Modeling Spatially Resolved Neutral Atom Densities in the PFRC-2 Using DEGAS 2

Krypton and atomic hydrogen densities have been measured in the PFRC-2 plasmas using a two-photon-absorption laser-induced-fluorescence (TALIF) diagnostic. Because of their disparate energies and masses, these two fill gases provide a range of ionization mean-free-paths, L, from (L/plasma radius) below 0.01 to above 10. The first condition is comparable to that in tokamaks, allowing smaller experiments to explore the effects of neutrals in larger denser plasma devices. Upon plasma initiation in the PFRC-2, the gas is partially ionized and the densities of the atomic H and Kr in the plasma increase from 0 to 10e11/cc and decrease from 2e13 to less than 2e12/cc respectively. We use the DEGAS 2 code to compare with the experimental results, testing, for example, the roles of wall collisions and molecular processes on neutral behavior.