Benchmarking an improved atom and molecule neutral fluid model in UEDGE with DEGAS2

A fluid neutral model is regularly used in UEDGE to simulate neutral gas transport. An improved neutral model was recently implemented in UEDGE. The new model solves for an atom temperature (T_a) separate from that of the ions, as opposed to the default neutral model that solves for a mean temperature of ions and atoms. The new model thus identifies that the atom temperature can be substantially different from the ion temperature. The implementation is verified using the Method of Manufactured Solution [1]. The simulation results show that for comparatively low collisional edge plasmas, the atom temperature can be much lower than ion temperature and thus lead to reduced atom penetration into the core region. Validation of the new model is also required. Therefore simulation results with the new atom temperature equation are compared to results from the kinetic neutral model of DEGAS 2 in various geometries.