Description
Plasma-neutral interactions mutually affect plasma and neutral transport in magnetized plasmas, such as divertor regions of fusion devices. However, in many divertor fluid models, the influence of plasma-neutral interaction on plasma transport is treated only as source terms. Recently, our research team developed a physical model for ion transport driven by ion-atom collisions, based on the Chapman-Enskog (CE) expansion and the Boltzmann collision integral (BCI). Braginskii derived plasma transport coefficients induced by Coulomb collisions using the CE expansion; our previous work extended this approach to include ion-atom collisions. It was found that the differential cross section (DCS) plays a crucial role in ion transport due to ion-atom collisions. In divertor plasmas, ion-molecule collisions also affect their transport processes and energy relaxation. The molecular density near divertor targets can reach the same order of magnitude as the ion density in detached plasmas. In this study, we develop a new ion transport model for ion-molecule collisions following a procedure similar to that used for ion-atom collisions. Transport coefficients and source terms for ion fluid equations in a magnetic field are derived while appropriately accounting for the DCS. Since the molecular temperature is usually much lower than the ion temperature, the expression of the transport coefficients can be simplified. Ion-molecule collisions can have effects on ion transport comparable to those of ion-atom collisions in linear devices used for divertor simulation experiments under low magnetic fields and high molecular densities. We also discuss an example of implementing the developed model in a divertor integrated code.