Spectroscopic study on the population densities of free electrons and excited states of helium in a P.I.G. plasma

A spectroscopic study is carried out on a helium plasma produced by the P.I.G. type discharge. The radial distributions of the emission coefficients of 23P-n3D lines and the recombination continuum are obtained from the measured chord intensity-distributions by means of the Abel inversion. The population densities of n3D states of helium atoms and free electrons are calculated from the emission coefficients. From the Boltzmann plot which is the population density distribution of the excited states and free electrons, it is revealed that the highly excited states of helium atoms are in equilibrium with the free electrons, that is, the Saha equilibrium is established between them. The electron temperature and the electron density are found to be 0.23 eV and 5.5x1013 at the radial position R=5mm, and 0.17 eV and 2.2x1013 cm-3 at R=10 mm, respectively. (auth.)