Electron Temperature Dependence of the Recombination Coefficient in Pure Helium

Abstract

The phenomenon of "afterglow quenching" is employed to determine the electron temperature dependence of the electron-ion recombination coefficient in plasmas produced in purified helium (estimated impurity 1:${10}^{9}$). The total visible light intensity was studied as a function of electron temperature. By means of 1.5% bandwidth filters, the light intensity of two helium spectral lines (5876 A and 3888 A) were also investigated. It is found that the recombination coefficient for highly purified helium varies as the minus three-halves power of the electron temperature from 300\ifmmode^\circ\else\textdegree\fi{} to \ensuremath{\sim}1500\ifmmode^\circ\else\textdegree\fi{}K at electron densities of \ensuremath{\sim}${10}^{11}$/cc, and gas pressures from 12.6 to 30.3 mm Hg. At 300\ifmmode^\circ\else\textdegree\fi{}K (temperature determined from collision frequency measurements), the recombination coefficient in purified helium is found to be (8.9\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}9}$ ${\mathrm{cm}}^{3}$/ion sec. It is found that both the recombination coefficient and its electron temperature dependence were strongly influenced by the addition of controlled amounts (2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ to 1300\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$%) of neon impurities.