Initiation of microplasma discharges at the edge of a dielectric film deposited on a metal surface

Excitation of microplasma discharges in the interaction of a plasma flow with a metal surface partially covered with a dielectric film is investigated experimentally and theoretically. A new phenomenon-the excitation of microplasma discharges at the boundary between the free metal surface and the area covered with the film-is discovered. Microplasma discharges at the edge of the dielectric film are initiated by a strong electric field that arises between the free metal surface and the outer surface of the film in the interaction with the plasma flow. This field gives rise to surface breakdowns at the film edge, followed by the development of primary microplasma discharges. In turn, the dense plasma of primary microplasma discharges causes secondary microplasma discharges, which also arise at the edge of the dielectric film after the external plasma flow has already terminated. Microplasma discharges gradually evaporate the dielectric film, and the surface cleaned of the film acquires a microrelief due to the local melting and subsequent fast cooling of the metal at the sites of microplasma discharges.