Energy Encyclopedia

Energy

Fusion

Stars shine because hydrogen nuclei fuse in their cores. On Earth, researchers try to recreate useful fusion with magnetic cages (tokamaks and stellarators) or with brief, intense compression of fuel capsules (inertial confinement). The scientific goal is a plasma hot and dense enough, for long enough, that fusion power exceeds the power required to sustain the plasma. ITER is the largest magnetic-fusion experiment under construction; laser facilities such as the National Ignition Facility study a different confinement approach.

The power that lights the stars

How it works

Positively charged nuclei repel each other. Fusion requires them to approach closely enough for the short-range nuclear force to bind them. In stars, gravity provides confinement and high core temperatures. In magnetic fusion, charged particles spiral along magnetic field lines inside a vacuum vessel. In inertial fusion, lasers or other drivers compress a small target so rapidly that fusion occurs before the fuel flies apart.

Key facts

  • Fusion of light nuclei can release energy because the products are more tightly bound.
  • Deuterium–tritium is the most accessible fuel mix for first-generation experiments.
  • No commercial fusion power plant is operating as of 2026; the field is experimental.
  • Magnetic and inertial confinement are the two leading laboratory approaches.

Environment

A fusion plant would not emit carbon dioxide from the fusion reaction. It would still need industrial materials, water or other coolants, and careful management of activated components. Tritium is radioactive and must be contained. These impacts are design-dependent and not yet observed at power-plant scale.

fusion basics

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fusion basics

Why it Works?

In small atoms, from hydrogen to sodium, the binding energy per nucleon increases with an increasing atomic number. This is because each additional nucleon is attracted by other nearby nucleons, and thus more tightly bound to the whole.

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fusion basics

How it Works?

In normal conditions, atom nuclei don't fuse spontaneously. The nucleus is positively charged and electrostatic forces will repel each other long before they come so close that strong nuclear forces can start to act and bind nuclei together.

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fusion basics

Fusion Fuel

All light elements and their isotopes could be used as a fusion fuel, but when talking about the use of nuclear fusion as source of energy and electricity, some types of fuel are more suitable than others.

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fusion basics

Fusion in Stars

The only functioning fusion reactor in our solar system is the Sun. Our central star, weighting 1,9 × 10´30 kg (more than 330,000 Earth masses) burns 500 million metric tons of hydrogen in its core every second at temperatures of about 15,7 million kelvin.

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fusion basics

Lawson Criterion

John D. Lawson wondered what conditions need to be fulfilled in order to get enough energy from a fusion reaction to use it in a power plant.

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fusion basics

Plasma

To enable thermonuclear fusion, the matter has to be heated to several million kelvin. But what will happen to such incredibly hot substances?

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fusion basics

How to Measure the Temperature in the Core of the Sun? or Diagnostics

Measuring the properties of something with extremely high temperatures like fusion plasma is difficult because every type of measuring device inserted into such a hostile environment will be instantly turned into plasma.

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fusion basics

Fusion: Key Ideas

A compact recap of fuels, confinement, ITER, and what remains unsolved.

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fusion basics

Artificial Fusion Principles

The Lawson criterion gives essentially two ways how to harness an effective fusion reaction.

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tokamaks

Magnetic Confinement

Charged particles follow magnetic field lines. Tokamaks and stellarators twist those lines into a torus so plasma cannot leak out too quickly.

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tokamaks

Tokamaks

The word "tokamak" is of Russian origin and means "toroidal chamber and magnetic coils." This magnetic confinement system holds plasma in magnetic fields of toroidal shape. The first tokamak, the T-1, started operation in 1958 in Russia, and since then the greatest advances in th

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tokamaks

Material for Magnetic Coils

The word "tokamak" is of Russian origin and means "toroidal chamber and magnetic coils." This magnetic confinement system holds plasma in magnetic fields of toroidal shape. The first tokamak, the T-1, started operation in 1958 in Russia, and since then the greatest advances in th

5 min read

tokamaks

Divertor

The word "tokamak" is of Russian origin and means "toroidal chamber and magnetic coils." This magnetic confinement system holds plasma in magnetic fields of toroidal shape. The first tokamak, the T-1, started operation in 1958 in Russia, and since then the greatest advances in th

5 min read

tokamaks

External Heating

The word "tokamak" is of Russian origin and means "toroidal chamber and magnetic coils." This magnetic confinement system holds plasma in magnetic fields of toroidal shape. The first tokamak, the T-1, started operation in 1958 in Russia, and since then the greatest advances in th

5 min read

tokamaks

Most Important Tokamaks in the World

The word "tokamak" is of Russian origin and means "toroidal chamber and magnetic coils." This magnetic confinement system holds plasma in magnetic fields of toroidal shape. The first tokamak, the T-1, started operation in 1958 in Russia, and since then the greatest advances in th

12 min read

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The Next Step on the Way Toward a Thermonuclear Fusion Power Plant

In the beginning of the 20th century, the potential energy of the atom was discovered.

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ITER Magnets, Vessel, and Blanket

ITER combines superconducting magnets, a massive vacuum vessel, a cryostat, and plasma-facing blankets.

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Main Parameters

The ITER is an experimental device designed to demonstrate the possibility of harnessing energy from thermonuclear fusion.

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Timeline

From 1985 to 2050 ...

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Record Breakers

Being the largest tokamak ever built, the ITER is a record holder in many ways.

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Magnets

The ITER magnet system will be the largest and most integrated superconducting magnet system ever built. It will produce magnetic fields that will initiate, confine, shape and control the ITER plasma.

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Vacuum Vessel

Plasma will be held inside a steel torus called a vacuum vessel. It was proven that the bigger the plasma volume, the better the confinement, so the ITER vacuum vessel will be really big.

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Blanket

Blanket protects vacuum vessel from harsh conditions provided by fusion plasma. Because the vessel cannot be replaced, any damage to it will incur would cause termination of experiments.

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Divertor

For a successful fusion reaction only the presence of fuel (deuterium and tritium in the case of ITER) in the plasma core is needed; all other particles, whether impurities or helium ash, are unwanted and need to be diverted away from the plasma, because they could cause energ…

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Cryostat

During ITER operation the 150 million kelvin hot plasma core will be just a few meters away from only 4 Kelvin cold toroidal magnetic coils.

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Tritium Production

The ITER machine will be the first thermonuclear reactor fully designed to operate with deuterium-tritium fusion reaction.

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Cooling

Tokamak ITER operation would not be possible without several types of cooling methods, because heat generated by fusion must be discarded.

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Diagnostics

The main goal of the ITER is not to just create fusion plasma but to get as much information about such plasma as possible.

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External Heating

Successful deuterium-tritium fusion reaction requires 150 million Kelvin, a temperature that is not easy to reach.

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The ITER Site

The ITER 180-hectare site is located near Saint Paul-lez-Durance, southern France.

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Disruptions and Instabilities

Plasma never behaves calmly and shortly after its creation begins to show an assortment of instabilities.

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