Spherical stratification of a glow discharge

Abstract

Spherically symmetrical strata (striation) in a dc glow discharge were discovered. Experiments were carried out in a low-pressure steel chamber that served as a cathode. An anode was placed in the center of the chamber. The stratification of the glow discharge was observed in some molecular gases: air, ${\mathrm{N}}_{2},$ ${\mathrm{O}}_{2},$ ${\mathrm{CO}}_{2},$ and acetone vapor. A simple relation between strata radii and their number ${r}_{n}{/r}_{n\ensuremath{-}1}=\ensuremath{\alpha},$ where $\ensuremath{\alpha}=1.4--2$ (depending on gas composition), were found. Gas pressure dependences of strata radii were measured. The values of bulk charge and electric potential radial distributions were estimated. A simplified Boltzmann equation for the electron energy distribution function (EEDF) in spherical geometry was used for theoretical consideration. The so-called ``black wall law'' assumption was used in the collisional integral. An analytical solution for the isotropic part of EEDF was obtained. The existence of converging and decaying stagnant waves reproducing the variation of the observed strata radii was shown.