Nuclear fusion releases energy when light atomic nuclei combine into heavier nuclei; on Earth, fusion-energy research focuses on creating and controlling extremely hot plasma so useful reactions can occur repeatedly.

Fusion combines light nuclei

Atomic nuclei carry positive electric charge and repel one another. At sufficiently high temperature, particles move fast enough that some nuclei can approach closely enough for the strong nuclear force to bind them. If the final nucleus has slightly less mass than the starting nuclei, the mass difference appears as released energy.

The Sun uses fusion under enormous gravitational pressure. Earth-based reactors cannot copy the Sun’s pressure, so they rely on much higher temperatures and engineered confinement.

Why deuterium and tritium are common research fuels

Many fusion-energy programs focus on deuterium and tritium, two isotopes of hydrogen. Their reaction produces a helium nucleus and a high-energy neutron and has a comparatively large reaction probability at temperatures achievable in experimental plasmas.

Deuterium exists naturally in water. Tritium is radioactive and scarce, so future systems would need careful fuel handling and likely breed tritium from lithium-containing materials.

How fusion plasma is confined

Magnetic-confinement devices such as tokamaks use strong magnetic fields to keep charged plasma away from material walls. Inertial-confinement experiments use intense lasers or other drivers to compress tiny fuel targets for very short times.

Both approaches must reach a combination of temperature, density and confinement time sufficient for fusion reactions to become energetically significant.

Fusion energy is not yet commercial electricity

Experiments have achieved important milestones, including laboratory fusion ignition in inertial-confinement targets, but a power plant must also operate repeatedly, survive neutron exposure, manage heat, produce or supply fuel, maintain components and generate electricity economically.

Fusion research therefore combines plasma physics, nuclear engineering, materials science, superconducting magnets, lasers, robotics and power-system design.

Sources and further reading

How nuclear fusion works

Nuclear fusion releases energy when light atomic nuclei combine into a heavier nucleus. The best-known laboratory fuel cycle uses isotopes of hydrogen, especially deuterium and tritium. Because both nuclei are positively charged, they repel each other electrically. Fusion research therefore focuses on creating conditions in which nuclei move fast enough and remain confined long enough for collisions at very short distances to produce fusion reactions.

In magnetic-confinement devices such as tokamaks and stellarators, the fuel is heated into a plasma and strong magnetic fields keep that plasma away from material walls. In inertial-confinement experiments, an intense burst of energy rapidly compresses a tiny fuel target. These approaches use different engineering methods, but both must balance temperature, density and confinement time while controlling heat, particles and plasma instabilities.

Where the energy comes from

The mass of the fusion products is slightly lower than the mass of the starting nuclei. That mass difference appears as energy according to mass-energy equivalence. In a deuterium-tritium reaction, much of the released energy is carried by a fast neutron. A future power plant would need to capture that energy as heat, use it to produce electricity and breed or otherwise manage its fuel while protecting reactor materials from neutron damage.