A fueling method that fires frozen hydrogen-isotope pellets into the plasma core at high velocity, providing deeper fuel penetration than gas puffing and enabling density profile control.
ReviewedLast reviewed: 9 Aug 2026·Category: Glossary
Principle
Pellet injection fires small (1–5 mm diameter) frozen pellets of deuterium, tritium, or mixtures at velocities of 100–1000 m/s into the plasma. As each pellet penetrates, it ablates (evaporates) due to the high plasma temperature, depositing fuel deeper in the plasma core than edge-based gas fueling can achieve.[1]
ITER fueling: ITER will use pellet injection as its primary fueling method, with pellets launched from the high-field side (inboard) at up to 300 m/s. High-field-side launch achieves better penetration because the curved magnetic field guides the ablation cloud inward.
ELM Pacing
Small, frequent pellets can trigger controlled edge-localized modes (ELMs), replacing fewer but more damaging natural ELMs with many smaller ones. This “ELM pacing” technique is a leading candidate for managing transient heat loads in ITER.[2]
Technology
Pellet injectors use centrifugal accelerators, pneumatic guns, or electromagnetic rail guns. Continuous pellet trains at rates up to 50 Hz have been demonstrated. Tritium-compatible pellet injectors require special containment and fuel processing systems.[3]
Sources
Baylor, L.R. et al. "Pellet fuelling, ELM pacing and disruption mitigation technology development for ITER." Nuclear Fusion, 49, 085013, 2009.
Lang, P.T. et al. "ELM pace making and mitigation by pellet injection in ASDEX Upgrade." Nuclear Fusion, 44, 665, 2004.
Wesson, J. Tokamaks. 4th ed., Oxford University Press, 2011.