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

Spectroscopic investigations of surface flashover of insulators have b een performed with materials such as alumina and PMMA in vacuum ambien ce under the application of a high voltage pulse. The spectra of emitt ed light from the flashover plasma reveal the roles played by the back ground gases in the system (H atomic line and N2 molecular band), deso rbed gases such as CO from the insulator, material defects (AlO molecu lar 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 o f the preflashover phenomenon shows only the AlO bands and a weak mole cular CO band as its constituents. This observation suggests that not only desorbed gases, but also material defects from the specimen insul ator, can be the dominant cause for the initiation of the surface flas hover plasma in vacuum.