Pellet Ablation Codes
Pellet ablation codes model how a frozen fuel or impurity pellet erodes as it flies into the plasma, setting fueling depth and injection strategy.
Fueling from the inside
Gas puffing fuels only the edge because neutrals ionize quickly. To fuel the core, cryogenic pellets of frozen hydrogen isotopes are fired into the plasma at high speed. As a pellet travels, plasma heat ablates its surface, forming a dense neutral cloud that shields the pellet and is then ionized, depositing particles along the flight path. Pellet ablation codes model this erosion and deposition to predict where fuel ends up.
The same physics governs impurity pellets used for disruption mitigation and radiative cooling, so ablation modeling serves both fueling and machine protection.
The ablation cloud
The key physics is the self-shielding neutral cloud around the pellet. Incoming plasma electrons deposit energy in the cloud rather than the solid, moderating the ablation rate. Codes model the cloud's density, its expansion along field lines, and the resulting ablation rate as functions of local plasma temperature and density.
Deposition and drift
After ionization, the deposited material can drift radially outward due to a pressure imbalance across the flux surface, so the final deposition profile differs from the naive ablation profile. Capturing this grad-B-driven drift is essential for predicting fueling efficiency correctly.
Design relevance
For the Hyperion breeder, pellet-ablation modeling estimates the pellet size and speed needed to fuel the core and to deliver material for disruption mitigation. Coupled with disruption codes, it informs the shattered-pellet mitigation design, all in simulation before construction.
- Models pellet erosion in the plasma
- Self-shielding neutral cloud sets ablation rate
- Grad-B drift shifts final deposition
- Serves fueling and disruption mitigation