DEGAS 2 Neutral Transport Modeling of High Density, Low Temperature Plasmas
Authors: D.P. Stotler, A. Yu. Pigarov, C.F.F. Karney, S.I. Krasheninnikov, B. LaBombard, B. Lipschultz, G.M. McCracken, A. Niemczewski, J.A. Snipes, J.L. Terry, R.A. Vesey
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 approximately 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, approximately 20% of the total recombination is due to molecular activated recombination.