Editing Fusion power (section)

=== Mechanism ===
Fusion reactions occur when two or more atomic nuclei come close enough for long enough that the [[nuclear force]] pulling them together exceeds the [[electrostatic force]] pushing them apart, fusing them into heavier nuclei. For nuclei heavier than [[iron-56]], the reaction is [[endothermic]], requiring an input of energy.<ref>{{cite web|url=http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html#c2|title=Fission and fusion can yield energy|publisher=Hyperphysics.phy-astr.gsu.edu|access-date=October 30, 2014}}</ref> The heavy nuclei bigger than iron have many more protons resulting in a greater repulsive force. For nuclei lighter than iron-56, the reaction is [[exothermic]], releasing energy when they fuse. Since hydrogen has a single [[proton]] in its nucleus, it requires the least effort to attain fusion, and yields the most net energy output. Also since it has one electron, hydrogen is the easiest fuel to fully ionize.

The repulsive electrostatic interaction between nuclei operates across larger distances than the strong force, which has a range of roughly one [[femtometer]]—the diameter of a proton or neutron. The fuel atoms must be supplied enough kinetic energy to approach one another closely enough for the strong force to overcome the electrostatic repulsion in order to initiate fusion. The "[[Coulomb barrier]]" is the quantity of [[kinetic energy]] required to move the fuel atoms near enough. Atoms can be heated to extremely high temperatures or accelerated in a particle accelerator to produce this energy.

An atom loses its electrons once it is heated past its [[ionization energy]]. The resultant bare nucleus is a type of [[ion]]. The result of this ionization is plasma, which is a heated cloud of bare nuclei and free electrons that were formerly bound to them. Plasmas are [[electrically conducting]] and magnetically controlled because the charges are separated. This is used by several fusion devices to confine the hot particles.