Investigation of Stationary Population Inversion between Low Excited States of He+ in a Recombining Plasma

Leading members of the Lyman series of He II emitted from a high-density helium plasma have been measured by the use of the Rare-gas Photoelectron Counter which is based on the energy analysis of photoelectrons liberated by XUV radiation. Stationary population inversion between low lying levels of He + is confirmed in a recombining plasma which is interacting with neutral helium. The ratio n 2 / g 2 : n 3 / g 3 : n 4 / g 4 : n 5 / g 5 is found to be 1: 0.6: 1.1: 1.2. A method of determining the electron temperature, the electron density and the ion density from the recombination continua is described. Collisional and recombination processes can explain reasonably the observed level populations.