The kinetic-kinetic neutral-neutral collision term in principle requires nonlinear Monte Carlo. However, this term is never dominant since, where neutral-neutral collisions are important, the majority of the neutrals are described by the fluid code. It is therefore possible to treat this term approximately, e.g., via a BGK collision operator, which maintains the linearity of the Monte Carlo method. (See adjacent poster by Kanzleiter)

Implementation of transfer reactions:

- Evaporation--when a kinetic neutral undergoes evaporation, its mass, momentum, and energy are transfered to the corresponding fluid equations.
- Condensation--ensure that mass, momentum, and energy are conserved
and this is most simply achieved by choosing the newly created kinetic
neutral from a Maxwellian with the appropriate moments. This choice is not
unique. However the Monte Carlo distribution will quickly adjust to the
local conditions and all that will matter will be the low order moments of
the distribution. Thus, the source appearing the the Boltzmann equation
may be written as

Wed Nov 26 10:29:07 EST 1997