Surface discharge propagation: the influence of surface charge

Surface discharges are of considerable importance, because of their influence on the reliability of high voltage pulsed power systems. It is possible to achieve long discharges with relatively low voltages particularly in the presence of surface charge. The theory of streamer development in gases has been the subject of major experimental studies into the precise mechanisms of their initiation and development. However, surface discharge development is complicated by the proximity of the underlying insulating surface and the coupling of the discharge to that surface. This leads to modifications of the electric field surrounding the streamer, particularly at the head of the discharge. Photons generated at the discharge head can interact with the surface, producing photo-emission thus changing the surface charge distribution. Ablation of the surface results in local modifications of the gas atmosphere. The present experimental study has investigated the influence of surface charging on guided streamers propagating over insulating surfaces. The streamers were initiated from a surface mounted electrode excited by a high voltage pulse, the duration of which was much shorter than the time taken for the streamer to propagate across the surface. It was found that the velocity and distance of propagation is strongly influenced by the presence and magnitude of the surface charge and that discharge propagation can occur in the absence of the HV pulse. Measurements have shown that the deposited surface charge decays with time and that there are two distinct decay rates. These changes in the surface charge distribution could have a bearing on the period of time that should elapse before the subsequent reapplication of HV pulses to produce consistent discharge behaviour or to avoid surface flashover.