Kinetics of Formation of an Oxide Film on the Surface of the Cathode in an Atmospheric-Pressure Glow Discharge in Helium

The kinetics of formation of an oxide film on the surface of the cathode of an atmospheric-pressure glow discharge in helium has been investigated by the method of laser reflectometry. It has been established that the film is formed at a cathode temperature exceeding 550 K, and in 200 sec from the time of discharge initiation at a current of 1 A it becomes thicker than 1 m. The film consists of several concentric zones. For each of these zones, a change in time of the directional hemispherical coefficient of reflection at a wavelength of 0.63 m was determined. It is shown that the formation of an oxide film on the cathode surface leads to an increase in the cathode drop.