Discharge characteristics of helium under inhomogeneous pressure distribution

Discharge characteristics of helium gas under inhomogeneous pressure distribution were examined both analytically and experimentally. The purpose of the study is to generate plasma within a limited space introducing gas through a very small aperture. First we derived an analytical expression of the Paschen's law for the discharge under inhomogeneous pressure distribution. It was obtained that larger pd product, where p is the pressure and d is the distance between the anode and cathode, is necessary, but the lowest spark voltage may become lower as compared to that of normal homogeneous pressure distribution. Experiments were also done, and current-voltage characteristics and relationship between the pressure and the discharge voltage were obtained. It was also confirmed that localized plasma could be formed. The voltage rapidly increased with a decrease in the gas pressure. Lowering of the discharge voltage was, however, not observed in the present study.