Influence of the Nonuniform Thickness of a Dielectric Film along a Cathode Surface on Its Heating in a Glow Discharge

A model of a cathode layer in a gas glow discharge is formulated taking into account the presence of a dielectric film with varying thickness on the cathode across different areas of its surface, and in some areas, the film may be absent. The model includes ion–electron emission from the cathode surface, thermal-field electron emission from the cathode substrate into the film, and thermal electron emission from the areas of the cathode without a film. Upon heating the cathode, the emission efficiency of the film, the effective electron emission yield of the cathode, and the discharge current density decrease, as the electric-field intensity within the film decreases. This decrease in field strength limits the current density required to sustain the thermal-field electron emission from the cathode substrate into the film. Therefore, when a dielectric film covers the entire working surface of a cathode, the glow discharge does not transition to an arc discharge for a long time. However, if the film is absent on some areas of the cathode surface, thermal electron emission begins from these areas after heating the cathode to a rather high temperature. The emitted electrons leave the cathode surface, which increases the effective electron emission yield and discharge current density. This leads to more intense heating of the cathode and accelerates the transition of the glow discharge into an arc discharge.