Fusion ignition is a condition in which heating from fusion products becomes strong enough to sustain or amplify the fusion burn without relying only on continued external heating of the fuel.
Ignition is about self-heating
Fusion reactions can produce energetic charged particles that deposit energy back into the fuel. In deuterium-tritium fusion, helium nuclei—alpha particles—can heat the surrounding fuel. If that self-heating becomes strong enough relative to energy losses, the burn can accelerate.
Different research communities use related gain and ignition metrics, so headlines should always specify what energy boundary is being compared.
How the National Ignition Facility creates fusion
At Lawrence Livermore National Laboratory’s National Ignition Facility, powerful lasers deliver energy to a small target. The target implodes, compressing a tiny amount of deuterium-tritium fuel to extreme density and temperature for a fraction of a second.
On December 5, 2022, NIF achieved a historic laboratory result in which the fusion energy released from the target exceeded the laser energy delivered to the target. Later experiments repeated and increased the yield.
Why target gain is not power-plant gain
A laser facility consumes much more electrical energy than the ultraviolet laser energy that actually reaches the target. A practical inertial-fusion plant would need efficient drivers, inexpensive mass-produced targets, rapid repetition, durable chambers and systems to capture heat and breed fuel.
Therefore ignition is a major plasma-physics milestone, not evidence that a commercial fusion power station already produces net electricity.
Ignition in magnetic confinement
The same basic idea of self-heating applies to magnetically confined burning plasmas, although the geometry and metrics differ. In a reactor-scale deuterium-tritium plasma, alpha-particle heating should become a major part of maintaining the temperature.
Researchers use quantities such as fusion gain and the Lawson criterion to describe progress toward regimes where self-heating dominates losses.
