Electric field measurement in a DBD in helium and helium–hydrogen mixture

Time–space-resolved optical emission spectroscopy was used for the investigation of a diffuse dielectric barrier discharge (DBD) in helium and in 95%He + 5%H2 gas mixture. The DBD in helium was diffuse in the whole range of the applied voltage, while in the gas mixture the discharge operated in diffuse mode only in the regime with more than three current peaks. In the helium discharge, the excitation of hydrogen H β is delayed compared with the excitation of the helium atomic line, while in the gas mixture both lines are excited simultaneously. Using the Stark polarization spectroscopy technique based on the He I 492.19 nm line and its forbidden counterpart, the electric field distribution (EFD) was measured in the cathode region of the DBD in helium and in the helium–hydrogen mixture. Electric field space distributions in both gas discharges, obtained at 20 kPa pressure, showed linear decreasing in the cathode region, which is a typical characteristic of the glow discharge. Linear fits of the EFDs showed that the length of the cathode fall region is smaller in the gas mixture than in pure helium. In the multiple current peak mode of the DBD, EFD was measured during each of the three current peaks and no noticeable difference between them is observed.