Deviations from Ionization Equilibrium in Plasmas Generated by Electric Shock Tubes

Abstract

Temperatures and particle concentrations of helium plasmas generated in a linear electric shock tube of 15‐mm diam. have been measured by spectroscopic techniques for initial pressures less than 1.0 Torr. The ratio of doubly‐charged to singly‐charged ions is always found to be greater than the value expected in ionization equilibrium, implying that the measured luminosity arises from a decaying plasma that has been heated by the discharge rather than gas excited by a shock wave. Although measured plasma parameters at luminosity fronts are close to values calculated from the Rankine—Hugoniot equations in some experiments, the use of shock theory to calculate the state of the plasma does not seem justifiable.