Microstructure of the regions on a plane copper electrode surface affected by a spark discharge in air in the point–plane gap

The microstructure of the regions affected by spark discharge on the surface of a plane copper electrode in atmospheric air in the point–plane gap has been studied using a scanning electron microscope for both the positive and negative polarity of the point electrode. It has been found that the affected regions have the shape of round spots or groups of spots with diameters of individual spots varying in the range of 20–200 $\mu$m. It has been revealed that the spots have an internal spatial structure in the form of an aggregate of concentric rings. These rings are aggregates of a large number of microscopic craters with diameters of 0.1–1.0 $\mu$m.