Editing Nuclear fusion (section)

=== Thermonuclear fusion ===
{{unreferenced section|date=August 2023}}
Thermonuclear fusion is the process of atomic nuclei combining or "fusing" using high temperatures to drive them close enough together for this to become possible. Such temperatures cause the matter to become a [[plasma physics|plasma]] and, if confined, fusion reactions may occur due to collisions with extreme thermal kinetic energies of the particles. There are two forms of thermonuclear fusion: ''uncontrolled'', in which the resulting energy is released in an uncontrolled manner, as it is in [[thermonuclear weapon]]s ("hydrogen bombs") and in most [[star]]s; and ''controlled'', where the fusion reactions take place in an environment allowing some or all of the energy released to be harnessed.

Temperature is a measure of the average [[kinetic energy]] of particles, so by heating the material it will gain energy. After reaching sufficient temperature, given by the [[Lawson criterion]], the energy of accidental collisions within the [[plasma (physics)|plasma]] is high enough to overcome the [[Coulomb barrier]] and the particles may fuse together.

In a [[Deuterium–tritium fusion|deuterium–tritium fusion reaction]], for example, the energy necessary to overcome the [[Coulomb barrier]] is 0.1&nbsp;[[Electronvolt|MeV]]. Converting between energy and temperature shows that the 0.1 MeV barrier would be overcome at a temperature [[Orders of magnitude (temperature)|in excess of 1.2 billion]] [[kelvin]].

There are two effects that are needed to lower the actual temperature. One is the fact that [[temperature]] is the ''average'' kinetic energy, implying that some nuclei at this temperature would actually have much higher energy than 0.1&nbsp;MeV, while others would be much lower. It is the nuclei in the high-energy tail of the [[Distribution function (physics)|velocity distribution]] that account for most of the fusion reactions. The other effect is [[quantum tunnelling]]. The nuclei do not actually have to have enough energy to overcome the Coulomb barrier completely. If they have nearly enough energy, they can tunnel through the remaining barrier. For these reasons fuel at lower temperatures will still undergo fusion events, at a lower rate.

''Thermonuclear'' fusion is one of the methods being researched in the attempts to produce [[fusion power]]. If thermonuclear fusion becomes favorable to use, it would significantly reduce the world's [[carbon footprint]].