Spatially-resolved spectral observations of pulsed surface flashover in a nitrogen environment

The development of streamers during the initial stage of a pulsed atmospheric discharge, which carries a high content of vacuum UV (VUV) emission, is investigated. Due to the high spectral absorptivity of atmospheric air in the VUV regime, few experiments have been conducted that observe the wavelength range shorter than 180 nm. However, direct photoionization is believed to play an important role in streamer formation during this phase of breakdown. VUV radiation (hν > 7 eV) is energetic enough to promote step-ionization and directly ionize background gas mixtures. Utilizing a VUV-sensitive experimental apparatus, spatially-resolved photomultiplier tube (PMT) measurements were recorded showing that initial VUV emission is dependent on the inhomogeneous field distribution near the electrodes. It was revealed that further into the developing streamer the position of instantaneous VUV emission is propagating from anode to cathode away from the initial VUV emissions. From these observations, the low temperature plasma is capable of producing high energy photons during the streamer phase as well as after voltage collapse.