DEGAS 2 neutral transport modeling of high density, low temperature plasmas

Neutral transport in the high density, low temperature plasma regime is examined using the degas 2 Monte Carlo neutral transport code. Degas 2 is shown to agree with an analytic fluid neutral model valid in this regime as long as the grid cell spacing is less than twice the neutral mean-free path. Using new atomic physics data provided by the collisional radiative code cramd, degas 2 is applied to a detached Alcator C-Mod discharge. A model plasma with electron temperature ∼ 1 eV along detached flux tubes, between the target and the ionization front, is used to demonstrate that recombination is essential to matching the experimental data. With the cramd data, ∼ 20 % of the total recombination is due to molecular activated recombination