Collisional-Radiative Model of Quasi-Stationary Helium Plasma and Its Application to the Plasma in Positive Column

Abstract

The collisional-radiative model is applied to a quasi-stationary helium plasma and the collisional-radiative and population coefficients are calculated, provided that the level system of helium atom is composed of the ground level¹S, the four lowest excited levels, 2³S, 2¹S, 2³P and 2¹P, and higher hydrogenic levels. The ranges of plasma parameters are 8 × 10³Tₑ1.28×10⁵ °K and 10⁵nₑ10⁹ cm⁻³, and the results are compared with the data by Drawin et al. Next, the model is applied to a positive-column helium plasma and the plasma balance equation in the case of ambipolar diffusion is simultaneously solved with a set of rate equations for excited helium levels which includes the diffusion of atoms in metastable states. The results give the relation among the filling gas pressure in a discharge tube, plasma parameters and population densities of the excited levels. The atomic processes of ionization, excitation and deexcitation in the plasma are analyzed in detail.