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In a nuclear fusion reaction [[nuclei]] of light [[elements]] join together (fuse) to produce heavier nuclei with a higher [[atomic number]]. The mass of these heavier nuclei is slightly less than the sum of the masses of the original nuclei and the missing mass is released as energy, in accordance with the famous equation [[E=mc²]].

In a nuclear fusion reaction [[nuclei]] of light [[elements]] join together (fuse) to produce heavier nuclei with a higher [[atomic number]]. The mass of these heavier nuclei is slightly less than the sum of the masses of the original nuclei and the missing mass is released as energy, in accordance with the famous equation [[E=mc²]].

For man-made fusion, the nuclei involved are usually two [[deuterium]] (heavy hydrogen) nuclei, each consisting of one [[proton]] and one [[neutron]] and combining to produce a [[helium]] nucleus or [[alpha particle]] (two protons and two neutrons). [[Tritium]] is sometimes also used, but the distinction is not relevant to this article.

For man-made fusion, the nuclei involved may be two [[deuterium]] (heavy hydrogen) nuclei, each consisting of one [[proton]] and one [[neutron]] and combining to produce a [[helium]] nucleus or [[alpha particle]] (two protons and two neutrons). [[Tritium]] is sometimes also used, but the distinction is not relevant to this article. Other forms of fusion may also be possible.

However, since deuterium nuclei have a positive charge, they repel one another and thus the chief problem in achieving fusion is to get the nuclei close enough together to fuse.

However, since deuterium nuclei have a positive charge, they repel one another and thus the chief problem in achieving ordinary fusion is to get the nuclei close enough together to fuse.

 

Cold fusion was given the name, popularly, because the discoverers claimed that the bulk of the heat they found was due to an "unknown nuclear reaction," and most observers thought that it must involve deuterium fusion.

== High Temperature Fusion ==

== High Temperature Fusion ==