Model of ablation flow near light-atom pellets with surface boundary conditions

A theory is formulated to describe the dynamics of the high density, partially ionized region of the ablation cloud in the vicinity of a spherical light-atom refractory pellet exposed to a tokamak plasma. Owing to the finite sublimation energy of refractory pellets, the surface boundary conditions require a more detailed treatment than in the case of frozen hydrogen. With the exception of conditions that lead to relatively cold ablation clouds (low plasma density, or small pellet radius), transonic flow solutions were found to exist for most parameters of interest. The shielding properties of the ablation cloud, degree of ionization at the M = 1 surface, and the surface flow Mach number were found to be in fairly good agreement with the heuristic model of Parks, Leffler and Fisher. (author). 29 refs, 11 figs