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Atmospheric pressure dielectric barrier discharge (DBD) has abundant application fields, and the influence of the barrier material on DBD characteristics has been the research focus in recent years. In this work, a two-dimensional fluid model is built to investigate the effects of the barrier dielectric surface layer with different permittivity distribution on DBD, including electric parameters, electron distribution, and surface charge evolution. It is demonstrated that higher dielectric permittivity can affect DBD by enhancing the electric field Espace of space charge and weakening electric field Esurf of the surface charge and have a more obvious influence on Esurf, which can make DBD transform from glowlike discharge to streamerlike discharge. The dielectric surface layer with linear distribution of permittivity is introduced in DBD, changing the discharge appearance and discharge channel forming sequence. This work may provide some theoretical experiences for the application of a functionally graded material as a barrier dielectric in DBD. [ABSTRACT FROM AUTHOR]

The discharge mode transitions and the characteristics of atmospheric pressure dielectric barrier discharge in pure helium (He-DBD) are studied. Different discharge modes of He-DBD are clarified, including filament-diffuse mixed mode, filamentary mode, diffuse mode, and multichannels coupled mode. The transitions of different modes are explored by changing the gap width and applied voltage. According to the luminous structure of discharge [short exposure (100~300 ns) image], it is found that there should be only Townsend-like and glow-like discharges that appear in the above modes. In Townsend-like discharge, the secondary electron emission coefficient (SEEC) of dielectric is estimated. Based on which, a fluid model coupled with an external circuit is built to explain the He-DBD mode transitions mechanism and the applied voltage drop’s influence on He-DBD. Through the temporal evolution of a luminous structure, a discharge filament is believed to be a contractive state of discharge channel, which should be an unstable glow-like discharge. The radius of discharge channel, changing with gap width and applied voltage, is measured. The discharge contraction is attributed to the nonlinear relationship between Townsend ionization coefficient and electric field. The enhancing interaction between different discharge channels inhibits the appearing of diffuse discharge around discharge filament, leading to the transition from mixed mode to filamentary mode. In the end, the multichannels coupled mode is proven to be glow-like discharge, and its formation mechanism is explained by the overlap of discharge channels. [ABSTRACT FROM AUTHOR]