds. This procedure also shows that there is still a large gap between this temperature demonstration and the operating method required of an actual power plant.
What General Fusion envisions for commercialization is a method that compresses plasma with a wall of liquid lithium. The liquid metal is meant not only to absorb neutrons and protect structures, but also to breed tritium, a fusion fuel, and to recover heat. The recovered heat generates steam, which turns a turbine to produce electricity. The company believes that by having the liquid metal perform these multiple functions, it can realize power generation facilities that can readily make use of existing materials and technologies. However, the experiment using a solid liner this time did not demonstrate fuel breeding or a power generation cycle using liquid metal.
Beyond the temperature target lies the "Lawson criterion." According to ITER's explanation, the conditions required for fusion to succeed are evaluated by a combination of temperature, particle number density, and energy confinement time. Raising temperature alone is not enough, nor is raising density alone. In its commercialization plan, General Fusion states its intention to use hydrogen fuel in LM26 to demonstrate that these conditions are met simultaneously, corresponding to a state in which, with deuterium-tritium (D-T) plasma, fusion output would exceed heat losses.
However, this is a separate stage from demonstrating that an entire power plant can extract more electricity than it takes in. Further engineering validation will be needed to repeat plasma compression and fuel supply, handle liquid metal, and integrate heat exchange equipment. The company's development plan also includes steps to demonstrate components and mechanisms that can withstand high-frequency repeated operation, liquid metal systems, and the plant's surrounding equipment. The result that electron temperature reached 1 keV alone does not allow estimates of equipment lifetime or the cost of generating electricity.
In an October 8 explanation, CEO Greg Twinney said the company aims to achieve the Lawson criterion by the end of 2028 and to begin operating its first power plant around 2035. Both are development goals set by the company, and the results of this experiment do not guarantee that they will be realized on schedule.
In the upcoming experiments aiming for 10 keV, key criteria will be how far the fuel ions can be heated and whether the hot state can be maintained into the later stage of compression. Furthermore, if operation that repeats this process using liquid metal can be demonstrated, it will become possible to evaluate more concretely the feasibility of the fusion power plant General Fusion envisions, which combines mechanical compression technology with heat exchange technology.