Fuel Density and Fueling

Plasma density is one factor of the triple product and must be kept high yet below a disruptive limit, replenished continuously as fuel burns.

How much fuel, and how it gets in

Density is one of the three factors in the fusion triple product, and fusion power rises with the square of density, so keeping density high is directly rewarded. But density cannot rise without limit: above a density threshold the plasma edge cools and the discharge is prone to disruption. Operation sits below that limit with margin.

Fuel must be replenished as it burns and as particles are lost. Gas puffing at the edge and pellet injection deeper into the plasma are the tools; pellets can reach further in and place fuel where it is most useful. Fueling also controls the density profile, which affects both confinement and the bootstrap current.

The balance the design strikes

The operating density is a compromise: high enough for the triple-product target and to support the bootstrap current, low enough to stay clear of the density limit and to keep heating and current drive effective, which generally prefer lower density. Finding a density profile that satisfies power, stability, and current-drive requirements simultaneously is part of defining the operating point, and it is a design-and-simulation result.

• Fusion power ∝ density squared — high density is rewarded
• A density limit caps operation to avoid edge cooling and disruption
• Gas puffing and pellets fuel and shape the density profile

This page describes a design-and-simulation study, not a built machine. Construction begins Q2 2027; first-of-a-kind first tritium is targeted near 2030. No hardware net-gain is claimed before FOAK.