Modeling of the Influence of Temperature on Interaction of a Cathode with a Thin Insulating Film and a Glow Gas Discharge Plasma in a Mixture of Argon and Mercury Vapor

A model of a glow gas discharge in a mixture of argon and mercury vapor is formulated in the presence of a thin insulating film on the cathode surface. Dependences of the discharge characteristics on the mixture temperature are calculated in the range of its variation, in which a noticeable contribution to ionization of the working gas is made by the ionization of mercury atoms by metastable excited argon atoms (the Penning reaction). It is shown that in the case of a cathode without an insulating film when the temperature increases until the relative mercury content in the mixture reaches 5 × 10–3, a reduction of the electric field strength in the discharge cathode layer takes place due to an increase of the mixture ionization coefficient. A further increase of the temperature, due to growing mercury content in the mixture and a decrease in the contribution of the Penning reaction to the mixture ionization coefficient, results in its reduction, followed by an increase of the electric field strength. At the existence of an insulating film on the cathode a contribution to its effective electron emission coefficient, along with the ion-electron emission, is also made by the temperature-enhanced field electron emission from the cathode metal substrate into the insulating film, caused by the existence of a strong electric field in it. As a result of the increase in temperature, the cathode effective ion-electron emission coefficient decreases due to a reduction in the discharge current density. This leads to a smaller decrease in the electric field strength in the discharge cathode layer than that in case of a cathode without a film, only in a small interval of cathode temperature variation. Therefore, the cathode without an insulating film under its heating in glow discharge is sputtered more intensively than the cathode with the film, which results in a shorter service life of lamps with such cathodes.