The subject of the present research is a quantitative study of opportunity to obtain a photoplasma in a low pressure mixture of alkali metal
vapor and noble gas by concentrated solar (or gas lamp) irradiation. The ground, resonance and high-excitation levels, and atomic and molecular
ions of an alkali metal were considered. The proposed self-consistent model along with plasma-chemical reactions and radiation transfer
accounted for charge transport processes and ambipolar diffusion, unlike previous studies (LIBORS project and others). Spatial uniformity of
resonance excitation rate in the all plasma volume was assumed. An iterative method to determine the main parameters of photoplasma was
proposed and tested on the example of a mixture of Na vapor and Ar gas for pressures p_Na=0.02 and p_Ar=1 Torr in a cylindrical cell of radius
R¼0.005 m and length L¼0.01 m in the range of resonance radiation flux density F_0=4*(1–10^3) Wm2nm–1 inside the gas cell. The minimal
value of resonance excitation rate, which is necessary to create a plasma in the considered gas cell, was evaluated as 1.1*10^22 m-3s-1.
According to our rough estimation, to provide this rate, the minimal value of F_0 of an external source should be 40 Wm–2nm–1. This can be
implemented by the concentration coefficient of solar irradiation about 30. The model and obtained results can be used for the calculation of
plasma parameters in different mixtures of an alkali metal vapor and a noble gas induced by a nonlaser irradiation source (concentrated solar or
gas lamp irradiation) and designing of photovoltaic converters on their base.