SPECTROSCOPIC OBSERVATIONS OF SURFACE FLASHOVER ACROSS AN INSULATOR IN VACUUM UNDER PULSED EXCITATION

Spectroscopic investigations of surface flashover of insulators have been performed with materials such as alumina and PMMA in vacuum ambience under the application of a high voltage pulse. The spectra of emitted light from the flashover plasma reveal the roles played by the background gases in the system (H atomic line and N2 molecular band), desorbed gases such as CO from the insulator, material defects (AlO molecular bands) and excited species of the electrode material (as seen from the atomic lines Al I, Al II and Al III). In contrast, the spectrum of the preflashover phenomenon shows only the AlO bands and a weak molecular CO band as its constituents. This observation suggests that not only desorbed gases, but also material defects from the specimen insulator, can be the dominant cause for the initiation of the surface flashover plasma in vacuum.