Fusion power

Fusion power is a potential method of electric power generation from heat released by nuclear fusion reactions. In fusion, two light atomic nuclei combine to form a heavier nucleus and release energy. Devices that use this process are known as fusion reactors.

Research on fusion reactors began in the 1940s. As of 2025, the National Ignition Facility (NIF) in the United States is the only laboratory to have demonstrated a fusion energy gain factor above one, but efficiencies orders of magnitude higher are required to reach engineering breakeven (a net electricity-producing plant) or economic breakeven (where the net electricity pays for the plant's whole-life cost).

Thermonuclear fusion reactions require fuel in a plasma state and a confined environment with high temperature, pressure, and sufficient confinement time. The relationship between these parameters is expressed by the Lawson criterion. In stars, gravity provides the conditions for fusing hydrogen isotopes. Experimental reactors use deuterium and tritium, heavier isotopes of hydrogen, in a process known as DT fusion. This reaction forms a helium nucleus and an energetic neutron.

Fusion fuel is extremely energy-dense, but tritium is scarce on Earth and decays with a half-life of about 12.3 years. Future reactors plan to use lithium breeding blankets that generate tritium when exposed to neutron radiation.

Fusion offers advantages compared with nuclear fission. It produces minimal high-level radioactive waste and involves lower inherent safety risks. However, the process generates intense neutron radiation that gradually damages the inner walls of a reactor. Achieving sustained energy gain beyond breakeven and converting it efficiently into electricity remain major technical challenges.

Research focuses mainly on two methods: magnetic confinement fusion (MCF) and inertial confinement fusion (ICF). MCF devices use magnetic fields to contain plasma. Early concepts included the z-pinch, stellarator, and magnetic mirror, with the tokamak design becoming dominant after Soviet experiments in the 1960s. ICF compresses and heats small fuel pellets using high-energy lasers, developed primarily since the 1970s. The largest active projects are ITER in France and the National Ignition Facility in the United States. Commercial and academic teams are also studying alternatives such as magnetized target fusion and modern stellarator designs.