A basic fusion diagram.
Fusion, the opposite of fission. In fusion, two nuclei are combined together and in the process some of the mass is lost, creating energy as a by product. Isotopes of hydrogen, such as deuterium or tritium produce the most efficent fusion reactions. Some reactors make use of the helium generated by the fusion process(Once the tritium/deuterium fuel is exausted.) to keep themselves going if new tritium/deuterium fuel is not available. This does not happen quite often as tritium and deuterium, very commen themselves, are also refinable from normal hydrogen, which is the most commen element in the universe.
Fusion is generally more efficient the larger the reactor is, however, micro fusion initiators, devices invented my most races who develope advanced fusion technology, allow for efficient controlled fusion reactors to be built on a smaller and smaller scale.
