Fusion power

From top, left to right

1. Scylla I, the first device to achieve laboratory thermonuclear fusion
2. T-1, the first tokamak device
3. Joint European Torus, the first device to fuse deuterium-tritium plasma
4. Princeton FRC, a modern field-reversed configuration experiment
5. Fusion plasma in China's Experimental Advanced Superconducting Tokamak
6. The National Ignition Facility, the largest inertial confinement fusion experiment and first to achieve fusion ignition and scientific breakeven
7. ITER, the largest magnetic confinement fusion experiment, scheduled to operate from 2034

Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion reactions. In a fusion process, two lighter atomic nuclei combine to form a heavier nucleus, while releasing energy. Devices designed to harness this energy are known as fusion reactors. Research into fusion reactors began in the 1940s, but as of 2025, no device has reached net power.

Fusion processes require fuel, in a state of plasma, and a confined environment with sufficient temperature, pressure, and confinement time. The combination of these parameters that results in a power-producing system is known as the Lawson criterion. In stellar cores the most common fuel is the lightest isotope of hydrogen (protium), and gravity provides the conditions needed for fusion energy production. Proposed fusion reactors would use the heavy hydrogen isotopes of deuterium and tritium for DT fusion, for which the Lawson criterion is the easiest to achieve. This produces a helium nucleus and an energetic neutron.^[1] Most designs aim to heat their fuel to around 100 million kelvins. The necessary combination of pressure and confinement time has proven very difficult to produce. Reactors must achieve levels of breakeven well beyond net plasma power and net electricity production to be economically viable. Fusion fuel is 10 million times more energy dense than coal,^[2] but tritium is extremely rare on Earth, having a half life of only ~12.3 years. Consequently, during the operation of envisioned fusion reactors, lithium breeding blankets are to be subjected to neutron fluxes to generate tritium to complete the fuel cycle.^[3]

As a source of power, nuclear fusion has a number of potential advantages compared to fission. These include little high-level waste, and increased safety. One issue that affects common reactions is managing resulting neutron radiation, which over time degrade the reaction chamber, especially the first wall.

Fusion research is dominated by magnetic confinement (MCF) and inertial confinement (ICF) approaches. MCF systems have been researched since the 1940s, initially focusing on the z-pinch, stellarator, and magnetic mirror. The tokamak has dominated MCF designs since Soviet experiments were verified in the late 1960s. ICF was developed from the 1970s, focusing on laser driving of fusion implosions. Both designs are under research at very large scales, most notably the ITER tokamak in France and the National Ignition Facility (NIF) laser in the United States. Researchers and private companies are also studying other designs that may offer less expensive approaches. Among these alternatives, there is increasing interest in magnetized target fusion, and new variations of the stellarator.