Measurement of Recombination-Rate Coefficient ofHe++

Abstract

The rate of recombination of doubly ionized helium in the afterglow of a $C$ stellarator discharge is deduced from measured light intensities of He II and He I, emitted by recombining ${\mathrm{He}}^{++}$ and ${\mathrm{He}}^{+}$. The electron temperature and the ${\mathrm{He}}^{++}$ and ${\mathrm{He}}^{+}$ and electron densities are determined from the Saha equations for the highly excited states and the condition of charge neutrality. The electron density is also measured directly with a 4-mm microwave interferometer. The rate of recombination of ${\mathrm{He}}^{+}$ is found to be in good agreement with previous measurements, at temperatures 0.25 eV. At higher temperatures, where ${\mathrm{He}}^{+}$ and ${\mathrm{He}}^{++}$ are both present, the recombination rate is found to follow a ${Z}^{3}$ relationship. The measurements appear to be in quite good agreement with the calculations of Bates, Kingston, and McWhirter over the entire range of measurement.