Influence of the applied voltage shape on the barrier discharge operation modes in helium

For the investigation of a barrier discharge (BD) operated in helium, a discharge cell configuration was used which allows an electrical characterization and simultaneous measurements of volume processes as well as the interaction of the BD with a dielectric surface. The emission development in the volume has been recorded spatio-temporally and spectrally resolved by the established cross-correlation spectroscopy (CCS) operating in the PPG mode. The phase resolved measurement (over one discharge period) of surface charges deposited on a BSO crystal was realized by the utilization of the electro-optic Pockels effect in combination with a high-speed camera. Depending on the gap distance, the dielectrics, and the shape of feeding voltage, the BD can operate either in the diffuse Townsend-like or glow-like mode. The emission is localized near the anode and cathode for the Townsend-like mode and glow-like mode, respectively. In small gaps (distance about 1mm), a sinusoidal feeding voltage leads to the unusual Townsend-like mode in helium. But, a square wave voltage shape induces the glow-like mode, probably due to the fast rise and fall time of the applied voltage slopes. A sawtooth voltage generates both discharge modes over one period. The presented results show clearly the correlation of the emission development with electrical measurements, and deposited surface charge and transported charges.