Fusion

Fusion is the nuclear process by which light atomic nuclei combine to form heavier nuclei, releasing energy as a consequence of mass being converted to energy. The most studied fusion reaction for energy production is deuterium-tritium fusion, where a deuteron and a triton fuse to form a helium-4 nucleus and a high-energy neutron.

Fusing nuclei requires extreme conditions to overcome electrostatic repulsion. In stars, gravity provides confinement and heat, but on Earth researchers aim to achieve sufficient temperature, density, and confinement time through controlled fusion. The Lawson criterion expresses the condition under which fusion power can exceed the power required to maintain the plasma, combining temperature, density, and confinement time.

Magnetic confinement fusion uses strong magnetic fields to keep the hot plasma from touching material walls. The most studied configurations are tokamaks, which employ toroidal magnetic fields, and stellarators, which rely on complex external coils to shape the magnetic field. Inertial confinement fusion uses short, intense energy pulses from lasers or particle beams to rapidly compress a small fuel pellet to high density and temperature for a fleeting moment.

Prominent research facilities include ITER in France, a large international magnetic confinement project aimed at demonstrating sustained high power gain; JET in the United Kingdom, a leading experimental device; and the National Ignition Facility in the United States, which pursues inertial confinement experiments.

Practical fusion power remains a goal. Challenges include achieving sustained net energy gain, developing materials that withstand neutron irradiation, ensuring safe and economical tritium handling, and scaling up to reactor-scale plants. If overcome, fusion could provide abundant, low-carbon electricity with favorable safety and waste profiles compared with some other energy sources.