Nuclear Fusion

Nuclear fusion: light nuclei combine to form heavier ones, releasing energy.

Most famous: ²H + ³H → ⁴He + n + 17.6 MeV (D-T reaction, basis of H-bomb and tokamaks).

Energy comes from mass defect: products are slightly lighter than reactants.

Fusion requires extreme temperatures (~10⁸ K) to overcome electrostatic repulsion between positive nuclei (Coulomb barrier).

In stars: gravity provides confinement; the Sun fuses H → He via proton-proton chain at ~15 million K.

On Earth: magnetic confinement (tokamaks) or inertial confinement (laser implosion of fuel pellets).

Fusion releases MORE energy PER NUCLEON than fission (~3.5 MeV/nucleon vs ~1 MeV/nucleon).

Advantages over fission: abundant fuel (deuterium from seawater), no long-lived radioactive waste, no chain-reaction runaway risk.