nuclear fusion
Thermonuclear fusion is a reaction of merging light nuclei, occurring with energy release due to the increase in the binding energy per nucleon. The most promising is the deuterium-tritium reaction: D + T → He-4 + n + 17.6 MeV. To initiate it, a temperature of about 100 million °C and high pressure are required. In stars, pressure is created by gravity; on Earth, by magnetic traps (tokamaks) or inertial confinement with lasers.
History
Arthur Eddington in the 1920s suggested the nuclear nature of stellar heat, and in the 1930s Hans Bethe described the reaction chains that power the stars. On Earth, controlled fusion has been researched since the mid-20th century, but a net energy gain has not yet been achieved.
How it works
Nuclei are positive and repel each other. To fuse them, matter is heated to millions of degrees, turning it into plasma — a gas of free electrons and ions. In the plasma, nuclei collide and, if they have enough energy, overcome the electric repulsion and stick together under the action of the strong nuclear force (the most powerful but short-range force of nature).
💡 The hydrogen bomb realizes uncontrolled fusion with a giant energy release, but the peaceful version has long remained a 'plasma trap': keeping the incandescent gas without touching the walls is extremely difficult.