What does keV mean as a plasma temperature?
An electronvolt (eV) is a tiny unit of energy. Plasma physicists also use it to state temperature. One keV, or 1,000 electronvolts, corresponds to roughly 11.6 million kelvin.
Also known as: keV, kiloelectronvolt, electron volt
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What the unit measures
An electronvolt is a unit of energy. NIST defines it as the kinetic energy an electron gains passing through a potential difference of 1 volt in a vacuum. That is a very small amount of energy. A kiloelectronvolt, or keV, is 1,000 electronvolts.
Fusion researchers also give plasma temperature in electronvolts, Zap Energy explains. NIST gives the conversion to temperature as about 11,604.5 kelvin per electronvolt. Rounded, one electronvolt corresponds to about 11,600 kelvin. So 1 keV, a thousand times more, is roughly 11.6 million kelvin. Zap put its own readings of 1 to 3 keV at roughly 11 to 37 million degrees Celsius.
Electron and ion temperatures
A plasma holds free electrons and much heavier atomic nuclei, called ions. Researchers can measure the temperature of each separately, Zap says. Ions are more than a thousand times heavier than electrons. So the two can heat and cool at different rates.
Fusion happens when ions collide, so the ions are what must reach fusion temperatures. But electrons can cool a plasma quickly. Physicists worry about cold electrons holding back ion heating, Zap says. That is why hot electrons count as a milestone.
Why 1 keV is a benchmark
The 1 keV mark has a long history. It was first reported on the Soviet T3 tokamak, announced in 1968, Nuclear Newswire notes. UK physicists verified it the following year with Thomson scattering, a laser measuring method. The newswire says only a handful of private fusion companies have reported the milestone.
On October 8, 2026, General Fusion and the UK Atomic Energy Authority reported 1.1 keV on the LM26 machine. They put that at 12.6 million degrees Celsius. The paper has been submitted for peer review. The company also reported ion heating to about 0.46 keV in a separate paper, also submitted for peer review. Its chief executive put its next target, 10 keV, at roughly 100 million degrees Celsius.
Fusion power needs hotter plasma still. ITER says the plasma in a tokamak must reach 150 million degrees Celsius to achieve fusion.
Sources
- NIST Guide to the SI, Chapter 5: Units Outside the SI, National Institute of Standards and Technology
- CODATA Value: electron volt-kelvin relationship, National Institute of Standards and Technology
- Zap Energy achieves 37-million-degree temperatures in a compact device, Zap Energy
- General Fusion reports electron temperatures exceeding 1 keV, American Nuclear Society (Nuclear Newswire)
- UKAEA, General Fusion announce Magnetised Target Fusion milestone, UK Atomic Energy Authority (GOV.UK)
- General Fusion Achieves World-First 1 keV Electron Temperature Milestone on its Path to Commercial Fusion Power, General Fusion
- 1 keV: A Milestone Achieved, and Why It Matters, General Fusion
- What is a tokamak?, ITER Organization
