Fusion energy

Fusion power is energy generated by nuclear fusion. Fusion reactions fuse two lighter atomic nuclei to form a heavier nucleus. It is a major area of plasma physics research that attempts to harness such reactions as a source of large scale sustainable energy. Fusion reactions are how stars transmute matter into energy.

In most large scale commercial programs, heat from neutron scattering in a controlled reaction is used to operate a steam turbine that drives electric generators. Many fusion concepts are under investigation. The current leading designs are the tokamak and inertial confinement by laser. As of February 2017, these technologies were not viable, as they cannot produce more energy than is required to initiate and sustain a fusion reaction.

Alternative approaches rely on other means of energy transfer, mostly that capture energy without relying on neutron capture.

Fusion reactions occur when two (or more) atomic nuclei come close enough for long enough that the strong nuclear force pulling them together exceeds the electrostatic force pushing them apart, fusing them into heavier nuclei. For nuclei lighter than iron-56, the reaction is exothermic, releasing energy. For nuclei heavier than iron-56, the reaction is endothermic, requiring an external source of energy. Hence, nuclei smaller than iron-56 are more likely to fuse while those heavier than iron-56 are more likely to break apart.

The strong force acts only over short distances. The repulsive electrostatic force acts over longer distances, so kinetic energy is needed to overcome this "Coulomb barrier" before the reaction can take place. Ways of doing this include speeding up atoms in a particle accelerator, or heating them to high temperatures.

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