Equilibrium and linear stability of gas flow near an ablating pellet

The present pellet ablation model is being refined because the feasibility of pellet fueling strongly depends upon the pellet ablation rate. The relevant atomic processes occurring in the ablation, such as thermal dissociation, excitation, and ionization affect the temperature and density of the ablation, and therefore must be included self-consistently. The temperature and degree of ionization determine the conductivity of the ablation, which is necessary to estimate the effect of electrical charging of the pellet on the ablation rate. The space-charge and the energy sinks of the atomic processes reduce the ablation rate. Nonlaminar flow, or turbulence, near the pellet can have a large effect on the ablation rate. A linear perturbation analysis of the compressible-flow equations, however, shows that the ablation cloud is stable. Several factors contribute to the stability. Because the rate of increase of the pellet surface recession is negligible compared to nabla p/rho, where p is the pressure and rho is the mass density, the Rayleigh-Taylor instability will be insignificant. Moreover, convection carries perturbations beyond the sonic point where they can no longer influence flows in the subsonic region of the cloud. Other stabilizing mechanisms are noted