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How Nuclear Fusion Works

Written by Arda Kızılkaya

Theoretical Space Objects: Exploring the Wonders of the Cosmos Beyond Reality

Nuclear fusion is a reaction when two or more light nuclei combine to form one or more heavy nuclei and neutrons or protons e.g. deuterium and tritium which are hydrogen variants fuse to make helium nuclei.

How was Fusion Found:

Robert d’Escourt Atkinson and Fritz Houtermans made the first calculations about the rate of nuclear fusion in stars. Around that time, Rutherford explored what the structure of the atom looked like. In Rutherford’s famous experiment in 1934, he showed the fusion of deuterium to helium and observed that “an enormous effect was produced” during the experiment. Mark Oliphant, who was a student of Rutherford, used updated equipment, instead of firing hydrogen he fired deuterium and discovered helium-3 and tritium, which showed that heavy hydrogen nuclei could be made to react with each other. This understanding of nuclear fusion was connected to Hans Bethe’s work on stellar nucleosynthesis where he described that it’s through proton chain reactions that the stars release energy.

How Does Nuclear Fusion Work and What We Need for It to Happen:

Nuclear fusion reaction is when two light nuclei merge to form a heavy nuclei, but when they merge it releases energy because the total mass of the resulting heavy nuclei is less than the two original light nuclei. The rest of the mass turns into energy. Einstein’s equation (E=mc), which says that mass and energy can be converted into each other, helps us understand why this process happens. In the sun fusion happens because of the sun’s massive gravitational force, without a force that massive fusion would need a temperature higher than the sun. On Earth, we need over a hundred fifty million degrees Celsius to make deuterium and tritium fuse while stabilizing the pressure and magnetic forces at the same time.

Why do scientists study nuclear energy:

Ever since nuclear fusion theory was understood in the 1930's, scientists and increasingly engineers have tried to recreate and harness it. This is because if nuclear fusion can be replicated on Earth at an industrial scale, it could provide limitless, clean, safe, and affordable energy to meet our planet's demands. Fusion could create four times more energy than fission per kilogram of fuel and nearly four million times more energy than fossil fuels. Most fusion reactor concepts will use a mix of deuterium and tritium. In theory, with a few grams of these reactants, it’s possible to create a terajoule of energy.

Where far are we in fusion technology development:

Nuclear fusion and plasma physics research is being implemented in more than 50 countries, and in recent years researchers have achieved scientific energy gain in fusion for the first time. Experts have come up with different designs for the machines in which fusion takes place, like stellarators and tokamaks.

Differences and Similarities between Fusion and Fission:

Both fusion and fission are physical processes that produce a ton of energy. But fusion is the process of two or more light nuclei like deuterium and tritium forming heavier nuclei like helium. For fusion to happen we need a tremendous amount of temperatures or an extremely dense gravity. Fusion happens naturally in stars like our Sun. Fission on the other hand is the process of a heavy nucleus like uranium being hit by a neutron, and forming two less stable light nuclei., and fusion releases energy four times larger than fission. Fusion is cleaner, and safer than fission because fission releases radiation and emits toxic gas to the environment while fusion does not release radiation and toxic gasses. Fusion is more renewable than fission because fission uses uranium which comes from the underground, and uranium cannot be produced easily while fusion uses hydrogen which can be produced from renewable resources and be produced easily.


  1. History of fusion. (2023, June 30). EUROfusion.

  2. Nuclear fusion reactions. (2023).

  3. Fission and fusion: What is the difference? (2021, April 1).


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