Pellet Fueling and Ablation Codes
Pellet codes model how frozen fuel pellets ablate as they enter the plasma, predicting where fuel is deposited and how the density profile responds.
Fueling from the inside
Gas puffing fuels only the plasma edge, from where particles must diffuse inward against transport. Injecting frozen deuterium or deuterium-tritium pellets delivers fuel deeper, because the pellet survives partway into the plasma before it is consumed. Pellet codes predict how far it penetrates and where the fuel ends up.
Ablation physics
As a pellet enters the hot plasma, its surface is heated and it sheds a cloud of neutral and then ionized material. This ablation cloud shields the pellet somewhat, slowing its erosion. Ablation models balance the incoming plasma heat flux against the pellet's mass loss to compute the ablation rate along the trajectory.
Deposition and drift
- The ablated material is deposited along the pellet path as a source
- The ionized cloud can drift outward across field lines before mixing
- The net density source profile determines the fueling efficiency
- Deep, high-field-side injection generally reaches further inward
Coupling to transport
The pellet code supplies a particle source that transport codes use to evolve the density profile. Because pellets perturb the profile strongly and transiently, capturing both the deposition and the subsequent relaxation matters for predicting the achievable density and its peaking.
Other uses
Pellet injection is also used to pace edge-localized modes by triggering them on demand, and shattered-pellet injection is a leading disruption-mitigation method. The same ablation and deposition physics underlies these applications, linking pellet modeling to edge stability and disruption studies.
Fueling analysis is part of confirming that a design can reach and sustain its target density profile with realistic injection.