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.

Porous dielectric discharge (PDD) is a critical phenomenon in plasma catalysis, biomedical tissue surface functionalization, and all-solid-state battery design. The dielectric constant of porous dielectric (PD) significantly impacts discharge characteristics and breakdown mechanisms across different applications. However, the complex spatial structure of porous media presents challenges in diagnosing and simulating PDD, limiting our understanding of its mechanism. In this study, the real geometric model of PD obtained from x-ray computed tomography (X-Ray-μ CT) and a two-dimensional fluid model were used to simulate and analyze the effect of dielectric constant on PDD-plasma characteristics, especially the generation and disappearance of charged particles. The simulation results reveal the following: (1) At the breakdown moment, PDD is a density-unbalanced discharge where the electron density is two orders of magnitude higher than the ion density; (2) The breakdown discharge follows the most accessible channel instead of filling the entire gap, which is guided by the electron temperature gradient; and (3) It was first discovered that the breakdown voltage exhibits a saturated growth curve under the control of the dielectric constant. By combining these mechanisms, a comprehensive explanation has been provided for this phenomenon. This study offers a robust simulation and theoretical basis for understanding the breakdown characteristics of PDD.

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