Fueling and Pellet Injection Control

Fueling control times and places fuel delivery, using gas and pellets to build and hold density where the plasma needs it.

Getting fuel to the core

Density is only useful where fusion happens, in the hot core, but fuel added at the edge often does not reach the center before it is lost. Fueling control is the art of delivering particles to the right depth at the right time, coordinating the different injectors available to shape the density profile, not just its total.

Gas puffing

Gas valves admit neutral fuel at the edge. Gas puffing is fast and simple but shallow: the neutrals ionize near the boundary and rely on transport to move inward. It is well suited to edge density and to supporting divertor detachment, and it responds quickly for feedback trimming of the density signal.

Pellet injection

Frozen fuel pellets fired into the plasma penetrate far deeper than gas, depositing particles in or near the core. Pellet timing and speed set the deposition depth. Because each pellet delivers a discrete packet, pellet fueling is pulsed rather than continuous, and the controller schedules pellets to build and maintain core density.

Coordinated control

A fueling controller blends gas and pellets: gas for fast edge trimming and detachment support, pellets for deep core sustainment. It must also coordinate with pellet use for edge-mode pacing, since the same injector may serve both fueling and pacing, and with the fuel mix in a two-species plasma.

In the Kronos program

The Hyperion breeder burns deuterium and tritium, so fueling control manages both the total density at the design operating point and the deuterium-tritium mix, using pellets for core sustainment and gas for the edge. Coordination with detachment and edge-mode control is designed in simulation ahead of operation. The burner's helium-3 fuel handling follows its own tandem-mirror scheme.