Assessment of physical correlations in a large DC discharge tube for multiple gases and electrode materials

Summary form only given. In 1889, Friedrich Paschen published a law that describes the voltage at which a gas breaks down into plasma. It describes the dependence of the breakdown voltage on the gas pressure, distance between the electrodes, the secondary electron emission coefficient, and a set of proportionality constants [1]. A study by V. A. Lisovskiy et al [2] concluded that the original Paschen's law and the modification presented by Townsend in 1915 [3] were incorrect in assuming that breakdown voltage is dependent only on the product of the pressure times the inter-electrode distance (pd), and the coefficient of secondary electron emission (γs
_e
) from the surface of the cathode. The electron diffusion and mobility were considered in this modified breakdown condition [2]. Ledernez et al. has related the famous proportionality constants A and B of the voltage breakdown equation to the electron-ion collision cross sections for the working gas [4].This work presents a comparison of the experimental results for a large discharge tube to the modifications made in the breakdown voltage equations. This experimental device is 9.65cm (3.8 inches) in inner diameter with 7.62 cm (3 inches) aluminum electrodes. The distance between the electrodes can be varied from 12.7 cm (5 inches) to 25.4 cm (10 inches). The modifications are tested for different noble gases at a range of pressures and inter-electrode distances. Various electrode materials are tested for each gas and the secondary electron emission coefficient will be calculated. The study compares new experimental results to published modified models. A new modified equation is discussed in which the collisional cross sections are utilized instead of the proportionality constant for the electron mean free path. The voltage is obtained from the integral of the electric field over the inter-electrode distance, and spectroscopy is discussed.