Microwave Studies of a Pulsed Glow Discharge

An investigation of the behavior of a pulsed glow discharge in helium has been made using a microwave method (3 Gc/sec) supplemented by light intensity and spectroscopic measurements. The discharge tube was mounted across a section of rectangular waveguide, parallel to the electric field vector of the TE₁₀ mode. Time-resolved microwave admittance measurements and dielectric post theory were used to determine the variation in parameters for the section of the discharge within the waveguide. The method is particularly suitable for high electron densities and resolutions of 1 cm along the axis of the discharge and 1 {μ}sec in time can be obtained without difficulty. The variation in discharge parameters was studied when rectangular current pulses of a few milliamperes were superimposed on a small dc maintaining current. A low-pulse repetition frequency was used and the admittance measurements were recorded photographically in order to minimize changes in discharge characteristics and to extend the useful life of the discharge tubes. Sufficient results have been obtained to give a qualitative picture of the behavior of a glow discharge under transient conditions, and a recombination coefficient for helium of approximately 10^-8 cm³/ion sec has been measured during the afterglow period. This is in good agreement with results obtained by other microwave methods.