Numerical simulation of gas breakdown characteristics in porous dielectric and theoretical analyisis based on the capillary network model


 Gas discharge in heterogeneous porous dielectric (PD) is becoming a reliable and popular low-temperature plasma technique in surface modification and plasma catalysis. However, the exact breakdown characteristics in the porous dielectric are not well studied due to experimental and diagnostic limitations. In this paper, a fluid model is then used to simulate the gas breakdown characteristics in real PD. It is found that the breakdown will selectively occur in porous dielectrics. The spatial distribution of PD determines regions of local breakdown. Varitions in pressure result in the rearrangement of breakdown probability in each region of PD so that breakdown regions will change. In order to explain the selective breakdown phenomenon, based on the assumption that a porous dielectric can be simplified into a network consisting of multiple curved capillaries, we developed a theoretical model of the breakdown in a capillary network. Three geometrical factors, i.e., capillary tortuosity, capillary radius, and line porosity, are taken into the model to account for the effect of electric field distortion and electron loss on the dielectric walls in the presence of PD. The calculated results explain the selective breakdown phenomenon occurring in the numerical simulation. This paper simulates the breakdown in a real porous dielectric and provides a quantitative theoretical model to analyze the effect of porous dielectric geometry on the breakdown. This paper will also provide insights into the design of optimal parameters for porous dielectric discharge (PDD) in surface modification and plasma catalysis.