Discharge and breakdown mechanism transition in the conditioning process between plane-plane copper electrodes in vacuum

Conditioning is an important and efficient method to improve the dielectric strength of vacuum devices. The objective of this paper is to propose a discharge and breakdown mechanism transition in the conditioning process. Three pairs of plane-plane copper electrodes machined by diamond turning were designed. Surface-analysis of the electrode surface was done before, in the middle, and after the conditioning process by X-ray photoelectron spectroscopy (XPS). Impulse voltage (64/700μs) was applied repetitively in the conditioning process till conditioning saturation. The results showed that four discharge and breakdown mechanisms occurred in the conditioning process, i.e. pulse current discharge (PCD), pulse current induced breakdown (PB), field emission induced breakdown (FEBD) and particles induced breakdown (PBD). Three regions were obvious and defined. In region 1, PCD and PB dominated, and dielectric strength increased with the conditioning. In region 2, FEBD and PBD mixed and PBD was dominant. The dielectric strength increased with the conditioning. In region 3, conditioning saturation region, FEBD and PBD mixed, and the dielectric strength reached the limit. The XPS results revealed that in region 1 the ratio of O and C decreased, and nearly disappeared. During the conditioning process, PCD and PB mechanism for the gases desorption reason first occurred. Then the PBD mechanism eliminated the particles on the electrode surface. At last, the FEBD and PBD dominated in the conditioning saturation region.