Breakdown characteristics in dielectric-confined microcavity discharge of plate electrodes

Breakdown characteristics in dielectric-confined microcavity discharge of plate-to-plate electrodes under DC voltage are investigated in this paper. Experimental and particle-in-cell/Monte Carlo code simulated results show that the breakdown characteristic curve (the relation between the breakdown voltage V _br and the product pd of gas pressure p and electrode gap d or the V _br-pd curve) with a microcavity effect will deviate from the traditional Paschen curve, and seed electron adsorption by the dielectric wall is considered as the deviation mechanism. A smaller microcavity height will enhance this deviation. Based on the extent of deviation, there exist two critical microcavity heights, h _cr1 and h _cr2, for the breakdown characteristic curve. When the cavity height h is larger than h _cr1, the V _br-pd curve conforms to Paschen’s law due to the minor adsorbed electrons. When h < h _cr1, the V _br values in the V _br-pd curve begin to increase overall, compared to those in the Paschen curve. Specifically, when h _cr2 < h < h _cr1, the V _br-1/h curve exhibits a positive linear relation; when h < h _cr2, V _br increases sharply with 1/h as a nonlinear relationship due to the massive adsorbed electrons. Additionally, the type of dielectric material used to construct the microcavity also has a significant impact on V _br, which is related to the different electron adsorbility η of various dielectric walls. For deeper insight, a ‘microcavity effect’ analysis model was developed to discuss the modified V _br-pd curve and provide the explanation for the critical values of microcavity heights and the influence of the dielectric material. Significant adsorption of charged particles (especially the seed electrons) by the dielectric wall will reduce the electron multiplication and further improve the breakdown voltage when the cavity height h is comparable to the product ηλ _e (the dielectric electron adsorbility and electron mean free path). On this basis, the modified breakdown criterion considering the microcavity effect was derived. The analytical expressions of the two critical height values h _cr1 and h _cr2 (h _cr1 = 100ηλ _e, h _cr2 = 10ηλ _e) and the linear relation of V _br-1/h curve in h _cr2 < h< h _cr1 are presented quantitatively.