Fusion power

Fusion power is electricity that would be generated from nuclear fusion, the process in which two light atomic nuclei merge into a heavier one and release energy. It is the reaction that powers the Sun and other stars, and researchers are working to reproduce it on Earth, but no fusion power plant is yet supplying electricity to a grid.

History of fusion power

Fusion was first understood as the energy source of the stars. The ITER organization describes how, over billions of years, gravity gathered the hydrogen clouds of the early universe into stars whose extreme density and temperature allow hydrogen nuclei to fuse into helium. Scientists later worked out how to approach the same reaction in a laboratory.

Twentieth-century fusion research concluded that the most efficient reaction for a machine on Earth is between two hydrogen isotopes, deuterium and tritium. The idea of an international joint experiment was launched in 1985, and thousands of engineers and scientists have contributed to the design of ITER since then.

A major milestone came on December 5, 2022, when a team at the National Ignition Facility at Lawrence Livermore National Laboratory in California carried out what the U.S. Department of Energy called the first controlled fusion experiment to reach scientific energy breakeven. The experiment delivered 2.05 megajoules of laser energy to a target and produced 3.15 megajoules of fusion energy output.

How fusion power works

Atomic nuclei carry positive charge and repel each other. To fuse, they have to collide fast enough to overcome that electrostatic repulsion, which happens when matter is extremely hot. ITER notes that the Sun’s core reaches about 15 million degrees Celsius, where hydrogen atoms are in constant agitation, and that the Sun converts about 600 million tonnes of hydrogen into helium every second.

The fusion product weighs slightly less than the nuclei that went into it. The missing mass becomes energy, as Einstein’s equation E=mc² describes. The Department of Energy explains that researchers are especially interested in deuterium-tritium fusion, which produces a helium nucleus and a neutron and releases much more energy than most fusion reactions.

Without the Sun’s gravity, a machine on Earth needs a different approach. ITER states that deuterium-tritium fusion in the laboratory requires temperatures of about 150 million degrees Celsius, ten times hotter than the Sun’s core. At such temperatures the fuel becomes a plasma, a hot, electrically charged gas that must be kept away from the walls of the vessel.

In a fusion power plant, neutrons from the reactions would carry energy into the walls of the device, where it would be absorbed as heat. As ITER describes, a plant would then use that heat to make steam, which drives turbines and generators in the same way as a conventional power station.

Types of fusion devices

The two main approaches are magnetic confinement and inertial confinement. Magnetic confinement holds the plasma in a doughnut-shaped vacuum chamber using strong magnetic fields. The best-known design is the tokamak, whose name comes from a Russian acronym meaning toroidal chamber with magnetic coils. The Department of Energy also names the stellarator as another candidate design for a future plant.

Inertial confinement takes the opposite route. At the National Ignition Facility, 192 laser beams are aligned on a deuterium-tritium target smaller than a pea. The Department of Energy compares the alignment to throwing a perfect baseball strike from a pitcher’s mound 350 miles from the plate.

Applications of fusion power

The main goal is carbon-free electricity on a large scale. ITER, a collaboration involving 34 nations as of early 2026, is building the world’s largest tokamak at Saint-Paul-lez-Durance in southern France to prove that fusion can be a large-scale and carbon-free energy source. Its primary objective is to demonstrate burning plasmas, in which the energy of the helium nuclei produced is enough to maintain the plasma’s temperature.

ITER will also test technologies a reactor would need, including superconducting magnets, remote maintenance, systems that exhaust power from the plasma and breeding modules that could make a plant self-sufficient in tritium. It is not equipped to produce electricity.

Fusion research has a second application. The National Ignition Facility supports the stockpile stewardship mission of the National Nuclear Security Administration, which the Department of Energy describes as a nuclear stockpile mission pursued without nuclear testing.

Advantages and disadvantages of fusion power

The case for fusion rests on its fuel and its output. The reaction produces energy from hydrogen isotopes, and ITER describes it as a carbon-free source based on the same principle that powers the Sun. The 2022 result also showed for the first time that a fusion reaction can release more energy than the laser energy delivered to the fuel.

The disadvantages are practical and large. Reaching 150 million degrees and holding a plasma steady for long periods is difficult, and a working plant also needs tritium, which is why ITER tests tritium breeding. The Department of Energy said after the 2022 result that many advanced science and technology developments are still needed to achieve simple, affordable fusion energy.

Gain also has to be read carefully. The 3.15 megajoules were measured against the 2.05 megajoules of laser energy that reached the target. Comparing the output with all the electricity needed to run the facility is a much harder standard, and it is a different question from the one answered in 2022.

Fusion power vs. fission power

Fusion and fission both release energy from atomic nuclei, but in opposite ways. Fusion merges light nuclei, as the Department of Energy describes. Nuclear power plants in operation today rely on fission, which splits heavy nuclei inside a nuclear reactor.

The fuels also differ. Fusion research centers on hydrogen isotopes, as described in the entry on hydrogen, while fission uses heavy elements. Plants of both kinds would produce heat that drives turbines, but a fusion plant has yet to be built.

Editorially reviewed by Specialty Digest Editorial TeamLast reviewed November 4, 2026Researched and drafted with AI assistanceReport an issue