A fusion plasma in which the dominant heating source is the alpha particles produced by fusion reactions themselves — a self-heated state that has never been achieved in a magnetic confinement device.
ReviewedLast reviewed: 9 Aug 2026·Category: Glossary
Definition
A burning plasma is one in which the 3.5 MeV alpha particles produced by D-T fusion reactions provide the majority of the plasma heating. In this regime, the plasma is largely self-sustaining — external heating is needed only for control and to compensate for losses at the edge, not to maintain the core temperature.[1]
New physics regime: A burning plasma exhibits fundamentally new physics not accessible in current experiments. The alpha particles, born with 3.5 MeV of energy, must slow down and transfer their energy to the thermal plasma without destabilising it. Alpha-driven instabilities (Alfvén eigenmodes) could eject fast alphas before they heat the plasma, degrading fusion performance. ITER and SPARC will be the first to explore this regime.
Threshold
A plasma is typically considered “burning” when the ratio of alpha heating power to total heating power (fα = Pα/(Pα + Pext)) exceeds 0.5. This corresponds to Q > 5. At Q = 10 (ITER baseline), fα = 0.67 — two-thirds of the heating is from alphas.[2]
Significance
The National Academies’ 2004 report “Burning Plasma: Bringing a Star to Earth” identified burning plasma physics as the next critical step for fusion science. Without experiencing and controlling a burning plasma, no commercial reactor can be designed with confidence.[3]
Sources
National Research Council. Burning Plasma: Bringing a Star to Earth. The National Academies Press, 2004.
ITER Physics Basis. "Chapter 5: Physics of energetic ions." Nuclear Fusion, 39, 2471, 1999.
Fasoli, A. et al. "Chapter 5: Physics of energetic ions." Nuclear Fusion, 47, S264, 2007.