Investigations of surface charging of DC insulator spacers

Several possible surface charging mechanisms of solid insulating spacers have been suggested by various authors. These included micro-corona discharge particularly at the triple junction, injection from the electrodes, non-linear surface conduction effects, charged micro-particles, electrochemical reaction at the electrodes and ionisation of the surrounding gas by cosmic rays. It is still unclear which of the above mechanisms predominates in any given case. By measuring surface charge densities as a function of time and of voltage it was possible to eliminate some of the above charging processes as the cause. The results were consistent with micro-corona activity and charge injection from the electrodes. Photon emission was observed from the electrode/insulator triple junction region. This photon activity increased when the applied voltage was either raised or lowered. The results are discussed in detail in the paper