Nuclear energy has been used since the 1950s. However all nuclear power plants have been fission reactors. Fission results from bombarding uranium or other large atoms with neutrons. The atom then breaks apart releasing energy and more neutrons leading to a chain reaction. Nuclear fusion however has never been used for energy. Fusion is when two light atomic nuclei fuse to form a heavier nucleus, vast amounts of energy is produced comes from binding energy due to the strong nuclear force. Fusion power would be the most efficient form of energy if it could be achieved. Deuterium (an isotope of hydrogen) would be the primary source of fuel and is abundant in the ocean and more easily assessable than fossil fuels. The only problem with using fusion as a power source is fusion requires a temperature of about 800 million kelvin. At these high temperatures, the atoms are stripped of there electrons and the positive nuclei breaks into plasma. The excess positive charge causes the fuel to repel from itself. Two approaches exist for confining the fuel for fusion once it reaches extreme temperatures, magnetic confinement and inertial confinement. Magnetic confinement is the more promising and developed approach. In would use a solenoid to cause particles to travel along magnetic field lines thus containing them. Fusion power is still a long way from being practical. However if it could be achieved, it would be the most efficient form of energy.