A new similarity law for the discharge plasma in gas mixtures has been obtained-its main feature being the smaller number of independent external parameters which are necessary to describe the plasma in question. This law is proposed for use in plasma research and some examples of such an application are presented.

This paper deals with the modelling of the medium pressure Hg and Hg-Ar positive column (Hg pressure range 5-350 Torr). The aim of this work is to simulate, in a first approximation, the middle phase of the Hg high-pressure lamp warm-up. In this approach, the main assumption is that time evolution of the discharge can be divided into a succession of stationary sub-phases characterized by the Hg partial pressure. Thus, we present here a self-consistent steady-state collisional-radiative model describing the middle sub-phase. This model includes volume recombination of Hg atomic and molecular ions, as well as several atom-atom inelastic scattering mechanisms. Calculations are carried out for both pure Hg and Hg-Ar discharges. Our results, which are in good agreement with experimental data from the literature, confirm that plasma thermalization occurs in the middle start-up phase (electron and gas temperatures become equal during this phase). Furthermore, this simulation shows the importance of different elementary processes, like atom-atom inelastic scattering, for the medium pressure plasma description. In fact, these mechanisms cannot be neglected until LTE conditions are reached.

The electrokinetic characteristics (the electron energy distribution function, the strength of the longitudinal electric field and the concentration and average energy of electrons) are measured and calculated in a -discharge plasma under a high pressure of argon (up to 30 Torr) and in narrow tubes (the tube radius is less than 1.0 cm). A simple method of treating the second derivative of the probe current with respect to the probe potential is proposed for a straightforward way to obtain the electron energy distribution function under a high pressure of a gas. It is shown that the main assumptions on which modelling of the plasma of mercury luminescent lamps is based are also valid for the plasma in question. This leads to the existence of special similarity laws and gives a new possibility for diagnostics based on the similarity properties of the plasma. The approach proposed in the work can be easily extended to the mixtures of mercury vapour and other rare gases.

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