Measurement of optical spectrum and mass spectrum in vacuum surface flashover for polymeric materials

The phenomenon of surface flashover in vacuum is a common problem in vacuum insulation systems. Although the theory of secondary electron emission avalanche is widely accepted, the developing process of vacuum surface flashover is not very clear and it needs to be further studied. The surface discharge process was diagnosed by spectral and mass spectrum analysis in this paper. The surface flashover was initiated by a microsecond pulse with a rise time of 500 ns and a full width at half maximum of 8 μs. Optical diagnostic methods were used to obtain the luminous properties of several polymeric materials. The time-domain optical signal was measured by a photomultiplier tube with wavelength range of 300-650 nm. The spectrograph was used to detect the optical emission from the surface discharge. The outgassing characteristics in the flashover were also measured by mass spectrometer connected to the vacuum experiment chamber. The results show that the optical signal appears before flashover and the light intensity reaches its maximum at about 80 ns after the flashover occurs. The optical emission spectrum is mainly in range of 400-800 nm, and C
₂
, H and Cu spectrum lines were detected in polymeric materials. The results of mass spectrum measurement show that the outgassing of polymeric materials in surface flashover includes the desorbed gases and decomposed gases of insulation materials. It is consistent between the results of emission spectrum and mass spectrum.