burning plasma is a fusion plasma heated predominantly by its own fusion reactions rather than by external power — the regime in which the fire, once lit, largely keeps itself hot.
The definition turns on the balance between 📝alpha heating and external heating. In deuterium-tritium fusion the charged 📝alpha particle carries one fifth of the energy released, so alpha power equals external power when the fusion gain Q reaches 5; beyond that threshold the plasma burns. Burning plasma is commonly confused with its limiting case, 📝ignition: an ignited plasma needs no external heating at all, while a burning plasma still takes some — self-sustaining in tendency, not yet in fact.
The regime was first reached in a laboratory at the National Ignition Facility, whose imploding fuel capsules crossed the burning-plasma threshold in results reported in 2022 and achieved ignition in December of that year. No magnetically confined plasma has yet burned: ITER is designed to reach Q of 10, where alpha heating supplies twice the external power. The regime matters because a burning 📝plasma is qualitatively new territory — its dominant heat source moves inside the plasma itself, coupling the fusion rate, the temperature profile, and fast-particle instabilities into a self-organizing system that can only be studied by making one.