Sputtering and Erosion Codes
Sputtering codes compute how incident ions eject surface atoms through collision cascades, providing the erosion yields wall models require.
Atomic-scale erosion
When an energetic ion strikes a solid, it initiates a cascade of atomic collisions that can eject surface atoms, a process called sputtering. Sputtering and erosion codes compute the sputtering yield, the number of atoms ejected per incident ion, as a function of ion species, energy, and angle of incidence, providing the source term that larger PMI and edge codes need.
Yields are strongly nonlinear in energy: there is a threshold below which no sputtering occurs, a rise, and a peak before yields fall again at very high energy. Angular dependence and surface composition add further complexity.
Binary-collision approximation
The most common method is the binary-collision approximation, which treats the cascade as a sequence of independent two-body collisions using screened interatomic potentials. This is fast and accurate for higher-energy impacts, making it the standard for generating yield databases over wide parameter ranges.
Molecular dynamics
Near threshold and for chemical effects, the binary-collision picture breaks down and full molecular-dynamics simulation, integrating the motion of all nearby atoms with realistic interatomic potentials, is needed. It is far costlier but captures cluster ejection, chemical sputtering, and surface roughening.
Design relevance
For the Hyperion breeder, sputtering yields feed the first-wall erosion and impurity-influx estimates that set component lifetime and plasma purity. Because the yields depend on surface state, simulation predictions are treated as bounds to be confirmed once the machine operates after the Q2 2027 construction start.
- Computes sputtering yield vs energy and angle
- Provides source terms for wall and edge codes
- Binary-collision approximation for speed
- Molecular dynamics near threshold and for chemistry