THE PLASMA IN HIGH-CURRENT PSEUDOSPARK SWITCHES

The discharge behavior and the erosion rate of pseudospark switches fo r high currents (50-150 kA) and pulse lengths of several microseconds were investigated for different electrode materials, A capacitor disch arge (3.3 mu F) without any load was used at a maximum voltage of 30 k V, Side-on optical investigations were performed either with a streak camera or a fast shutter camera, Using metal electrodes, the discharge ignites on axis, then widens up radially and burns homogeneously at t he edge of the central apertures, After about 500 ns, a stable anode s pot is observed on the plane electrode surface (at currents exceeding 45 kA), the location of which is statistical, The discharge is transfo rmed to a metal vapor are discharge and the erosion rate increases by more than one order of magnitude, With semiconductor electrodes (i.e., silicon carbide), a different discharge behavior is observed, After i gnition on axis, the discharge burns homogeneously on the whole carbid e surface, No contraction to a small area occurs in comparison to meta l electrodes, The reignition of later current half cycles starts at th e triple point metal-carbide-gas. Then the discharge again spreads hom ogeneously over the total carbide surface, The erosion rate is about t wo magnitudes lower in comparison to metals, We assume that the curren t is conducted in a thin surface sheath which is heated to more than 2 000 K.