fusions

Fusion is a nuclear reaction in which light atomic nuclei merge to form a heavier nucleus, releasing energy due to the conversion of some mass into energy. The process powers stars and also underpins thermonuclear weapons. The most studied fusion reaction for energy production is deuterium-tritium fusion: a deuteron (D) combines with a triton (T) to yield helium-4 and a high-energy neutron, releasing about 17.6 MeV of energy.

Achieving practical fusion requires extreme conditions to overcome the electrostatic repulsion between positively charged nuclei. Typical targets are temperatures of tens of millions of kelvin and sufficient confinement to allow nuclei to collide frequently. The Lawson criterion expresses the need for a balance of plasma temperature, density, and confinement time to attain net energy gain.

Two main approaches are pursued. Magnetic confinement fusion uses strong magnetic fields to keep a hot plasma stable for long enough to sustain reactions; the most developed designs are tokamaks and stellarators. Inertial confinement fusion relies on lasers or particle beams to rapidly compress a small fuel pellet to extreme densities and temperatures for a brief moment, creating a fusion burst.

Current status and prospects: as of the early 2020s, no fusion system has produced sustained net energy for practical power generation. Major international projects aim to demonstrate burning plasmas and net energy gain, with projects like ITER developing large-scale magnetic confinement and other facilities advancing inertial confinement research. If achieved, fusion promises a potentially abundant fuel supply, with deuterium from seawater and lithium for tritium breeding, low operational greenhouse gas emissions, and relatively low long-lived radioactive waste compared to fission. Safety concerns center on neutron activation and material handling rather than uncontrolled chain reactions.