Topic/Type: 1.5 Low-temperature, dusty and nano-plasmas, Poster

Simulation of Gas Ionization in Argon-Mercury Mixture Townsend Discharge

G.G. Bondarenko1, M.R. Fisher2, V.I. Kristya2

1 Research Institute of Advanced Materials and Technologies of Moscow Institute of Electronics and Mathematics, Moscow, Russia
2 Kaluga Branch of Bauman Moscow State Technical University, Kaluga, Russia

In modern gas-discharge illuminating lamps, a mixture of argon with mercury vapor which concentration depends on temperature is used as the background gas. Under electric current flowing in the mixture, besides of direct ionization of argon and mercury atoms by energetic electrons, mercury atom ionization by metastable excited argon atoms (Penning reaction) is also possible. This process can substantially influence the mixture ionization coefficient (MIC) as well as the discharge ignition voltage (DIV). But the charged and excited particle kinetics in argon-mercury gas discharge plasma is not well studied up to now.
In this work, simulation of electron, ion and metastable excited atom motion and interactions in a low-current Townsend discharge between the flat electrodes in argon-mercury mixture is fulfilled. Trajectories of electrons in the interelectrode gap are calculated with the Monte Carlo method, and ion and metastable motion is described on the basis of their transport equations. The MIC obtained as a function of mercury relative concentration corresponds to available experimental data [1,2]. It is found that the MIC takes on its maximum under the mercury relative concentration of the order of 10-3, which takes place at the temperature of about 60 C under the argon concentration typical for high-intensity lamps. Calculations show that the MIC increase is mainly the result of penning ionization of mercury atoms, whereas their direct ionization by electrons is of no importance, and the contribution of penning ionization into the MIC increases with electric field strength reduction. The dependence of the DIV on the interelectrode distance in pure argon and argon-mercury mixture is also calculated. In argon it agrees quite well with measured DIV values [3], and in the mixture penning ionization results in a substantial decrease of the DIV. Presented model can be useful in investigations of electrode material and mixture composition effects on the DIV in illuminating lamps.

[1] A.E. Ataev, ?Ignition of High-Pressure Mercury-Vapor Discharge Radiation Sources?, Moscow: MEI(1995). (In Russian)

[2] Y. Sakai, Appl. Surf. Sci. 192(2002) 327.

[3] V.A. Lisovskiy, S.D. Yakovin, V.D. Yegorenkov // J. Phys. D: Appl. Phys. 33(2000) 2722.