Gas Electronegativity Influence οn Electrical Breakdown Mechanisms

This paper discusses the role of different gas breakdown mechanisms depending on electronegativity of the gas, at low values of pressure and inter-electrode gap. Static (dc) electrical breakdown of electropositive, electronegative and noble gases has been investigated theoretically, experimentally and numerically. In the case when the electron mean free path is comparable with characteristic dimension of the electrode system (inter-electrode distance d), then the breakdown occurs through the Townsend mechanism. In the case when the electron mean free path is much shorter than the characteristic dimension of the electrode system, the breakdown is said to occur through the streamer mechanism. But, between the regions where the breakdown occurs solely by either the Townsend or the streamer mechanism, there is a region where breakdown occurs by the combination of these two mechanisms. The width of this region expressed by the quantity of pd product (product of pressure, p, and inter-electrode distance, d) depends on observed gas tendency to form negative or positive ions (electronegative and noble gases, respectively). The level of the anomalous Paschen effect expression is dependent on whether the observed gas is electronegative or noble. The combined mechanism effects of breakdown and anomalous Paschen effect are quantitatively determined and theoretically explained within this paper.