deuteriumdeuterium

Deuterium-deuterium fusion, or D-D fusion, refers to nuclear fusion reactions between two deuterium nuclei (hydrogen-2). The two main channels are D + D → He-3 + n and D + D → T + p. The overall energy released per reaction is about 3.27 MeV in the center-of-mass frame. In the He-3 + n branch, the lighter neutron carries roughly 2.45 MeV and the heavier He-3 about 0.82 MeV. In the T + p branch, the proton carries about 2.45 MeV while the tritium carries about 0.82 MeV.

Conditions for occurrence are extreme: high temperature and density are required to overcome the electrostatic repulsion between positively charged nuclei. In laboratory settings, this typically means temperatures around tens of millions of kelvin or higher, achieved in magnetic confinement devices or via inertial confinement with intense laser pulses. In stars, D-D fusion can occur but is less dominant than other reactions such as D-T fusion due to comparatively smaller reaction rates at stellar core temperatures.

Compared with deuterium-tritium (D-T) fusion, D-D fusion has a lower cross-section at reachable temperatures, making net energy gain more challenging. Nevertheless, it is of interest as a source of 2.5 MeV neutrons for materials testing and as a pathway in some fusion concepts and tritium breeding schemes. Deuterium is abundant in nature, especially in seawater, which makes D-D fusion attractive for experimental neutron sources, even though its practical use for large-scale energy production remains under active research.

Applications and challenges: D-D fusion provides useful neutron production and a testbed for fusion physics, but achieving sustained net energy gain continues to be difficult with current technology.