Optical investigation of fast pulsed discharge on surface of ceramics for environmental applications
Pulsed surface discharge on the surface of ceramics was investigated experimentally. Photon counting method was applied to clarify preceding phase of the discharges. The results indicated the effect of charge injection from electrodes. Pulsed surface discharge reactor for decomposition of nitrogen oxides utilizing honeycomb ceramics was proposed. Framing and streak observation was carried out with image converter cameras. Emission spectra from the discharge were investigated with spectrometer. Uniform surface discharges on honeycomb ceramics were successfully obtained utilizing pulsed power generator with a SI-thyristor.
Luminescence characteristics before flashover across alumina ceramic under steady voltage in vacuum
The surface flashover issue has always been a hot topic in the insulation field and it has been reported that various luminescent phenomena occur before flashover under a high electrical field in vacuum, which are closely related to the behavior of charge carriers induced by discharge. However, it is still not so clearly about the intrinsic relationship between the luminescence phenomenon and the mechanism of flashover. This paper studies the luminescence on alumina ceramic under DC and AC excitation in vacuum, and the results show that under a relatively low voltage, the electroluminescence phenomenon on sample surface will be caused by radiative electron-hole recombination following charge injection. The luminescence intensity and spatial distributions for DC and AC voltage are obviously distinctive with each other due to the quite different recombination process. However, when it comes to a relatively higher voltage, making it possible for electrons to release from cathode triple junction due to field-enhanced emission, the cathode-like luminescence process will dominate, which is generated by a self-stabilizing secondary electron emission process and subsequent collision on insulator surface. This study might be helpful to comprehensively reveal the luminescence phenomenon regarding surface flashover.
SI-thyristor as a high power switching device for fast high voltage pulse generators
Characterization of SI-thyristors as a fast closing switch for pulsed power application was examined. Since the SI-thyristors employed in this study are normally on-state, a negative bias voltage is necessary at the gate electrode to establish hold-off-state. As a consequence, fast current rise rate can be strongly expected. A low impedance gate driving circuit built with MOSFETs improved turn-on characteristics. By adjusting anode voltage distribution and gate timing, carefully stacked SI-thyristors were successfully operated to make turn on. The highest di/dt obtained in this study is 55 kA//spl mu/s. A fast high voltage pulse generator with magnetic pulse compression scheme was built by using stacked SI-thyristors. To obtain a faster high voltage pulse a nonlinear transmission line as an additional circuit for pulse sharpening was employed.