Cold fusion

Cold fusion is a type of nuclear reaction that occurs at, or near, room temperature. It would contrast starkly with the nuclear fusion that takes place naturally within stars and artificially in hydrogen bombs and prototype fusion reactors under immense pressure and at temperatures of millions of degrees, and be distinguished from muon-catalyzed fusion.

Muons are used to catalyse the initiation of a fusion reaction without the need of immense pressures and temperatures. The heat generated by the reaction will then act to provide the conditions needed for further reactions. This works because muons are much more massive than electrons and so orbit the nucleus of a hydrogen atom much closer. This means by replacing the electrons of hydrogen with muons, the nuclei can get closer together without Van der Waals repulsion and can fuse at room temperatures.

The early reactors used low-energy nuclear reactions (LENR) or condensed matter nuclear science (CMNS).

This was a key technology to move towards Type II and beyond.