SNAP tracks the linear beam trajectory for each component of each
source, locally depositing beam neutrals as fast ions through the
If SNAP's rotation switch is turned on, then the cross-sections for
all of these interactions are performed in the rotating plasma frame.
- Charge-exchange on thermal ions.
- Ionization by thermal ions.
- Ionization by beam ion population.
- Ionization by thermal electrons.
- Charge-exchange with impurities.
SNAP does not consider ``multi-step'' ionization processes, by
which a beam neutral is kicked into an excited state (but not ionized)
by an initial collision, and subsequently ionized in a second
collision. These processes have the net effect of increasing beam
attenuation, but they are thought to be relatively unimportant for