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Dielectric barrier discharge (DBD) is widely applied in many fields, and the discharge characteristics of insert gas have been the research focus for years. In this paper, fluid models of atmospheric Ar and He DBDs driven by 22 kHz sinusoidal voltage are built to analyze their ignition processes. The contributions of different electron sources in ignition process are analyzed, including the direct ionization of ground state atom, stepwise ionization of metastable particles, and secondary electron emission from dielectric wall, and they play different roles in different discharge stages. The Townsend direct ionization coefficient of He is higher than Ar with the same electrical field intensity, which is the direct reason for the different ignition thresholds between He and Ar. Further, the electron energy loss per free electron produced in Ar and He DBDs is discussed. It is found that the total electron energy loss rate of Ar is higher than He when the same electrical field is applied. The excitation reaction of Ar consumes the major electron energy but cannot produce free electrons effectively, which is the essential reason for the higher ignition threshold of Ar. The computation results of He and Ar extinction voltages can be explained in the view of electron energy loss, as well as the experimental results of different extinction voltages between Ar/NH3 and He DBDs. [ABSTRACT FROM AUTHOR]

Inspired by the Penning effect, we obtain a glow-like plasma jet by mixing ammonia (NH3) into argon (Ar) gas under atmospheric pressure. The basic electrical and optical properties of an atmospheric pressure plasma jet (APPJ) are investigated. It can be seen that the discharge mode transforms from filamentary to glow-like when a little ammonia is added into the pure argon. The electrical and optical analyses contribute to the explanation of this phenomenon. The discharge mode, power, and current density are analyzed to understand the electrical behavior of the APPJ. Meanwhile, the discharge images, APPJ's length, and the components of plasma are also obtained to express its optical characteristics. Finally, we diagnose several parameters, such as gas temperature, electron temperature, and density, as well as the density number of metastable argon atoms of Ar/NH3 APPJ to help judge the usability in its applications. [ABSTRACT FROM AUTHOR]

Charge trap is considered to be one of the effective characteristic parameters for qualitatively evaluating the aging status of insulating material. In this paper, the trap characteristics in oil-impregnated paper with different aging types (non-treatment, thermal treatment and electrical treatment) are investigated using a dual-level (shallow and deep energy) trap model based on space charge profiles and thermally stimulated depolarization current (TSDC) data. The simulated results based on the model are well consistent with the experimental results. On the other hand, the TSDC method can acquire much information related to the shallower traps, and the dual-level trap model can obtain much charge dynamics characteristics. It has been observed that thermally aging makes the shallow trap energy become deeper while electrically aging makes it shallower. Moreover, the trap density in oil-impregnated paper increases after aging regardless of thermal or electrical aging. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]