Observation of the transition from a Townsend discharge to a glow discharge in helium at atmospheric pressure

Dielectric barrier discharge in helium at atmospheric pressure was studied by taking fast images of the discharge during one current pulse using an intensified charge couple device. It was observed that there appears a weakly luminous layer close to the anode at the very beginning of the discharge, then the luminous area gradually expands into the entire gap as the anode layer moves toward the cathode, and finally a highly luminous layer forms close to the cathode at the time around the maximum of the current pulse. The evolution of the discharge pattern indicates a transition from Townsend discharge to glow discharge.