Electrons stimulated gas desorption of some dielectrics in vacuum

Surface flashover phenomena in vacuum across dielectrics usually happen in many pulsed power devices, high power microwave (HPM) equipment and particle accelerators. Secondary electron emission avalanche (SEEA) model is generally accepted to analyze this phenomena. During the evolution of flashover development, the process of electrons desorption stimulated (ESD) gases plays a dominant role and then leads to final discharge formation. Accurate measurement of ESD gas components and its quantity is very helpful to investigate flashover mechanism and make theoretical simulation. In this paper, an ESD measurement apparatus is set up with a modified quadrupole mass spectrometer (QMS) surround with double cooling shrouds. The incident electron energy varies from 2keV to 7keV. First, residual gas in the experiment chamber is analyzed. Next, pulsed electron beam impacts the sample surface and release ESD gases, and then mass spectrum analysis of ionized gases is carried out by QMS. The differences before and during electron irradiation are regarded as the amount of desorbed gases. Some typical dielectrics are measured including PTFE, PE and Al₂O₃. It is found that main desorbed gas components are similar, i.e. H₂, H₂O, CO, CO₂, etc. Additionally, electrons irradiation can break chemical bonds to produce new components. H₂ accounts for the majority of total desorption gases. Organic material (PE) has higher desorption gas than that of Al₂O₃.