Fusion power in the context of "Fusion energy gain factor"

Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced by nuclear fission of uranium and plutonium in nuclear power plants. Nuclear decay processes are used in niche applications such as radioisotope thermoelectric generators in some space probes such as Voyager 2. Reactors producing controlled fusion power have been operated since 1958 but have yet to generate net power and are not expected to be commercially available in the near future.

The first nuclear power plant was built in the 1950s. The global installed nuclear capacity grew to 100 GW in the late 1970s, and then expanded during the 1980s, reaching 300 GW by 1990. The 1979 Three Mile Island accident in the United States and the 1986 Chernobyl disaster in the Soviet Union resulted in increased regulation and public opposition to nuclear power plants. Nuclear power plants supplied 2,602 terawatt hours (TWh) of electricity in 2023, equivalent to about 9% of global electricity generation, and were the second largest low-carbon power source after hydroelectricity. As of November 2025, there are 416 civilian fission reactors in the world, with overall capacity of 376 GW, 63 under construction and 87 planned, with a combined capacity of 66 GW and 84 GW, respectively. The United States has the largest fleet of nuclear reactors, generating almost 800 TWh per year with an average capacity factor of 92%. The average global capacity factor is 89%. Most new reactors under construction are generation III reactors in Asia.

ITER (originally an acronym for International Thermonuclear Experimental Reactor, and also meaning "the way" or "the path" in Latin) is an international nuclear fusion research and engineering project designed to demonstrate the feasibility of fusion power. The facility is under construction near the Cadarache research center in southern France. ITER has been under construction since 2013. It is expected to achieve first plasma in 2033–2034, at which point it will be the world's largest fusion reactor, with a plasma volume about six times that of Japan's JT-60SA, previously the largest tokamak.

The long-term goal of fusion research is to generate electricity; ITER's stated purpose is scientific research, and technological demonstration of a large fusion reactor, without electricity generation. ITER's goals are to achieve enough fusion to produce 10 times as much thermal output power as thermal power absorbed by the plasma for short time periods; to demonstrate and test technologies that would be needed to operate a fusion power plant including cryogenics, heating, control and diagnostics systems, and remote maintenance; to achieve and learn from a burning plasma; to test tritium breeding; and to demonstrate the safety of a fusion plant.

Experiments directed toward developing fusion power are invariably done with dedicated machines which can be classified according to the principles they use to confine the plasma fuel and keep it hot.

The major division is between magnetic confinement and inertial confinement. In magnetic confinement, the tendency of the hot plasma to expand is counteracted by the Lorentz force between currents in the plasma and magnetic fields produced by external coils. The particle densities tend to be in the range of 10 to 10 m and the linear dimensions in the range of 0.1 to 10 m. The particle and energy confinement times may range from under a millisecond to over a second, but the configuration itself is often maintained through input of particles, energy, and current for times that are hundreds or thousands of times longer. Some concepts are capable of maintaining a plasma indefinitely.

Deuterium–tritium fusion (D-T fusion) is a type of nuclear fusion in which one deuterium (H) nucleus (deuteron) fuses with one tritium (H) nucleus (triton), giving one helium-4 nucleus, one free neutron, and 17.6 MeV of total energy coming from both the neutron and helium. It is the best known fusion reaction for fusion power and thermonuclear weapons.

Tritium, one of the reactants for D-T fusion, is radioactive. In fusion reactors, a 'breeding blanket' made of lithium orthosilicate or other lithium-bearing ceramics, is placed on the walls of the reactor, as lithium, when exposed to energetic neutrons, will produce tritium.

A tokamak (/ˈtoʊkəmæk/; Russian: токамáк) is a machine which uses a powerful magnetic field generated by external magnets to confine plasma in the shape of an axially symmetrical torus. The tokamak is the leading candidate of magnetic confinement fusion designs being developed to produce controlled thermonuclear fusion power.

Tokamaks use a combination of a central solenoid and toroidal and poloidal magnets to shape a ring of plasma. This is heated by a range of methods, including neutral-beam injection, electron and ion cyclotron resonance, lower hybrid resonance. Nuclear fusion may be achieved, measured by neutron detectors. Due to requiring a continuously changing magnetic field, modern tokamaks sustain "plasma discharges" on the timescales of seconds or minutes.

Magnetic confinement fusion (MCF) is an approach to generate thermonuclear fusion power that uses magnetic fields to confine fusion fuel in the form of a plasma. Magnetic confinement is one of two major branches of controlled fusion research, along with inertial confinement fusion.

Fusion reactions for reactors usually combine light atomic nuclei of deuterium and tritium to form an alpha particle (helium-4 nucleus) and a neutron, where the energy is released in the form of the kinetic energy of the reaction products. In order to overcome the electrostatic repulsion between the nuclei, the fuel must have a temperature of hundreds of millions of kelvin, at which the fuel is fully ionized and becomes a plasma. In addition, the plasma must be at a sufficient density, and the energy must remain in the reacting region for a sufficient time, as specified by the Lawson criterion (triple product). The high temperature of a fusion plasma precludes the use of material vessels for direct containment. Magnetic confinement fusion attempts to use the physics of charged particle motion to contain the plasma particles by applying strong magnetic fields.

JT-60 (short for Japan Torus-60) is a large research tokamak, the flagship of the Japanese National Institute for Quantum Science and Technology's fusion energy directorate. As of 2023 the device is known as JT-60SA and is the largest operational superconducting tokamak in the world, built and operated jointly by the European Union and Japan in Naka, Ibaraki Prefecture. SA stands for super advanced tokamak, including a D-shaped plasma cross-section, superconducting coils, and active feedback control.

JT-60 claimed that it held the record for the highest value of the fusion triple product achieved: 1.77×10 K·s·m = 1.53×10 keV·s·m. The product quoted is not a valid fusion triple product since the plasmas did not satisfy the steady state of the Lawson criterion as discussed below.