Viscous-Flux Approximation Modeling in Anisotropic-Ion-Pressure Fluid Scheme

Anisotropic-Ion-Pressure (AIP) fluid model describes more accurately the characteristics of plasmas in openmagnetic-field systems, e.g., magnetic mirror, scrape-off layer, and divertor. AIP model combined with the virtual divertor model has a merit to be free from the boundary condition of flow speed at the end plate [S. Togo et al., J. Comput. Phys. 310, 109 (2016); Contrib. Plasma Phys. 58, 556 (2018)]. In order to compare the AIP modeling with the conventional plasma fluid modeling by using only a single AIP code, we introduce a kind of "viscous-flux approximation (VFA) " into the AIP energy equations, where the anisotropic pressure relaxation term is modified artificially to equalize the pressure anisotropy with the parallel viscous stress. One-dimensional simulations are carried out with the original AIP modeling and with the VFA-AIP modeling, respectively. Expected numerical results are obtained for a simple mirror configuration.