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

Abstract

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 n₂⁄g₂ : n₃⁄g₃ : n₄⁄g₄ : n₅⁄g₅ 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.