Investigation of geometric effect in capillary discharge plasma generator using an improved ablation model

The wall material and the electrode material together determine the composition of the capillary discharge plasma. In this paper, an improved ablation model considering polyethylene (PE) and copper ablation and deposition was developed. Generators with different geometric sizes were calculated and tested. The results show that the concentration distributions of copper and PE in the generator were the pair-wise opposite, and the aspect ratio (AR) had a threshold (AR = 8.67). The copper mass density distribution varied from uniform to inhomogeneous with the increase in AR, which was similar to that of its concentration distribution. The maximum copper mass density increased with the increase in AR, and the AR threshold was also 8.67. The relationship between the copper or PE ablated mass and capillary length or diameter approximately followed a power law, and the relationship between the copper or PE ablated mass and AR approximately followed a proportional law. The PE mass density distribution was not similar to that of its concentration for AR >= 8.67. The PE ablated mass increased with the increase in AR, and its variation was similar to that of the maximum PE mass density. When the AR(AR > 5.2) was large enough, the PE mass density distribution determined the total mass density distribution. Otherwise, the total mass density distribution was determined by the mass density distribution of PE and copper. Overall, the simulation results were in good agreement with the experiments. These can be used to select the size and material of the capillary in simulating high heat flux plasma or electrothermal chemical gun ignition.