Characterization of a partially‐ionized, detached, divertor plasma

A combined edge plasma/Navier–Stokes neutral transport model is used to characterize divertor plasma detachment, in the collisional limit for neutrals, on a simplified two‐dimensional slab geometry with Alcator‐C‐MOD‐like plasma conditions [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)]. The neutral model contains three momentum equations which are coupled to the plasma through ionization, recombination, and ion–neutral elastic collisions. The neutral transport coefficients are evaluated including both ion–neutral and neutral–neutral collisions. Detachment is brought about via impurity radiation using a fixed fraction impurity model. The transport model is shown to reproduce all salient features of experimentally observed detachment, such as large drops in ion saturation current and plasma heat flux at the divertor plate. The solutions are also shown to be sensitive to volume recombination. A region of relatively high toroidal neutral Mach number is observed upon detachment. Due to the high neutral densities, 75% of the Lyman α radiation is assumed trapped in the problem. A total edge radiative loss (neutrals and impurities) of approximately 75% of the power crossing the separatrix is needed to observe strong detachment on Alcator‐C‐MOD‐like plasmas using the described model.