The use of carbides as electrode material in a pseudospark switch

Abstract

In the following, we report tests of a semiconductor as electrode material in a pseudospark switch, which is a low pressure gas discharge switch. Polycrystalline SiC or BC disks with central apertures were embedded in molybdenum outer electrodes in a typical single stage pseudospark geometry. The maximum voltage applied was 15 kV. Tests were done with peak currents from 50 up to 500 kA at pulse lengths of a few microseconds. We found no difference in the voltage breakdown or the rise in current when compared to conventional metal electrodes such as molybdenum or tungsten. Fast shutter photographs showed that the discharge burns in an intense column at the center and is distributed very homogeneously over the SiC surfaces. Neither cathode nor anode spots were observed. Small sparks occurred at the metal–carbide interface after current zero, which led to a reignition in the second current half-wave. An estimation after the tests showed an erosion rate of about 5 μg/C approximately one order of magnitude lower than in metals. We assume that the current is transported in a thin surface layer. Ion bombardment in the pseudospark discharge heats this layer to more than 2000 K, lowering the specific resistance. The negative temperature–resistance characteristic means that cathode spots are avoided.