Electric-Field Distribution in Pulsed High-Current-Density Discharges in Helium and Helium-Hydrogen Mixtures

Abstract

The results of a study on high-current-density, pulsed glow discharges in He and He–H2 mixtures are presented. These results trace the temporal development of the electric-field and wall-potential distribution appearing between the electrodes of a discharge tube as the discharges approach dynamic equilibrium. These discharges, of 1.3 microsecond duration, are sustained in 2.5-cm-diameter pyrex tubes with interelectrode gaps variable between 10 and 40 cm. The pressure range runs from 0.50–5.0 Torr. As the discharge approaches dynamic equilibrium late in the discharge pulse, current densities of the order of 15 A/cm2 are maintained. The buildup of the electric field in the vicinity of the cathode is determined by time-resolved measurements of the Stark splitting of lines in the helium and hydrogen spectrum. The axial component of the electric-field and wall-potential distribution in the rest of the discharge are obtained from signals induced on a series of externally placed electrostatic ring probes. Fields as high as 78 kV/cm were detected at the cathode face, while uniform fields of the order of 10 V/cm Torr were found in most of the rest of the discharge. Comments are made on the transition region between high- and low-field regions in the discharge.