Level population densities and line intensities in helium discharges at intermediate pressures

A scheme for calculating populations of excited levels and intensities of spectral lines in the positive column of helium discharges at intermediate pressures (p>5 Torr) is proposed. The electron distribution obtained from the Boltzmann equation is taken into account. The distribution is strongly non-Maxwellian for electrons of energy more than 19.8 eV. Concentrations of atoms on excited levels (n=2,3,4,5) are obtained from balance equations for the population of those levels. The concentration of level 2 3 S is the highest. The concentration of 2 1 S is much less than that which would exist in the case of quasithermodynamic equilibrium between levels 2 3 S and 2 1 S. The population of higher levels (n>2) is determined by excitation from levels 2 3 S and 2 1 S. For singlet levels the excitation from level 2 1 S is important. Population inversion is obtained between levels 3 1 P-3 1 D, 4 1 P-4 1 D, 5 1 S-4 1 P, 4 3 S-3 3 P, 5 3 S-4 3 P and 5 3 P-4 3 D.