Abstract
The luminescence evolution phenomena from alumina ceramic surface in vacuum under high voltage of direct and alternating current are reported, with the voltage covering a large range from far below to close to the flashover voltage. Its time resolved and spatial distributed behaviors are examined by a photon counting system and an electron-multiplying charge-coupled device (EMCCD) together with a digital camera, respectively. The luminescence before flashover exhibits two stages as voltage increasing, i.e., under a relative low voltage (Stage A), the luminescence is ascribed to radiative recombination of hetero-charges injected into the sample surface layer by Schottky effect; under a higher voltage (Stage B), a stable secondary electron emission process, resulting from the Fowler-Nordheim emission at the cathode triple junction (CTJ), is responsible for the luminescence. Spectrum analysis implies that inner secondary electrons within the surface layer of alumina generated during the SSEE process also participate in the luminescence of Stage B. A comprehensive interpretation of the flashover process is formulated, which might promote a better understanding of flashover issue in vacuum.
Highlights
For a vacuum-dielectric insulation system, discharge often happens across the dielectric surface with a much lower electric field than that for a pure vacuum gap of the same length, and too many researches have focused on this phenomenon in recent several decades.[1,2,3,4] Generally, the flashover process can be divided into three stages, i.e., the initiation stage, the development stage, and the last breakdown stage
A comprehensive interpretation of the flashover process is formulated, which might promote a better understanding of flashover issue in vacuum
In order to make a comprehensive understanding of these two physical processes and their intrinsic relationship with flashover, in this study, we continuously focus on the luminescence evolution characteristics under direct and alternating current (DC and AC) voltage, with the applied voltage covering a large range from far below to close to the flashover voltage
Summary
For a vacuum-dielectric insulation system, discharge often happens across the dielectric surface with a much lower electric field than that for a pure vacuum gap of the same length, and too many researches have focused on this phenomenon in recent several decades.[1,2,3,4] Generally, the flashover process can be divided into three stages, i.e., the initiation stage, the development stage, and the last breakdown stage. It is considered that the surface discharge in vacuum initiates with field emission of electrons from the cathode triple junction (CTJ), where the cathode, dielectric and vacuum meet and is breakdown in the desorbed gas from insulator surface.[4,5] it is still under debate about the development process, and the secondary electron emission avalanche (SEEA)[3] model maybe the one of the most acceptable theories.
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