Effect of Trigger Electrode on the Channel Behavior of Surface Discharge Switch

The effects of trigger electrodes on the behavior of multichannel gas breakdown in a gas-filled surface discharge switch was investigated experimentally. A straight wire or a metal plate was placed under dielectric surfaces at various distances from the main electrodes. These served as the trigger electrode. Various geometric configurations and polarities of the trigger electrode were studied. The experiments were mainly carried out in a N2 environment of 0.1 to 0.2 MPa pressure, and with voltage pulses of 40 to 90 kV peak and 150 to 500 ns risetimes. The location and number of the plasma channels formed during breakdown was observed to be strongly dependent of the geometric configuration and polarities of the trigger electrode. For example, when a wire trigger electrode was placed near the cathode, almost all the channels were found to be concentrated in a region directly above the wire, whereas if the wire electrode was placed near the anode, no such concentration was noted. The observations were qualitatively analyzed. It was concluded that the results were mainly due to the presence of the third electrode and space charges in a non-uniform filed. Based on this analysis, an effective plate trigger electrode for surface discharge switches was successfully developed.