Implementation and benchmarking of improved atom and molecule neutral fluid models in UEDGE

Fluid neutral model is regularly used in UEDGE to simulate neutral transport. For high

collisional edge plasmas, the model of using the mean temperature of ions and atoms

works well owing to strong charge-exchange collisions between ions and atoms.

However, for comparatively low collisional edge plasmas, atoms can have substantially

lower temperature than ions and thus lead to reduced atom penetration into the core

region. The new model solves for an atom temperature (T_a) separate from that of the

ions. Additionally, the existing UEDGE molecular temperature (T_m) model is improved

by including the v_g*grad_Pg term in the energy equation, which is shown to be an

important contributor to both Ta and Tm equations. Simulation results with the newlyimplemented

atom and molecule temperature equations are compared against the

previous model for typical DIII-D parameters. The new results are also compared to atom

and molecular simulations using the DEGAS 2 Monte Carlo.