Effect of Space Charge in Cold-Cathode Gas Discharges

Townsend's basic ionization equations for cold-cathode gas discharges between parallel plates are modified by Poisson's equation to account for space-charge effects. Numerical calculations have been made for argon on the IBM 704 computer. Calculated voltage current static characteristics in general show a negative slope region indicating "breakdown". For low $\mathrm{pd}$ products ($p$ being the gas pressure and $d$ the gap distance), a second region of positive slope (abnormal glow) is obtained at higher currents. The electric field distribution across the gap is shown, at high currents, to approach that measured in glow discharges, and the formation of a positive column plasma is indicated by the charge distributions.