A general plasma-neutral fluid model with molecules*

The plasma-neutral model [Meier and Shumlak, PoP 19 (2012)] is extended to include atomic and molecular fluids. In magnetic confinement and electric propulsion, molecules are generated due to recycling of ions and atoms on walls. Accurately modeling these plasmas requires accounting for the energetics of dissociation, and redistribution of energy to the product atoms and ions. Dynamics of the molecular fluid, which couples weakly to the main ion species through elastic scattering, differs from atomic dynamics, which is dominated by resonant charge exchange. The model presented here captures electron-impact dissociation through both excited and ionized molecular states, and elastic scattering of molecules on ions. Derivation of a four-fluid model—with electrons, ions, atoms, and molecules—is presented, along with results from an implementation in WARPXM, a DG code developed at U. Washington. In a 1D plasma accelerator problem, a current sheet interacts with a slug of either molecular or atomic gas. The atomic gas is almost fully entrained in the passing current sheet, while a significant fraction of molecules is left in its wake. Application of the model to a tokamak-like SOL plasma is also under development and results will be presented.