Propagation of Microplasma Discharge over Titanium Surface Covered with Thin Dielectric Film

Abstract

Propagation and structure of the pulsed microplasma discharge initiated on the titanium sample surface covered with a thin dielectric film with a thickness of approximately 10 nm was studied experimentally. The discharge duration was 100 μs; the amplitude of the discharge electric current was 200 A. The microplasma discharge was initiated by the plasma flow with wide aperture, a plasma density of 2 × 10¹³ cm^–3 and pulse duration of 25 μs. It was visually found that, on the macroscale, the microplasma discharge glow has a branched structure of the dendrite type, which, on the microscale, it consists of a large number of brightly glowing “point” formations, namely, cathode spots localized on the metal surface. The interaction of microplasma discharge with the titanium sample results in erosion of its surface. In this case, the erosion structure is visually “identical” to the structure of the discharge glow and consists of a large number of individual microcraters with characteristic sizes from 0.3 to 10 microns, localized on the metal surface within an area of ≈1 cm². On the macroscale, the entire set of microcraters forms a branched structure of the dendrite type. It was ascertained that the microplasma discharge propagates over the titanium surface covered with a thin dielectric film at an average velocity of 70 m/s. Moreover, the microplasma discharge propagation has a “jumping” character: the plasma of “immovable” burning cathode spots initiates the excitation of new cathode spots at distances of 3–30 microns from them.