Study of Different Models of the Wall Ablation Process in Capillary Discharge

Wall ablation is a critical physical process in the capillary plasma generator for electrothermal-chemical (ETC) guns, and its characteristics directly determine the generator's performance. In this paper, three different ablation models for the capillary discharge are studied. First, based on a recently developed two-layer kinetic model that takes into account the structure of the sheath in the plasma-wall transition region, ablation characteristics of two typical materials used in the ETC gun plasma generator, polytetrafluoroethylene and polyethylene, are calculated. These data are required for magnetohydrodynamic (MHD) plasma modeling, and for analysis of the characteristics of different materials from the viewpoint of capillary material selection. Then, using discharge parameters of a typical ETC plasma generator working cycle, three widely used ablation models are compared and analyzed. These models are the two-layer kinetic model (model-K), a model based on the Langmuir law (model-L) and a simplified arc-wall interaction model (model-E). The time dependence of the ablation rate and total ablated mass are calculated with each method, and then the features of the different ablation models are discussed. It demonstrates that the model-K is the most reliable model in terms of predictions accuracy, while its computational efficiency is poorer when applied in MHD simulations compared with the model-E.