What Is Nuclear Fusion?
The energy that powers the Sun and every star — and the process humanity is now racing to recreate here on Earth. A quick, plain-language overview for anyone who's never worked with it.
In the Sun's core, immense heat and pressure force hydrogen atoms to fuse into helium, releasing enormous amounts of energy. On Earth we can't replicate the Sun's gravity — so fusion reactors instead heat a hydrogen fuel (a mix of deuterium and tritium) to over 100 million degrees, far hotter than the Sun's core, until the atomic nuclei fuse. The most advanced reactor design for doing this is called a tokamak — a doughnut-shaped chamber that uses magnetic fields to hold the superheated fuel in place.
The fusion fuel, heated to over 100 million °C — hotter than the core of the Sun. At this temperature, atomic nuclei fuse together and release energy.
Click a layer to learn what it does.
Tokamak — and Other Approaches
The tokamak is the most researched and most funded approach (used by ITER, the world's largest fusion project), but it isn't the only one. Stellarators use a more complex magnet geometry to hold the plasma without needing an internal current. Inertial confinement fusion (used at the US National Ignition Facility) compresses a fuel pellet with powerful lasers instead of magnets. Several private companies are also exploring magnetic mirrors, field-reversed configurations, and other alternatives. Cluster 3 works with suppliers and researchers across all of these approaches — the material and fuel-cycle challenges are largely shared.
Why Bother? The Energy Math
Fusion's appeal comes down to how much energy a tiny amount of fuel can release.
1 kg of fusion fuel (deuterium + tritium) releases roughly as much energy as 10,000 tonnes of coal.
Deuterium is extracted from seawater — practically inexhaustible, available to every coastal nation.
No CO₂, no soot, no combustion by-products — fusion releases energy without burning anything.
Built-in Safety
If conditions inside the reactor are disturbed even slightly, the plasma cools within seconds and the reaction simply stops — a runaway reaction like a fission chain reaction is physically impossible.
Only a few grams of fuel are present in the reactor at any moment — nowhere near a critical mass — so a meltdown scenario cannot occur.
Fusion doesn't produce long-lived fission products. Its main radioactive by-products are activated structural material and tritium, with a half-life of about 12 years rather than thousands.
Deuterium and lithium aren't fissile materials — fusion fuel can't be diverted into a weapons program the way enriched uranium or plutonium can.
Select a marker to see which company is active there.
Click a marker for details.
55 fusion companies across 14 countries
Source: organization data compiled from the Fusion Industry Association (fusionindustryassociation.org) and independent research.