Population densities of excited states of helium atoms in a brush cathode discharge in a magnetic field

Abstract

Spectral line intensities emitted by a brush cathode helium discharge in a magnetic field have been measured for the 2 1 S − n 1 P, 2 1 P − n 1 S, 2 1 P − n 1 D, 2 3 S − n 3 P, 2 3 P − n 3 S, and 2 3 P − n 3 D series up to a principal quantum number n = 10 and the population densities of the excited states have been obtained. For n ≳ 5, the states are in thermal equilibrium. The electron density and the electron temperature obtained from the Saha-Boltzmann equation are 1·7 × 10 13 cm -3 and 0·17 eV. These values are in good agreement with the values obtained from the measured recombination continuum. For the lower states, measured populations are in good agreement with those calculated by Drawin, Emard and Katsonis on the basis of a collisional-radiative model.