Progress in the understanding of electrical breakdown in condensed matter

The phenomenon of electrical breakdown in condensed matter has been the subject of many studies. While the ultimate result is relatively easy to observe and study, attempts to uncover its initial phases that lead to the short circuit as evidenced by light and acoustical emissions defied discovery. In the past decades some of the initial phases of the breakdown process have been elucidated with the help of sophisticated devices that permit registration on photographic film and/or on transient digitizing instruments. The progress made in this field is summarized and an attempt is made to establish the significance of these observations. Starting with the events occurring at the metal surface, it is shown how streamers and tree-like structures develop; how, on the surface of these primary streamers, instabilities initiate fast growing secondary streamers; and how these events lead to the establishment of a conducting channel. These stages are examined in the light of published information. The implications of these findings in terms of the performance of actual systems are also considered.