Initiation of Electrical Breakdown by Ionic Bombardment in a Vacuum Gap after Arc Extinction

This report presents a theoretical model of development of the post-arc gap breakdown in vacuum as a result of surface processes following cathode bombardment by energetic ions flowing from residual plasma after zero arc current. The most important surface processes for this model are sputtering and secondary electron emission. For a considerable group of metals, the sputtering yield Sr and secondary electron emission γc can assume relatively high values when the ions have a high energy. Based on the ion flux from the plasma and the time of its flow as well as the ionization of sputtered atoms, a quantitative criterion for a breakdown will be derived. It has been proven that breakdown will occur if there is at least a minimum ion charge Qi which is dependent on the product of Sr · γc. Qualitative consistency was also demonstrated between experimental results and the conclusion derived from our breakdown criterion.